ORCID Profile
0000-0002-1670-5545
Current Organisation
Monash University
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Publisher: S. Karger AG
Date: 2007
DOI: 10.1159/000108934
Abstract: Sex in birds is controlled genetically (ZZ male: ZW female), but the genetic mechanism remains unclear. While some evidence points to the involvement of Z sex chromosome dosage, other data favour a dominant female-determining gene carried on the W sex chromosome. An intriguing candidate gene located on the chicken W chromosome is i HINTW /i , which encodes an aberrant form of a hydrolase enzyme. In chicken embryos, i HINTW /i is strongly expressed in the gonads and other tissues of ZW (female) embryos i . /i In vitro biochemical data show that HINTW can interfere with the action of a Z-linked orthologue, HINTZ, which is a bona fide hydrolase enzyme. i HINTW /i is conserved among carinate (flying) birds, and recent molecular analysis indicates that it has undergone positive selection over evolution. However, a differentiated i HINTW /i gene appears to be absent in the flightless ratites. This review examines the evidence for and against a role for i HINTW /i in avian sex determination.
Publisher: Elsevier BV
Date: 06-2009
DOI: 10.1016/J.GEP.2009.03.004
Abstract: The tescalcin gene (Tesc) encodes an EF-hand calcium-binding protein that interacts with the sodium/hydrogen exchanger, NHE1. Previous studies indicated that Tesc was expressed in mouse embryonic testis, but not in ovary, during the critical period of testis and ovary determination. In this paper we compared the expression of Tesc in embryonic tissues of chicken and mouse. Tesc expression was sexually dimorphic in the embryonic gonads of both mouse and chicken. Tescalcin (TESC) was detected in both Sertoli cells and germ cells. In the embryonic brain of both mouse and chicken, Tesc was highly expressed in the nasal placode and in fibers extending from the olfactory epithelium to the primordial olfactory bulb. Tesc was expressed in the embryonic heart of both chicken and mouse. In mouse Tesc expression was also detected in embryonic adrenal. These studies indicate very specific expression of Tesc in various tissues in chicken and mouse during embryologic development, and conservation of Tesc expression in both species.
Publisher: Springer New York
Date: 2017
Publisher: Springer Science and Business Media LLC
Date: 25-07-2017
DOI: 10.1038/S41467-017-00112-7
Abstract: The ratites are a distinctive clade of flightless birds, typified by the emu and ostrich that have acquired a range of unique anatomical characteristics since erging from basal Aves at least 100 million years ago. The emu possesses a vestigial wing with a single digit and greatly reduced forelimb musculature. However, the embryological basis of wing reduction and other anatomical changes associated with loss of flight are unclear. Here we report a previously unknown co-option of the cardiac transcription factor Nkx2.5 to the forelimb in the emu embryo, but not in ostrich, or chicken and zebra finch, which have fully developed wings. Nkx2.5 is expressed in emu limb bud mesenchyme and maturing wing muscle, and mis-expression of Nkx2.5 throughout the limb bud in chick results in wing reductions. We propose that Nkx2.5 functions to inhibit early limb bud expansion and later muscle growth during development of the vestigial emu wing.
Publisher: Elsevier BV
Date: 12-2009
DOI: 10.1016/J.CELL.2009.11.036
Abstract: Conventional wisdom holds that the ovary and testis are terminally differentiated organs in adult mammals. However, Uhlenhaut et al. (2009) now report that deletion of a single gene, Foxl2, is sufficient to induce transdifferentiation of ovary into testis in adult mice, suggesting that testicular development is actively repressed throughout the life of females.
Publisher: Wiley
Date: 13-04-2005
DOI: 10.1002/DVDY.20388
Abstract: P450-aromatase is the terminal estrogen-synthesizing enzyme and a key gene in avian sex determination. Aromatase is expressed specifically in female gonads, but not male gonads, at the onset of sexual differentiation. This enzyme shows temporal and spatial colocalization with the forkhead transcription factor FOXL2 in the embryonic chicken ovary, suggesting a causal link. Mutations in FOXL2 are associated with premature ovarian failure in humans. Foxl2 null mice also present with premature ovarian failure. Here, we show that FOXL2 expression is reduced but not abolished in chicken embryos subjected to experimental female to male sex-reversal with an aromatase inhibitor. This finding suggests that FOXL2 lies upstream of aromatase in avian sex determination, but that it responds to depleted estrogen synthesis. The reduction in FOXL2 expression may be accounted for by interruption of a positive feedback loop by means of estrogen, or the influence of testis promoting factors such as SOX9 and DMRT1 in the masculinized gonads.
Publisher: Elsevier BV
Date: 02-1999
Abstract: The orphan nuclear receptor, steroidogenic factor-1 (SF-1), regulates steroidogenic enzyme expression and is essential for gonadal and adrenal development in mammals. We have examined expression of the chicken homologue, cSF-1, during gonadal sex differentiation using whole mount in situ hybridisation and RNase protection assays (RPA). In the youngest embryos examined (day 3.5 stages 21-22), cSF-1 transcripts were already detectable by in situ hybridisation in the undifferentiated genital ridge of both sexes. Expression continued in the gonads of both sexes at the time of sexual differentiation (days 5.5-6.5 stages 28-30). Expression then became higher in developing ovaries compared to testes at days 6.5-8. 5 (stages 30-35). At day 13.5 (stage 40), when the gonads are well differentiated, both ovaries and testes showed cSF-1 expression, with higher levels of expression in the left ovary compared to the right (regressing) gonad in females and compared to testes. RPA analysis of isolated gonads confirmed higher expression of SF-1 in differentiating ovaries relative to testes. Expression of cSF-1 in the developing adrenal gland was similar for both sexes at all stages examined. In tissue sections of day 8.5 whole mount gonads, cSF-1 expression was localised in the medulla of the ovary and was weakly detectable in the testis. These observations indicate that SF-1 has a conserved role in early gonadal and adrenal development in vertebrates. However, upregulation of cSF-1 expression during ovarian differentiation is opposite to the pattern seen in mammals, in which SF-1 is downregulated in females. This difference between the birds and mammals may reflect differences in steroidogenic activity of the embryonic ovary versus the testis in the two groups.
Publisher: Springer Science and Business Media LLC
Date: 12-1999
DOI: 10.1038/45130
Publisher: S. Karger AG
Date: 2005
DOI: 10.1159/000084205
Publisher: Wiley
Date: 15-09-1994
Publisher: Wiley
Date: 19-01-2018
DOI: 10.1002/WDEV.310
Abstract: The Müllerian ducts are part of the embryonic urogenital system. They give rise to mature structures that serve a critical function in the transport and development of the oocyte and/or embryo. In most vertebrates, both sexes initially develop Müllerian ducts during embryogenesis, but they regress in males under the influence of testis‐derived Anti‐Müllerian Hormone (AMH). A number of regulatory factors have been shown to be essential for proper duct development, including Bmp and Wnt signaling molecules, together with homeodomain transcription factors such as PAX2 and LIM1. Later in development, the fate of the ducts erges between males and females and is regulated by AMH and Wnt signaling molecules (duct regression in males) and Hox genes (duct patterning in females). Most of the genes and molecular pathways known to be involved in Müllerian duct development have been elucidated through animal models, namely, the mouse and chicken. In addition, genetic analysis of humans with reproductive tract disorders has further defined molecular mechanisms of duct formation and differentiation. However, despite our current understanding of Müllerian duct development, some questions remain to be answered at the molecular genetic level. This article is categorized under: Early Embryonic Development Development to the Basic Body Plan
Publisher: Springer Science and Business Media LLC
Date: 17-09-2008
Abstract: Meiosis in higher vertebrates shows a dramatic sexual dimorphism: germ cells enter meiosis and arrest at prophase I during embryogenesis in females, whereas in males they enter mitotic arrest during embryogenesis and enter meiosis only after birth. Here we report the molecular analysis of meiosis onset in the chicken model and provide evidence for conserved regulation by retinoic acid. Meiosis in the chicken embryo is initiated late in embryogenesis (day 15.5), relative to gonadal sex differentiation (from day 6). Meiotic germ cells are first detectable only in female gonads from day 15.5, correlating with the expression of the meiosis marker, SCP3. Gonads isolated from day 10.5 female embryos and grown in serum-free medium could still initiate meiosis at day 16.5, suggesting that this process is controlled by an endogenous clock in the germ cells themselves, and/or that germ cells are already committed to meiosis at the time of explantation. Early commitment is supported by the analysis of chicken STRA8 , a pre-meiotic marker shown to be essential for meiosis in mouse. Chicken STRA8 is expressed female-specifically from embryonic day 12.5, preceding morphological evidence of meiosis at day 15.5. Previous studies have shown that, in the mouse embryo, female-specific induction of STRA8 and meiosis are triggered by retinoic acid. A comprehensive analysis of genes regulating retinoic acid metabolism in chicken embryos reveals dynamic expression in the gonads. In particular, the retinoic acid-synthesising enzyme, RALDH2 , is expressed in the left ovarian cortex at the time of STRA8 up-regulation, prior to meiosis. This study presents the first molecular analysis of meiosis onset in an avian embryo. Although aspects of avian meiosis differ from that of mammals, a role for retinoic acid may be conserved.
Publisher: Wiley
Date: 2005
DOI: 10.1002/DVDY.20309
Abstract: In a screen for transcripts differentially expressed during gonadal development in mouse embryos, we identified the novel armadillo-related gene, Alex2. The armadillo (arm) family of proteins share a 42 amino acid tandem repeat motif called the arm domain, through which they interact with different binding partners. These intracellular proteins are implicated in a variety of developmental processes, including cell proliferation, migration, maintenance of tissue integrity, and tumorigenesis. Alex2 is a member of a novel subgroup within the arm family, encoding a protein with a single arm domain and a putative transmembrane or signal sequence. Alex2 has a developmentally regulated expression profile during embryogenesis in the mouse. In the urogenital system, it is strongly expressed in the developing testis but is down-regulated during ovarian development. Alex2 expression is localized within the interstitial cell lineage of the developing testis, which gives rise to peritubular myoid, endothelial, and fetal Leydig cells. Alex2 is also expressed in the developing forebrain and somites and in dorsal root ganglia. In testicular cell lines, Alex2 fusion proteins localize to membrane structures within the cell. The expression profile of Alex2 suggests that it plays a role in the development of several tissues during embryogenesis, notably testicular differentiation. In the developing testis, its expression profile suggests that Alex2 has a role in specification or development of the interstitial cell lineage.
Publisher: The Endocrine Society
Date: 2016
DOI: 10.1210/EN.2015-1697
Abstract: Estrogens play a key role in sexual differentiation of both the gonads and external traits in birds. The production of estrogen occurs via a well-characterized steroidogenic pathway, which is a multistep process involving several enzymes, including cytochrome P450 aromatase. In chicken embryos, the aromatase gene (CYP19A1) is expressed female-specifically from the time of gonadal sex differentiation. Ectopic overexpression of aromatase in male chicken embryos induces gonadal sex reversal, and male embryos treated with estradiol become feminized however, this is not permanent. To test whether a continuous supply of estrogen in adult chickens could induce stable male to female sex reversal, 2 transgenic male chickens overexpressing aromatase were generated using the Tol2/transposase system. These birds had robust ectopic aromatase expression, which resulted in the production of high serum levels of estradiol. Transgenic males had female-like wattle and comb growth and feathering, but they retained male weights, displayed leg spurs, and developed testes. Despite the small s le size, this data strongly suggests that high levels of circulating estrogen are insufficient to maintain a female gonadal phenotype in adult birds. Previous observations of gynandromorph birds and embryos with mixed sex chimeric gonads have highlighted the role of cell autonomous sex identity in chickens. This might imply that in the study described here, direct genetic effects of the male chromosomes largely prevailed over the hormonal profile of the aromatase transgenic birds. This data therefore support the emerging view of at least partial cell autonomous sex development in birds. However, a larger study will confirm this intriguing observation.
Publisher: The Company of Biologists
Date: 15-09-2022
DOI: 10.1242/DEV.200702
Abstract: The lateral plate mesoderm (LPM) is a transient tissue that produces a erse range of differentiated structures, including the limbs. However, the molecular mechanisms that drive early LPM specification and development are poorly understood. In this study, we use single-cell transcriptomics to define the cell-fate decisions directing LPM specification, sub ision and early initiation of the forelimb mesenchyme in chicken embryos. We establish a transcriptional atlas and global cell-cell signalling interactions in progenitor, transitional and mature cell types throughout the developing forelimb field. During LPM sub ision, somatic and splanchnic LPM fate is achieved through activation of lineage-specific gene modules. During the earliest stages of limb initiation, we identify activation of TWIST1 in the somatic LPM as a putative driver of limb bud epithelial-to-mesenchymal transition. Furthermore, we define a new role for BMP signalling during early limb development, revealing that it is necessary for inducing a somatic LPM fate and initiation of limb outgrowth, potentially through activation of TBX5. Together, these findings provide new insights into the mechanisms underlying LPM development, somatic LPM fate choice and early initiation of the vertebrate limb.
Publisher: Elsevier BV
Date: 07-1999
DOI: 10.1016/S0378-1119(99)00179-1
Abstract: Genes implicated in vertebrate sex determination and differentiation were studied in embryonic chicken gonads using reverse transcription and the polymerase chain reaction (RT-PCR). Expression profiles were obtained during gonadal sex differentiation for AMH, SOX9, SOX3, the Wilm's Tumour gene, WT1, and the orphan nuclear receptor genes, SF1 and DAX1. Some of these genes showed sexually dimorphic expression profiles during gonadal development, whereas others were expressed at similar levels in both sexes. The gene encoding Anti-Müllerian hormone (AMH) was expressed in both sexes prior to and during sexual differentiation of the gonads, with levels of expression consistently higher in males than in females. SOX9 expression was male-specific, and was up-regulated after the detection of AMH transcripts. SOX3 expression was observed prior to clear SOX9 expression and was up-regulated in both sexes at the onset of gonadal sex differentiation (but declined later in development). The WT1 gene was highly expressed in both sexes, whereas SF1 expression was clearly higher in developing ovaries compared to testes. DAX1 transcripts were observed in both sexes at all stages examined, but expression appeared somewhat higher in developing ovaries. These expression profiles are analysed in terms of current theories of vertebrate sex determination.
Publisher: The Endocrine Society
Date: 28-02-2021
Abstract: Reproduction in males requires the transfer of spermatozoa from testis tubules via the rete system to the efferent ductules, epididymis, and vas deferens. The rete therefore forms an essential bridging system between the testis and excurrent ducts. Yet the embryonic origin and molecular regulation of rete testis development is poorly understood. This review examines the anatomy, endocrine control, and development of the mammalian rete testis, focusing on recent findings on its molecular regulation, identifying gaps in our knowledge, and identifying areas for future research. The rete testis develops in close association with Sertoli cells of the seminiferous cords, although unique molecular markers are sparce. Most recently, modern molecular approaches such as global RNA-seq have revealed the transcriptional signature of rete cell precursors, pointing to at least a partial common origin with Sertoli cells. In the mouse, genes involved in Sertoli cell development or maintenance, such as Sox9, Wt1, Sf1, and Dmrt1, are also expressed in cells of the rete system. Rete progenitor cells also express unique markers, such as Pax8, E-cadherin, and keratin 8. These must directly or indirectly regulate the physical joining of testis tubules to the efferent duct system and confer other physiological functions of the rete. The application of technologies such as single-cell RNA-seq will clarify the origin and developmental trajectory of this essential component of the male reproductive tract.
Publisher: S. Karger AG
Date: 2016
DOI: 10.1159/000448365
Abstract: Sexual differentiation in birds is controlled genetically as in mammals, although the sex chromosomes are different. Males have a ZZ sex chromosome constitution, while females are ZW. Gene(s) on the sex chromosomes must initiate gonadal sex differentiation during embryonic life, inducing paired testes in ZZ in iduals and unilateral ovaries in ZW in iduals. The traditional view of avian sexual differentiation aligns with that expounded for other vertebrates upon sexual differentiation, the gonads secrete sex steroid hormones that masculinise or feminise the rest of the body. However, recent studies on naturally occurring or experimentally induced avian sex reversal suggest a significant role for direct genetic factors, in addition to sex hormones, in regulating sexual differentiation of the soma in birds. This review will provide an overview of sex determination in birds and both naturally and experimentally induced sex reversal, with emphasis on the key role of oestrogen. We then consider how recent studies on sex reversal and gynandromorphic birds (half male:half female) are shaping our understanding of sexual differentiation in avians and in vertebrates more broadly. Current evidence shows that sexual differentiation in birds is a mix of direct genetic and hormonal mechanisms. Perturbation of either of these components may lead to sex reversal.
Publisher: Elsevier BV
Date: 04-2020
Publisher: S. Karger AG
Date: 2007
DOI: 10.1159/000103177
Abstract: Sex is determined genetically in all birds, but the underlying mechanism remains unknown. All species have a ZZ/ZW sex chromosome system characterised by female (ZW) heterogamety, but the chromosomes themselves can be heteromorphic (in most birds) or homomorphic (in the flightless ratites). Sex in birds might be determined by the dosage of a Z-linked gene (two in males, one in females) or by a dominant ovary-determining gene carried on the W sex chromosome, or both. Sex chromosome aneuploidy has not been conclusively documented in birds to differentiate between these possibilities. By definition, the sex chromosomes of birds must carry one or more sex-determining genes. In this review of avian sex determination, we ask what, when and where? What is the nature of the avian sex determinant? When should it be expressed in the developing embryo, and where is it expressed? The last two questions arise due to evidence suggesting that sex-determining genes in birds might be operating prior to overt sexual differentiation of the gonads into testes or ovaries, and in tissues other than the urogenital system.
Publisher: Elsevier BV
Date: 03-1997
DOI: 10.1016/S0960-0760(96)00196-3
Abstract: Estrogen is implicated in sexual differentiation of the avian gonad. Expression of the estrogen receptor and aromatase genes was therefore examined at the time of gonadal sex differentiation in chicken embryos, using reverse transcription and the polymerase chain reaction (RT-PCR). Estrogen receptor (cER) transcripts were detected in the gonads of both presumptive sexes at embryonic days 4.5, 5.5 and 6.5, and in female but not male urogenital tissues at day 3.5. Aromatase (cAROM) transcripts were detected in female but not male gonads from day 6.5 of embryogenesis, and in adult gonads of both sexes. Both female and male embryos thus express cER mRNA before morphological differentiation of the gonads, which begins on day 5, whereas cAROM expression begins at or shortly after the onset of differentiation and is female-specific. Examination of other tissues showed that, in 5.5-day-old embryos, cER expression was limited to the gonads no transcripts were detected in the mesonephric kidney, liver, brain, hindlimb or heart of either sex. In 9.5-day-old female embryos, cER and cAROM transcripts were present in both the left (ovarian) and the right (regressing) gonads. Altogether, these observations imply that the gonads of both sexes develop the capacity to respond to estrogens early in embryogenesis, before morphological differentiation, whereas the capacity to synthesize estrogens is female-specific and occurs later, at the time of differentiation. These observations are consistent with estrogens having a key role in ovarian development.
Publisher: Wiley
Date: 13-05-2005
DOI: 10.1002/DVDY.20392
Abstract: The hermes gene encodes an RNA-binding protein containing an RNA-recognition motif. Its expression has been described previously in Xenopus and in the developing heart of very young chicken embryos. We have analyzed the expression of cHermes in later heart development, where expression is maintained in the myocardium, and also in previously undescribed sites. cHermes expression first appears in the somites in the first terminally differentiated myocytes of both the epaxial and the hypaxial myotome. Expression is also seen in the primordium of the allantois and continues in the developing allantoic sac. cHermes expression in the pronephric and mesonephric kidneys coincides temporally and spatially with the appearance of the vascular components of the glomeruli. In addition, cHermes expression was seen in the mesoderm of the gut and in the notochord.
Publisher: Oxford University Press (OUP)
Date: 07-2011
DOI: 10.1095/BIOLREPROD.110.088476
Abstract: Tissue-specific patterns of microRNA (miRNA) expression contribute to organogenesis during embryonic development. Using the embryonic chicken gonads as a model for vertebrate gonadogenesis, we previously reported that miRNAs are expressed in a sexually dimorphic manner during gonadal sex differentiation. Being male biased, we hypothesised that up-regulation of microRNA 202* (MIR202*) is characteristic of testicular differentiation. To address this hypothesis, we used estrogen modulation to induce gonadal sex reversal in embryonic chicken gonads and analyzed changes in MIR202* expression. In ovo injection of estradiol-17beta at Embryonic Day 4.5 (E4.5) caused feminization of male gonads at E9.5 and reduced MIR202* expression to female levels. Female gonads treated at E3.5 with an aromatase inhibitor, which blocks estrogen synthesis, were masculinized by E9.5, and MIR202* expression was increased. Reduced MIR202* expression correlated with reduced expression of the testis-associated genes DMRT1 and SOX9, and up-regulation of ovary-associated genes FOXL2 and CYP19A1 (aromatase). Increased MIR202* expression correlated with down-regulation of FOXL2 and aromatase and up-regulation of DMRT1 and SOX9. These results confirm that up-regulation of MIR202* coincides with testicular differentiation in embryonic chicken gonads.
Publisher: Wiley
Date: 28-04-2005
DOI: 10.1002/DVDY.20397
Abstract: We isolated the novel gene Gonad Expressed Transcript (GET) from a chicken embryonic gonad library enriched for differentially expressed male transcripts. Chicken GET encodes a predicted protein containing a Pfam-B 30624 domain with homology to a putative orthologue in mammals. Chicken GET expression was confined to the developing urogenital system. It was first detected in the glomerulus of the mesonephros of both sexes from embryonic day (E) 2.5. At E4.5, expression switches to the gonad of both sexes and then localizes to the gonadal cortex. We isolated the putative mouse orthologue and examined expression in the mouse embryo. Gonadal expression was conserved. Ovarian expression localized to the cortex as in the chicks. However, in contrast to the chicken, testis expression localized to the cords. In the adult, GET is expressed in the ovary but not the testis of both the chicken and the mouse. Expression of GET in the müllerian duct, wolffian duct, metanephric kidney, and external genitalia, suggests that GET may play a wider role in the development of the urogenital system.
Publisher: Wiley
Date: 10-1994
Publisher: Bioscientifica
Date: 09-2015
DOI: 10.1530/REP-15-0106
Abstract: A complex network of gene regulation and interaction drives male sex determination and differentiation. While many important protein-coding genes that are necessary for proper male development have been identified, many disorders in human sex development are still unexplained at the molecular level. This suggests that key factors and regulatory mechanisms are still unknown. In recent years, extensive data have shown that different classes of non-coding RNAs (ncRNAs) play a role in almost all developmental and physiological pathways. Here we review what is known about their role in male sex determination and differentiation not only in mammals, but also other species. While for some processes a key role for ncRNA has been identified, we are still far from having a complete picture.
Publisher: Elsevier BV
Date: 07-1997
Publisher: Public Library of Science (PLoS)
Date: 08-07-2014
Publisher: Informa UK Limited
Date: 12-2010
DOI: 10.1071/MU10030
Publisher: Springer Science and Business Media LLC
Date: 16-09-2015
Publisher: Humana Press
Date: 29-08-2013
DOI: 10.1007/978-1-62703-119-6_12
Abstract: Since the first application of RNA interference (RNAi) in mammalian cells, the expression of short hairpin RNAs (shRNAs) for targeted gene silencing has become a benchmark technology. Using plasmid and viral vectoring systems, the transcription of shRNA precursors that are effectively processed by the RNAi pathway can lead to potent gene knockdown. The past decade has seen continual advancement and improvement to the various strategies that can be used for shRNA delivery, and the use of shRNAs for clinical applications is well underway. Driving these developments has been the many benefits afforded by shRNA technologies, including the stable integration of expression constructs for long-term expression, infection of difficult-to-target cell lines and tissues using viral vectors, and the temporal control of shRNA transcription by inducible promoters. The use of different effector molecule formats, promoters, and vector types, has meant that experiments can be tailored to target specific cell types and minimize cellular toxicities. Through the application of combinatorial RNAi (co-RNAi), multiple shRNA delivery strategies can improve gene knockdown, permit multiple transcripts to be targeted simultaneously, and curtail the emergence of viral escape mutants. This chapter reviews the history, cellular processing, and various applications of shRNAs in mammalian systems, including options for effector molecule design, vector and promoter types, and methods for multiple shRNA delivery.
Publisher: Wiley
Date: 16-04-2018
DOI: 10.1002/WDEV.320
Abstract: The cover image, by Zahida Yesmin Roly et al., is based on the Advanced Review The cell biology and molecular genetics of Müllerian duct development , DOI: 10.1002/wdev.310 . image
Publisher: Springer Science and Business Media LLC
Date: 24-04-2000
Abstract: Vertebrates exhibit a variety of sex determining mechanisms which fall broadly into two classes: environmental or genetic. In birds and mammals sex is determined by a genetic mechanism. In mammals males are the heterogametic sex (XY) with the Y chromosome acting as a dominant determiner of sex due to the action of the testis-determining factor, SRY. In birds females are the heterogametic sex (ZW) however, it is not known whether the W chromosome carries a dominant ovary-determining gene, or whether Z chromosome dosage determines sex. Using an experimental approach, which assumes only that the sex-determining event in birds is accompanied by sex-specific changes in gene expression, we have identified a novel gene, ASW (Avian Sex-specific W-linked). The putative protein for ASW is related to the HIT (histidine triad) family of proteins. ASW shows female-specific expression in genital ridges and maps to the chicken W chromosome. In addition, we show that, with the exception of ratites, ASW is linked to the W chromosome in each of 17 bird species from nine different families of the class Aves.
Publisher: Wiley
Date: 2004
DOI: 10.1002/BIES.10400
Abstract: Not all vertebrates share the familiar system of XX:XY sex determination seen in mammals. In the chicken and other birds, sex is determined by a ZZ:ZW sex chromosome system. Gonadal development in the chicken has provided insights into the molecular genetics of vertebrate sex determination and how it has evolved. Such comparative studies show that vertebrate sex-determining pathways comprise both conserved and ergent elements. The chicken embryo resembles lower vertebrates in that estrogens play a central role in gonadal sex differentiation. However, several genes shown to be critical for mammalian sex determination are also expressed in the chicken, but their expression patterns differ, indicating functional plasticity. While the genetic trigger for sex determination in birds remains unknown, some promising candidate genes have recently emerged. The Z-linked gene, DMRT1, supports the Z-dosage model of avian sex determination. Two novel W-linked genes, ASW and FET1, represent candidate female determinants.
Publisher: Elsevier BV
Date: 11-1997
Abstract: Estrogens have been implicated in sexual differentiation of both the gonads and the genitalia of birds. In chicken embryos, the gonads are steroidogenically active from an early age, and the aromatase gene, (cAROM), necessary for estrogen synthesis, is expressed only in females at the time of gonadal sex differentiation. However, no studies have directly demonstrated the distribution of estrogen receptor (cER) transcripts or proteins in the embryonic avian reproductive system. Whole-mount in situ hybridization and immunohistochemistry were used here to identify sites of estrogen receptor expression in the embryonic chicken urogenital system. Estrogen receptor mRNA was observed in both male and female gonads prior to morphological differentiation, at Stage 26 (4.5 days of incubation), and continued until after sexual dimorphism at Stage 32 (7.5 days). Transcripts of cER were also detected in the Müllerian ducts and developing external genitalia of both sexes. Estrogen receptor protein was analysed in the embryonic gonads by immunohistochemistry and found to be most abundant in the cortex of the left ovary, although it was also present in the medulla of both female gonads. No significant cER protein expression was detected in the male gonad by immunohistochemistry. In contrast, the aromatase gene was expressed in the gonads of female embryos from the onset of sexual dimorphism but was not detectable in male gonads at any stage examined. These findings suggest that estrogen involvement in both gonadogenesis and genital development in chickens is mediated by the estrogen receptor.
Publisher: Cold Spring Harbor Laboratory
Date: 14-01-2022
DOI: 10.1101/2022.01.13.475748
Abstract: The lateral plate mesoderm (LPM) is a transient embryonic tissue that gives rise to a erse range of mature cell types, including the cardiovascular system, the urogenital system, endoskeleton of the limbs, and mesenchyme of the gut. While the genetic processes that drive development of these tissues are well defined, the early cell fate choices underlying LPM development and specification are poorly understood. In this study, we utilize single-cell transcriptomics to define cell lineage specification during development of the anterior LPM and the forelimb field in the chicken embryo. We identify the molecular pathways directing differentiation of the aLPM towards a somatic or splanchnic cell fate, and subsequent emergence of the forelimb mesenchyme. We establish the first transcriptional atlas of progenitor, transitional and mature cell types throughout the early forelimb field and uncover the global signalling pathways which are active during LPM differentiation and forelimb initiation. Specification of the somatic and splanchnic LPM from undifferentiated mesoderm utilizes distinct signalling pathways and involves shared repression of early mesodermal markers, followed by activation of lineage-specific gene modules. We identify rapid activation of the transcription factor TWIST1 in the somatic LPM preceding activation of known limb initiation genes, such as TBX 5, which plays a likely role in epithelial-to-mesenchyme transition of the limb bud mesenchyme. Furthermore, development of the somatic LPM and limb is dependent on ectodermal BMP signalling, where BMP antagonism reduces expression of key somatic LPM and limb genes to inhibit formation of the limb bud mesenchyme. Together, these findings provide new insights into molecular mechanisms that drive fate cell choices during specification of the aLPM and forelimb initiation.
Publisher: Public Library of Science (PLoS)
Date: 28-06-2013
Publisher: Elsevier BV
Date: 04-1995
Publisher: Wiley
Date: 30-03-2013
DOI: 10.1002/DVG.22382
Publisher: Springer Science and Business Media LLC
Date: 14-05-2014
Publisher: Elsevier BV
Date: 06-2009
DOI: 10.1016/J.DIFF.2009.02.001
Abstract: Functional genomics in avian models has lagged behind that of mammals, and the production of transgenic birds has proven to be challenging and time-consuming. All current methods rely upon breeding chimeric birds through at least one generation. Here, we report a rapid method for the ubiquitous expression of GFP in chicken embryos in a single generation (G-0), using the avian retroviral vector, Replication-Competent Avian sarcoma-leukosis virus, with a Splice acceptor, Bryan RSV Pol (RCASBP). High-titre RCASBP retrovirus carrying eGFP was injected into unincubated (stage X) blastoderms in ovo. This resulted in stable and widespread expression of eGFP throughout development in a very high proportion of embryos. Transgenic tissues were identified by fluorescence and immunohistochemistry. These results indicate that chicken blastodermal cells are permissive for infection by the RCASBP virus. This system represents a rapid and efficient method of producing global gene expression in the chicken embryo. The method can be used to generate avian cells with a stable genetic marker, or to induce global expression of a gene of choice. Interestingly, in day 8.5 embryos, somatic cells the embryonic gonads were predominantly GFP positive but primordial germ cells were GFP negative, indicating viral silencing in the embryonic germline. This dichotomy in the gonads allows the isolation or enrichment of the germ cells through negative selection during embryonic stages. This transgenic chicken model is of value in developmental studies, and for the isolation and study of avian primordial germ cells.
Publisher: The Endocrine Society
Date: 15-08-2018
Abstract: Birds have a ZZ male and ZW female sex chromosome system. The relative roles of genetics and hormones in regulating avian sexual development have been revealed by studies on gynandromorphs. Gynandromorphs are rare bilateral sex chimeras, male on one side of the body and female on the other. We examined a naturally occurring gynandromorphic chicken that was externally male on the right side of the body and female on the left. The bird was diploid but with a mix of ZZ and ZW cells that correlated with the asymmetric sexual phenotype. The male side was 96% ZZ, and the female side was 77% ZZ and 23% ZW. The gonads of this bird at sexual maturity were largely testicular. The right gonad was a testis, with SOX9+ Sertoli cells, DMRT1+ germ cells, and active spermatogenesis. The left gonad was primarily testicular, but with some peripheral aromatase-expressing follicles. The bird had low levels of serum estradiol and high levels of testosterone, as expected for a male. Despite the low percentage of ZW cells on that side, the left side had female sex-linked feathering, smaller muscle mass, smaller leg and spur, and smaller wattle than the male side. This indicates that these sexually dimorphic structures must be at least partly independent of sex steroid effects. Even a small percentage of ZW cells appears sufficient to support female sexual differentiation. Given the lack of chromosome-wide dosage compensation in birds, various sexually dimorphic features may arise due to Z-gene dosage differences between the sexes.
Publisher: Elsevier BV
Date: 02-1994
Abstract: It has been hypothesized that steroid hormone production is involved in sexual differentiation of the gonads in reptiles with temperature-dependent sex determination. We have therefore examined steroidogenic enzymes and ovarian differentiation in Crocodylus porosus embryos incubated at 30 degrees, a temperature producing 100% female hatchlings. delta 5-3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) activity was detected only in the adrenal gland before, during, and after the period of ovary differentiation. The same pattern was observed during testis differentiation in embryos incubated at 32 degrees (predominantly male-producing). At no stage was 3 beta-HSD activity detected in the gonads. The tritiated water assay was used to measure aromatase enzyme activity in the gonad-adrenal-mesonephric complex (GAM) during development at 30 degrees C. Aromatase activity in the GAM increased during the period of ovary differentiation. In female C. porosus hatchlings, 85% of the aromatase activity within the GAM was derived from the ovary, 10% from the adrenal, and 5% from the regressing mesonephros. The aromatase inhibitors aminoglutethimide and 4-hydroxyandrostenedione significantly reduced aromatase activity in female hatchling GAMs. In some stage 25 embryos incubated at 32.5 degrees, aromatase activity was low in testes and high in ovaries. These observations show that urogenital tissues of C. porosus are steroidogenically active during gonadal differentiation and that increased aromatase enzyme activity accompanies ovary development at 30 degrees. Steroid synthesis in the GAM of C. porosus embryos may involve interaction between the adrenal glands and the gonads.
Publisher: The Company of Biologists
Date: 03-2023
DOI: 10.1242/DEV.201466
Abstract: During gonadal sex determination, the supporting cell lineage differentiates into Sertoli cells in males and pre-granulosa cells in females. Recently, single cell RNA-seq data have indicated that chicken steroidogenic cells are derived from differentiated supporting cells. This differentiation process is achieved by a sequential upregulation of steroidogenic genes and downregulation of supporting cell markers. The exact mechanism regulating this differentiation process remains unknown. We have identified TOX3 as a previously unreported transcription factor expressed in embryonic Sertoli cells of the chicken testis. TOX3 knockdown in males resulted in increased CYP17A1-positive Leydig cells. TOX3 overexpression in male and female gonads resulted in a significant decline in CYP17A1-positive steroidogenic cells. In ovo knockdown of the testis determinant DMRT1 in male gonads resulted in a downregulation of TOX3 expression. Conversely, DMRT1 overexpression caused an increase in TOX3 expression. Taken together, these data indicate that DMRT1-mediated regulation of TOX3 modulates expansion of the steroidogenic lineage, either directly, via cell lineage allocation, or indirectly, via signaling from the supporting to steroidogenic cell populations.
Publisher: Wiley
Date: 07-1995
Publisher: Wiley
Date: 17-07-2008
DOI: 10.1002/DVDY.22024
Abstract: Balanced production and degradation of retinoids is important in regulating development of several organ systems in the vertebrate embryo. Among these, it is known that retinoic acid (RA), and the retinoid-catabolyzing enzyme CYP26B1 together regulate the sex-specific behavior of germ cells in developing mouse gonads. We report here that the gene encoding a cytosolic class-1 aldehyde dehydrogenase, ALDH1A1, a weak catalyst of RA production, is strongly expressed in a male-specific manner in somatic cells of the developing mouse testis, beginning shortly after Sry expression is first detectable. This expression pattern is conserved in the developing male gonad of the chicken and is dependent on the testis-specific transcription factor SOX9. Our data suggest that low levels of RA may be required for early developmental events in the testis, or that Aldh1a1 expression in the fetus may prefigure a later requirement for ALDH1A1 in regulating spermatogenesis postnatally.
Publisher: Oxford University Press (OUP)
Date: 07-2009
Publisher: Elsevier BV
Date: 08-2005
DOI: 10.1016/J.YDBIO.2005.05.030
Abstract: Male-specific migration of cells from the mesonephric kidney into the embryonic gonad is required for testis formation in the mouse. It is unknown, however, whether this process is specific to the mouse embryo or whether it is a fundamental characteristic of testis formation in other vertebrates. The signalling molecule/s underlying the process are also unclear. It has previously been speculated that male-specific cell migration might be limited to mammals. Here, we report that male-specific cell migration is conserved between mammals (mouse) and birds (quail-chicken) and that it involves proper PDGF signalling in both groups. Interspecific co-cultures of embryonic quail mesonephric kidneys together with embryonic chicken gonads showed that quail cells migrated specifically into male chicken gonads at the time of sexual differentiation. The migration process is therefore conserved in birds. Furthermore, this migration involves a conserved signalling pathway/s. When GFP-labelled embryonic mouse mesonephric kidneys were cultured together with embryonic chicken gonads, GFP+ mouse cells migrated specifically into male chicken gonads and not female gonads. The immigrating mouse cells contributed to the interstitial cell population of the developing chicken testis, with most cells expressing the endothelial cell marker, PECAM. The signalling molecule/s released from the embryonic male chicken gonad is therefore recognised by both embryonic quail and mouse mesonephric cells. A candidate signalling molecule mediating the male-specific cell migration is PDGF. We found that PDGF-A and PDGF receptor-alpha are both up-regulated male-specifically in embryonic chicken and mouse gonads. PDGF signalling involves the phosphotidylinositol 3-kinase (PIK3) pathway, an intracellular pathway proposed to be important for mesonephric cell migration in the mammalian gonad. We found that a component of this pathway, PI3KC2alpha, is expressed male-specifically in developing embryonic chicken gonads at the time of sexual differentiation. Treatment of organ cultures with the selective PDGF receptor signalling inhibitor, AG1296 (tyrphostin), blocked or impaired mesonephric cell migration in both the mammalian and avian systems. Taken together, these studies indicate that a key cellular event in gonadal sex differentiation is conserved among higher vertebrates, that it involves PDGF signalling, and that in mammals is an indirect effect of Sry expression.
Publisher: Springer Science and Business Media LLC
Date: 07-1993
DOI: 10.1007/BF00304622
Publisher: Springer Science and Business Media LLC
Date: 03-2021
Publisher: Springer Science and Business Media LLC
Date: 02-10-2020
DOI: 10.1186/S12864-020-07106-8
Abstract: Müllerian ducts are paired embryonic tubes that give rise to the female reproductive tract in vertebrates. Many disorders of female reproduction can be attributed to anomalies of Müllerian duct development. However, the molecular genetics of Müllerian duct formation is poorly understood and most disorders of duct development have unknown etiology. In this study, we describe for the first time the transcriptional landscape of the embryonic Müllerian duct, using the chicken embryo as a model system. RNA sequencing was conducted at 1 day intervals during duct formation to identify developmentally-regulated genes, validated by in situ hybridization. This analysis detected hundreds of genes specifically up-regulated during duct morphogenesis. Gene ontology and pathway analysis revealed enrichment for developmental pathways associated with cell adhesion, cell migration and proliferation, ERK and WNT signaling, and, interestingly, axonal guidance. The latter included factors linked to neuronal cell migration or axonal outgrowth, such as Ephrin B2, netrin receptor, SLIT1 and class A semaphorins. A number of transcriptional modules were identified that centred around key hub genes specifying matrix-associated signaling factors SPOCK1, HTRA3 and ADGRD1 . Several novel regulators of the WNT and TFG-β signaling pathway were identified in Müllerian ducts, including APCDD1 and DKK1 , BMP3 and TGFBI . A number of novel transcription factors were also identified, including OSR1, FOXE1, PRICKLE1, TSHZ3 and SMARCA2 . In addition, over 100 long non-coding RNAs (lncRNAs) were expressed during duct formation. This study provides a rich resource of new candidate genes for Müllerian duct development and its disorders. It also sheds light on the molecular pathways engaged during tubulogenesis, a fundamental process in embryonic development.
Publisher: UPV/EHU Press
Date: 2009
Abstract: Birds have a ZZ/ZW sex chromosome system, but the mechanism of sex determination remains unknown. The heterogametic sex is female (ZW) and one hypothesis holds that the W chromosome carries a dominant-acting ovary-determining gene. The strongest candidate ovary-determinant on the W chromosome is HINTW, which encodes an aberrant nucleotide hydrolase enzyme. HINTW is conserved amongst all carinate (flying) birds and it is strongly expressed in the gonads and other tissues of female chicken embryos. This and other lines of circumstantial evidence support the proposal that HINTW is the female-determining gene in birds. However, in vivo gain-of-function or loss-of-function studies have not hitherto been reported to test this hypothesis. We tested the potential role of HINTW by mis-expressing it in genetically male (ZZ) embryos, using the RCASBP avian retroviral vector. Strong, widespread expression was delivered throughout the embryo, including the urogenital system, as assessed by whole mount in situ hybridisation. This expression pattern mimicked that seen in normal ZW females, in which HINTW is widely expressed. Strong mis-expression was observed throughout the gonads of genetic male (ZZ) embryos. However, despite strong HINTW expression, ZZ gonads developed normally as bilateral testes. In tissue sections of ZZ urogenital systems transgenic for HINTW, normal testicular histology was observed. Female (ZW) gonads over-expressing HINTW also developed normally, with normal ovarian structure and left/right asymmetry. These results provide genetic evidence against a dominant role for HINTW in avian sex determination.
Publisher: Wiley
Date: 2001
DOI: 10.1002/JEZ.1119
Abstract: The chicken embryo represents a suitable model for studying vertebrate sex determination and gonadal sex differentiation. While the basic mechanism of sex determination in birds is still unknown, gonadal morphogenesis is very similar to that in mammals, and most of the genes implicated in mammalian sex determination have avian homologues. However, in the chicken embryo, these genes show some interesting differences in structure or expression patterns to their mammalian counterparts, broadening our understanding of their functions. The novel candidate testis-determining gene in mammals, DMRT1, is also present in the chicken, and is expressed specifically in the embryonic gonads. In chicken embryos, DMRT1 is more highly expressed in the gonads and Müllerian ducts of male embryos than in those of females. Meanwhile, expression of the orphan nuclear receptor, Steroidogenic Factor 1 (SF1) is up-regulated during ovarian differentiation in the chicken embryo. This contrasts with the expression pattern of SF1 in mouse embryos, in which expression is down-regulated during female differentiation. Another orphan receptor initially implicated in mammalian sex determination, DAX1, is poorly conserved in the chicken. A chicken DAX1 homologue isolated from a urogenital ridge library lacked the unusual DNA-binding motif seen in mammals. Chicken DAX1 is autosomal, and is expressed in the embryonic gonads, showing somewhat higher expression in female compared to male gonads, as in mammals. However, expression is not down-regulated at the onset of testicular differentiation in chicken embryos, as occurs in mice. These comparative data shed light on vertebrate sex determination in general.
Publisher: Wiley
Date: 25-02-2011
DOI: 10.1111/J.1742-4658.2011.08032.X
Abstract: The sex of birds is determined by the inheritance of sex chromosomes (ZZ male and ZW female). Genes carried on one or both of these sex chromosomes control sexual differentiation during embryonic life, producing testes in males (ZZ) and ovaries in females (ZW). This minireview summarizes our current understanding of avian sex determination and gonadal development. Most recently, it has been shown that sex is cell autonomous in birds. Evidence from gynandromorphic chickens (male on one side, female on the other) points to the likelihood that sex is determined directly in each cell of the body, independently of, or in addition to, hormonal signalling. Hence, sex-determining genes may operate not only in the gonads, to produce testes or ovaries, but also throughout cells of the body. In the chicken, as in other birds, the gonads develop into ovaries or testes during embryonic life, a process that must be triggered by sex-determining genes. This process involves the Z-linked DMRT1 gene. If DMRT1 gene activity is experimentally reduced, the gonads of male embryos (ZZ) are feminized, with ovarian-type structure, downregulation of male markers and activation of female markers. DMRT1 is currently the best candidate gene thought to regulate gonadal sex differentiation. However, if sex is cell autonomous, DMRT1 cannot be the master regulator, as its expression is confined to the urogenital system. Female development in the avian model appears to be shared with mammals both the FOXL2 and RSPO1/WNT4 pathways are implicated in ovarian differentiation.
Publisher: Bioscientifica
Date: 02-2000
Abstract: DAX1 is an unusual member of the orphan nuclear receptor family of transcription factors. Mutations in human DAX1 cause X-linked adrenal hypoplasia congenita, while abnormal duplication of the gene is responsible for male-to-female dosage-sensitive sex reversal. Based on these and other observations, DAX1 is thought to play a role in adrenal and gonadal development in mammals. As DAX1 has not previously been described in any other vertebrate, a putative avian DAX1 clone was isolated from an embryonic chicken (Gallus domesticus) urogenital ridge cDNA library. The expression profile of this cDNA was then examined during gonadogenesis. The clone included the conserved 3' ligand-binding motif identified in humans and mice but the 5' region lacked the repeat motif thought to specify a DNA-binding domain in mammals. Southern blot analysis and fluorescence in situ hybridisation mapping showed that the gene is autosomal, located on chromosome 1q. Sequence comparisons showed that the putative chicken DAX1 protein has 63 and 60% identity with the human and mouse proteins respectively over the region of the conserved ligand-binding domain. However, stronger identity (74%) exists with a putative alligator DAX1 sequence over the same region. Northern blotting detected a single 1.4 kb transcript in late embryonic chicken gonads, while RNase protection assays revealed expression in the embryonic gonads of both sexes during the period of sexual differentiation. Expression increased in both sexes during gonadogenesis, but was higher in females than in males. This is the first description of a DAX1 homologue in a non-mammalian vertebrate.
Publisher: Oxford University Press (OUP)
Date: 02-2003
DOI: 10.1095/BIOLREPROD.102.007294
Abstract: Sex in birds is chomosomally based (ZZ male, ZW female), but the mechanism underlying sex determination remains unknown. An unresolved question is whether Z gene dosage plays a role in avian sex determination. DMRT1 is an avian Z-linked gene that shows higher expression in male gonads during embryogenesis and has been proposed as a putative testis-determining gene in birds. The Z-linkage of this gene makes it an ideal candidate for testing the question of gene dosage in avian testis determination. A higher level of DMRT1 expression in male (ZZ) versus female (ZW) embryonic gonads may reflect the presence of two Z-linked copies in the male, or it may be due to specific and active upregulation of DMRT1 during testis formation. A functional interventionist strategy was used to distinguish between these two possibilities. DMRT1 expression was analyzed in chicken embryos during experimentally induced female-to-male sex reversal, using the aromatase enzyme inhibitor fadrozole. DMRT1 expression was analyzed by whole mount in situ hybridization and reverse transcription polymerase chain reaction (for mRNA) and indirect immunofluorescence (for protein). Female-to-male sex-reversed embryos (genetically ZW) showed elevated levels of DMRT1 expression similar to those of normal males (with two copies of the Z chromosome). Elevated levels of DMRT1 are therefore associated with testis development, both in normal males (ZZ) and in sex-reversed females (ZW). SOX9 expression was also activated during female-to-male sex reversal but appeared delayed relative to DMRT1 upregulation. These results show that testis development does not require two Z-linked copies of DMRT1, but it does involve active upregulation of the gene. Higher levels of DMRT1 expression during testis differentiation therefore do not simply reflect a gene dosage difference between the two sexes but imply active involvement in male development.
Publisher: UPV/EHU Press
Date: 2018
Publisher: Cold Spring Harbor Laboratory
Date: 31-03-2021
DOI: 10.1101/2021.03.30.437645
Abstract: During early embryogenesis in amniotic vertebrates, the gonads differentiate into either ovaries or testes. The first cell lineage to differentiate gives rise to the supporting cells Sertoli cells in males and pre-granulosa cells in females. These key cell types direct the differentiation of the other cell types in the gonad, including steroidogenic cells. The gonadal surface epithelium and the interstitial cell populations are less well studied, and little is known about their sexual differentiation programs. Here, we show the requirement of the transcription factor gene TGIF1 for ovarian development in the chicken embryo. TGIF1 is expressed in the two principal ovarian somatic cell populations, the cortex and the pre-granulosa cells of the medulla. TGIF1 expression is associated with an ovarian phenotype in sex reversal experiments. In addition, targeted over-expression and gene knockdown experiments indicate that TGIF1 is required for proper ovarian cortical formation. TGIF1 is identified as the first known regulator of juxtacortical medulla formation. These findings provide new insights into chicken ovarian differentiation and development, specifically in the process of cortical and juxtacortical medulla formation, a poorly understood area. The transcription factor TGIF1 is required for proper ovarian sex differentiation in chicken embryos, regulating development of the cortical and juxtacortical medulla, independently of the supporting cell sex lineage.
Publisher: Elsevier BV
Date: 04-2014
Publisher: Public Library of Science (PLoS)
Date: 07-03-2011
Publisher: Springer Science and Business Media LLC
Date: 26-08-2009
DOI: 10.1038/NATURE08298
Abstract: Sex in birds is chromosomally based, as in mammals, but the sex chromosomes are different and the mechanism of avian sex determination has been a long-standing mystery. In the chicken and all other birds, the homogametic sex is male (ZZ) and the heterogametic sex is female (ZW). Two hypotheses have been proposed for the mechanism of avian sex determination. The W (female) chromosome may carry a dominant-acting ovary determinant. Alternatively, the dosage of a Z-linked gene may mediate sex determination, two doses being required for male development (ZZ). A strong candidate avian sex-determinant under the dosage hypothesis is the conserved Z-linked gene, DMRT1 (doublesex and mab-3-related transcription factor 1). Here we used RNA interference (RNAi) to knock down DMRT1 in early chicken embryos. Reduction of DMRT1 protein expression in ovo leads to feminization of the embryonic gonads in genetically male (ZZ) embryos. Affected males show partial sex reversal, characterized by feminization of the gonads. The feminized left gonad shows female-like histology, disorganized testis cords and a decline in the testicular marker, SOX9. The ovarian marker, aromatase, is ectopically activated. The feminized right gonad shows a more variable loss of DMRT1 and ectopic aromatase activation, suggesting differential sensitivity to DMRT1 between left and right gonads. Germ cells also show a female pattern of distribution in the feminized male gonads. These results indicate that DMRT1 is required for testis determination in the chicken. Our data support the Z dosage hypothesis for avian sex determination.
Publisher: The Company of Biologists
Date: 15-08-2021
DOI: 10.1242/DEV.199646
Abstract: During early embryogenesis in amniotic vertebrates, the gonads differentiate into either ovaries or testes. The first cell lineage to differentiate gives rise to the supporting cells: Sertoli cells in males and pre-granulosa cells in females. These key cell types direct the differentiation of the other cell types in the gonad, including steroidogenic cells. The gonadal surface epithelium and the interstitial cell populations are less well studied, and little is known about their sexual differentiation programs. Here, we show the requirement of the homeobox transcription factor gene TGIF1 for ovarian development in the chicken embryo. TGIF1 is expressed in the two principal ovarian somatic cell populations: the cortex and the pre-granulosa cells of the medulla. TGIF1 expression is associated with an ovarian phenotype in estrogen-mediated sex reversal experiments. Targeted misexpression and gene knockdown indicate that TGIF1 is required, but not sufficient, for proper ovarian cortex formation. In addition, TGIF1 is identified as the first known regulator of juxtacortical medulla development. These findings provide new insights into chicken ovarian differentiation and development, specifically cortical and juxtacortical medulla formation.
Publisher: S. Karger AG
Date: 12-09-2013
DOI: 10.1159/000342358
Abstract: In birds as in mammals, sex is determined at fertilization by the inheritance of sex chromosomes. However, sexual differentiation – development of a male or female phenotype – occurs during embryonic development. Sex differentiation requires the induction of sex-specific developmental pathways in the gonads, resulting in the formation of ovaries or testes. Birds utilize a different sex chromosome system to that of mammals, where females are the heterogametic sex (carrying Z and W chromosomes), while males are homogametic (carrying 2 Z chromosomes). Therefore, while some genes essential for testis and ovarian development are conserved, important differences also exist. Namely, the key mammalian male-determining factor SRY does not exist in birds, and another transcription factor, DMRT1, plays a central role in testis development. In contrast to our understanding of testis development, ovarian differentiation is less well-characterized. Given the presence of a female-specific chromosome, studies in chicken will provide insight into the induction and function of female-specific gonadal pathways. In this review, we discuss sexual differentiation in chicken embryos, with emphasis on ovarian development. We highlight genes that may play a conserved role in this process, and discuss how interaction between ovarian pathways may be regulated.
Publisher: Springer Science and Business Media LLC
Date: 2013
Publisher: The Endocrine Society
Date: 11-06-2021
Publisher: MDPI AG
Date: 10-09-2020
DOI: 10.3390/IJMS21186614
Abstract: The gonads are unique among the body’s organs in having a developmental choice: testis or ovary formation. Gonadal sex differentiation involves common progenitor cells that form either Sertoli and Leydig cells in the testis or granulosa and thecal cells in the ovary. Single-cell analysis is now shedding new light on how these cell lineages are specified and how they interact with the germline. Such studies are also providing new information on gonadal maturation, ageing and the somatic-germ cell niche. Furthermore, they have the potential to improve our understanding and diagnosis of Disorders/Differences of Sex Development (DSDs). DSDs occur when chromosomal, gonadal or anatomical sex are atypical. Despite major advances in recent years, most cases of DSD still cannot be explained at the molecular level. This presents a major pediatric concern. The emergence of single-cell genomics and transcriptomics now presents a novel avenue for DSD analysis, for both diagnosis and for understanding the molecular genetic etiology. Such -omics datasets have the potential to enhance our understanding of the cellular origins and pathogenesis of DSDs, as well as infertility and gonadal diseases such as cancer.
Publisher: Springer Science and Business Media LLC
Date: 24-07-2008
Publisher: S. Karger AG
Date: 16-11-2012
DOI: 10.1159/000334059
Abstract: Sex in birds is determined genetically, as in mammals. However, in birds, female is the heterogametic sex (ZW), while the male is homogametic (ZZ). Although the exact mechanism of avian sex determination is still unclear, genes on one or both of the sex chromosomes must control sexual differentiation of the embryonic gonads into testes or ovaries, and eventually all other sexually dimorphic features. In this review of disorders of sexual development in poultry, we focus upon the gonads and external dimorphisms. Abnormalities of sexual development in poultry can be broadly ided into 2 types: those due to disturbances in sex hormone production by the gonads, and those due to abnormal inheritance of sex chromosomes. Recent studies on gynandromorphic chickens (half male, half female) point to the importance of genetic over hormonal factors in controlling sexual development in fowl.
Publisher: Cold Spring Harbor Laboratory
Date: 25-11-2022
DOI: 10.1101/2022.11.23.516993
Abstract: Between tetrapods the limbs have undergone considerable remodelling to achieve unique adaptive behaviours. The forelimb is an ideal model for exploring the molecular basis of adaptive limb development, as it shows remarkable structural variation and is accessible for experimental manipulation. Of the most striking alterations to limb shape is the evolution of powered flight in birds. However, subsequently the flightless ratites (Paleognathae) have further evolved multiple instances of wing reductions, each utilizing distinct molecular mechanisms and displaying heterochrony with flighted birds (Neoaves). The emu has evolved a greatly reduced wing, consisted of a single digit. Thus, the emu is an excellent model to comparatively determine the cellular and molecular basis of wing heterochrony. We utilize comparative single cell transcriptomics of the developing forelimb field in the emu and chicken, to identify the source of the emus reduced wing. This was observed to occur via reduced specification and commitment of lateral plate mesoderm limb progenitor cells, which was accompanied by differential gene expression, persisting during limb initiation and outgrowth. These data suggest a progenitor allocation model, whereby altered limb morphologies may be achieved through altered commitment of precursor cells which act as an underlying template for pre- and post-patterning mechanisms.
Publisher: MDPI AG
Date: 21-09-2021
Abstract: As in other vertebrates, avian testes are the site of spermatogenesis and androgen production. The paired testes of birds differentiate during embryogenesis, first marked by the development of pre-Sertoli cells in the gonadal primordium and their condensation into seminiferous cords. Germ cells become enclosed in these cords and enter mitotic arrest, while steroidogenic Leydig cells subsequently differentiate around the cords. This review describes our current understanding of avian testis development at the cell biology and genetic levels. Most of this knowledge has come from studies on the chicken embryo, though other species are increasingly being examined. In chicken, testis development is governed by the Z-chromosome-linked DMRT1 gene, which directly or indirectly activates the male factors, HEMGN, SOX9 and AMH. Recent single cell RNA-seq has defined cell lineage specification during chicken testis development, while comparative studies point to deep conservation of avian testis formation. Lastly, we identify areas of future research on the genetics of avian testis development.
Publisher: Springer Science and Business Media LLC
Date: 02-03-2016
Publisher: Elsevier BV
Date: 12-2002
DOI: 10.1016/S0925-4773(03)00094-7
Abstract: Vertebrate DM domain genes encode a novel group of proteins related to the Drosophila doublesex and Caenorhabditis elegans mab-3 transcription factors. It is shown here that the recently identified gene, DMRT3, has a restricted embryonic expression profile that is conserved in chicken and mouse embryos. DMRT3 is expressed primarily in the forebrain, neural tube and nasal placode of both species. In the chicken, DMRT3 is also expressed in newly forming tail somites at early developmental stages and, later, in the Müllerian ducts of the urogenital system.
Publisher: Elsevier BV
Date: 06-2012
DOI: 10.1016/J.YDBIO.2012.03.025
Abstract: MHM is a chicken Z chromosome-linked locus that is methylated and transcriptionally silent in male cells, but is hypomethylated and transcribed into a long non-coding RNA in female cells. MHM has been implicated in both localised dosage compensation and sex determination in the chicken embryo, but direct evidence is lacking. We investigated the potential role of MHM in chicken embryonic development, using expression analysis and retroviral-mediated mis-expression. At embryonic stages, MHM is only expressed in females. Northern blotting showed that both sense and antisense strands of the MHM locus are transcribed, with the sense strand being more abundant. Whole mount in situ hybridization confirmed that the sense RNA is present in developing female embryos, notably in gonads, limbs, heart, branchial arch and brain. Within these cells, the MHM RNA is localized to the nucleus. The antisense transcript is lowly expressed and has a cytoplasmic localization in cells. Mis-expression of MHM sense and antisense sequences results in overgrowth of tissues in which transcripts are predominantly expressed. This includes altered asymmetric ovarian development in females. In males, MHM mis-expression impairs gonadal expression of the testis gene, DMRT1. Both MHM sense and antisense mis-expression cause brain abnormalities, while MHM sense causes an increase in male-biased embryo mortality. These results indicate that MHM has a role in chicken normal embryonic development, including gonadal sex differentiation.
Start Date: 2010
End Date: 2014
Funder: Australian Research Council
View Funded ActivityStart Date: 2011
End Date: 2013
Funder: Australian Research Council
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End Date: 2013
Funder: Australian Research Council
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End Date: 2008
Funder: Australian Research Council
View Funded ActivityStart Date: 2016
End Date: 2018
Funder: Australian Research Council
View Funded ActivityStart Date: 2019
End Date: 2021
Funder: Australian Research Council
View Funded ActivityStart Date: 2016
End Date: 2018
Funder: Australian Research Council
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