ORCID Profile
0000-0001-7158-3360
Current Organisation
Université de Montreal
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: UPV/EHU Press
Date: 2014
Abstract: Embryonic diapause, the temporary suspension of development of the embryo, is a fascinating reproductive strategy that has been frequently exploited across the animal kingdom. It is characterized by an arrest in development that occurs at the blastocyst stage in over 130 species of mammals. Its presumed function is to uncouple mating from parturition, to ensure that both occur at the most propitious moment for survival of the species. Diapause can be facultative, i.e. induced by physiological conditions, or obligate, i.e. present in every gestation of a species. In the latter case, the proximal signals for regulation are related to photoperiod. Three erse models, the mouse, the mustelid carnivores and the wallaby have been studied in detail. From these studies it can be discerned that, although the endocrine cues responsible for induction of diapause and re-initiation of development vary widely between species, there are a number of commonalities. Evidence to date indicates that the uterus exercises the proximal regulatory influence over whether an embryo enters into and when it exits from diapause. Some factors have been identified that appear crucial to this regulation, in particular, the polyamines. Recent studies indicate that diapause can be induced in species where it does not exist in nature. This suggests that the potential for diapause in mammals to be due to a single evolutionary event, to which control mechanisms adapted when the trait was beneficial to reproductive success. Further work at the molecular, cellular and organismic levels will be required before the physiological basis of diapause is resolved.
Publisher: Oxford University Press (OUP)
Date: 25-05-2016
DOI: 10.1095/BIOLREPROD.116.139204
Abstract: Embryonic diapause is an evolutionary strategy to ensure that offspring are born when maternal and environmental conditions are optimal for survival. In many species of carnivores, obligate embryonic diapause occurs in every gestation. Reciprocal embryo transplant studies indicate that embryo arrest during diapause is conferred by uterine conditions and is due to a lack of specific factors necessary for continued development. In previous studies, global gene expression analysis revealed reduced uterine expression during diapause of a cluster of genes in the mink that regulate the abundance of polyamines, including ornithine decarboxylase 1 (ODC1). In addition, in vivo inhibition of the conversion of ornithine to the polyamine, putrescine, induced a reversible arrest in mink embryonic development and an arrest in trophoblast cell proliferation in vitro. Previous studies have implicated prolactin as the principal endocrine signal to terminate diapause. In this study, uterine expression of both the progesterone and estrogen receptors remained low at reactivation whilst the prolactin receptor was expressed at all times. Treatment of mink uterine epithelial cells with varying doses of prolactin indicated that this hormone induces ODC1 expression in the uterus via pSTAT1 and mTOR, thereby regulating uterine polyamine levels. In addition, we performed global gene expression analysis on mink embryos to further explore dynamic changes during diapause and found 94 genes upregulated at reactivation from diapause. Three polyamine-related genes, including ODC1, were also upregulated at reactivation from diapause. To establish whether polyamines mitigate escape from embryonic diapause, we collected mink embryos in diapause and incubated them in vitro with putrescine. Increase in embryo volume, the first indication of emergence from diapause, was observed within the first 5 days of culture in all viable embryos treated with putrescine, and the duration of embryo survival was increased threefold. Concomitant increases were also observed in both the total number of cells and the proportion of iding cells in putrescine-treated embryos whilst control embryos remained in the diapause state. In further studies, inhibition of polyamine synthesis abrogated proliferation in cells derived from the inner cell mass of the mink embryo, while putrescine induced dose-dependent increases in cell ision. We conclude that supplementation of embryos in diapause with putrescine results in their escape from developmental dormancy. These results provide strong evidence that obligate diapause in vivo is caused by the paucity of polyamines necessary for activation of the embryo after prolactin-induced termination of diapause.
Publisher: Oxford University Press (OUP)
Date: 31-03-2017
Abstract: Embryonic diapause is a period of developmental arrest which requires coordination of a molecular cross-talk between the endometrium and blastocyst to ensure a successful reactivation, but the exact mechanisms are undefined. The objectives of this study were to screen the tammar blastocyst for potential diapause control factors and to investigate the potential for members of the epidermal growth factor (EGF) family to coordinate reactivation. A select number of factors were also examined in the mink to determine whether their expression patterns were conserved across diapause species. The full-length sequences of the tammar genes of interest were first cloned to establish their level of sequence conservation with other mammals. The uterine expression of EGF family members EGF and heparin-binding EGF (HBEGF) and their receptors (EGFR and erb-b2 receptor tyrosine kinase 4 (ERBB4)) was determined by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. Both HBEGF and EGF were significantly upregulated at reactivation compared to diapause. In the blastocyst, the expression of the potential diapause factors Forkhead box class O family members (FOXO1, FOXO3, and FOXO4), tumor protein 53 (TP53), cyclin-dependent kinase inhibitor 1A (CDKN1A), and the EGF family were examined by RT-PCR and immunofluorescence. Nuclear (and hence active) FOXO expression was confirmed for the first time in a mammalian diapause blastocyst in both the tammar and the mink-CDKN1A was also expressed, but TP53 is not involved and EGFR was not detected in the blastocyst. These results indicate that the EGF family, FOXOs, and CDKN1A are promising candidates for the molecular control of embryonic diapause in mammals.
Publisher: Oxford University Press (OUP)
Date: 16-06-2017
Abstract: Embryonic diapause is a common reproductive strategy amongst mammals, requiring an intimate cross-talk between the endometrium and the blastocyst. To date, the precise molecular signals responsible are unknown in the mouse or any other mammal. Previous studies in the mink implicate polyamines as major regulators of the control of diapause. In the mouse, inhibiting the rate-limiting enzyme of polyamine synthesis, ornithine decarboxylase (ODC1) during early pregnancy largely prevents implantation, but the fate of the nonimplanted embryos is unknown. To determine whether polyamines control mouse embryonic diapause, we treated pregnant mice with an ODC1 inhibitor from d3.5 to d6.5 postcoitum. At d7.5, 72% of females had no signs of implantation whilst the remaining females exhibited disrupted placental formation and degenerate embryos. In the females with no implantation, we obtained viable blastocysts that had attenuated cell proliferation, indicating a state of diapause. When cultured in vitro, these exhibited trophoblast outgrowth, indicative of reactivation of embryogenesis. In contrast, direct culture of d3.5 blastocysts with an ODC1 inhibitor failed to cause entry into diapause. Examination of the polyamine pathway enzymes and a number of implantation factors indicated inhibition of ODC1 resulted in a uterine phenotype that resembled diapause, with some compensatory increases in crucial genes. Thus, we conclude that an absence or paucity of polyamines induces the uterine quiescence that causes entry of the blastocyst into embryonic diapause.
Publisher: CSIRO Publishing
Date: 2019
DOI: 10.1071/RD18235
Abstract: Implantation is essential for the establishment of a successful pregnancy, and the preimplantation period plays a significant role in ensuring implantation occurs in a timely and coordinated manner. This requires effective maternal–embryonic signalling, established during the preimplantation period, to synchronise development. Although multiple factors have been identified as present during this time, the exact molecular mechanisms involved are unknown. Polyamines are small cationic molecules that are ubiquitously expressed from prokaryotes to eukaryotes. Despite being first identified over 300 years ago, their essential roles in cell proliferation and growth, including cancer, have only been recently recognised, with new technologies and interest resulting in rapid expansion of the polyamine field. This review provides a summary of our current understanding of polyamine synthesis, regulation and function with a focus on recent developments demonstrating the requirements for polyamines during the establishment of pregnancy up to the implantation stage, in particular the role of polyamines in the control of embryonic diapause and the identification of an alternative pathway for their synthesis in sheep pregnancy. This, along with other novel discoveries, provides new insights into the control of the peri-implantation period in mammals and highlights the complexities that exist in regulating this critical period of pregnancy.
Publisher: The Royal Society
Date: 04-2013
DOI: 10.1098/RSOB.130035
Abstract: Mammalian embryonic diapause is a phenomenon defined by the temporary arrest in blastocyst growth and metabolic activity within the uterus which synchronously becomes quiescent to blastocyst activation and implantation. This reproductive strategy temporally uncouples conception from parturition until environmental or maternal conditions are favourable for the survival of the mother and newborn. The underlying molecular mechanism by which the uterus and embryo temporarily achieve quiescence, maintain blastocyst survival and then resume blastocyst activation with subsequent implantation remains unknown. Here, we show that uterine expression of Msx1 or Msx2 , members of an ancient, highly conserved homeobox gene family, persists in three unrelated mammalian species during diapause, followed by rapid downregulation with blastocyst activation and implantation. Mice with uterine inactivation of Msx1 and Msx2 fail to achieve diapause and reactivation. Remarkably, the North American mink and Australian tammar wallaby share similar expression patterns of MSX1 or MSX2 as in mice — it persists during diapause and is rapidly downregulated upon blastocyst activation and implantation. Evidence from mouse studies suggests that the effects of Msx genes in diapause are mediated through Wnt5a, a known transcriptional target of uterine Msx . These studies provide strong evidence that the Msx gene family constitutes a common conserved molecular mediator in the uterus during embryonic diapause to improve female reproductive fitness.
No related grants have been discovered for Bruce Murphy.