ORCID Profile
0000-0001-8281-3045
Current Organisations
Hudson Institute of Medical Research
,
Monash University
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Publisher: Oxford University Press (OUP)
Date: 25-01-2016
DOI: 10.1534/GENETICS.115.181321
Abstract: The maternally inherited mitochondrial genome (mtDNA) is present in multimeric form within cells and harbors sequence variants (heteroplasmy). While a single mtDNA variant at high load can cause disease, naturally occurring variants likely persist at low levels across generations of healthy populations. To determine how naturally occurring variants are segregated and transmitted, we generated a mini-pig model, which originates from the same maternal ancestor. Following next-generation sequencing, we identified a series of low-level mtDNA variants in blood s les from the female founder and her daughters. Four variants, ranging from 3% to 20%, were selected for validation by high-resolution melting analysis in 12 tissues from 31 animals across three generations. All four variants were maintained in the offspring, but variant load fluctuated significantly across the generations in several tissues, with sex-specific differences in heart and liver. Moreover, variant load was persistently reduced in high-respiratory organs (heart, brain, diaphragm, and muscle), which correlated significantly with higher mtDNA copy number. However, oocytes showed increased heterogeneity in variant load, which correlated with increased mtDNA copy number during in vitro maturation. Altogether, these outcomes show that naturally occurring mtDNA variants segregate and are maintained in a tissue-specific manner across generations. This segregation likely involves the maintenance of selective mtDNA variants during organogenesis, which can be differentially regulated in oocytes and preimplantation embryos during maturation.
Publisher: Wiley
Date: 03-05-2018
DOI: 10.1002/MRD.22985
Abstract: Mitochondrial DNA (mtDNA) deficient metaphase II porcine oocytes are less likely to fertilize and more likely to arrest during preimplantation development. However, they can be supplemented with autologous populations of mitochondria at the time of fertilization, which significantly increases mtDNA copy number by the 2-cell stage due to the modulation of DNA methylation at a CpG island of the gene encoding the mtDNA-specific polymerase, POLG, and promotes preimplantation development. Although mitochondrial supplementation does not increase development rates or mtDNA copy number in oocytes with normal levels of mtDNA copy number, we tested whether this approach would also impact on chromosomal gene expression patterns in these oocytes at each stage of preimplantation development. Here, we have compared the gene expression profiles of embryos produced by mitochondrial supplementation at the time of fertilization with embryos produced by in vitro fertilization (IVF) using a panel of genes associated with different stages of preimplantation development. When compared to IVF-derived embryos, 27 (34%) genes were differentially expressed in supplemented embryos but this was restricted to one or two developmental stages. However, 53 (66%) genes were comparably expressed across all six stages and by the blastocyst stage 4 (5%) genes were differentially expressed. We conclude that additional copies of mtDNA can induce changes in gene expression at various stages of preimplantation development with the first changes occurring prior to maternal-to-zygotic transition (MZT). However, these changes appear to be transitory suggesting that some genomic resetting is taking place.
Publisher: Springer Science and Business Media LLC
Date: 18-03-2016
DOI: 10.1038/SREP23229
Abstract: An increasing number of women fail to achieve pregnancy due to either failed fertilization or embryo arrest during preimplantation development. This often results from decreased oocyte quality. Indeed, reduced mitochondrial DNA copy number (mitochondrial DNA deficiency) may disrupt oocyte quality in some women. To overcome mitochondrial DNA deficiency, whilst maintaining genetic identity, we supplemented pig oocytes selected for mitochondrial DNA deficiency, reduced cytoplasmic maturation and lower developmental competence, with autologous populations of mitochondrial isolate at fertilization. Supplementation increased development to blastocyst, the final stage of preimplantation development, and promoted mitochondrial DNA replication prior to embryonic genome activation in mitochondrial DNA deficient oocytes but not in oocytes with normal levels of mitochondrial DNA. Blastocysts exhibited transcriptome profiles more closely resembling those of blastocysts from developmentally competent oocytes. Furthermore, mitochondrial supplementation reduced gene expression patterns associated with metabolic disorders that were identified in blastocysts from mitochondrial DNA deficient oocytes. These results demonstrate the importance of the oocyte’s mitochondrial DNA investment in fertilization outcome and subsequent embryo development to mitochondrial DNA deficient oocytes.
Publisher: CSIRO Publishing
Date: 2018
DOI: 10.1071/RD17408
Abstract: In mammalian species, the mitochondrial genome is between 16.2 and 16.7 kb in size and encodes key proteins associated with the cell’s major energy-generating apparatus, the electron transfer chain. The maternally inherited mitochondrial genome has, until recently, been thought to be only involved in the production of energy. In this review, we analyse how the mitochondrial genome influences the developing embryo and cellular differentiation, as well as fetal and offspring health and wellbeing. We make specific reference to two assisted reproductive technologies, namely mitochondrial supplementation and somatic cell nuclear transfer, and how modulating the mitochondrial content in the oocyte influences embryo viability and the potential to generate enhanced offspring for livestock production purposes. We also explain why it is important to ensure that the transmission of only one population of mitochondrial (mt) DNA is maintained through to the offspring and why two populations of genetically distinct mitochondrial genomes could be deleterious. Finally, we explain how mtDNA influences chromosomal gene expression patterns in developing embryos and cells primarily by modulating DNA methylation patterns through factors associated with the citric acid cycle. These factors can then modulate the ten–eleven translocation (TET) pathway, which, in turn, determines whether a cell is in a more or less DNA methylated state.
Publisher: Elsevier BV
Date: 07-2016
DOI: 10.1016/J.DOMANIEND.2016.03.005
Abstract: The vast majority of cellular energy is generated through the process of oxidative phosphorylation, which takes place in the electron transport chain in the mitochondria. The electron transport chain is encoded by 2 genomes, the chromosomal and the mitochondrial genomes. Mitochondrial DNA is associated with a number of traits, which include tolerance to heat, growth and physical performance, meat and milk quality, and fertility. Mitochondrial genomes can be clustered into groups known as mtDNA haplotypes. Mitochondrial DNA haplotypes are a potential genetic source for manipulating phenotypes in farm animals. The use of assisted reproductive technologies, such as nuclear transfer, allows favorable chromosomal genetic traits to be mixed and matched with sought after mtDNA haplotype traits. As a result super breeds can be generated.
Publisher: Oxford University Press (OUP)
Date: 13-03-2018
Abstract: What are the molecular differences between mitochondrial DNA (mtDNA)-deficient and mtDNA-normal oocytes and how does mitochondrial supplementation alter these? Changes to DNA methylation in a 5' cytosine-phosphate-guanine 3' (CpG) island in the mtDNA-specific replication factor (DNA polymerase gamma (POLG)) of mtDNA-deficient oocytes mediates an increase in mtDNA copy number by the 2-cell stage that positively modulates the expression of nuclear genes, which affect cellular and metabolic processes, following autologous mitochondrial supplementation. Too few copies of mtDNA in mature oocytes can lead to fertilisation failure or preimplantation embryo arrest. mtDNA-deficient oocytes that progress to blastocyst express genes associated with poor cellular and metabolic processes, transcriptional activation and mitochondrial biogenesis. Using a pig oocyte model, we assessed mtDNA-deficient and mtDNA-normal oocytes during in vitro maturation for mtDNA variants and levels of DNA methylation in POLG. We supplemented mtDNA-deficient oocytes with autologous populations of mitochondria to determine if there were changes to DNA methylation in POLG that coincided with increases in mtDNA copy number. We assessed metaphase II mtDNA-deficient and mtDNA-normal oocytes by RNA sequencing to identify differentially expressed genes and compared their profiles to blastocysts derived from mtDNA-normal, mtDNA-deficient and supplemented mtDNA-deficient oocytes. mtDNA variant analysis (n = 24), mtDNA copy number (n = 60), POLG gene expression (n = 24), and RNA sequencing (n = 32 single and 12 pooled cohorts of n = 5) were performed on oocytes and embryos. DNA methylation of a CpG island in POLG was determined quantitatively by pyrosequencing on oocytes to 2-cell embryos (n = 408). Bioinformatics tools were used to assess differences between mtDNA-normal and mtDNA-deficient oocytes and between mtDNA-normal and mtDNA-deficient oocytes and supplemented oocytes and their blastocyst stage equivalents. Whilst mtDNA-deficient oocytes regulated variants less stringently during maturation (P < 0.05), there were no differences in the ratio of variants in mature-stage oocytes. However, mtDNA-normal mature oocytes had significantly more molecules affected due to their higher copy number (P < 0.0001). Normal mature oocytes differently DNA methylated a CpG island in POLG compared with mtDNA-deficient oocytes (P < 0.01). Supplementation of mtDNA-deficient oocytes modulated DNA methylation at this CpG island leading to a mtDNA replication event prior to embryonic genome activation inducing significant increases in mtDNA copy number. RNA-Seq identified 57 differentially expressed genes (false discovery rate (FDR) < 0.05) between the two cohorts of oocytes with blastocyst stage gene expression altered by supplementation of mtDNA-deficient oocytes (P < 0.05) including genes associated with metabolic disorders. One key factor was branched chain amino acid transaminase 2 (BCAT2), a regulator of amino acid metabolism and associated with diabetes. Sequence data are available on the NCBI Sequence Read Archive under the project number PRJNA422295. RNA sequencing data were deposited into NCBI Gene Expression Omnibus, under the accession number GSE108900. Whilst this work was conducted in a species that is highly relevant to human reproduction, the outcomes need to be tested in human oocytes and blastocysts prior to clinical application. The outcomes demonstrate a mechanism of action following mtDNA supplementation of mtDNA-deficient oocytes that results in improved gene expression at the blastocyst stage of development. This work was funded by OvaScience Inc. OvaScience did not influence the study design, analysis of results or interpretation of the data.
Publisher: Springer Science and Business Media LLC
Date: 11-09-2017
DOI: 10.1038/CDDISCOVERY.2017.62
Abstract: Mitochondrial DNA copy number is strictly regulated during development as naive cells differentiate into mature cells to ensure that specific cell types have sufficient copies of mitochondrial DNA to perform their specialised functions. Mitochondrial DNA haplotypes are defined as specific regions of mitochondrial DNA that cluster with other mitochondrial sequences to show the phylogenetic origins of maternal lineages. Mitochondrial DNA haplotypes are associated with a range of phenotypes and disease. To understand how mitochondrial DNA haplotypes induce these characteristics, we used four embryonic stem cell lines that have the same set of chromosomes but possess different mitochondrial DNA haplotypes. We show that mitochondrial DNA haplotypes influence changes in chromosomal gene expression and affinity for nuclear-encoded mitochondrial DNA replication factors to modulate mitochondrial DNA copy number, two events that act synchronously during differentiation. Global DNA methylation analysis showed that each haplotype induces distinct DNA methylation patterns, which, when modulated by DNA demethylation agents, resulted in skewed gene expression patterns that highlight the effectiveness of the new DNA methylation patterns established by each haplotype. The haplotypes differentially regulate α -ketoglutarate, a metabolite from the TCA cycle that modulates the TET family of proteins, which catalyse the transition from 5-methylcytosine, indicative of DNA methylation, to 5-hydroxymethylcytosine, indicative of DNA demethylation. Our outcomes show that mitochondrial DNA haplotypes differentially modulate chromosomal gene expression patterns of naive and differentiating cells by establishing mitochondrial DNA haplotype-specific DNA methylation patterns.
Publisher: Springer Science and Business Media LLC
Date: 18-05-2016
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-2016
Publisher: Impact Journals, LLC
Date: 28-06-2017
Location: New Zealand
No related grants have been discovered for Te-Sha Tsai.