Year: 2021
Type: dissertation
Abstract: Oocytes and embryos are highly susceptible to intrinsic and extrinsic stressors. In particular, physiological cues, such as obesity and aging, are sensed by mitochondria. Mitochondria are inherited solely through the maternal lineage; meaning all mitochondria in offspring are derived from those in the mature oocyte. Therefore, oocyte mitochondria quality and quantity are of utmost importance to embryonic development and postnatal health. In parallel, telomere length is regenerated in offspring during embryogenesis to ensure viability and longevity of each new generation. Despite the importance of telomere elongation during development, little is known about this process. This thesis aims to better understand how maternal obesity and aging affects mitochondria and telomere length in the oocyte and pre-implantation embryo, and by identifying these pathways, develop strategies to enhance these early determinants of lifetime health. First, a highly sensitive qPCR assay to analyse relative telomere lengths and mtDNA copy number in individual oocytes and embryos was developed, termed the ‘Triple Test’. This assay elucidated natural variability in mtDNA and telomeric DNA content between individual oocytes and embryos. It also enabled robust and precise measurements in physiological contexts where tissue availability is limited. Next, the Triple Test was implemented to conduct a thorough examination of telomere length kinetics throughout pre-implantation embryogenesis. This identified two elongation phases, specific to embryo type. Genes involved in telomere elongation processes and telomere protection roles were analysed throughout oocyte maturation and pre-implantation embryogenesis, and displayed dynamic regulation of expression throughout. Mitochondrial function and telomere length are the two most well characterised markers of cellular aging, and it was hypothesised that mitochondrial activity is a key factor regulating telomere elongation. This was tested by using rotenone to induce mitochondrial dysfunction in oocytes and tracking telomere length throughout embryogenesis. Reducing mitochondrial bioenergetics decreased telomere length in MII oocytes and cells of the ICM. On a molecular level, rotenone altered global epigenetic reprogramming in zygote pronuclei. These results demonstrate that optimal mitochondrial activity is required for numerous reprogramming processes, and indicates a functional link between mitochondria and telomeres. Two physiological scenarios that involve perturbed oocyte mitochondrial function are advanced maternal ageing and obesity; and whether this is associated with perturbed telomere length reprogramming was investigated. While oocyte quality and embryo development were not compromised, telomere length and mtDNA copy number were decreased in oocytes and ICM. Further, treatment of females in vivo with BGP-15, a mitochondrial therapeutic, reversed the deficiencies seen in ICM telomere length, and normalised perturbed epigenetic reprogramming in zygotes. Cumulatively, this work provides critical insights into the patterns of telomere elongation during pre-implantation embryogenesis, and how telomere length and epigenetic re-programming are compromised in subfertility. By manipulating mitochondrial bioenergetics, the relationship between mitochondrial function and telomere health is demonstrated. Additionally, new strategies are identified that positively modulate telomere length during development. This work has identified novel links between mitochondrial activity and telomere elongation and new information about the regulation of these mechanisms that are fundamental to the creation of a new embryo and the lifetime health of that individual.
Author: Winstanley, Yasmyn Ellaynah
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7020937979