Contribution of mitochondrial DNA replication and mitophagy to purifying selection against deleterious mitochondrial mutation in mouse oocytes

• Grant number: 25/09613-2
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: September 01, 2025
• End date: August 31, 2026
• Field of knowledge: Biological Sciences - Genetics - Animal Genetics
• Principal Investigator: Marcos Roberto Chiaratti
• Grantee: Thiago Marques Possato
• Host Institution: Centro de Ciências Biológicas e da Saúde (CCBS). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 23/02226-8 - Bilateral BBSRC-FAPESP: molecular mechanisms shaping the germ-line transmission of mtDNA variants, AP.TEM

Abstract

The human mitochondrial DNA (mtDNA) contains 10-15 times more single nucleotide variants (mtSNVs) than the nuclear DNA, which can cause extremely severe pathologies and influence a wide range of physiological functions, such as kidney and liver function, height, and even longevity. Since each cell contains from hundreds to thousands of copies of mtDNA, mutant and wild-type molecules coexist in the same cell, resulting in a condition termed heteroplasmy. The level of heteroplasmy in an individual is a function of both new mutations (e.g., mtSNVs) and preexisting mutations inherited from the maternal lineage. Regarding the inheritance of mtDNA mutations, several lines of evidence point to the existence of purifying selection that prevents the exacerbated accumulation of deleterious mutations though generations. Indeed, female mice with a nonsense mtDNA mutation produce litters with decreasing levels of the mutation through aging. Although preliminary results from our and other groups suggest that this purifying selection occurs in the oocyte during the transition from preantral to antral follicles, the underlying molecular mechanism is still unknown. Therefore, the aim of the present proposal is to investigate whether mtDNA replication, autophagy and mitophagy are involved in the elimination of this mutant mtDNA in oocytes. These processes were also selected based on evidence obtained by us and other groups. Regarding the experimental design, 100-day-old females containing different levels of mutant mtDNA (0%, 20-40% and 60-80%) will be used for isolation of oocytes from preantral and antral follicles. The resulting oocytes will then be analyzed for mtDNA replication, autophagy and mitophagy using confocal microscopy to determine whether these processes vary according to mutation level and stage of follicular development. We hope that the results obtained will contribute to the understanding of the mechanisms that modulate the transmission of heteroplasmic mtDNAs between mothers and their offspring. (AU)