TFAM-Mediated mtDNA Replication is Essential for Developmental Competence of In Vitro Grown Oocytes

Purpose
Mitochondria are essential for oocyte maturation and early embryonic development, supplying ATP and maintaining mitochondrial DNA (mtDNA) integrity. During oogenesis, mtDNA undergoes dramatic amplification, but the mechanisms and functional significance of this process remain unclear. The purpose of this study was to elucidate the role of mitochondrial transcription factor A (TFAM) in mouse oocytes using an in vitro growth (IVG) system.
Methods
Oocytes at different growth stages were analyzed for mtDNA copy number and expression of mitochondrial biogenesis genes. To assess TFAM function, siRNA targeting Tfam was microinjected into secondary follicles, which were then cultured for 12 days under IVG conditions. Following culture, oocyte growth, mtDNA content, mitochondrial membrane potential, and developmental competence after in vitro fertilization (IVF) were evaluated.
Results
mtDNA copy number increased nonlinearly during oocyte growth, with a pronounced rise at the secondary follicle stage accompanied by TFAM upregulation. TFAM knockdown reduced mtDNA copy number and mitochondrial function without affecting oocyte size or meiotic maturation, but significantly decreased blastocyst formation and total cell numbers per blastocyst.
Conclusions
TFAM-mediated mtDNA replication is crucial for mitochondrial function and developmental competence of IVG-derived oocytes, underscoring its importance in early embryonic development.