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

Area of Science:

• Reproductive biology
• Cellular and molecular biology
• Developmental biology

Background:

• Mitochondria are critical for oocyte maturation and early embryonic development, providing ATP and maintaining mitochondrial DNA (mtDNA).
• The amplification of mtDNA during oogenesis is essential but not fully understood.
• Mitochondrial transcription factor A (TFAM) is a key regulator of mitochondrial biogenesis and mtDNA maintenance.

Purpose of the Study:

• To investigate the role of TFAM in mouse oocytes during in vitro growth (IVG).
• To understand the mechanisms and functional significance of TFAM in mtDNA amplification during oogenesis.

Main Methods:

• Analyzed mtDNA copy number and mitochondrial gene expression in oocytes at various growth stages.
• Utilized siRNA to knockdown TFAM in secondary follicles, followed by 12 days of IVG culture.
• Assessed oocyte growth, mtDNA content, mitochondrial membrane potential, and in vitro fertilization (IVF) developmental competence post-culture.

Main Results:

• mtDNA copy number increased nonlinearly with oocyte growth, showing a significant rise and TFAM upregulation at the secondary follicle stage.
• TFAM knockdown decreased mtDNA copy number and impaired mitochondrial function.
• While oocyte size and meiotic maturation were unaffected, TFAM knockdown significantly reduced blastocyst formation rates and cell numbers.

Conclusions:

• TFAM-mediated mtDNA replication is essential for mitochondrial function in IVG-derived oocytes.
• TFAM plays a critical role in ensuring the developmental competence of oocytes, highlighting its importance for early embryonic development.