Top3α is the replicative topoisomerase in mitochondrial DNA replication

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Mitochondrial DNA (mtDNA) maintenance is essential but not fully understood.
• Topoisomerases regulate topological tension in genomes, including mtDNA.
• The specific roles of mitochondrial topoisomerases, like Topoisomerase 3α (Top3α), are poorly defined.

Purpose of the Study:

• To investigate the role of Topoisomerase 3α (Top3α) in mitochondrial DNA (mtDNA) replication and transcription.
• To elucidate the dual functions of Top3α in mtDNA maintenance beyond its previously known role in segregation.

Main Methods:

• Top3α knockdown and overexpression experiments in mammalian cells.
• Analysis of mtDNA replication fork progression, catenation, and integrity.
• Assessment of mitochondrial RNA transcription levels and transcript stability.

Main Results:

• Top3α knockdown led to replication fork stalling, increased mtDNA catenation, and reduced mtDNA levels.
• Top3α overexpression caused double-strand breaks near the replication origin and impaired early replication but resolved termination intermediates.
• Both knockdown and overexpression of Top3α negatively impacted mitochondrial RNA transcription and transcript levels.

Conclusions:

• Mitochondrial Top3α plays a critical role in supporting mtDNA replication fork progression, not just segregation.
• Top3α influences mtDNA transcription, affecting steady-state transcript levels.
• Top3α is a key enzyme for maintaining mtDNA integrity and function through its roles in replication and transcription.