Functional analysis of pathological mutations in DNA topoisomerase 3A

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• DNA topoisomerase IIIα (TOP3A) is essential for genome maintenance.
• TOP3A mutations are linked to Bloom's syndrome-like phenotypes and mitochondrial dysfunction.
• Understanding TOP3A's physiological role is limited by embryonic lethality in knockout models.

Purpose of the Study:

• To investigate the function of TOP3A, particularly its C-terminal domain (CTD), in vivo.
• To create and analyze a Top3a mutant mouse model mimicking human mutations.
• To elucidate the role of TOP3A in both nuclear and mitochondrial DNA maintenance.

Main Methods:

• Generation of a Top3a mutant mouse model with a truncated CTD.
• Analysis of embryonic viability and mitochondrial DNA levels in mutant embryos and stem cells.
• Biochemical assays to assess DNA binding and enzymatic activity of TOP3A and its CTD.

Main Results:

• Homozygous Top3a mutant mice exhibit embryonic lethality around 7.5 days post coitum.
• Mutant embryos and stem cells show progressive loss of mitochondrial DNA.
• CTD truncation impairs TOP3A's DNA binding and relaxation activity, while the isolated CTD binds DNA.

Conclusions:

• The C-terminal domain of TOP3A is critical for its function in both nuclear and mitochondrial DNA maintenance.
• The Top3a mutant mouse model provides insights into TOP3A's essential roles during embryonic development.
• TOP3A mutations impacting the CTD have severe consequences for genome stability and mitochondrial integrity.