Break-induced replication forms long mutable single-strand DNA during meiosis.

Area of Science:

• Genetics
• Molecular Biology
• Cell Biology

Background:

• Meiosis involves homologous recombination (HR) for genetic shuffling and halving of genomic content.
• HR during meiosis may be mutagenic, with single-stranded DNA (ssDNA) from double-strand breaks (DSBs) proposed as a mutagenic source.

Purpose of the Study:

• To investigate the mutagenic potential of ssDNA formed during meiosis.
• To identify the mechanisms responsible for ssDNA accumulation and mutagenesis during meiosis.

Main Methods:

• Expression of human APOBEC3A (A3A) in meiotic yeast cells to detect and map ssDNA.
• Analysis of mutation clusters to quantify ssDNA extent and identify associated genetic elements.
• Investigating the role of Spo11-induced DSBs, break-induced replication, and hyper-resection in ssDNA formation.

Main Results:

• Meiotic cells accumulate long ssDNA tracts, forming A3A-mutation clusters with up to 134 mutations over >25 kb.
• Formation of these mutation clusters requires Spo11-induced DSBs.
• Break-induced replication and hyper-resection of DSBs are key mechanisms for generating long meiotic ssDNA.
• ssDNA accumulation occurs in promoters and tRNA genes, indicating additional mutagenesis sources.

Conclusions:

• Meiosis possesses significant mutagenic potential, driven by the formation of extensive ssDNA.
• Understanding these ssDNA-driven mutagenic mechanisms is crucial for insights into evolution and congenital diseases.
• Spo11-induced DSBs, coupled with specific replication and resection pathways, underlie meiotic ssDNA accumulation and mutagenesis.