Multi-step processing of replication stress-derived nascent strand DNA gaps by MRE11 and EXO1 nucleases

Area of Science:

• Molecular Biology
• Genetics
• Environmental Health

Background:

• Single-stranded DNA (ssDNA) gaps in nascent strands during replication are linked to cytotoxicity and genotoxic stress sensitivity, especially when the BRCA tumor suppressor pathway is compromised.
• The precise mechanisms by which ssDNA gaps contribute to genotoxicity remain incompletely understood.

Purpose of the Study:

• To elucidate the nucleolytic processing of replication stress-induced ssDNA gaps.
• To investigate the role of the BRCA pathway in suppressing ssDNA gap processing.
• To determine if environmental contaminants like bisphenol A (BPA) and diethylhexyl phthalate (DEHP) induce ssDNA gaps and subsequent DNA damage.

Main Methods:

• Characterization of nucleolytic processing of ssDNA gaps using molecular biology techniques.
• Investigation of the involvement of MRE11 and EXO1 in ssDNA gap extension and processing.
• Assessment of the impact of BRCA pathway status on ssDNA gap processing.
• Exposure of cells to BPA and DEHP to evaluate their effect on ssDNA gap formation and processing.

Main Results:

• Replication stress-induced ssDNA gaps are processed into cytotoxic double-strand DNA breaks (DSBs) through a multi-step nucleolytic pathway.
• MRE11 and EXO1 enzymes bidirectionally extend ssDNA gaps, a process inhibited by the BRCA pathway.
• MRE11 endonuclease activity cleaves the parental strand at the ssDNA gap, generating DSBs.
• Exposure to BPA and DEHP induces nascent strand ssDNA gaps that are processed into DSBs via the same mechanism.

Conclusions:

• ssDNA gaps are significant drivers of genomic instability and cytotoxicity.
• A conserved nucleolytic mechanism processes ssDNA gaps into DSBs, highlighting the importance of DNA replication and repair pathways.
• Environmental contaminants BPA and DEHP can contribute to genomic instability by inducing ssDNA gaps and subsequent DSB formation.