DNA polymerase eta is the sole contributor of A/T modifications during immunoglobulin gene hypermutation in the mouse

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair

Background:

• A/T mutations in immunoglobulin genes are linked to the MSH2-MSH6 mismatch repair complex and DNA polymerase eta (pol eta).
• Residual A/T mutagenesis persists even when these factors are inactivated, suggesting additional repair mechanisms.
• Previous work implicated DNA polymerase kappa in A/T mutagenesis in pol eta-deficient mice.

Purpose of the Study:

• To investigate the complete absence of A/T mutations in mice lacking both MSH2 and pol eta.
• To elucidate the role of DNA polymerase eta (pol eta) and uracil N-glycosylase in A/T mutagenesis.
• To understand how the mismatch repair complex influences DNA repair pathways during hypermutation.

Main Methods:

• Generation and analysis of MSH2-pol eta double-deficient mice.
• Assessment of A/T mutation frequencies in immunoglobulin genes.
• Investigating the recruitment of DNA repair enzymes.

Main Results:

• Complete absence of A/T mutations was observed in MSH2-pol eta double-deficient mice.
• Residual A/T mutagenesis in MSH2-deficient mice is attributed to pol eta recruited by uracil N-glycosylase.
• MSH2-MSH6 complex appears to prevent error-free repair by uracil N-glycosylase during hypermutation.

Conclusions:

• DNA polymerase eta (pol eta) is the primary contributor to A/T mutations in the normal physiological context.
• The MSH2-MSH6 complex plays a critical role in directing uracil N-glycosylase towards error-free repair.
• A complex interplay exists between mismatch repair and other DNA repair pathways in maintaining genomic integrity.