DNA polymerases ν and θ are required for efficient immunoglobulin V gene diversification in chicken

Abstract

The chicken DT40 B lymphocyte line diversifies its immunoglobulin (Ig) V genes through translesion DNA synthesis-dependent point mutations (Ig hypermutation) and homologous recombination (HR)-dependent Ig gene conversion. The errorprone biochemical characteristic of the A family DNA polymerases Polν and Polθ led us to explore the role of these polymerases in Ig gene diversification in DT40 cells. Disruption of both polymerases causes a significant decrease in Ig gene conversion events, although POLN -/-/POLQ-/- cells exhibit no prominent defect in HRmediated DNA repair, as indicated by no increase in sensitivity to camptothecin. Polη has also been previously implicated in Ig gene conversion. We show that a POLH-/-/POLN-/-/POLQ -/- triple mutant displays no Ig gene conversion and reduced Ig hypermutation. Together, these data define a role for Polν and Polθ in recombination and suggest that the DNA synthesis associated with Ig gene conversion is accounted for by three specialized DNA polymerases. © 2010 Kohzaki et al.