Possible contribution of DNase γ to immunoglobulin V gene diversification

Somatic hypermutation (SHM) diversifies the rearranged immunoglobulin variable (V) region gene in B cells, contributing to affinity maturation of antibodies. It is believed that SHM is generated either by direct replication or by error-prone repair systems resolving V region DNA lesions caused directly or indirectly by cytidine deaminase AID. In accord with a part of these mechanisms, it was reported that SHM is associated with staggered double-strand DNA breaks (DSBs) occurring in the rearranged V regions. However, endonucleases responsible for the DSBs remain elusive. Here we show that DNase γ, a member of DNase I family endonucleases, contributes to the generation of SHM including point mutation, and nucleotide insertion and deletion in chicken DT40 B cell line. DNase γ also contributes to the generation of staggered DSBs in the rearranged V region. These results raise a possibility that DNase γ is involved in the V gene mutation machinery.