Somatic hypermutation in the absence of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) or recombination-activating gene (RAG)1 activity

Somatic hypermutation and isotype switch recombination occur in germinal ce nter B cells, are linked to transcription, and are similarly affected by de ficiency in MutS homologue (MSH)2. Class-snitch recombination is abrogated by disruption of genes encoding components of the catalytic subunit of DNA- dependent protein kinase (DNA-PKcs)/Ku complex and Likely involves nonhomol ogous end joining (NHEJ). That somatic hypemutation might also be associate d with end joining is suggested by its association with the creation of del etions, duplications, and sites accessible to terminal transferase. However , a requirement for NHEJ in the mutation process has not been demonstrated. Here we show that somatic mutation in mice deficient in NHEJ can be tested by introduction of rearranged immunoglobulin and T cell receptor trans-gen es: the transgene combination not only permits reconstitution of peripheral lymphoid compartments but also allows formation of germinal centers, despi te the wholly monoclonal nature of the lymphocyte antigen receptors in thes e animals. Using this strategy, we confirm that somatic hypermutation like class-switching can occur in the absence of recombination-activating gene ( RAG)1 but show that the two processes differ in that hypermutation can proc eed essentially unaffected by deficiency in DNA-PKcs activity.