Somatic mutations during an immune response in Xenopus tadpoles.

The tadpole B-cell repertoire is less diverse than that of the adult frog; their antibodies are of lower affinity and are less heterogenous. In order to determine whether this difference is due to a lack of or a reduced rate of somatic hypermutation, we analyzed and compared cDNA sequences utilizing VH1 elements with germline counterparts in isogenic LG7 tadpoles during an immune response. Indeed, tadpole VH1 sequences contained somatic mutations. There were zero to 5 mutations per sequence, all single base-point mutations, with the high ratio of GC to AT base-pair alterations similar to that observed in adult frogs.