Recombination, transcription, and diversity of a partially germline-joined VH in a mammal

Full or partially germline-joined V genes have been described in a number of different vertebrate lineages where they can contribute to the expressed antibody repertoire through different mechanisms. Here we demonstrate that VH3.1, a partially germline-joined VH gene in the opossum Monodelphis domestica, can undergo V(D)J recombination to generate productive IgH transcripts. VH3.1 is fused to a DH gene segment in the germline DNA and is the only known example of a germline-joined VH in a mammal. B cells that have recombined VH3.1 were not detected until nearly 2 months of age, around the time of weaning, and much later than B cells using the conventional VH. Compared to opossum IgH transcripts using the conventional VH genes, those with VH3.1 have unusually long CDR3 due to the length of the germline-joined DH.