Rabbit DQ52 and DH gene expression in early B-cell development

Abstract Rabbits predominantly rearrange the most 3′ V H gene (VH1); thus combinatorial diversity is very limited. In man and mouse, the most 3′ D H gene, DQ52, is preferentially rearranged early in B-cell development. To test whether this preference for rearranging a D H gene segment based on 3′ end proximity exists in rabbit, we cloned and sequenced the rabbit DQ52 gene. The 11 base pair coding region sequence is identical to a published mouse DQ52, and 81.8% similar to the human sequence. It is localized ∼805 bp upstream of the J H 1 gene. However, the 3′ recombination signal sequence has an atypical nonamer. We prepared mRNA from 15- to 28-day fetal rabbits and amplified expressed VDJ sequences of μ mRNA by RT-PCR. The PCR products with VDJ rearrangements were cloned and sequenced. As expected, 44 of 45 VDJ sequences reflected use of the 3′ V H 1a2 gene, but the DQ52 gene was utilized very infrequently, if at all. We found only one VDJ sequence from 28-day fetal liver B-cells with 8 bp that matched the germline DQ52 sequence. Instead of expressing DQ52, another D H gene, Df was frequently expressed. We cloned the genomic Df gene and localized it about 32 kb upstream of the J H region. Thus, in contrast to man and mouse, rabbits preferentially express a D H gene located in the middle of the D H region early in B cell ontogeny. This may correlate with more frequent initial rearrangement of V H to D H in rabbit B cells.