RABBIT DQ52 AND D-H GENE-EXPRESSION IN EARLY B-CELL DEVELOPMENT

Rabbits predominantly rearrange the most 3' V-H gene (VH1); thus combi natorial 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 bas ed on 3' end proximity exists in rabbit, we cloned and sequenced the r abbit 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 similar to 805 bp upstream of the J(H)1 gene. However, t he 3' recombination signal sequence has an atypical nonamer. We prepar ed mRNA from 15- to 28-day fetal rabbits and amplified expressed VDJ s equences of mu mRNA by RT-PCR. The PCR products with VDJ rearrangement s were cloned and sequenced. As expected, 44 of 45 VDJ sequences refle cted use of the 3' V(H)1a2 gene, but the DQ52 gene was utilized very i nfrequently, if at all. We found only one VDJ sequence from 28-day fet al liver B-cells with 8 bp that matched the germline DQ52 sequence. In stead of expressing DQ52, another D-H gene, Df was frequently expresse d. 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 prefe rentially express a DH gene located in the middle of the D-H region ea rly in B cell ontogeny. This may correlate with more frequent initial rearrangement of V-H to D-H in rabbit B cells.