Organization of genes and spacers within the mouse immunoglobulin VH locus

The germline organization of mouse immunoglobulin VH genes has been investigated using cloned VH sequences. Hybridization studies with VH probes from plasmacytomas HPC76 (H76), S107, HOPC1 (H1), and lymphoma ABLS-8 (A8) demonstrated that the VH locus contains at least three distinct VH gene families. Comparison with other results suggests a total of about 10 such families, and of the order of 160 germline VH genes. Nucleotide sequencing revealed that the H76 family includes anti-inulin VH sequences, and the S107 family is known to encode antiphosphorylcholine sequences. The three VH gene families studied were mapped in the order H76-S107-A8/H1-CH by determining which VH genes had been deleted from several plasmacytomas by VH rearrangement events. Nine genomic clones from athe H76 family, and one each from the S107 and A8/H1 families, were characterized; collectively they span 103 kilobases (kb). Two clones from the H76 family and one from the S107 family each bore a pair of VH genes separated by approximately 14 kb, suggesting that related VH genes in these families are clustered with a typical spacing of approximately 14 kb. No other VH genes were detected within the spacers, arguing against intermingling of different families. Within the VH76 family cluster, however, two closely homologous VH genes were shown not to be adjacent. While spacer sequences were strongly conserved in the A8/H1 family, the H76 family had minimal conservation and that was restricted to regions immediately surrounding the genes. Hence conservation of spacer sequences cannot be essential for VH gene function, nor for maintenance of a VN family. Spacers in both the H76 and S108 family contained small repeat elements, some of which behaved like mobile DNA sequences.