ABSTRACT
Although the mouse immunoglobulin heavy chain (Igh) locus contains 15 heavy chain V (Vh) gene families, at least half of the Vh gene segments are members of the VhJ558 family. This large Vh gene family represents the least characterized germline coding regions of any of the mouse antigen receptor loci and the contribution of individual VhJ558 genes to the preimmune repertoire is poorly understood. In fact, relatively few germline VhJ558 sequences have been reported for BALB/c, the foundation strain for mouse immunoglobulin genetics and the prototypic strain of the Igh(a) haplotype. Here we present a database consisting of 66 sequences estimated to represent one-half of the total number of functional BALB/c VhJ558 genes. Our results indicate that a subset of the VhJ558 genes is highly expressed in the preimmune repertoire, with just nine Vh sequences accounting for nearly 50% of the VhJ558 heavy chains expressed by splenic B cells. We show that this disparity in the expressed Vh gene repertoire is not due to the position of the Vh genes relative to the Dh cluster or to multiple germline copies of the highly expressed VhJ558 genes. Together, these data constitute the first detailed analysis of functional BALB/c VhJ558 genes, demonstrate a striking bias in the use of particular VhJ558 genes in the preimmune repertoire, and provide sufficient information to study the regulation of the Dh-distal region of the Igh-V locus at the level of individual genes.
Subject(s)
Genetic Variation , Germ-Line Mutation , Immunoglobulin Heavy Chains/genetics , Immunoglobulin Variable Region/genetics , Amino Acid Sequence , Animals , Base Sequence , Chromosome Mapping , DNA, Complementary , Gene Expression , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Molecular Sequence DataABSTRACT
Ab heavy chains encoded by mouse VH10 genes have been of particular interest due to their frequent association with DNA binding. We reported previously that VH10 sequences are over-represented in the preimmune repertoire considering the apparent number of germline-encoded VH10 gene segments. In this report, we show that the VH10 family consists of three and two germline genes in the Igha and Ighb haplotypes, respectively. The complete nucleotide sequences of these five genes, including promoters and recombination signal sequences, were determined and allow unambiguous assignment of allelic relationships. The usage of individual VH10 genes varied significantly and ranged from 0.2% to an extraordinary 7.2% of the VH genes expressed by splenic B cells. Since the promoter and recombination signal sequence elements of all five VH10 genes are identical, we suggest that the few amino acid differences encoded by these five germline VH10 genes determine their representation in the preimmune repertoire. Rearrangements of the most frequently used VH10 gene have an apparent bias for histidine at position 95 of complementarity-determining region-3 (CDR3). These CDR3s are also biased for asparagine, an amino acid associated with the CDRs of DNA binding Abs. Together, these results suggest that high VH10 gene use is the result of B cell receptor-mediated selection and may involve DNA and/or ligands that share antigenic features with DNA.
Subject(s)
Genes, Immunoglobulin , Immunoglobulin Heavy Chains/genetics , Alleles , Amino Acid Sequence , Animals , Antibodies, Monoclonal/genetics , Antibody Diversity , Antibody Specificity , Antigens/metabolism , B-Lymphocytes/immunology , Base Sequence , Cloning, Molecular , DNA/immunology , DNA/metabolism , DNA Probes/genetics , DNA, Complementary/genetics , Gene Rearrangement, B-Lymphocyte , Immunoglobulin Heavy Chains/chemistry , Immunoglobulin Heavy Chains/metabolism , Immunoglobulin Variable Region , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Molecular Sequence Data , Multigene Family , Sequence Homology, Amino Acid , Sequence Homology, Nucleic AcidABSTRACT
During their development, B and T lymphocytes are thought to undergo several cycles of chromatin remodeling at their antigen receptor loci that serve to regulate access of a common V(D)J recombinase to particular gene segments. We used germ-line transcription and susceptibility to DNasel as markers to examine tissue and stage-specific changes in chromatin structure surrounding genes of the VHJ558, VH10, and VHS107 families, whose members are located at discreet subregions of the locus. Germ-line VH transcripts from all three families were detectable at pro- and pre-B cell stages. Transcripts from the VH10 and VHS107 families, but not VHJ558, remained detectable at the immature and mature B cell stages. Unexpectedly, none of the germ-line VH loci examined were markedly nuclease sensitive, regardless of cell type or transcriptional activity. A modest degree of nuclease sensitivity was noted at the VHJ558 loci of pro-B and pre-B cells, however. Our data suggest that the entire Igh-V locus becomes accessible at early B cell stages, and returns thereafter to an inaccessible state. However, the timing of these accessibility changes does not occur uniformly across the VH array. These results imply that multiple long-range elements are involved in targeting VH genes for rearrangement.
