Organization and genomic complexity of bovine λ-light chain gene locus

Abstract

Complete characterization and physical mapping of bovine lambda (λ) light chain locus, spanning 412 kbp, on chromosome 17, has revealed twenty-five V λ genes, seventeen being functional, organized in three sub-clusters 23.7 kbp 5′ of the J λ-C λ units. Three V λ sub-clusters are separated by two large introns of 126.8 and 138.3 kbp. The predominantly expressed V λ1 genes are present in the two 5′ sub-clusters, while J λ-proximal V λ sub-cluster comprises rarely expressed V λ2 and V λ3 genes. The preferential expression of V λ1 genes in the bovine immunoglobulin repertoire is influenced by the composition of recombination signal sequences (RSS). Of the J λ-C λ cluster, it is mainly J λ3-C λ3 unit that is expressed in reading frame 2, though J λ2 and J λ3 have identical RSS. The predominant expression of J λ3-C λ3 genes over J λ2-C λ2 is likely due to endogenous counter selection for J λ2 encoded CDR3 and framework 4 regions. Differences in the genomic complexity of V λ genes in Hereford and Holstein cattle are due to polymorphism at the λ-light chain gene locus. Despite more potential germline encoded combinatorial diversity, restricted V λ1-J λ3-C λ3 recombinations encode the most λ-light chain repertoire in cattle.