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

Complete characterization and physical mapping of bovine lambda (λ) light chain locus, spanning 412 kbp, on chromosome 17, has revealed twenty-five Vλ genes, seventeen being functional, organized in three sub-clusters 23.7 kbp 5′ of the Jλ-Cλ units. Three Vλ sub-clusters are separated by two large introns of 126.8 and 138.3 kbp. The predominantly expressed Vλ1 genes are present in the two 5′ sub-clusters, while Jλ-proximal Vλ sub-cluster comprises rarely expressed Vλ2 and Vλ3 genes. The preferential expression of Vλ1 genes in the bovine immunoglobulin repertoire is influenced by the composition of recombination signal sequences (RSS). Of the Jλ-Cλ cluster, it is mainly Jλ3-Cλ3 unit that is expressed in reading frame 2, though Jλ2 and Jλ3 have identical RSS. The predominant expression of Jλ3-Cλ3 genes over Jλ2-Cλ2 is likely due to endogenous counter selection for Jλ2 encoded CDR3 and framework 4 regions. Differences in the genomic complexity of Vλ 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 Vλ1-Jλ3-Cλ3 recombinations encode the most λ-light chain repertoire in cattle.