Organization and genomic complexity of sheep immunoglobulin light chain gene loci

Abstract

Sheep is the representative of the artiodactyla and is an agriculturally important animal, but limited knowledge is available with regard to its immunoglobulin genes and their expression mechanisms in the sheep. Based on the recently released sheep genome, we have characterized the genomic organization of the sheep immunoglobulin light gene loci. The sheep Igλ locus, located on chromosome 17, contains 2Cλ segments each preceded by a Jλ, but the Cλ2 appears to be a pseudogene. A total of 42 Vλ segments (14 potentially functional genes, 1 ORF and 27 pseudogenes) were identified. In contrast, the Igκ locus on chromosome 3 contains only a single Cκ gene, 3 Jk segments and 13 Vκ segments (8 potentially functional genes and 5 pseudogenes). Analysis of junctions of the recombined VJ transcripts revealed a restricted Vλ4–Jλ1–Cλ1 recombination and Vk6–Jk3–Cκ recombination, respectively encode most of λ and κ chain antibody repertoire in the sheep despite more potential germline encoded combinatorial diversity. Therefore, the sheep may use gene conversion in combination with somatic hypermutation for antibody repertoire formation.