Multiple germline functional VL genes contribute to the IgL repertoire in ducks

In the immunoglobulin light chain gene loci of nearly all bird species examined to date, there is only a single functional variable gene segment that can recombine with joining gene segments. Thus, Ig light chain diversity relies on gene conversion using pseudogenes as sequence donors to modify the single rearranged variable gene. In the present study, we have sequenced a bacterial artificial chromosome (BAC) clone containing the entire duck Igλ light chain gene locus. Although only a single pair of Jλ and Cλ was found, 88 Vλ gene segments were identified upstream of the Jλ and Cλ segments. Among the identified Vλ gene segments, 79 appear to be pseudogenes, the remaining 9 are structurally intact and all are able to functionally rearrange with the Jλ. Phylogenetic analyses suggest that the 9 functional variable genes may have been derived from a single gene through duplication events. Although these multiple functional variable gene segments can be subject to VJ recombination, both gene conversion and somatic hypermutation are also actively involved in the generation of diversity in duck Igλ light chains. These data provide significant insight into understanding the duck Ig system.