Marsupial Light Chains: Complexity and Conservation of λ in the Opossum Monodelphis domestica

Abstract The Igλ chains in the South American opossum, Monodelphis domestica, were analyzed at the expressed cDNA and genomic organization level, the first described for a nonplacental mammal. The Vλ segment repertoire in the opossum was found to be comprised of at least three diverse Vλ families. Each of these families appears to be related to distinct Vλ families present in placental mammals, suggesting the divergence of these genes before the separation of metatherians and eutherians more than 100 million years ago. Based on framework and constant region sequences from full-length cDNAs and intron sequences from genomic clones, it appears that there are multiple functional Jλ-Cλ pairs in the opossum locus. The opossum Jλ-Cλ sequences are phylogenetically clustered, suggesting that these gene duplications are more recent and species specific. Sequence analysis of a large set of functional, expressed Vλ-Jλ recombinations is consistent with an unbiased, highly diverse λ light chain repertoire in the adult opossum. Overall, the complexity of the Igλ locus appears to be greater than that found in the Ig heavy chain locus in the opossum, and light chains are therefore likely to contribute significantly to Ig diversity in this species.