Marsupial light chains: IGK with four V families in the opossum Monodelphis domestica

A full-length and several partial cDNAs encoding IGK light chains from the marsupial South American opossum, Monodelphis domestica, were isolated and characterized. Using these clones as a starting point, the expressed IGKV r epertoire was sampled by anchored polymerase chain reaction using an IGKC-s pecific primer. Based on nucleotide sequences of twenty unique, expressed I GKV-J combinations, there are at least four IGKV families and two J segment s. Southern blot analysis revealed each IGK-V family contains multiple gene segments totaling at least thirty-five IGKV in the opossum genome. No evid ence for particular, recurrent IGKV-J combinations in the opossum IGK reper toire was seen, rather the V-J combinations appeared random and diverse. Ea ch of the four IGKV families appear more closely related to V segments from placental mammals than to each other, suggesting the duplication of the IG KV families prior to the separation of marsupials and placental mammals mor e than one-hundred-million years ago. Overall, the complexity of opossum li ght chain V segments appears greater than that found in the heavy chain, an d light chains are likely to contribute significantly to Ig diversity in th is species. With this report, the homologues encoding all three classes of eutherian Ig chains, IGH, IGL, and IGK, have been described in a non-placen tal mammal.