Identification of Igσ and Igλ in channel catfish, Ictalurus punctatus, and Igλ in Atlantic cod, Gadus morhua

Immunoglobulin light (IGL) chain genes encoding σ and λ from channel catfish, Ictalurus punctatus, and λ from Atlantic cod, Gadus morhua, were identified by mining of expressed sequence tag databases, 5'-RACE and RT-PCR protocols. cDNAs for each of these IGL chains encode typical variable (V), joining (J), and constant (C) regions and Southern blot analyses and genomic sequencing show that genes encoding these isotypes, like other teleost IGL genes, are found in a cluster organization of one or two V gene segments, followed by single J and C gene segments, all in the same transcriptional orientation. However, unlike the teleost κ genes, genes encoding catfish σ and λ are few in number and the two isotypes are each encoded by only two clusters. Similarly, Atlantic cod λ genes are predicted to be encoded by two or three clusters. As expected, sequence and phylogenetic analyses comparisons demonstrate that catfish Vσ and Cσ genes are most similar to Vσ and Cσ genes of other ectothermic vertebrates. Although catfish and Atlantic cod Vλ genes cluster with other vertebrate Vλ genes, their Cλ sequences cluster in a distinct group separate from other vertebrate IGL C sequences. However, support for classifying these sequences as λ, is their V and J recombination signal sequence (RSS) organization. The catfish and Atlantic cod genes have typical λ-like RSS with the Vλ RSS consisting of heptamer-23 bp spacer-nonamer and the Jλ RSS consisting of heptamer-12 bp spacer-nonamer. This is the first report demonstrating the presence of Igλ in teleosts.