title: Genomic organization of the immunoglobulin light chain gene loci in Xenopus tropicalis: evolutionary implications.
abstract: Based on presently available genome data, we characterized the genomic organization of all three light chain gene (rho, sigma and type III) loci in Xenopus tropicalis. The rho gene locus in X. tropicalis, structurally similar to the kappa gene loci in mammals, was shown to contain a single C rho gene and nine J rho segments. The sigma locus also contains a single C gene, although two distinct C sigma genes have previously been found in Xenopus laevis (most likely due to chromosome polyploidy). Four J sigma gene segments were identified upstream of the C sigma. The type III light chain gene locus, spanning approximately 170 kb DNA, structurally resembles the topology of mammalian lambda gene loci, containing three C genes (C III 1-3). C III 2 and C III 3 are both preceded by single, unique, J genes, whereas C III 1 contains three J gene segments. Furthermore, two additional J gene segments, termed J III x1 and J III x2, were found in the intron separating V III 2 and pV III 1 (a pseudogene). Based on BLAST searches against the X. tropicalis EST database, all the C genes identified in this study were shown to be functional. On the basis of similarity of protein sequences, genomic organization and chromosomal location of the light chain genes among frogs and mammals, our data strongly support the previous suggestions that the rho genes belong to the kappa gene lineage, whereas the type III genes share a common origin with the lambda genes.
authors.affiliation: State Key Laboratories for AgroBiotechnology, College of Biological Sciences, China Agricultural University, Beijing 100094, PR China.
authors.forename: Tong
authors.initials: T
authors.lastname: Qin
authors.forename: Liming
authors.initials: L
authors.lastname: Ren
authors.forename: Xiaoxiang
authors.initials: X
authors.lastname: Hu
authors.forename: Ying
authors.initials: Y
authors.lastname: Guo
authors.forename: Jing
authors.initials: J
authors.lastname: Fei
authors.forename: Qinghong
authors.initials: Q
authors.lastname: Zhu
authors.forename: John E
authors.initials: JE
authors.lastname: Butler
authors.forename: Changxin
authors.initials: C
authors.lastname: Wu
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: Lennart
authors.initials: L
authors.lastname: Hammarstrom
authors.forename: Yaofeng
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019143:Evolution, Molecular; D005803:Genes, Immunoglobulin; D007147:Immunoglobulin Light Chains / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D016415:Sequence Alignment; D026801:Synteny; D014981:Xenopus / Q000235:genetics*
chemical_list: D007147:Immunoglobulin Light Chains