title: Identification of IgF, a hinge-region-containing Ig class, and IgD in Xenopus tropicalis.
abstract: Only three Ig isotypes, IgM, IgX, and IgY, were previously known in amphibians. Here, we describe a heavy-chain isotype in Xenopus tropicalis, IgF (encoded by C(phi)), with only two constant region domains. IgF is similar to amphibian IgY in sequence, but the gene contains a hinge exon, making it the earliest example, in evolution, of an Ig isotype with a separately encoded genetic hinge. We also characterized a gene for the heavy chain of IgD, located immediately 3' of C(mu), that shares features with the C(delta) gene in fish and mammals. The latter gene contains eight constant-region-encoding exons and, unlike the chimeric splicing of muC(H)1 onto the IgD heavy chain in teleost fish, it is expressed as a unique IgD heavy chain. The IgH locus of X. tropicalis shows a 5' V(H)-D(H)-J(H)-C(mu)-C(delta)-C(chi)-C(upsilon)-C(phi) 3' organization, suggesting that the mammalian and amphibian Ig heavy-chain loci share a common ancestor.
authors.affiliation: State Key Laboratory for AgroBiotechnology, China Agricultural University, Beijing 100094, People's Republic of China. yaofeng.zhao@ki.se
authors.forename: Yaofeng
authors.initials: Y
authors.lastname: Zhao
authors.forename: Qiang
authors.initials: Q
authors.lastname: Pan-Hammarström
authors.forename: Shuyang
authors.initials: S
authors.lastname: Yu
authors.forename: Nancy
authors.initials: N
authors.lastname: Wertz
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Zhang
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: John E
authors.initials: JE
authors.lastname: Butler
authors.forename: Lennart
authors.initials: L
authors.lastname: Hammarström
mesh_terms: D000818:Animals; D002397:Catfishes; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D050438:Genes, Immunoglobulin Heavy Chain; D016678:Genome; D007072:Immunoglobulin D / Q000502:physiology*; D007143:Immunoglobulin Heavy Chains / Q000502:physiology*; D007136:Immunoglobulins / Q000737:chemistry; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D014981:Xenopus / Q000378:metabolism*
chemical_list: C016512:IgY; D007072:Immunoglobulin D; D007143:Immunoglobulin Heavy Chains; D007136:Immunoglobulins