A third broad lineage of major histocompatibility complex (MHC) class I in teleost fish; MHC class II linkage and processed genes.
Most of the previously studied teleost MHC class I molecules can be classified into two broad lineages: "U" and "Z/ZE." However, database reports on genes in cyprinid and salmonid fishes show that there is a third major lineage, which lacks detailed analysis so far. We designated this lineage "L" because of an intriguing linkage characteristic. Namely, one zebrafish L locus is closely linked with MHC class II loci, despite the extensively documented nonlinkage of teleost class I with class II. The L lineage consists of highly variable, nonclassical MHC class I genes, and has no apparent orthologues outside teleost fishes. Characteristics that distinguish the L lineage from most other MHC class I are (1) absence of two otherwise highly conserved tryptophan residues W51 and W60 in the alpha1 domain, (2) a low GC content of the alpha1 and alpha2 exons, and (3) an HINLTL motif including a possible glycosylation site in the alpha3 domain. In rainbow trout (Oncorhynchus mykiss) we analyzed several intact L genes in detail, including their genomic organization and transcription pattern. The gene Onmy-LAA is quite different from the genes Onmy-LBA, Onmy-LCA, Onmy-LDA, and Onmy-LEA, while the latter four are similar and categorized as "Onmy-LBA-like." Whereas the Onmy-LAA gene is organized like a canonical MHC class I gene, the Onmy-LBA-like genes are processed and lack all introns except intron 1. Onmy-LAA is predominantly expressed in the intestine, while the Onmy-LBA-like transcripts display a rather homogeneous tissue distribution. To our knowledge, this is the first description of an MHC class I lineage with multiple copies of processed genes, which are intact and transcribed. The present study significantly improves the knowledge of MHC class I variation in teleosts.
Dijkstra
Johannes Martinus
JM
Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi, Japan. dijkstra@fujita-hu.ac.jp
Katagiri
Takayuki
T
Hosomichi
Kazuyoshi
K
Yanagiya
Kazuyo
K
Inoko
Hidetoshi
H
Ototake
Mitsuru
M
Aoki
Takashi
T
Hashimoto
Keiichiro
K
Shiina
Takashi
T
D000595:Amino Acid Sequence; D000818:Animals; D005091:Exons; D015870:Gene Expression; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D008040:Genetic Linkage; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000145:classification* / Q000235:genetics; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000145:classification* / Q000235:genetics; D007438:Introns; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000235:genetics* / Q000276:immunology*; D011544:Pseudogenes
D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II