MHC class II A genes in the channel catfish (Ictalurus punctatus)

In order to characterize the Major histocompatibility complex (MHC) class I I A genes of the channel catfish (Ictalurus punctatus) a cDNA library was s creened and PCR was performed. Four different full-length cDNA sequences fo r MHC class II A genes were obtained from a clonal B cell line derived from an outbred fish. Two different genomic sequences and corresponding cDNAs w ere obtained from a presumably homozygous gynogenetic catfish. The A genes have five exons and four phase one introns. The first exon encodes the 5' u ntranslated region (UTR) and leader peptide, the second and third exons enc ode the alpha 1 and alpha 2 domains, respectively. The connecting peptide, transmembrane and cytoplasmic domains, as well as part of the 3' UTR, are e ncoded by the fourth exon and the rest of the 3' UTR is encoded by the fift h exon. Southern blot analyses using an exon three probe revealed two to fo ur hybridizing fragments with considerable restriction fragment length poly morphisms evident among randomly selected outbred channel catfish. These fi ndings are consistent with the presence of at least two functional polymorp hic MHC class II A gene loci. An unusual aspect of the channel catfish MHC class II alpha chain is its lack of N-linked glycosylation sites. (C) 2000 Elsevier Science Ltd. All rights reserved.