MHC class II A genes in the channel cat®sh (Ictalurus punctatus ) Ulla B. Godwin a , Mike Flores a , Sylvie Quiniou b , Melanie R. Wilson b , Norman W. Miller b , L. William Clem b , Thomas J. McConnell a, * a N108 Howell Science Complex, Department of Biology, East Carolina University, 1000 East 10th Street, Greenville, NC 27858-4353, USA b Department of Microbiology, University of Mississippi Medical Center, Jackson, MS 39216, USA Received 27 August 1999; received in revised form 10 December 1999; accepted 14 December 1999 Abstract In order to characterize the Major histocompatibility complex (MHC) class II A genes of the channel cat®sh (Ictalurus punctatus ) a cDNA library was screened and PCR was performed. Four dierent full-length cDNA sequences for MHC class II A genes were obtained from a clonal B cell line derived from an outbred ®sh. Two dierent genomic sequences and corresponding cDNAs were obtained from a presumably homozygous gynogenetic cat®sh. The A genes have ®ve exons and four phase one introns. The ®rst exon encodes the 5 ' untranslated region (UTR) and leader peptide; the second and third exons encode the a1 and a2 domains, respectively. The connecting peptide, transmembrane and cytoplasmic domains, as well as part of the 3 ' UTR, are encoded by the fourth exon and the rest of the 3 ' UTR is encoded by the ®fth exon. Southern blot analyses using an exon three probe revealed two to four hybridizing fragments with considerable restriction fragment length polymorphisms evident among randomly selected outbred channel cat®sh. These ®ndings are consistent with the presence of at least two functional polymorphic MHC class II A gene loci. An unusual aspect of the channel cat®sh MHC class II a chain is its lack of N-linked glycosylation sites. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Channel cat®sh; Major histocompatibility complex; MHC class II A genes; Gynogenetic cat®sh; N-linked glycosylation 1. Introduction Mammalian classical major histocompatibility complex (MHC) class I and class II antigens are polygenic and highly polymorphic cell surface glycoproteins that are known to play a central role in adaptive immunity via their ability to Developmental and Comparative Immunology 24 (2000) 609±622 0145-305X/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0145-305X(00)00005-7 www.elsevier.com/locate/devcompimm * Corresponding author. Tel.: +1-252-328-4244; fax: +1- 252-328-4178. E-mail address: mcconnellt@mail.ecu.edu (T.J. McCon- nell). Abbreviations: b 2 m, Beta 2 microglobulin; CP, Connecting peptide; CY, Cytoplasmic tail; MHC, Major histocompatibil- ity complex; MLC, Mixed leukocyte culture; PBR, Peptide binding region; PBL, Peripheral blood leukocytes; RFLP, Restriction fragment length polymorphism; RT-PCR, Reverse transcribed PCR; TM, Transmembrane region; UTR, Untranslated region.