T-CELL RECEPTORS IN CHANNEL CATFISH - STRUCTURE AND EXPRESSION OF TCRALPHA-GENE AND BETA-GENE

Herein are reported full length cDNA sequences for TCR alpha- and beta -chains of the channel catfish. Included are sequences belonging to fo ur Va and six Vp families which share hallmarks in common with the Va and VP genes of other species. Similar to the situation in other verte brates, the catfish C alpha and C beta sequences exhibit distinct immu noglobulin, connecting peptide, transmembrane and cytoplasmic domains. However, the catfish TCR Ct and CP regions are shorter than those of mammals and the catfish CP chain lacks a cysteine in its connecting pe ptide region. Two different catfish CP cDNA sequences were identified, suggesting the existence of either two Cg loci or allotypes. Based on Southern blot analyses, each of the catfish TCR gene loci appear to b e arranged in a translocon (as opposed to multicluster) organization w ith multiple V elements and a single or few copies of C region DNA. At the deduced amino acid level, the catfish C beta sequence exhibits 42 % identity with the C beta of Atlantic salmon, 41% identity with the C beta of the identity with CB of the horned shark. The catfish C alpha amino acid sequence exhibits 44 and 29% identity of rainbow trout and 26% with Ca of the rainbow trout and southern pufferfish, respectivel y. TCR alpha and beta messages are selectively expressed and rearrange d in a catfish clonal cell line that appears to be of the T lineage. T his TCR alpha/beta expressing clonal lymphocyte line, designated 28S.1 , has T-cell like function in that it constitutively produces a supern atant factor(s) with growth promoting activity. These findings should facilitate functional studies of fish TCRs and T cells in ways not pre viously possible with other 'lower' vertebrate models. (C) 1998 Elsevi er Science Ltd. All rights reserved.