Diversity of the immunoglobulin heavy chain in the Atlantic salmon (Salmo salar L.) is contributed by genes from two parallel IgH isoloci.

Immunoglobulin heavy chain (IgH) variable (V) region cDNAs from the Atlanti c salmon, Salmo salar L., have been isolated and analysed with respect to d iversity and transcription of the two parallel IgH isoloci in this species. A total of nine V-H families were defined according to the 80% identity cr iterion, of which seven were highly related (>80% identity) to the V-H fami lies defined in rainbow trout and arctic charr. The variability of the CDR1 and 2 was low, although mutational hot-spot consensus sequences were accum ulated in these regions. The CDR3 showed largest variability. expressing at least eight different groups of D motifs diversified by fusion of the D mo tifs, possible N and P nucleotide insertions and exonuclease activity. Pres umably functional transcripts expressing D motifs in all three reading fram es were identified for two of the motifs. The cDNAs were mapped to tither o f the two parallel loci, and sequence analysis revealed that the repertoire of V-H segments was contributed by transcription of genes: from both of th e IgH isoloci, Transcription of genes from both isoloci generated no obviou s effects on variability in the CDR3 of the Atlantic salmon IgH chains, alt hough one additional J(H)-segment with altered N-terminal was generated by the process of duplication and divergence. Thus, the issue of biological si gnificance of the two IgH isoloci remains unclear. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.