Cloning and sequence analysis of two isotypic IgM heavy chain genes from Atlantic salmon, Salmo salar L

Abstract

A leukocyte cDNA library from Atlantic salmon, based on oligo-dT priming, was constructed in lambda-gt10. Immunoglobulin heavy chain (IgH) cDNA were isolated from the library using a specific probe generated by polymerase chain reaction (PCR) between two conserved areas within the variable region (second and fourth frame region). Two cDNA clones encoding the entire constant region of membrane-bound IgH, and one cDNA encoding the entire constant region of secretory IgH were sequenced, revealing messages from two isotypic IgM genes. Both genes were shown to be present in haploid embryos and have been isolated from a genomic library, the exons and deduced amino acid sequences of which are presented here (salmon CHA and CHB). The splicing of transcripts encoding the membrane-bound IgH excises the whole fourth exon as in other teleosts. The nucleotide and amino acid identity between salmon CHA and CHB are 98.2%, and 96.2%, respectively. Two subfractions of IgM from Atlantic salmon separated by ion chromatography can be explained by a net exchange of basic residues in salmon CHB compared to CHA. The finding of two closely related salmon CH genes is in accordance with the quasi-tetraploid state of the Atlantic salmon genome.

Immunoglobulin in fish—genes, expression and structure

“…This site is also used in sharks (and most probably in all Chondrichthyes) (Kokubu et al, 1988a) but is lost in teleost fish. In these species the exon of the transmembrane peptide splices to the end of the CH3 exon eliminating the whole CH4 domain (Bengtén et al, 1991;Hordvik et al, 1992;Lee et al, 1993;Wilson et al, 1990). The truncated B-cell receptor seems to function normally as an antigen receptor and mediate allelic exclusion (Ledford et al, 1993;Miller et al, 1994).…”

B cells develop in the zebrafish pancreas

“…The expression of Ig during development was initially evaluated by RT-PCR. As in other teleosts (15)(16)(17), transcripts encoding the membrane form of zebrafish Ig are generated by splicing from the 3Ј end of the C H 3 exon to the membrane exons, thereby excluding the C H 4 exon, which is present only in transcripts encoding the secreted form of Ig (N.D. and L.A.S., unpublished data). Accordingly, the two types of transcript can be selectively amplified by choosing specific downstream primers.…”

Monoclonal antibodies reactive with serum IgM and leukocytes from Atlantic salmon (Salmo salarL.)

“…The Atlantic salmon (Salmo salar L.) serum Ig, IgM, is tetrameric, and two isotypic IgM heavy chain genes have been sequenced (Hordvik et al, 1992). Isotype specific antibodies to salmonid Ig have not been described.…”

“…At present, the genes encoding only a few leukocyte surface components have been sequenced, i.e. the two heavy chain immunoglobulin genes (Hordvik et al, 1992) and the MHC class I and II genes Grimholt et al, 1993). The possibility of using recombinant proteins both as immunogens and in the selection of MAbs would ease the tailoring of MAbs to leukocytes.…”