Submitted to: Immunogenetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2006
Publication Date: 8/29/2006
Citation: Bengten, E., Quiniou, S.M., Hikima, J., Waldbieser, G.C., Warr, G.W., Miller, N.W., Wilson, M. 2006. Structure of the Catfish IGH Locus: Analysis of the Region Including the Single Functional IGHM Gene. Immunogenetics 58:831-844. Interpretive Summary: Immunoglobulins are a critical element of the immune response to pathogens. They are not completely described in fish and recently a new type was found. In this study the genome region surrounding the two known and functional immunoglobulin genes in catfish was characterized by DNA sequencing. It showed that this region varied greatly from fish to fish. The newly discovered type of immunoglobulin in some other fish was not seen in this region and its presence or absence in catfish still need to be validated. As a major component of immunity, this information on immunoglobulins will help understand mechanisms involved in disease resistance.
Technical Abstract: The catfish IGH locus is large (~1Mb) and complex, having undergone multiple internal duplications and transpositions. To define the structure of the locus that contains the single expressed IGHM gene, two overlapping bacterial-artificial-chromosome (BAC) clones spanning the most 3’ end of the channel catfish immunoglobulin heavy (IGH) chain locus have been completely sequenced. The analyses created a contig of 257,153 bp containing 55 VH, 6 D, 12 JH genes and the IGH constant region genes encoding the functional secreted and membrane forms of IgM and the membrane form of IgD. This analysis revealed three major features. First, no C region genes were found in addition to the previously-described IGHM1 and IGHD1, with the latter gene being the most 3’ C-region gene of the catfish IGH locus. There was no evidence in the region sequenced for genes that could encode an Ig class similar to the IgT/IgZ described in zebrafish, trout and pufferfish. Second, there are a high number of VH pseudogenes, 28 out of 55 (51%). By contrast, in the entire zebrafish IGH locus there are 40 functional VH genes and 8 pseudogenes (17%). Third, an internal duplication of a 52.4 kb block of VH genes has occurred. These observations suggest that the IGH locus of teleost fish varies significantly from species to species in the diversity of C region genes as well as the numbers of genes encoding V regions.