Structure of the catfish IGH locus: analysis of the region including the single functional IGHM gene.
The catfish IGH locus is large ( approximately 1 Mb) 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 aside from 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 IgZ/IgT described in zebrafish, trout and pufferfish. Second, there are a high number of VH pseudogenes, 28 out of 55 (51%). In contrast, the entire zebrafish IGH locus has 40 functional VH genes and eight 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.
Bengtén
E
E
Department of Microbiology, University of Mississippi Medical Center, Jackson, MS 39216, USA. ebengten@microbio.umsmed.edu
Quiniou
S
S
Hikima
J
J
Waldbieser
G
G
Warr
G W
GW
Miller
N W
NW
Wilson
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D022202:Chromosomes, Artificial, Bacterial; D018628:Gene Dosage; D050438:Genes, Immunoglobulin Heavy Chain; D007059:Ictaluridae / Q000235:genetics* / Q000276:immunology*; D007133:Immunoglobulin Joining Region / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics; D007148:Immunoglobulin mu-Chains / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011544:Pseudogenes; D016415:Sequence Alignment
D007133:Immunoglobulin Joining Region; D007135:Immunoglobulin Variable Region; D007148:Immunoglobulin mu-Chains