ISSN:
1432-1211
Keywords:
Key words MHC class I
;
Chimpanzee
;
Inter-species allele
;
Intron
;
Evolution
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract Immunoglobulin heavy chain (IgH) genes in representative chondrichthyan fishes (sharks and skates) consist of independently functioning clusters, containing separate variable (V H ), diversity (D H ), and joining (J H ) region elements and constant (C H ) region exons. IgH loci have been characterized in Hydrolagus colliei (spotted ratfish), a modern representative of a major independent chondrichthyan lineage. Three distinct families of IgH gene clusters were identified. The most numerous genes consist of unjoined V H -D 1 -D 2 -J H segments that correspond to the most abundant Hydrolagus spleen (cDNA) transcripts which apparently arise from a diversified gene family. In the second cluster type, V H , D H , and J H segments are germline-joined, whereas the C H exons exhibit typical organization. This gene type is found in only a few copies per haploid genome and both transmembrane and secretory transcripts have been identified. A third cluster type has been identified that consists of unjoined V H elements but lacks a typical C H 1 exon, which is substituted with a second C H 2-like exon. Transcripts from this third cluster type also appear to derive from a diversified gene family. Genomic D regions of the two unjoined clone types exhibit structural differences that are consistent with incorporation of recombination machinery-mediated events. Genomic library screening indicates that 90% of V H + clones are truncated, nearly identical pseudogenes (lacking J H and C H ). These studies demonstrate an early phylogenetic origin for the cluster type of gene organization and document extensive organizational diversification within an apparent single class of IgH genes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002510050353
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