ISOLATION AND IDENTIFICATION OF M HC-DRB GENE EXON 2 IN THE YANGTZE FINLESS PORPO ISE

The major histocompatibililty complex (MHC) is a large gene family encoding a set of trans membrane proteinsthat p lay a key role to initiate immune responses in the vertebrates. DRB gene is one member of the MHC gene family andusually with high diversity,thus,it is prevalently used as an adaptive genetic marker in conservation genetics study. Theendangered Yangtze finless porpoise (N eophocaena phocaenoides asiaeorientalis) is also known as the only freshwater fin-less porpoise population in Chinese waters. In order to develop MHC genetic marker that suitable for conservation geneticsstudy,aprimer pair that originally designed for DRB gene of North elephant seal (Mirounga angustirostris) was used toamp lify the genome of the Yangtze finless porpoise. As a result,5 DRB exon 2 unique sequences of 188bp ( including par-tial pep tide binding region,PBR) were first isolated from 5 individuals via PCR and sequencing. When BLAST in Gen-Bank,these sequences showed high similarity (97% ) with the DRB- allele of the beluga (Delphinapterus leucas),indicating the expected DRB lociwere successfully obtained for the Yangtze finless porpoise. In further sequence analysis,nu-cleotide substitutionswere decided at 4 siteswith inducing amino acid substitutions at 3 sites,all of the 5 DRB unique se-quences showing entire open reading frames,and also much more non-synonymous substitutions than synonymous substitu-tions were detected especially at PBR. Additionally,more than two unique sequenceswere identified from one individual,suggesting possible gene dup lication at this DRB locus. All of the above results indicated that DRB gene in the Yangtzefinless porpoise had potential function and high variability,and also underwent strong positive selection. Thus,the DRBlocus isolated and identified in this study could serve as useful adaptive genetic marker in the conservation genetics studiesof the Yangtze finless porpoise,such asMHC genetic diversity and population adap tability estimation.