The major histocompatibililty complex (MHC) is a large gene family encoding a set of trans-membrane proteins that play a key role to initiate immune responses in the vertebrates. DRB gene is one member of the MHC gene family and usually with high diversity, thus, it is prevalently used as an adaptive genetic marker in conservation genetics study. The endangered Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) is also known as the only freshwater finless porpoise population in Chinese waters. In order to develop MHC genetic marker that suitable for conservation genetics study, a primer pair that originally designed for DRB gene of North elephant seal (Mirounga angustirostris) was used to amplify the genome of the Yangtze finless porpoise. As a result, 5 DRB exon 2 unique sequences of 188bp ( including partial peptide binding region, PBR) were first isolated from 5 individuals via PCR and sequencing. When BLAST in GenBank, these sequences showed high similarity (97%) with the DRB2 allele of the beluga (Delphinapterus leucas), indicating the expected DRB loci were successfully obtained for the Yangtze finless porpoise. In further sequence analysis, nucleotide substitutions were decided at 4 sites with inducing amino acid substitutions at 3 sites, all of the 5 DRB unique sequences showing entire open reading frames, and also much more non-synonymous substitutions than synonymous substitutions were detected especially at PBR. Additionally, more than two unique sequences were identified from one individual, suggesting possible gene duplication at this DRB locus. All of the above results indicated that DRB gene in the Yangtze finless porpoise had potential function and high variability, and also underwent strong positive selection. Thus, the DRB locus isolated and identified in this study could serve as useful adaptive genetic marker in the conservation genetics studies of the Yangtze finless porpoise, such as MHC genetic diversity and population adaptability estimation.
Du He-Jun (duhejun21@sohu.com) ; Zheng Jin-Song (zhengjinsong@ihb.ac.cn) ; Wu Min; Zhao Qing-Zhong; Wang Ding (wangd@ihb.ac.cn).ISOLATION AND IDENTIFICATION OF MHC-DRB GENE EXON 2 IN THE YANGTZE FINLESS PORPOISE,Acta Hydrobiologica Sinica,2009,33(5):804-810
