Genetic polymorphism of the major histocompatibility complex （MHC） B-LBⅡ gene was studied by amplification of exon 2 using PCR, followed by cloning and DNA sequencing in eight indigenous Chinese chicken populations...Genetic polymorphism of the major histocompatibility complex （MHC） B-LBⅡ gene was studied by amplification of exon 2 using PCR, followed by cloning and DNA sequencing in eight indigenous Chinese chicken populations. To reveal the genetic variation of the B-LB Ⅱ gene, 37 types of patterns detected by PCR-SSCP were investigated first, which would be used to screen novel B-LB Ⅱsequences within the breeds. The types of PCR-SSCP patterns and final sequencing allowed for the identification of 31 novel MHC B-LBⅡ alleles from 30 unrelated individuals of Chinese chickens that were sampled. These are the first designators for the alleles of chicken MHC B-LBⅡ gene based on the rule of assignment for novel mammalian alleles. Sequence alignment of the 31 B-LB Ⅱ alleles revealed a total of 68 variable sites in the fragment of exon 2, of which 51 parsimony informative and 17 singleton variable sites were observed. Among the polymorphic sites, the nucleotide substitutions in the first and second positions of the codons accounted for 36.76% and 35.29%, respectively. The sequence similarities between the alleles were estimated to be 90.6%-99.5%. The relative frequencies of synonymous and nonsynonymous nucleotide substitutions within the region were 2.92%±0.94% and 14.64%±2.67%, respectively. These results indicated that the genetic variation within exon 2 appeared to have largely arisen by gene recombination and balancing selection. Alignment of the deduced amino acid sequences of the β1 domain coded by exon 2 revealed 6 synonymous mutations and 27 nonsynonymous substitutions at the 33 disparate sites. In particular, the nonsynonymous substitutions at the putative peptide-binding sites are considered to be associated with immunological specificity of MHC B-LB Ⅱ molecule in Chinese native chickens. These results can provide a molecular biological basis for the study of disease resistance in chicken breeding.展开更多
基金This work was supported by "948" Project of China (No. 2001-361), Chinese National Programs for High Technology Research and Development (No. 2004AA222170), and Key Project of Chinese National Programs for Fundamental Research and Develop-ment (No. G2000016103).
文摘Genetic polymorphism of the major histocompatibility complex （MHC） B-LBⅡ gene was studied by amplification of exon 2 using PCR, followed by cloning and DNA sequencing in eight indigenous Chinese chicken populations. To reveal the genetic variation of the B-LB Ⅱ gene, 37 types of patterns detected by PCR-SSCP were investigated first, which would be used to screen novel B-LB Ⅱsequences within the breeds. The types of PCR-SSCP patterns and final sequencing allowed for the identification of 31 novel MHC B-LBⅡ alleles from 30 unrelated individuals of Chinese chickens that were sampled. These are the first designators for the alleles of chicken MHC B-LBⅡ gene based on the rule of assignment for novel mammalian alleles. Sequence alignment of the 31 B-LB Ⅱ alleles revealed a total of 68 variable sites in the fragment of exon 2, of which 51 parsimony informative and 17 singleton variable sites were observed. Among the polymorphic sites, the nucleotide substitutions in the first and second positions of the codons accounted for 36.76% and 35.29%, respectively. The sequence similarities between the alleles were estimated to be 90.6%-99.5%. The relative frequencies of synonymous and nonsynonymous nucleotide substitutions within the region were 2.92%±0.94% and 14.64%±2.67%, respectively. These results indicated that the genetic variation within exon 2 appeared to have largely arisen by gene recombination and balancing selection. Alignment of the deduced amino acid sequences of the β1 domain coded by exon 2 revealed 6 synonymous mutations and 27 nonsynonymous substitutions at the 33 disparate sites. In particular, the nonsynonymous substitutions at the putative peptide-binding sites are considered to be associated with immunological specificity of MHC B-LB Ⅱ molecule in Chinese native chickens. These results can provide a molecular biological basis for the study of disease resistance in chicken breeding.
