Linkage analysis between the upstream regulatory region and the second exon of bovine DRB3 gene

RIPOLI MV; DIAZ S; PERAL-GARCIA P; GIOVAMBATTISTA G

Japon

Congreso; XXIX Conference of the International Society for Animal Genetics ISAG; 2004

International Society for Animal Genetics ISAG

The BoLA-DRB3 gene extended polymorphism are located mainly in the second exon that encode the antigen binding site (ABS) of the molecule. Additional variation have also been reported in the promoter and in the third exon. It can be hypothesized that the exon 2 and the promoter (URR) are under different types of natural selection. In order to underline the coevolution of these sequences that are tightly linked and probably suffer different types of selection, we analyzed the polymorphism within each, URR and exon 2 of the gene. The URR and the exon 2 of DRB3 gene were genotyped by PCR-SSCP and -RFLP respectively, in 112 DNA samples from 12 cattle breeds. All URR variants and some DRB3.2 alleles were cloned and sequenced. We associate the seven URR variants detected in the sample studied with the exon 2 genotypes. This study may evidence the following: (i) lack of a clear pattern of linkage association between the URR and exon 2; (ii) the most abundant URR variants were spreading along the entire neighbour-joining tree of DRB3 exon 2 peptide sequences, while rare alleles were restricted to a specific cluster; (iii) each URR variant corresponded to more than one DRB3.2 allele; and (iv) any DRB3 type could be associated with more than one URR variant. A plausible explanation for these evidences was that the URR variation are stable, and old polymorphism was purified by positive selection, while the exon 2 alleles were originated by both point mutation and gene conversion and maintained by overdominace selection.