Analysis of DRB1 exon 2 genotyping by STR size analysis in Suffolk and Texel sheep breeds

摘要

Alleles of the DRB1 exon 2 locus of the major histocompatibility complex have recently been associated with genetic resistance to gastrointestinal nematodes in sheep. While sequence-based typing is the standard method for allele discrimination, a rapid, high throughput method for DRB1 exon 2 genotyping is required if such information is to be incorporated into national breeding programmes. Previous studies have highlighteda simple tandem repeat (STR) located within intron 2 of the DRB1 gene, which couldpotentially be used to accurately assess the allele present within the adjacent exon 2.The aims of this study were firstly to compare two methods of STR analysis,Genescan™ and autoradiography, and secondly to investigate if STR analysis of DRB1intron 2 could be used to accurately assess the profile of DRB1 exon 2. Six DRB1 exon2 alleles were identified by sequence-based typing in Suffolk (n = 31) and eight in Texel(n = 60) sheep. The results indicated that Genescan™ was a more accurate method ofSTR analysis than autoradiography. The expected 1:1 correspondence between STRsize, analysed by Genescan™ and DRB1 exon 2 allele, determined by sequence-basedtyping, was not observed. However, the correspondence was found to be degenerate,whereby some alleles were associated with two STR sizes. Thus, irrespective of the STRsize identified, STR analysis by Genescan™ identified the correct allele in all caseswithin both populations of animals studied. However, the Genescan™ method of alleleidentification cannot be used for Suffolk × Texel crossbred progeny or in other breedswhere the relationship between STR size and DRB1 exon 2 allele is not known.