Single-strand conformational polymorphism and sequence polymorphism of Mhc-DRB in Latxa and Karrantzar sheep: implications for Caprinae phylogeny

Single-strand conformational polymorphism analysis and DNA sequencing were used to characterize Mhc-DRB second exon variability in the Latxa and Karra ntzar breeds of sheep. The presence of more than two sequences in some anim als indicates that alleles of two different loci have been amplified. Six n ew alleles were identified by sequencing. The allele frequency distribution of the DRB1 gene is striking, with two alleles accounting for half of the gene pool in both breeds under study. The most frequent allele in both bree ds was the same (named DRB1*0702), with some specific amino acids: Tyr in p osition 31 and Thr in 51. A species variability analysis was also performed including the entire set of sheep DRB exon 2 sequences. Based on the patch work patterns of different alleles, interallelic recombination appears to b e playing a significant role in the generation of allelic diversity at this locus in sheep. The phylogenetic tree of all known Caprinae DRB sequences shows that certain alleles from one species are more closely related to tho se from other species than they are to each other. Allele DRB1"'0702 merits special attention due to its high similarity to the Mufflon allele. As thi s is the most frequent in both breeds analyzed, one can hypothesize that in sheep, both Mufflon and Argali have had different influences depending on the sheep breed under study and that the relationship between domestic shee p and Mufflon is greater than previously thought. The data generated in thi s study can serve as a basis for developing a typing assay for the sheep DR B genes in the Latxa and Karrantzar populations.