Characteristics of the allele pool of the Southern Meat sheep breed based on the PRPN prion protein gene associated with genetic resistance to scrapie

Purpose: to study polymorphism in the PRPN gene in sheep of the Southern Meat breed and determine their genetic resistance to the classical and atypical scrapie.
Materials and methods. The biomaterial was ear plucks from 442 sheep of the gene pool herd of the Southern Meat breed, selected from the Ladozhsky Breeding Plant. Sheep genotypes associated with scrapie resistance were determined based on sequencing of a fragment of the ovine PRNP gene. Sanger sequencing of the sheep PRNP gene fragment was carried out on a Nanofor 05 genetic analyzer, according to the methodological recommendations by T.E. Deniskova et al. Sequencing data were processed using the Mutation Surveyor V5.1.2 program (Release), and allele polymorphism in codons 136 (A/T/V), 141 (L/F), 154 (R/H) and 171 (Q/R/ H/K) were determined based on the analysis of the obtained sequences. Statistical data processing was carried out using Microsoft Excel and GenAlEx 6.501.
Results. Analysis of PRPN gene polymorphism showed the presence of seven alleles (ARR, ARQ, AHQ, ARH, AHH, AHR, and VRQ) in the studied sample. The desired haplotype ARR was found in all sheep groups, the frequency across the sample was 21,43 %. It`s minimum frequency was 18,18 % in the group of ewes, and the maximum was 23,08 % in the group of young ewes. The undesirable allele VRQ, associated with sensitivity to the classical scrapie, was not detected in the group of rams (sires) in the studied sample. In the remaining groups, this allele varied from 7,14 % in young rams to 9,09 % in ewes, and the frequency in the entire sample was 6,12 %. In this study, we discovered a new rare haplotype AHH, which was not previously reported either in the Southern Meat or in other sheep breeds. The AHH allele was present in all studied groups of the Southern Meat sheep breed with frequency varied from 7,69 % in young ewes to 13,64 % in ewes. The analysis of the frequency of genotypes in the studied sample of sheep of the Southern Meat breed, sixteen genotypes were identified (ARR/ARR, ARR/AHQ, ARR/ARH, ARR/ARQ, ARQ/ARQ, ARQ/AHQ, ARQ/ARH, ARQ/AHH, ARH /ARH, ARH/AHH, AHQ/AHQ, AHH/AHH, AHR/AHR, ARR/VRQ, ARQ/VRQ, VRQ/VRQ), corresponded to five classes of genetic resistance to scrapie. The frequencies of the desired genotypes varied widely among different age groups of sheep. The F allele at codon 141, associated with genetic susceptibility to the Nor98 strain, was not detected in any individual in the studied sample. We recommend analyzing the polymorphism of the PRPN gene for susceptibility to classical and atypical scrapie as an additional selection criterion for effective breeding work. This procedure will significantly increase the genetic resistance to scrapie in new generations of sheep of the Southern Meat breed.

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