An examination of melanogenic traits and <i>TYRP1</i> polymorphism in Nanping and Romney Marsh sheep breeds

Abstract

The effects of mutations of the gene for tyrosinase-related protein 1 (TYRP1) on the black muscles and coat color in Nanping black-boned sheep were investigated. Tyrosinase activity and melanin content in plasma were measured and compared in three random groups of sheep: Nanping black-boned (101 heads), Nanping normal (106 heads) and Romney Marsh sheep (82 heads, Ovis aries). Eight exons and their partial flanking regions of the TYRP1 gene were amplified. Six intronic mutations and six exonic polymorphisms including two non-synonymous mutations [c.203C > T (p.A68V) and c.1202T > C (p.V401A)] were identified. Using a bi-directional polymerase chain reaction allele-specific amplification (bi-PASA) of the mutation c.203C > T it was shown that the frequencies of allele C in the Nanping black-boned, Nanping normal and Romney Marsh sheep were respectively 0.955, 0.967 and 0.744. For the mutation c.1202T > C, the frequencies of allele T in the three populations of sheep were respectively 0.777, 0.745 and 0.793 as measured using the single-strand conformation polymorphism. When the data from sheep of all three populations with the CC genotype of SNP c.203C > T were pooled, it was found that there was significantly higher (P < 0.05) tyrosinase activity, content of alkali-soluble melanin and ratio of eumelanin : total melanin than in the plasma of sheep with the CT and TT genotypes. This was not so within each of the three groups of sheep. No significant effect of the TRYP1 genotype on coat color was found. Further studies will be necessary to determine the cause of the black traits in Nanping black-boned sheep.