A unique characteristic of the Silkie chicken is its fibromelanosis phenotype.The dermal layer of its skin,its connective tissue and shank dermis are hyperpigmented.This dermal hyperpigmentation phenotype is controlled by the sex-linked inhibitor of dermal melanin gene(ID)and the dominant fibromelanosis allele.This study attempted to confirm the genomic region associated with ID.By genotyping,ID was found to be closely linked to the region between GGA_rs16127903 and GGA_rs14685542(8406919 bp)on chromosome Z,which contains ten functional genes.The expression of these genes was characterized in the embryo and 4 days after hatching and it was concluded that MTAP,encoding methylthioadenosinephosphorylase,would be the most likely candidate gene.Finally,target DNA capture and sequence analysis was performed,but no specific SNP(s)was found in the targeted region of the Silkie genome.Further work is necessary to identify the causal ID mutation located on chromosome Z.
Ming TIANRui HAOSuyun FANGYanqiang WANGXiaorong GUChungang FENGXiaoxiang HUNing LI
The dermal hyperpigmentation phenotype in chickens is controlled by the dominant fibromelanosis allele.One of the ten unique characteristics of Silkie chickens is the fibromelanosis phenotype,which is pigmentation in the dermal layer of the skin and connective tissue.In this study,we found a mutation of fibromelanosis,a genomic rearrangement that included an inverted duplication of endothelin3(EDN3),is responsible.We show that,as a stimulator of melanoblast proliferation,EDN3 expression was increased in silkie embryos and in both skin and muscle throughout adulthood.EDN3 expression led to an increase in expression of the downstream genes EDNRB2 and TYRP2,and was closely relate with the hyperpigmentation phenotype.We examined eight different Chinese chicken breeds showing hyperpigmentation and conclude that this structural genetic variant exists in all fibromelanosis chicken breeds.
Ming TIANSuyun FANGYanqiang WANGXiaorong GUChungang FENGRui HAOXiaoxiang HUNing LI
