Comparative linkage mapping of the Grey coat colour gene in horses.

The research article presents a study on how grey coat colour in horses is inherited and its link to melanoma development. The scientists further their previous research to precisely locate the “Grey” gene on horse chromosome 25.

Study Context

• The study looks into the genetic basis for the grey coat colour in horses. Unlike other mammals, grey horses are not born with the grey colour. They are born coloured and progressively turn grey as they age.
• This study follows up on previous research where the location of the Grey gene was mapped to horse chromosome 25 (ECA25). This gene is inherited in an autosomal dominant manner, this means if a horse inherits the Grey gene from one of its parents, it will become a grey horse.
• It was also observed that grey horses often develop melanomas later in their life. This is a skin cancer that is also related to pigmentation.

Research Method

• The researchers developed eight new single nucleotide polymorphisms (SNPs). These are differences in one nucleotide (the building blocks of DNA and RNA) within a gene. These SNPs were associated with various genes on ECA25.
• They did this by mapping the order of genes on human chromosome 9q and utilizing the human and mouse coding sequences. This was done because the gene organisation (linear order) is usually conserved among mammals.
• The team then used over 300 offspring from two Swedish Warmblood grey stallions and non-grey mares to map these SNPs in relation to the Grey gene.

Findings

• The Grey gene was confirmed to be within a certain region on ECA25, where it was more precisely mapped to a region between the genes NANS and ABCA1. In human chromosome terms, this would be a 6.9 Mb region on chromosome 9q.
• No genetic recombination was observed between Grey, TGFBR1, and TMEFF1, suggesting that these genes could have a functional relationship or are co-regulated. Note that in humans, the TGFBR1 and TMEFF1 genes are 1.4 Mb apart from each other.

Conclusions

• Despite having identified the chromosomal region where the Grey gene is located, no obvious candidate gene was found that could be linked to pigmentation disorders or melanoma development.
• This suggests that the grey phenotype in horses could be caused by a mutation in a novel gene, which has yet to be identified. Future research will need to focus on identifying and characterizing this gene.