A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse.

This research explores how a specific mutation in horses causes them to gray prematurely and become more susceptible to melanoma, a type of skin cancer. The study further examines the relationship between this mutation and the increased risk of melanoma in horses carrying it.

Study Objective and Findings

• This research aimed to elucidate the genetic factors underlying premature graying in horses, as well as the seeming link between this graying and an elevated risk of melanoma.
• The Gray phenotype in horses, associated with premature graying, vitiligo-like depigmentation, and a high incidence of melanoma, was found to be caused by a 4.6-kb duplication in intron 6 of the STX17 (syntaxin-17) gene.
• This duplication is a type of cis-regulatory mutation, meaning it’s a mutation in a sequence of DNA that regulates the transcription of a gene.

Gene Overexpression and its Implications

• The researchers noticed that both the STX17 gene and the neighbouring NR4A3 gene were overexpressed in melanomas from Gray horses.
• Overexpression refers to a scenario where a gene is more active than it would typically be, leading to the production of more of the associated protein than normal.
• This overexpression in the context of premature graying suggests a link between these genes and the higher incidence of melanoma.

Interplay of Genetic Factors

• The study found that Gray horses carrying a loss-of-function mutation in ASIP (agouti signalling peptide) had a higher incidence of melanoma.
• A loss-of-function mutation in a gene causes that gene to produce a non-functional protein, possibly disrupting normal body functions.
• This finding suggests that increased melanocortin-1 receptor signalling, brought about by the malfunctioning ASIP, promotes melanoma development in Gray horses.

Human Impact and Genetic Selection

• The study’s conclusion reinforces that the Gray phenotype in horses is an example of how humans have historically selected for mutations with perceived positive effects in domesticated animals, in this case, a distinctive coat color.
• This human-driven genetic selection, while resulting in desirable traits, can also inadvertently lead to increased disease susceptibility, as observed with the increased melanoma risk in Gray horses.