Evidence for eumelanin and pheomelanin producing genotypes in the Arabian horse.

The research article explores the presence of two types of pigmentation genotypes, eumelanin and pheomelanin, in Arabian horses. This is established by studying the pigments found in melanocytes of the horses’ hair and skin.

Methodology and Findings

The researchers’ work was split into several parts:

• They used ultrastructural imaging of melanocytes (skin pigment cells) and energy-dispersive X-ray spectroscopy to detect sulfur-containing melanosomes, which are associated with certain pigmentation types.
• The analyses found that pheomelanosomes (associated with yellowish-red pigment) were present in hair follicles of chestnut horses. This provided evidence to suggest pheomelanogenesis occurs in these horses.
• The presence of eumelanosomes (associated with black pigment) in black horse hair follicles suggests eumelanogenesis taking place.
• Using skin biopsies, the researchers also found that different types of melanosomes were produced in different areas in the same horse. For instance, in a chestnut horse, skin melanocytes produced eumelanosomes while the hair follicle melanocytes produced pheomelanosomes.
• In light bay horses, they found a correlation between the type of follicular melanosome present and the color of the hair.

Confirming Hypotheses

• The results from the research provide evidence for the Odriozola-Adalsteinsson hypothesis. This states that the e allele, a variation of a gene typically responsible for black pigmentation, is responsible for the chestnut phenotype in horses.
• This research also confirms and provides further detail on the workings of the A (Agouti) and E (Extension) loci in horses. These gene locations have been proposed to control horse color in a manner similar to how they function in mice and other mammals.