Distribution and sequence analysis of the melanocortin 2 receptor in horses and ponies

The melanocortin 2 receptor (MC2R) has relevance to equine pituitary pars intermedia dysfunction (PPID), as it is the primary binding site for ACTH, which circulates at elevated concentrations in animals affected by PPID. Despite this, little is known about MC2R in equine species. The overall aim of this investigation was to determine MC2R mRNA expression in tissues relevant to PPID in healthy horses and to examine the MC2R gene sequence in a cohort of horses and ponies with and without PPID. The study found that the MC2R gene was expressed in both adrenal and pituitary gland tissues as reported in other mammalian species. However, no expression was seen in adipose or skin tissue. An investigation of the tissue distribution and functionality of the MC2R in individuals with PPID is now recommended. Then, we investigated the coding regions (exons) of the equine MC2R gene for variations associated with PPID in a limited number of animals. This was performed using a hybridised gene capture and next generation sequencing method which found a 100% pairwise identity between all 28 individuals in the study, and with the reference genome sequence. This preliminary study found no evidence of major genetic variations in the coding region of the MC2R gene associated with PPID, though variants affecting expression may occur in the introns or remain unidentified within the exons of the gene and studies on a larger scale are required.