Linked markers exclude KIT as the gene responsible for appaloosa coat colour spotting patterns in horses

The appaloosa coat colour pattern of the horse is similar to that caused by the rump-white (Rw) gene in the mouse. In the mouse Rw colour pattern is the result of an inversion involving the proto-oncogene c-kit (KIT). Therefore, we investigated KIT as a candidate gene that encodes the appaloosa coat colour gene (Lp) in horses. KIT plays a critical role in haematopoiesis, gametogenesis, and melanogenesis and encodes a transmembrane tyrosine kinase receptor that belongs to the PDGF/CSF-1/c-KIT receptor subfamily. Half-sib families segregating for Lp were uninformative for a reported polymorphism in KIT. However, KIT is located on horse chromosome 3 close to albumin (ALB), serum carboxylesterase (ES), vitamin D-binding protein (GC) and microsatellite markers ASB23, LEX007, LEX57, and UCDEQ437. Indeed, KIT and ASB23 were localized to ECA3q21-22.1 and 3q22.1-22.3, respectively, by fluorescent in situ hybridization. Family studies were conducted to investigate linkage of Lp to these markers using eight half-sib families in which Appaloosa stallions were mated to solid coloured mares. Linkage of Lp to the chromosome region containing ES, ALB, GC, ASB23, UCDEQ437, LEX57, and LEX007 was investigated by a multipoint linkage analysis using the computer program GENEHUNTER. LOD scores over the interval under investigation ranged from -4.28 to -12.48, with a score of -12.48 at the location for ASB23. Therefore, it was concluded that appaloosa (Lp) is not linked to any of the tested markers on ECA3, and thus Lp is unlikely to be the product of KIT.