Appaloosa horse study reveals gene for blindness, colour | Horsetalk

How the appaloosa gets its spots has been revealed by researchers. © Petra Davidson

A study in the US of appaloosa horse genetics has revealed the potential gene responsible for Appaloosa coat patterning and related traits, including congenital stationary night blindness (CSNB). The results of the study, led by Dr Rebecca Bellone, PhD, have just been published in the August 2008 issue of "Genetics", the journal of The Genetics Society of America. The researchers concluded that TRPM1 is the probable gene causing both Appaloosa spotting and CSNB.

In 2004, Dr Bellone (formerly Terry) and associates published the results of a genome scan that determined the location of the main Appaloosa gene. This gene known as LP (for "leopard complex"), was mapped to equine chromosome 1.

A genome scan tells scientists which region on one of the 32 pairs of horse chromosomes the gene resides. The next step is to identify several genes from this mapped region that have functions which make them likely suspects for causing the trait. These candidate genes are then further investigated. One way to investigate several candidate genes is to look at their level of expression in a cell.

The recently published study involved the investigation of five genes from the LP candidate region. © Petra Davidson
Often gene expression study involves isolating RNA from the tissue under investigation and quantifying how much RNA from a particular gene is present. The amount of RNA from the sample group is compared to the RNA from the control population. The recently published study involved the investigation of 5 genes from the LP candidate region. Samples from homozygotes (LP/LP) were compared to solid non appaloosa horses (lp/lp). The only gene with dramatically different expression was TRPM1 (Transient Receptor Potential Cation Channel, Subfamily M, Member 1).

Bellone and her associates are now working to sequence TRPM1 in order to isolate the LP mutation. Isolation of LP will make possible the development of a DNA test. Breeders will be able to confirm if LP is present or not in young horses that do not immediately show the classic Appaloosa characteristics required for regular registration. It will also allow for the accurate identification of horses that are homozygous for LP.

The research was carried out as part of the Appaloosa Project, a research initiative being conducted by teams from Canada and the US. It is a long-term effort designed to identify and isolate the main genes responsible for Appaloosa patterning, and to investigate key physical traits associated with these genes. By finding the genetic mechanisms involved in the Appaloosa's physical traits, The Appaloosa Project contributes to worldwide efforts to study the genome of the horse.