Differential gene expression of TRPM1, the potential cause of congenital stationary night blindness and coat spotting patterns (LP) in the Appaloosa horse (Equus caballus) - PubMed (original) (raw)

Differential gene expression of TRPM1, the potential cause of congenital stationary night blindness and coat spotting patterns (LP) in the Appaloosa horse (Equus caballus)

Rebecca R Bellone et al. Genetics. 2008 Aug.

Abstract

The appaloosa coat spotting pattern in horses is caused by a single incomplete dominant gene (LP). Homozygosity for LP (LP/LP) is directly associated with congenital stationary night blindness (CSNB) in Appaloosa horses. LP maps to a 6-cM region on ECA1. We investigated the relative expression of two functional candidate genes located in this LP candidate region (TRPM1 and OCA2), as well as three other linked loci (TJP1, MTMR10, and OTUD7A) by quantitative real-time RT-PCR. No large differences were found for expression levels of TJP1, MTMR10, OTUD7A, and OCA2. However, TRPM1 (Transient Receptor Potential Cation Channel, Subfamily M, Member 1) expression in the retina of homozygous appaloosa horses was 0.05% the level found in non-appaloosa horses (R = 0.0005). This constitutes a >1800-fold change (FC) decrease in TRPM1 gene expression in the retina (FC = -1870.637, P = 0.001) of CSNB-affected (LP/LP) horses. TRPM1 was also downregulated in LP/LP pigmented skin (R = 0.005, FC = -193.963, P = 0.001) and in LP/LP unpigmented skin (R = 0.003, FC = -288.686, P = 0.001) and was downregulated to a lesser extent in LP/lp unpigmented skin (R = 0.027, FC = -36.583, P = 0.001). TRP proteins are thought to have a role in controlling intracellular Ca(2+) concentration. Decreased expression of TRPM1 in the eye and the skin may alter bipolar cell signaling as well as melanocyte function, thus causing both CSNB and LP in horses.

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Figures

Figure 1.—

Horses displaying different Appaloosa coat color patterns. (a) Lace blanket (LP/lp). (b) Spotted blanket (LP/lp). (c) Leopard (LP/lp). (d) Snowcap blanket (LP/LP). (e) Fewspot (LP/LP).

Figure 2.—

Scotopic electroretinogram from an lp/lp Appaloosa (left) and an LP/LP Appaloosa with CSNB (right). Note the absence of a b-wave in the ERG tracing from the LP/LP horse. (50 msec, 100 mV).

Figure 3.—

Genomic map highlighting those genes tested for differential expression within LP candidate region.

Figure 4.—

Retinal and skin gene expression for five genes in the LP candidate region normalized to β_-actin_. Relative mRNA expression is represented as a log 2 relative expression ratio (means ± SE). (A) CSNB affected (LP/LP) and CSNB unaffected (LP/lp) retinal RNA samples. Data are expressed as relative to CSNB unaffected (lp/lp) mRNA levels. (B) Pigmented and unpigmented skin samples of homozygous (LP/LP) and heterozygous (LP/lp) horses. Data are expressed as relative to non-appaloosa (lp/lp) mRNA levels. An asterisk indicates significant results (P < 0.05).

Figure 4.—

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Differential gene expression of TRPM1, the potential cause of congenital stationary night blindness and coat spotting patterns (LP) in the Appaloosa horse (Equus caballus) - PubMed (original) (raw)