Specifying and sustaining pigmentation patterns in domestic and wild cats

Abstract

Color markings among felid species display both a remarkable diversity and a common underlying periodicity. A similar range of patterns in domestic cats suggests a conserved mechanism whose appearance can be altered by selection. We identified the gene responsible for tabby pattern variation in domestic cats as Transmembrane aminopeptidase Q (Taqpep), which encodes a membrane-bound metalloprotease. Analyzing 31 other felid species, we identified Taqpep as the cause of the rare king cheetah phenotype, in which spots coalesce into blotches and stripes. Histologic, genomic expression, and transgenic mouse studies indicate that paracrine expression of Endothelin3 (Edn3) coordinates localized color differences. We propose a two-stage model in which Taqpep helps to establish a periodic pre-pattern during skin development that is later implemented by differential expression of Edn3.

Fig. 1

(A) Allelic variation at Tabby [mackerel (Ta^M) is dominant to blotched (Ta^b)] controls the arrangement of dark- and light-colored areas. Diagrams indicate how the distribution of black or brown eumelanin versus yellow or pale pheomelanin within individual hairs underlies the macroscopic color patterns, although in reality cat hairs frequently exhibit multiple pheomelanic bands. (B) Taqpep encodes a type II membrane protein with aminopeptidase activity encoded by the ectodomain. Mutant allele frequencies are from a survey of 119 feral and outbred cats (table S1). The T139N allele is associated (P = 0.0017, Fisher’s exact test) with an atypical swirled pattern but is incompletely penetrant (table S1 and fig. S2).

Fig. 2

(A) Black-haired areas are larger, more irregular, and associated with dorsal stripes in the king cheetah. (B) Chromatogram of Taqpep cDNA from a spotted (+/+) as compared to a king (fs/fs) cheetah.

Fig. 3

Skin sections of fetal cats [(A), at 3, 5, and 7 weeks of gestation] stained with hematoxylin and eosin, together with unstained flat-mount (en face) skin preparations of fetal cats [(B), at 7 weeks of gestation]. The 7-week images in (B) are from an orange (O/Y or O/O) individual, which allows the dark component of the tabby pattern (which is orange-colored) to be more easily visualized. In the trans-illuminated “dermis-up” panel, hair follicle outlines (dashed red lines) appear light-colored; melanin incorporation and blood vessels appear dark-colored. Scale bars in (A), 150, 50, and 250 μm in 3-, 5-, and 7-week fetal cat sections, respectively, and 50 μm in the 7-week epidermis close-up. Scale bars in (B), 2 mm, 100 μm, and 600 μm in epidermis-up, follicle histology, and dermis-up panels, respectively.

Fig. 4

(A) A cheetah skin biopsy that includes a black-yellow boundary (also see fig. S6). (B) EDGE (13) determination of differential gene expression in black- as compared to yellow-colored areas of cheetah skin. Transcript frequency (observations per million sequence reads, mean of five samples) is plotted as a function of differential expression. The 74 genes with significant differential expression are shown in black or yellow (FDR < 0.05, see methods and tables S8 and S9); 7 additional pigmentation genes that are not differentially expressed are shown in pink. (C) Relative mRNA levels (mean ± SE) for the indicated genes as assessed by qRT-PCR from paired samples (n = 4) of dark and light neonatal tabby skin; *P < 0.05 (dark versus light, two-tailed t test). Dermal papilla expression of Edn3 mRNA (purple stain, white arrows) as detected by in situ hybridization, from a brown tabby individual. The left panel illustrates the expression of Edn3 mRNA in both pheomelanin- and eumelanin-containing follicles. (D) Phenotypes of 2-week-old mice of the indicated genotypes. Relative mRNA levels (mean ± SE) for the indicated genes from qRT-PCR of cDNA from control (n = 4) and transgenic (n = 4) mice are shown; *P < 0.05 (A^y versus A^y;Tg.K5-tTA;Tg.TRE-Edn3, two-tailed t test). Scale bars in (A), 40 and 200 μmin epidermis and whole-skin sections, respectively. In (C), 60 and 20 μmin left and right panels, respectively.

Fig. 5

A tabby pre-pattern is established at or before hair follicle development (A), specifying regions as dark (gray-colored) or light (yellow-colored). In the absence of Taqpep, dark regions are expanded, and there is less periodicity. Regional identity is manifested and implemented (B) by differential expression of Edn3 in the dermal papilla, a permanent part of the hair follicle that releases paracrine factors to act on overlying melanocytes. Yellow and black pigment are synthesized by melanocytes in hair follicles that produce low and high levels of Edn3, respectively.