It’s been a more than 70-year mystery in the making, but now we may finally understand how the leopard got its spots – thanks in part to the decades-old workings of one of the UK’s greatest minds.
Turing suggested that the markings on fur and skin – which develop in the embryo – occur in response to a systematic relationship between two interacting substances that inhibit and activate one another. When the substances are distributed throughout the skin at different concentrations, their interactions would produce ordered patterns rather than chaotic markings, known as a reaction-diffusion model.
To test this theory, a team from the HudsonAlpha Institute for Biotechnology, Atlanta, USA, examined the development of patterns on domestic cats. The team had already shown that colour patterns in domestic cats appear when adjacent hair follicles produce different types of melanin pigment, but the developmental process behind these differences remained obscure.
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As described in a study out today in Nature Communications, the researchers, led by Gregory Barsh, studied skin samples from cat embryos at varying stages of development, and analysed the genes of single cells and proteins found in the tissue samples. The authors found that a signalling molecule encoded by the gene Dkk4 plays a central role in the reaction-diffusion that creates the differentiated markings in tabby cats.
Interestingly, the team found that the expression of Dkk4 in the foetal epidermis (the outermost portion of the skin) marked areas of foetal skin that would later give rise to hair follicles that would then produce darker pigment consistently throughout successive hair loss cycles. According to the authors, this suggests that the skin cells expressing Dkk4 acquire “time-sensitive epigenetic changes that are later incorporated into hair follicles”. It’s these changes that will ultimately determine whether the underlying skin will produce darker or lighter hairs.
The team also found that Dkk4 is mutated in cats with the ticked pattern type, such as Abyssinian and Burmese cats, which have fewer or no obvious markings.
The authors believe further research may reveal the role of Dkk4 and its interactions with other genes in creating the complex patterns found in bigger cats, like the rosettes on jaguars or the artistically shaped spots of the ocelot.