Your sedentary cat may not seem to share many similarities with its fierce parents who roam the African savannah. But researchers at Stanford Medicine have discovered a specific gene that is responsible for much of the development of the stripes, spots, and spots that adorn all feline fur.
“Color patterns are one of those unsolved biological mysteries; there is no benchmark model organism to study it – mice don’t have any scratches or spots, ”said Gregory Barch, MD, PhD, Emeritus Professor of Genetics. “The color patterns and variability that you see in animals like tigers, cheetahs and zebras have raised some central questions for us: what are the genetic mechanisms of development and the cellular mechanisms that give rise to these patterns and how have they been altered during mammalian evolution to give rise to the astonishing variety of shapes and forms we see today? “
Barsh and his team have answered this question in part: They have identified a gene, DKK4, which helps regulate the early development of different fur patterns in domestic cats. DKK4, the team suspects, is likely involved in color patterns in all cats and possibly other mammals as well.
What makes cats tick?
Researchers previously identified a different gene that controls variation in coat color in tabby cats. It’s the same gene that explains the difference between cheetahs and king cheetahs, which have thicker and more prominent fur patterns.
“We knew from studying domestic cats that there were other genes that contributed to the formation of color patterns; we just didn’t know what they were, ”Barsh said.
They found a clue in the cat’s fetal tissue that seemed to foreshadow the color of the fur: thickening of skin tissue in some areas. These thickened regions constitute a “pre-pattern” which mimics any color patterns in the fur of an adult cat. The thick area marks the patches of fur which will be darker later; the thin area marks the spots which will be lighter.
“We call this step ‘establishment’, and it happens long before color appears and long before the hair follicles are mature,” Barsh said.
There are still other genes that explain why, for example, some cats have spots and why some cats have stripes.
The pre-model provided the researchers with a sort of map, showing which cells were involved in creating the model and when the model formed. The researchers then inspected the genetic makeup of individual cells in the thick and thin areas of the skin. DKK4 was particularly active in thickened skin, but not in relatively thin skin.
But to really lock in the connection between DKK4 and the pattern’s early formation, the team turned to the Abyssinian Cat. Abyssinians are known to sport a blur of color in their coat, with tiny, darker markings squashed in, as if someone were using a pencil to lightly shade a layer of gray on their orange-brown coat. Barsh and his team identified disruptive mutations in the DKK4 gene responsible for the Abyssinian cat’s apparent lack of tabby tags, an aspect called “ticked”.
“If you remove DKK4, the dark areas don’t go away completely, but they get smaller and more compact,” Barsh said.