Researchers in the laboratory of Michel Milinkovitch have identified in the corn snake the mutation responsible for amelanism, a form of albinism due to a defect in the production of melanin (the black and brown pigments of the skin). The skin of the wild type corn snake exhibits a light orange background colour covered with a pattern of dark orange dorsal saddles and lateral blotches that are outlined with black. However, some individuals do not correspond to that standard morphology: they lack all signs of melanin in the skin and eyes. The Swiss team decided to search for the DNA mutation that determines that specific coloration. To this end, they bred wild-type corn snakes with amelanistic individuals and they sequenced each offspring born from that cross. “Thanks to that large amount of sequencing data, we identified the malfunctioning gene”, explains Milinkovitch. That gene is called OCA2 and codes for a receptor located in the membranes of intracellular compartments, called melanosomes, that contain melanin. This receptor controls the proper level of acidity allowing for the synthesis of melanin.
Thanks to the newly-sequenced genome of the corn snake, the precise identification of other mutations responsible for multiple variations of snake skin coloration will be greatly facilitated. This will allow us to save much time in our future research. As in amelanism, these spontaneous mutations that can appear randomly in any individual, are the fuel of evolution on which natural selection will act. Without mutations, genetic variation and novelties, explaining the evolution of new species, are impossible. The researchers will now attempt to understand how some mutant corn snakes exhibit strongly modified colours patterns such as longitudinal lines rather than transversal saddles, opening the way to comparisons among species with different skin colour patterns… such as tigers and cheetahs for example.