A team of genetic determinism specialists has shown how the mutation of a gene involved in creating lysosomes — the "garbage disposal" vesicles in cells — is responsible for the dull color of corn snakes of the lavender variety, according to a new study from the Université de Genéve (USIGE) shared with Interesting Engineering (IE) via email.
'Garbage disposal' cell feature determines snake color
In an incredibly elegant find, this single mutation is enough to alter every skin color — which ties both pigment and reflective crystals are stored in lysosome-adjacent vesicles. Stemming from USIGE, the study marks a substantial step forward in human understanding of the origin of patterns and colors in vertebrate skin, according to the embargoed release.
Chromatophores are the cells responsible for skin color — which work because of pigments or crystals capable of reflecting light. They come in three types: melanophores — for black and brown colors; xanthophores — for red and yellow; and iridophores — which possess crystals that reflect several colors.
'Garbage disposal' feature digests nonfunctional cells
Mammals only have melanophores, but reptiles and fish also have the other two types, which means they can reflect light in a much wider array of colors and patterns. Scientists know the pigments of melanophores are stored in organelles called lysosome-related organelles (LROs).
LROs are small intracellular vesicles that come from the same "garbage disposals" that digest molecules in cells no longer capable of functioning. However, the storage location of yellow and red crystals and pigments in other chromatophore types remains unknown.
Corn snakes turn pink because of single mutation
Corn snakes — technically called Pantherophis guttatus — have an orange base, adorned with red lateral and dorsal spots encircled with black. The species experiences mutations capable of varying skin color — with the lavender corn snake shifting pink with gray spots.
Athanasia Tzika — a researcher at the department of genetics and evolution in UNIGE's faculty of sciences, along with her doctoral student Asier Ullate-Agote successfully determined how these altered colors happen because of a single mutation within the LYST gene — which regulates lysosome traffic.
"It's very long-term work," began Tzika, according to the embargoed release shared with IE via email, "since snakes only have one litter a year. Also, we had to sequence the entire genome of the corn snake and identify all the genes within."
The liver is the crucial ingredient
Mutations within the LYST gene in humans are responsible for the Chediak-Higashi syndrome — which comes with albinism, an accumulation of enlarged lysosomes, and an impaired immune system. The research team from Geneva carried out their study of corn snakes via an analysis of the snakes' hepatocytes, and the main liver cells in vertebrates — which carry numerous lysosomes.
The scientists found the hepatocytes of corn snakes of the lavender variety contain significantly larger and more aggregated lysosomes. Making use of electron microscopy, the scientists saw how the morphology and distribution of colored vesicles in all chromatophores were modified.
"By characterizing the mutant gene, the study has shown for the first time that the different chromatophores were not created from scratch during evolution but that they all entail a basic mechanism involving LROs," said Professor Michel Milinkovitch of UNIGE's department of genetics and evolution.
Additional studies are needed to better grasp how the extraordinary array of skin colors and patterns in vertebrates — which play a crucial role in a diverse range of functions from camouflage to protection against the negative effects of solar radiation. At the risk of making a religious reference, it seems snakes have much more knowledge to give humankind.