Evolutionary Origin of Skin Colors Revealed by Genetic Mutation in Snakes

A mutation of the lavender variant of corn snake allows a UNIGE team to understand the mechanisms responsible for the extraordinary variety of skin colors in vertebrates.

The skin color of vertebrates depends on chromatophores — cells found in the deep layers of the skin. A team of specialists in genetic determinism and color evolution in reptiles from the University of Geneva (UNIGE) is studying the wide variety of colors sported by different individuals within the corn snake species.

The research, published in the journal PNAS, demonstrates that the dull color of the lavender variant of corn snake is caused by the mutation of a gene involved in forming lysosomes, the “garbage disposal” vesicles of cells. This single mutation is enough to affect every skin color, demonstrating that both the reflective crystals and pigments are stored in lysosome-related vesicles. The UNIGE study marks a significant step forward in our understanding of the origin of colors and patterns in the skin of vertebrates. 

The chromatophores are the cells that determine skin color, thanks to the presence of pigments or crystals that reflect light. There are three types of chromatophores: melanophores, which are responsible for the black or brown color; xanthophores, for red and yellow; and iridophores, with crystals that reflect multiple colors. Mammals only have melanophores, while reptiles and fish carry all three types of chromatophore, meaning they can display a very wide variety of colors and color patterns. The pigments of melanophores are known to be stored in organelles known as LROs or lysosome-related organelles. These are small intracellular vesicles that have the same origin as lysosomes, the “garbage disposals” that digest the non-functional molecules in cells. On the other hand, the storage location of the red and yellow pigments and crystals in the other types of chromatophore is unknown. 

When snakes turn pink

The skin of corn snakes (Pantherophis guttatus) has an orange base, decorated with red dorsal and lateral spots circled in black. The species can undergo mutations that lead to variations in skin color, with the lavender corn snake being pink with grey spots. The experiments carried out by Athanasia Tzika, a researcher in the Department of Genetics and Evolution in UNIGE’s Faculty of Sciences and her doctoral student Asier Ullate-Agote have identified that these altered colors are due to a single mutation pinpointed in the LYST gene, a gene that regulates lysosome trafficking. “It’s very long-term work,” begins Tzika, “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 key

Mutations in the LYST gene in humans cause the Chediak-Higashi syndrome, which is characterized by albinism, an impaired immune system and an accumulation of enlarged lysosomes. The Geneva team continued its study into corn snakes by analyzing their hepatocytes, the main liver cells in vertebrates, which contain numerous lysosomes. The scientists found that the hepatocytes of lavender corn snakes contain much larger and more aggregated lysosomes. Using electron microscopy, the authors observed that the morphology and arrangement of colored vesicles in all the chromatophores were altered.

The result of evolution

Michel Milinkovitch, a professor in UNIGE’s Department of Genetics and Evolution, explains further: “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.” Further studies will provide a better understanding of the mechanisms responsible for the extraordinary variety of skin colors and color patterns in vertebrates, features that play a part in functions as diverse and essential as camouflage, intraspecific communication, and protection against the harmful effects of solar radiation.

Reference: “Genome mapping of a LYST mutation in corn snakes indicates that vertebrate chromatophore vesicles are lysosome-related organelles” by Asier Ullate-Agote, Ingrid Burgelin, Adrien Debry, Carine Langrez, Florent Montange, Rodrigue Peraldi, Jean Daraspe, Henrik Kaessmann, Michel C. Milinkovitch and Athanasia C. Tzika, 5 October 2020, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2003724117

BiodiversityCell BiologyEvolutionGeneticsSnakeUniversity of Geneva
Comments ( 2 )
Add Comment
  • Sekar Vedaraman

    Very Interesting.

    Extend the thinking to Humans.

    Balck absorbs Light. White Reflects Light.

    Species of Fish have been discovered in the deep Ocean which absorb 97% of the Light shown on them and are practically invisible!

    From peronal experience I suspect some species of Cockroaches have this ability and repeated observations (both Black & brown cckroaches)also have the ability to become invisible when a loud noise is made.

    Maybe the secret to inviaibility is to make humans so black that they do not reflect any light! Wouldn’t that be something.

  • Sekar Vedaraman

    Another thought I am putting out into the Ether.

    Humans are warm blodded vertebrates. Sankaes are Cold Blodded Vertebtrates.

    Was wondering if the Cold Blodded Vertebrates are susceptible to Covid 19. From recent research ita is leart that Hamsters are susceptible as are about 25 pets and a Tiger in a New York Zoo, who got infected early!

    I wonder if Scientists can establish a link between the Blood Temperature of the Mamallian Vertebrates vis-a-vis the Cold Blodded Vertebrates and susceptibilityto various diseases. The Red Blood is is the one which appears to carry the Covid 19 Virus to all the Organs and takes them down.

    Maybe, there is also a link between the Blood Temperature and the Thoughts of murder, violence and mayhem generated in the Human Brain and the Neuro transmitters released which send signals leading to such acts, which turns Humans into cold blodded Killers. I have always wondered why a cold chill runs up the spine at the scenes of gory murders. Maybe, there is a connection we do not understand as yet. If research into such blood temperatures can be monitored and connections to the brain chemistry and thoughts is firmly established , then maybe we can device methodologies to warm up theCold Blooded killers blood, to prevent the killing, with Sensors and other devices? Another option is to distract the Tought generating brain when such thoughts arise and manage the same? Thought Control! Ha! Ha! Love that song by todays rebel generation. ” Don’t want No Thought Control…”.

    On a lighter note, maybe Cains behaviour and the killing of Abel could have been prevented by Adam & Eve, if they had such tools available when they were expelled from the Garden of Eden by “God”. If they had such tools the History of Humanity may have been different! Well it is not too late even now!