Scientists found that a single gene controls striking corn snake patterns like stripes and blotches. While essential for brain function in mammals, in snakes, its mutation uniquely alters skin color without affecting behavior.
In many animals, skin coloration and patterning are essential for camouflage, communication, and temperature regulation. In corn snakes, certain morphs show a range of vibrant colors, such as red, yellow, or pink, and their dorsal spots may either merge or transform into stripes. But what genetic and cellular processes create these striking patterns? A research team from the University of Geneva (UNIGE) has identified a key player: a single gene called CLCN2. Their findings, published in Genome Biology, offer new insights into the evolution and genetic control of animal coloration.
Skin Coloration and Patterns in Corn Snakes
The distinctive skin colors and patterns of the corn snake (Pantherophis guttatus) are created by the arrangement and positioning of chromatophores, specialized skin cells found in many animals that contain pigments or light-reflecting crystals. Most corn snakes have a classic appearance: red blotches outlined in black set against an orange background on their backs, and a black-and-white checkered pattern on their bellies. However, different morphs can display a wide variety of other colors and patterns.
Two commonly seen morphs are the Motley and Stripe varieties. In the Motley morph, the usual dorsal spots are fused or broken, creating a more linear design. In the Stripe morph, continuous longitudinal stripes run along the snake’s back. Despite their differences, both morphs share a key feature: their bellies lack the typical checkered pattern and are plain.
A Single Gene Behind Distinct Patterns
A research team led by Athanasia Tzika and Michel Milinkovitch, Senior Lecturer and Professor at the University of Geneva’s Department of Genetics and Evolution, set out to investigate the genetic basis behind these patterns. By breeding Motley and Stripe snakes and sequencing the genomes of their offspring, the researchers discovered that both morphs are linked to mutations in the same gene: CLCN2. This gene encodes a protein that forms a chloride ion channel in the cell membrane. The movement of chloride ions across the membrane generates an electrical potential between the inside and outside of the cell, allowing cellular signals to be transmitted.
In Motley snakes, the variation is not due to a mutation in the gene itself but rather a strong reduction in its expression level. In Stripe snakes, however, a small piece of DNA – a transposon – is inserted into the CLCN2 gene, rendering the protein non-functional.
“These results were quite surprising, because in humans and mice, the CLCN2 channel is essential for neuronal activity, and mutations in this gene are associated with serious conditions such as leukoencephalopathy, a disease affecting the brain’s white matter,” explain Sophie Montandon and Pierre Beaudier, researchers in the Milinkovitch/Tzika lab and co-first authors of the study. “We therefore developed genetic experiments in corn snakes to inactivate the CLCN2 gene. The resulting mutants displayed the Stripe phenotype, confirming the gene’s involvement.”
An Unexpected Player in Pattern Formation
To better understand the role of CLCN2, the scientists investigated in which organs and cell types the gene is expressed in corn snakes. Transcriptomic analyses revealed that CLCN2 is expressed in the adult brain, similar to mice and humans, but also in chromatophores during embryonic development. The researchers then focused on how color patterns form in embryos. They observed that in mutants, chromatophores fail to aggregate properly to form the characteristic blotches. Instead, they organize into stripes, as seen in Stripe individuals.
“Our results show that a mutation in the CLCN2 gene in corn snakes does not cause neurological or behavioral disorders. However, the protein plays an essential, and previously unknown, role in the development of skin coloration patterns,” concludes Asier Ullate-Agote, co-first author of the study.
Future Research: Unlocking the Secrets of Color Diversity
The next phase of the research will focus on understanding the role of the CLCN2 chloride ion channel in chromatophore membranes, particularly how it influences the interactions between pigmented cells. The goal is to decipher the cellular mechanisms that give rise to the spectacular diversity of coloration patterns observed not only in corn snakes but also in other reptiles.
Reference: “Regulatory and disruptive variants in the CLCN2 gene are associated with modified skin color pattern phenotypes in the corn snake” by Sophie A. Montandon, Pierre Beaudier, Asier Ullate-Agote, Pierre-Yves Helleboid, Maya Kummrow, Sergi Roig-Puiggros, Denis Jabaudon, Leif Andersson, Michel C. Milinkovitch and Athanasia C. Tzika, 26 March 2025, Genome Biology.
DOI: 10.1186/s13059-025-03539-0
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