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The coloration and patterning of skin in a variety of animal species serve key functions including camouflage, communication, and the regulation of body temperature. One fascinating example is the corn snake, which showcases a range of morphs displaying vibrant red, yellow, or pink blotches that may blend or transform into stripes along their backs. A recent investigation conducted by researchers at the University of Geneva (UNIGE) has identified a critical genetic factor involved in shaping these distinct patterns. The findings, published in Genome Biology, shed light on the genetic and evolutionary processes related to animal coloration.
The skin hues and patterns observed in the corn snake, scientifically known as Pantherophis guttatus, originate from the arrangement of specialized skin cells known as chromatophores. These cells, which harbor pigments or light-reflecting crystals, contribute to the snake’s typical appearance—red blotches edged in black set against an orange backdrop, paired with a ventral side characterized by a black-and-white checkered design. Variations among morphs can yield an extensive array of colors and patterns.
Among the notable morphs is the Motley variant, which features dorsal spots that are either fused or disrupted, creating a more streamlined outline. Alternatively, the Stripe morph presents with a continuous pattern of stripes extending along its back, but both variants share a unique commonality: their undersides are plain, devoid of any checkerboard design.
A Single Gene Behind Distinct Patterns
Under the leadership of Athanasia Tzika and Michel Milinkovitch, both prominent figures within the Department of Genetics and Evolution at UNIGE’s Faculty of Science, the research team set out to explore the genetic mutations responsible for these patterns. By conducting controlled breedings between Motley and Stripe morphs and sequencing the genomes of the offspring, they unearthed a connection between both phenotypes and a specific gene: CLCN2. This gene encodes a protein integral to the cell membrane, which forms a channel facilitating the transport of chloride ions. The differing ion distribution generates a voltage across the cell’s membrane, essential for transmitting cellular signals.
In Motley morphs, researchers found that the observed variation is not attributed to a mutation of the gene but rather a significant decrease in its expression. Conversely, in Stripe morphs, a transposon—a small segment of DNA—has inserted itself into the CLCN2 gene, thereby disrupting the function of the protein. “These findings were quite unexpected, as the CLCN2 channel is critical for neuronal function in humans and mice, and mutations in this gene have been linked to severe neurological disorders such as leukoencephalopathy, which affects the brain’s white matter,” commented Sophie Montandon and Pierre Beaudier, co-first authors of the study from the Milinkovitch/Tzika lab. They further noted, “We performed genetic experiments to disable the CLCN2 gene in corn snakes; the resultant mutants displayed the Stripe phenotype, affirming the gene’s pivotal role.”
An Unexpected Player in Pattern Formation
To delve deeper into the function of CLCN2, the researchers examined its expression in various organs and cell types within the corn snakes. Their transcriptomic analysis indicated that CLCN2 is present in both the adult brain and chromatophores during the embryonic stage. This led them to investigate how color patterns form in embryos, revealing that in mutants, chromatophores do not aggregate correctly, resulting in stripe formations instead of the characteristic blotches found in other morphs. “Our findings demonstrate that mutations in the CLCN2 gene in corn snakes do not lead to neurological or behavioral issues. Instead, this protein plays a crucial and previously unrecognized role in the development of skin coloration patterns,” stated Asier Ullate-Agote, another co-first author of the study.
Future research efforts will aim to further investigate the function of the CLCN2 chloride ion channel in the membranes of chromatophores, specifically how it affects the interactions between these pigmented cells. This work seeks to clarify the cellular mechanisms that drive the remarkable variety of color patterns seen not just in corn snakes, but across a range of reptilian species.
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