Corn Snake Genome Paves Way For Understanding Reptile Evolution

In order to better understand how certain characteristics have evolved in reptiles, researchers from the University of Geneva (UNIGE) in Switzerland have created a large database that holds the genetic information for a wide range of species. Among others, their dataset includes the newly sequenced genome of the corn snake. Using the snake's DNA, researchers believe they have finally unraveled the exact mutation that causes albinism in the species.

Essentially, examining the function of individual genes allows researchers to better understand certain evolutionary characteristics, such as how snakes lost their limbs or how various skin colorations -- including albinism and camouflage -- have evolved. Additioanlly, genetic mutations are key for understanding the evolutionary history of a species.

For the recent study, researchers took a specific interest in reptiles because they are poorly represented in terms of DNA sequencing, otherwise known as genomics, according to a news release.

"Our aim was to produce ourselves a substantial portion of the missing data by sequencing all genes from several reptilian species. To reach this goal, we used tissues, such as the brain and the kidney, expressing the largest number of genes," Dr. Athanasia Tzika, one of the study researchers from the Department of genetics and evolution at UNIGE, explained in the release.

The Reptilian Transcriptomes Database 2.0 includes sequenced genomes from the major evolutionary lineages of reptiles. Collecting genetic information was not an easy feat and requires a careful and detailed analysis of over two billion nucleotides, which are the basic molecules contained in one's DNA. Researchers chose to sequence the corn snake's genome because it breeds easily, it reproduces by laying eggs, and it is nonvenomous.

Generally speaking, corn snakes are found throughout the eastern U.S. in wooded or grassy areas. While corn snakes are nonvenemous, they are constrictors that essentially bite their prey to get a firm grip and then coil their bodies around them. Corn snakes do not feed every day, but when they are hungry adult snakes prefer to feed on mice, rats, birds or bats, while the young stick to smaller lizards and tree frogs.

So what did they find? The skin of a wild corn snake is characterized by a light orange background color, with an overlaying pattern of dark orange blotches outlined in black. Researchers discovered amelanism -- a form of albinism -- results from a mutation or defect in the animals' production of melanin, which is simply a pigment that controls black or brown coloration of the skin. Individual corn snakes that lack all signs of melanin in the skin and eyes are considered to have amelanism.

In order to determine the percise DNA mutation responsible for the snake's specific coloration, researchers bred wild corn snakes with amelanistic individuals and sequenced their offspring's DNA. This revealed a gene called OCA2 that basically codes for a receptor located in the snake's melanosomes, which contains melanin. This means that the OCA2 genes are responsible for controlling the synthesis, or production, of brown or black skin coloration.

"Thanks to that large amount of sequencing data, we identified the malfunctioning gene," Michel Milinkovitch, one of the study researchers and a professor in the Department of Genetics and Evolution at UNIGE, added.

Their findings, recently published in the journal Scientific Reports, will help lead the way for the future discovery of other mutations responsible for variations of snake skin coloration.

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