March 28, 2013
Unraveling The Bizarre Features Of The Turtle Genome
Lawrence LeBlond for redOrbit.com - Your Universe Online
The western painted turtle (Chrysemys picta bellii) is one of the most widespread species of turtle in North America. This creature is found in fresh, slow-moving waters from southern Canada to northern Mexico and from the Atlantic to the Pacific. And because this species has been widely studied, it only makes sense for researchers to sequence its genome, and that they´ve done.
Publishing the work in this week´s Genome Biology, researchers describe that much like the turtle itself, the rate of genome evolution is very slow. Their data show that turtle genomes evolve at a rate that is about a third that of the human genome and a fifth that of the python, the fastest genome analyzed to date.
Through extensive research, scientists have discovered many interesting facts about these abundant North American reptiles. They are long-lived, can withstand low temperatures and can survive long periods with no oxygen. The sex of the turtle is determined by the temperature at which the egg develops rather than through genetics. The painted turtle can survive up to four months under water depending on the temperature.
Previously, analyses of fossils have shown that the painted turtle has existed for more than 15 million years, and four regionally based subspecies have evolved during the last Ice Age. The western painted turtle is by far the largest of the four subspecies and can grow to 10 inches long.
The painted turtle is the first of its genus to have its genome fully sequenced, and only the second non-avian reptile to undergo the analysis. Data has revealed some very interesting insights about the bizarre features and adaptations that exist only in the turtle genome.
Bradley Shaffer, a professor at UCLA, and colleagues discovered through genome mapping that turtles are more closely related to birds and crocodilians than to any other vertebrates. They discovered 19 genes in the brain and 23 in the heart whose expression is increased in low oxygen conditions. Furthermore, they found one gene whose expression changes nearly 130 fold. They also discovered through experiments with hatchlings that common microRNA was involved in freeze tolerance adaptation.
Their work indicates clearly that common vertebrate regulatory networks, some of which have analogs in human diseases, are often involved in the western painted turtle achieving its extraordinary physiological capacities.
Shaffer and his team believe that the painted turtle may offer significant insights into human health disorders and the way they are managed and cared for. They particularly see the turtle genome offering important insights into conditions such as anoxia and hypothermia.