Top Story: May 5, 2010

Frog Genome


Frogs. Just like us, only different.

Last week, a team of scientists led by the Department of Energy's Joint Genome Institute (JGI) and UC Berkeley published the first genome sequence of a frog, the western clawed frog Xenopus tropicalis, in the journal Science.

“A lot of furry animals have been sequenced, but far fewer other vertebrates,” says co-author Richard Harland, UC Berkeley professor of molecular and cell biology. “Having a complete catalog of the genes in Xenopus, along with those of humans, rats, mice and chickens, will help us reassemble the full complement of ancestral vertebrate genes.”

And, according to Nature:

What's most surprising, researchers say, is how closely the amphibian's genome resembles that of the mouse and the human, with large swathes of frog DNA on several chromosomes having genes arranged in the same order as in these mammals. “There are megabases of sequence where gene order has changed very little since the last common ancestor” of amphibians, birds and mammals about 360 million years ago, says bioinformaticist Uffe Hellsten at the US Department of Energy's Joint Genome Institute in Walnut Creek, California, a co-author on the study.

For some, it may be surprising that X. tropicalis was chosen as the subject for this genome sequencing study since its relative, the African clawed frog, Xenopus laevis, is more well known as the “go-to” study organism for developmental and cell biology research.  However, it was decided that since X. tropicalis has a shorter developmental time and has the typical two copies per gene rather than four, as is found in X. laevis, it would be the more practical model to go with this time around.

By studying the frog genome, researchers are also hoping to learn more about the mechanisms by which certain man-made chemicals are detrimentally affecting frogs around the world. In some cases, these chemicals mimic frogs' own hormones, ultimately disrupting normal biological function.  So their presence in lakes and streams may be contributing to the decline of frog populations worldwide. (You can learn more about UC Berkeley’s Tyrone Hayes’ research on the affects of the pesticide atrazine on frogs’ endocrine (controls hormones) and reproductive systems here.)

“Hopefully,” Hellsten says, “understanding the effects of these hormone disruptors will help us preserve frog diversity and, since these chemicals also affect humans, could have a positive effect on human health.”


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