Chew on this: 3 genes led to jaws

U. COLORADO (US) — A half-billion years ago, jawless vertebrates lacked the ability to chew food. Instead, their heads consisted of a flexible, fused basket of cartilage.

An international team of researchers has published evidence in the Proceedings of the National Academy of Sciences that three genes in jawless vertebrates might have been key to the development of jaws in higher vertebrates.

The finding is potentially significant in that it might help explain how vertebrates shifted from a life of passive “filter feeding” to one of active predation.

“Essentially what we found is that the genetic roots of the vertebrate jaw can be found in the embryos of a weird jawless fish called the sea lamprey,” says study leader Daniel Meulemans Medeiros, an assistant professor of ecology and evolutionary biology at the University of Colorado at Boulder.

Lampreys are eel-like fish with no jaws and a “very strange skeleton compared to their cousins” with jaws, Medeiros says.

But “when we looked carefully at how genes are used during the development of the lamprey head, we saw that the basic plan for a jaw is there, and that only a few genes likely had to be moved around to create full-blown jaws.”

Between jawless vertebrates—called agnathans—and vertebrates with jaws—called gnathosomes—only three genes of the 12 genes the team looked at appeared to be used differently, Medeiros says. This finding suggests that “creating a jaw in a jawless ancestor was a relatively simple matter of altering when and where these few genes are used.”

The findings support a new scenario for jaw evolution, an area that has been an open question in vertebrate evolution.

Viewing the eel-like fish, “It was hard to imagine how something like that could evolve into the strong, snapping, biting, chewing jaws of a shark, fish, or mammal,” Medeiros says.

Researchers from Charles University in Prague and the California Institute of Technology contributed to the work, which is supported by the National Science Foundation, National Institutes of Health, and the Academy of Sciences in the Czech Republic.

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