Conquest of land began in shark genome( GAINESVILLE Fla. When the first four...)

GAINESVILLE, Fla. When the first four-legged animals sprouted fingers and toes, they took an ancient genetic recipe and simply extended the cooking time, say University of Florida scientists writing in Wednesdays issue of the journal PLoS ONE.

Even sharks which have existed for more than half a billion years have the recipe for fingers in their genetic cookbook not to eat them, but to grow them.

While studying the mechanisms of development in shark embryos, UF scientists identified a spurt of genetic activity that is required for digit development in limbed animals.

Previous work suggested that the transition from fins to limbs involved the addition of a late phase of gene activity during embryonic development, something thought to be absent during the development of fish fins.

The finding shows what was thought to be a relatively recent evolutionary innovation existed eons earlier than previously believed, shedding light on how life on Earth developed and potentially providing insight for scientists seeking ways to cure human birth defects, which affect about 150,000 infants annually in the United States.

Weve uncovered a surprising degree of genetic complexity in place at an early point in the evolution of appendages, said developmental biologist Martin Cohn, Ph.D., an associate professor with the UF departments of zoology and anatomy and cell biology and a member of the UF Genetics Institute. Genetic processes were not simple in early aquatic vertebrates only to become more complex as the animals adapted to terrestrial living. They were complex from the outset. Some major evolutionary innovations, like digits at the end of limbs, may have been achieved by prolonging the activity of a genetic program that existed in a common ancestor of sharks and bony fishes.

Researchers say the same genes that produced ancient fins likely enlarged their role about 365 million years ago in amphibians struggling to
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