News in brief: Fins to limbs with flip of genetic switch

Boost of gene activity may help explain how arms and legs evolved

Evolving limbs from fins may be as easy as taking the activity of a few genes and kicking it up a notch, a new study suggests.

LOOK MA, HANDS Throwing a simple genetic switch was enough to turn one of this zebra fish embryo’s fins into a primitive limb with a bulge where a future hand or foot might have grown. Freitas et al/Developmental Cell 2012

Many evolutionary biologists have thought that four-limbed creatures evolved from finned ancestors. Forming limbs involves turning on body patterning genes in two precisely timed phases, first in the back legs and then, later, in the part of the limb that will become the hand or foot. Fish have those genes but turn them on only once, or at very low levels during the second phase.

Working with zebra fish, researchers in Spain added a genetic switch called an enhancer to turn up activity of a gene called Hoxd13 at the tips of developing fins. Fish usually lack these genetic switches, but adding them and making more Hoxd13 than usual produced rudimentary limbs that had more cartilage and less fin material, the researchers report in the Dec. 11 Developmental Cell. Ancestors of four-legged creatures may have acquired these enhancers, leading to limb development.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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