Evolutionary biology: Fin to limb within our grasp.

Abstract

There was thought to be little in common between fish fin bones and the finger bones of land-dwellers. But zebrafish studies reveal that hox genes have a surprisingly similar role in patterning the two structures. See Letter p.225 Hox genes are major players in limb and digit development in tetrapods, prompting the question of whether or how they might have been involved in the transition between the fins of fishes and the limbs of tetrapods. Neil Shubin and colleagues have compared Hox function in fins and limbs by performing cell lineage and knockout assays of Hox genes in zebrafish fins. They find that zebrafish deficient in HoxA and HoxD gene clusters show reduced fin rays and increased endochondral elements. The results establish homology between the developmental programs creating digits and the radials in fins, and represent an important step forward in understanding the transition from water to land and the evolution of tetrapods.