May 3, 1996. Copyright, 1996, Graphic News. All rights reserved

CHEMICAL SIGNAL FOR WEBBED FEET
By Laura Spinney, Science Editor

LONDON, May 3, Graphic News- Why do chickens have toes? The answer is that they donÕt, at least until a crucial stage in their development. According to American researchers, a chickÕs extremities appear webbed like a duckÕs until a chemical signal triggers the death of cells in the tissue connecting the digits, and the chickÕs toes separate.

Programmed cell death is an important part of embryonic development in all animals, but until now nobody understood what triggered it. When it comes to the development of limbs, Dr Hongyan Zou and Dr Lee Niswander of the Memorial Sloan-Kettering Cancer Center and Cornell University in New York suspected that a substance called bone morphogenetic protein 4 (BMP4), which is present in the tissue between a chickÕs toes but not in a duckÕs, might have something to do with it.

Zou and Niswander tested their hypothesis by blocking receptors of this chemical signal, paradoxically known for its role in cell growth, in the developing limbs of chick embryos. Not only did the tissue between the digits of those embryos fail to recede properly as they grew, so that their feet began to resemble the webbed feet of ducks, but they also grew feathers on their feet where they were supposed to have scales. The researchers publish their findings in this weekÕs issue of the journal Science.

According to Niswander, BMPs are likely to be responsible for programmed cell death in the limbs of other animals too. ÔIt is interesting to speculate that BMPs may mediate interdigital cell death in humans,Õ says Niswander. ÔIf this is the case, then it is possible that disruption of BMP signalling may result in webbing in humans.Õ

Sources: Science, Memorial SLoan-Kettering Cancer Center and Cornell University