s development, it remains a single large cell with an unusual characteristic: Unlike other cells, which have a single nucleus, the embryo has thousands, each of which awaits a signal from the mother to form itself into a specialized cell. This signal arrives in the form of a droplet of protein called Bicoid that enters the embryo at one end and, like food coloring in water, diffuses out molecule by molecule through the nuclei. The concentration decreases with distance and forms the first blueprint that defines which part of the embryo will become the head and which the backside of the fly.

The team's findings indicate that two neighboring nuclei can determine their different places and functions within the embryo accurately if the concentration of Bicoid between them varies by only about 10 percent -- a quantity that on the scale of the tiny embryo amounts to only a few molecules of Bicoid.

"This signaling requires a sensitivity approaching the limits set by basic physical principles," Bialek said. "Perhaps more important than the answers we have found so far, this work has led us to sharpen the kinds of questions we ask about living cells as we try to understand them with the same kind of mathematical precision that we understand the rest of the physical world."

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Contact: Chad Boutin
cboutin@princeton.edu
609-258-5729
Princeton University
18-Jul-2007


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