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July 20, 2007
Scientists have always thought that embryos developed and specified their cell fates using a substance referred to as a morphogen – a molecular gradient which establishes the fates of the cells in the embryo. However, whether or not there was any precision to development was not known. Now one of the workhorses of developmental biology, the little banana shaped egg of the fruit fly, Drosophila has shed some light on this old problem so much light in fact that it seems that morphogens such as bicoid are so precise that they operate on the level of single molecules.
Bicoid in the fruit fly embryo is one of the best studied morphogen gradients. It determines what part of the egg will become the front of the fly and what part of the egg will become the back of the fruit fly, something scientists refer to the establishment of the anterior/ posterior axis.
Scientists from Princeton University in the July 13 issue of the journal, Cell have published two papers. In the first the scientists show how using methods from physics and molecular biology they can see how the little fruit fly embryo sets up its anterior/posterior live and in color. In the second paper the research team shows that only a few molecules are needed to determine fate of early embryonic cells.
"I think the prevailing view has been that cells accomplish all their functions using a complicated combination of mechanisms, each one of which is rather sloppy or noisy," says team member William Bialek, a physics professor at Princeton. "This research, however, indicates that in the initial hours of a fly embryo's development, cells make decisions to become one part of the body or another by a process so precise that they must be close to counting every available signaling molecule they receive from the mother."
"This signaling requires a sensitivity approaching the limits set by basic physical principes," says Bialek. "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." A precision that until now has eluded biologists.
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