Scientists trace molecular origin of proportional d...(to begin formation of proportional body ...)

Date:10/13/2008

to begin formation of proportional body parts in the fruit fly's head and thoracic regions. Hunchback is switched on in the anterior half of the embryo, where the level of Bicoid is high. In normal (wild-type) embryos, the process begins when Bicoid diffuses from the anterior toward the posterior end, a principal already established in existing research literature. Bicoid, which comes from the mother, then forms a gradient along this body axis.

Dr. Ma and his colleagues discovered the amount of Bicoid in early embryos depends on the size of the egg. Larger embryos in the study showed higher Bicoid levels in the anterior region, while smaller embryos showed lower levels. This relationship between embryo size and Bicoid amount helps Bicoid establish a gradient scaled precisely according to each embryo's length, which is necessary for Hunchback to respond precisely, they said.

One area of messiness in the system is that the precision levels of Bicoid and Hunchback are different. The research team reported that imaging analyses of 28 wild-type embryos showed even a precise Bicoid gradient still has positional errors that go beyond the boundaries set up by its target Hunchback. Dr. Ma's team suggests that Bicoid can self correct its positional errors through a coupling that develops between Bicoid's forming gradient and the protein's activation of target genes. The correction essentially fine tunes the mechanism to achieve further developmental precision.

Other studies have suggested Bicoid level differences among individual embryos play little or no role in the precision of fruit fly embryo development. Bicoid gradient, they say, is inherently so precise at switching on its target genes that it approaches the limits set by basic physical principles. While offering important new insights into how Bicoid establishes a precise gradient along the embryo's length, Dr. Ma said the previous research also begged the questions: What then makes the Bi
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Contact: Nick Miller nicholas.miller@cchmc.org 513-803-6035 Cincinnati Children's Hospital Medical Center Source:Eurekalert

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