the amnioserosa contract, the purse-string along the boundary contracts, the lateral epidermis cells are stretched, and the two sheets of lateral epidermis along those purse-strings are zipped together into a seam. And so those four processes contribute to how dorsal closure proceeds, explained Hutson.

The mystery, said Hutson, was precisely how these different tissues, and the forces they exert, work together to effect dorsal closure.

There are lots of ways you could build a model such that closure would occur, said Hutson. It could be the amnioserosa doing all the work. It could be the purse-strings doing all the work. It could be zipping. It could be the lateral epidermis actually growing and pushing itself over the amnioserosa.

And so, we wanted to systematically investigate the forces in the system to figure out which of these processes were really contributing to closure, and which were simply following along.

To attack the problem, the team needed to be able to selectively dissect the force-producing tissues, and to simultaneously observe the result through a high-powered microscope. Thus, they designed an optical and steering system for the laser beam scalpel that was implemented and refined by graduate students Yoichiro Tokutake and Ming-Shien Chang at the FELL. The resulting system can produce and guide a laser beam as small as a half-micron in diameter -- roughly a hundredth the diameter of a human hair. Tokutake and Chang went on to become the groups master laser surgeons.

Said FELL Director Glenn Edwards, one of the papers senior authors, These four forces are working in concert, so in essence we are trying to understand the symphony of dorsal closure -- how these forces are coordinated in space and time. The dissection of the symphony produced surprises, said Hutson. For example, we found that the system was very resilient, he said. When we perturbed only one or another of the tissues, the process kept r
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Contact: Dennis Meredith
dennis.meredith@duke.edu
919-681-8054
Duke University
27-Mar-2003

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