Cagan and Bao found that the primary cells in the "holes of the net" express Hibris and the support cells that form the net express Roughest. Roughest and Hibris proteins stick to each other, but they don't stick to their own kind.
As the proteins appear on the surface of the cells, the laws of physics kick in to move the support cells into positions determined by the energy of attraction. Because Roughest is strongly attracted to Hibris, but not to other Roughest molecules, the support cells are attracted to the surfaces of the primary cells but not to each other. In competition with its neighbors, each Roughest-expressing support cell stretches out as far as it can along a primary cell. Support cells that express less Roughest lose the competition for primary-cell attachment and die off.
At the end of the process, a neat one-cell-thick hexagonal wall of support cells surrounds the primary cells. The repetition of this pattern across the entire fly eye is responsible for the regular honeycomb pattern of the 800 optical units present in the fruit fly compound eye.
"We and others searched for a long time for human equivalents to Roughest and Hibris," Cagan says. "Surprisingly, they were found in the kidney."
The equivalent kidney proteins are called Neph1 and Nephrin. They draw together certain kidney-cell junctions in a tight but porous seal that filters urea and other unwanted molecules from the blood vessels within kidney nephrons. Without functioning Neph1 and Nephron, kidneys do not filter properly, leading to neuropathy. Alterations within nephrons also have been linked to hypertension.
The mammalian-kidney versions and the fruit-fly-eye versions of these proteins are fairly specific to their own organs. That is,
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Contact: Gwen Ericson
ericsong@wustl.edu
314-286-0141
Washington University School of Medicine
9-Jun-2005