Researchers unlock secrets of directional cel...( to commune with its fellow amoebae in s...)

to commune with its fellow amoebae in survival maneuvers. Research in the last decade on Dictyostelium demonstrated that cells use receptors coupled to G-proteins to sense chemoattractants. Just like other chemotactic cells, the amoebae can sense shallow gradients and have only one leading edge.

Devreotes and his colleagues searched for unevenly distributed proteins within the social amoebae that could explain how cells sense direction. They knew that when chemoattractant molecules dock on receptors, the receptors change their shape, and this change attracts G proteins floating in the cell's membranes. When researchers examined the distribution of receptors, however, they found that the receptors were distributed equally around the cell.

In 1998, Devreotes and his colleagues hit the lottery when, after sorting through a number of chemicals inside cells, they discovered that the leading edge of a cell contain greater amounts of specific proteins. These proteins, called PH domain-containing proteins, float freely in the body of the cell but are pulled to one side when the G-protein signals are activated. The researchers did this by attaching fluorescent green protein tags to PH domain proteins and then peering through a microscope to determine to which side of the cell these tagged proteins flocked after being subject to cAMP. They discovered that the fluorescent proteins reliably marked the places on the membrane where the G-protein signals are active.

In the current Science, the researchers say they now know what makes the cell's leading edge more sensitive to stimulation. They attached the fluorescent green protein to a part of the G-protein. When they examined the cells under the microscope, they found the G-proteins were accumulated on the cell membrane toward the leading edge. In another experiment, the Hopkins researchers chemically paralyzed the cells and caused them to lose their leading edge. The researchers found that the G-proteins t
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Contact: Kate O'Rourke
korourke@jhmi.edu
410-955-8665
Johns Hopkins Medical Institutions
10-Feb-2000

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