These tiny single-celled organisms have a thing for a certain molecule, called cAMP, and move toward it with striking efficiency. Similarly, directed movement also guides human cells in their normal travels and in diseases such as arthritis, asthma, multiple sclerosis and cancer, says Devreotes. He has been using the amoeba to examine how this process, known as "chemotaxis," works.
Now, in the Oct. 26 issue of the journal Science, Japanese scientists and Devreotes describe success in imaging single molecules of cAMP as they interact with docking points, or receptors, on the surface of these amoebae. The technique provides real-time video of how the receptors and cAMP behave. [To view or download video, see http://www.hopkinsmedicine.org/cellbio/devreotes/Joanna%20Downer.htm].
Copies of the receptor are distributed throughout the amoeba's outer membrane, allowing the cell to detect cAMP all around it and even to distinguish which direction has the highest amounts. Detecting this "gradient" of cAMP, the cell moves constantly toward higher concentrations of the attractant, says Devreotes, professor and director of cell biology at the Johns Hopkins School of Medicine's Institute for Basic Biomedical Sciences.
"It's sort of like looking for the ice cream stand at the county fair," explains Devreotes. "You may see a few people with ice cream cones, then look around and head off in the direction more of them seem to be coming from."
By tagging single molecules of cAMP with a fluorescent dye, the scientists have obtained images of glowing red spots on living amoebae. Over a period of a few seconds, the spots, which represent single molecules of cAMP bound to its recep
Contact: Joanna Downer
Johns Hopkins Medical Institutions