Two-speed cell specification

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Two-speed cell specification

The Rockefeller University Press
DOI: 10.1083/jcb1723rr3
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untitled T H E J O U R N A L O F C E L L B IO L O G Y RESEARCH ROUNDUP • THE JOURNAL OF CELL BIOLOGY 327 Text by Alla Katsnelson [email protected] <doi>10.1083/jcb.1723r r3</doi><aid>jcb17 23rr3</aid><au>Alla Katsnelson</au>< cor> [email protected] </cor>E. col i squeezed into action E scherichia coli chemoreceptors double as osmotic sensors by me-chanically compressing in response to increased osmolarity, say Ady Vaknin and Howard Berg (Harvard University, Cambridge, MA). E. coli is always on the look-out for a better environment. As it swims, chemoattractant receptors talk to the fl agellar motors, thus orienting the bacterium’s travels. Using fl uorescence polarization to image the recep- tors’ position in living cells, Vaknin and Berg found that increased osmo- larity caused receptors, joined in triplets like the legs of a tripod, to move closer together by about 10%. The squeeze stimulates kinase activity and the subsequent signaling pathway, prompting the bacterium to swim away from the potentially damaging environment. This compression can be explained by simple cell membrane dynam- ics. As osmotic stress increases, water leaves the cell. Reduced pressure from within causes a slackness in the membrane and an increase in its thickness— much as a rubber balloon acts as some air is let out. “We think that when the membrane thickens in response to osmotic stress, that changes the orientation of the receptors, making them move closer together,” says Berg. How changes in relative receptor position stimulate kinase activity is still un- known. The group is now investigating whether chemoattractant stimuli cause re- ceptors to move further apart. They are also looking downstream at the effect of such mechanical perturbations on the fl agellar motor’s control of direction. Reference: Vaknin, M., and H.C. Berg. 2005. Proc. Natl. Acad. Sci. USA. doi:10.1073/pnas.0510047103. N euron subtypes are specifi ed through diversity: each subtype g

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