Monday, February 3, 2014
General Biology Seminar
Systematic Analysis of Speed, Direction, and Signaling in Chemotaxis
Sean Collins, Postdoctoral Fellow , Department of Chemical and Systems Biology, Stanford University
Abstract: Tools for systematic genetic analysis of quantitative phenotypes in yeast, developed by myself and others, have been very successful for revealing pathway architectures and identifying the genes responsible for important molecular mechanisms. Recently, I have been developing similar techniques to study a complicated mammalian process: the motility response of neutrophils to chemical attractants. Neutrophils process chemical signals with great spatial accuracy that allows them to detect as little as a 1% difference in concentration across the cell, but also with the sensitivity and decisiveness to polarize and move even in response to weak or spatially uniform stimuli. In order to discover how the signaling system achieves and balances these response features, I developed an automated system to image large numbers of individual cells responding to chemoattractant gradients generated rapidly by photo-uncaging. Systematic gene perturbation revealed for the first time distinct sets of genes regulating stimulus-induced increases in motility and directional responses. Specialization is evident already at the level of the alpha and beta heterotrimeric G-protein subunits immediately downstream of the receptor. Further high resolution imaging with several fluorescent biosensors revealed that the GTPase Cdc42 plays a central role in defining the cell's protrusive front and that the G-protein subunits promote different features of Cdc42 dynamics.