The Meyer laboratory seeks to understand how human cells sense hormones, growth factors and stress and how they integrate and transduce these signals to make decisions to polarize, move or divide. We investigate these cellular regulatory systems by identifying the key signaling components and measuring when and where signaling occurs as we watch cells decide to move forward or enter the cell cycle. We have been intrigued by the near universal importance of locally acting Ca2+ and phosphoinositide lipid second messenger signals, Rho and Ras family small GTPases and protein kinases in controlling these decision processes. Our projects are focused on understanding the general principles of how signal transduction systems work which often requires the development of new experimental and analysis tools involving fluorescent microscopy, small molecule and light perturbations, systematic siRNA screens, bioinformatics, genomics and quantitative modeling of signaling pathways.
The actin cortex both facilitates and hinders the exocytosis of secretory granules. How cells consolidate these two opposing roles was not well understood. Here we show that antigen activation of mast cells induces oscillations in Ca(2+) and PtdIns(4,5)P(2) lipid levels that in turn drive cyclic recruitment of N-WASP and cortical actin level oscillations. Experimental and computational analysis argues that vesicle fusion correlates with the observed actin and Ca(2+) level oscillations. A vesicle secretion cycle starts with the capture of vesicles by actin when cortical F-actin levels are high, followed by vesicle passage through the cortex when F-actin levels are low, and vesicle fusion with the plasma membrane when Ca(2+) levels subsequently increase. Thus, cells employ oscillating levels of Ca(2+), PtdIns(4,5)P(2) and cortical F-actin to increase secretion efficiency, explaining how the actin cortex can function as a carrier as well as barrier for vesicle secretion.
Many of the more than 20 mammalian proteins with N-BAR domains1, 2 control cell architecture3 and endocytosis4, 5 by associating with curved sections of the plasma membrane6. It is not well understood whether N-BAR proteins are recruited directly by processes that mechanically curve the plasma membrane or indirectly by plasma-membrane-associated adaptor proteins that recruit proteins with N-BAR domains that then induce membrane curvature. Here, we show that externally induced inward deformation of the plasma membrane by cone-shaped nanostructures (nanocones) and internally induced inward deformation by contracting actin cables both trigger recruitment of isolated N-BAR domains to the curved plasma membrane. Markedly, live-cell imaging in adherent cells showed selective recruitment of full-length N-BAR proteins and isolated N-BAR domains to plasma membrane sub-regions above nanocone stripes. Electron microscopy confirmed that N-BAR domains are recruited to local membrane sites curved by nanocones. We further showed that N-BAR domains are periodically recruited to curved plasma membrane sites during local lamellipodia retraction in the front of migrating cells. Recruitment required myosin-II-generated force applied to plasma-membrane-connected actin cables. Together, our results show that N-BAR domains can be directly recruited to the plasma membrane by external push or internal pull forces that locally curve the plasma membrane
A two-dimensional ERK-AKT code decides between proliferation and differentiation ► Single-cell signal variation creates two cell fates in an identical cell population ► Different growth factor inputs are integrated at the level of ERK and AKT ► Rasa2 enhances proliferation over differentiation in a population of PC12 cells.
Last modified Tuesday, 16-Apr-2013 12:53:37 PDT