Mechanisms of membrane organization and endocytosis

How a eukaryotic cell constructs signaling complexes (regulation of local composition) and engages in membrane traffic, in particular during endocytosis (constructing endocytic platforms) is the primary focus of my laboratory. My laboratory’s goal is to uncover physico-chemical rules and principles that govern local regulated organization of the cell membrane. This will help understand how the cell constructs functional signaling complexes and responsive endocytic platforms.

To study phenomena at the cellular scale, we utilize principles from the physical sciences to frame questions about movement of molecules and organelles inside cells. We have also have developed numerous microscopy tools to study organization of cellular components, from the nanometer scale in specialized domains in cell membranes to the micron scale prevalent in mapping endocytic pathways. We study sorting properties and endocytic pathways of a variety of molecules, including membrane proteins, lipids and lipid-tethered proteins in vivo. Our studies provide a compelling picture of the cell membrane as an active composite of the lipid bilayer and a dynamic cortical actin layer beneath, wherein, dynamic actin filaments help in controlling the local composition of membranes, and shaping endocytic trafficking.

We are now involved in several specific lines of inquiry. These include:
i) theoretical and experimental studies on the basis for the formation of specific membrane domains in living cells;
ii) in vitro reconstitution of actin and myosin-driven membrane composition;
iii) exploring the dynamics of such membrane complexes during signaling and templated differentiation in multiple cell systems, including stem cells;
iv) uncovering molecular mechanism of dynamin-independent endocytosis using cell-based assays at the individual gene scale, and genome wide-RNAi screening methods to study its regulation and evolution;
v) understanding the functional role(s) of clathrin and dynamin-independent endocytic pathways in cell and animal physiology;
vi) understanding the scales of organization in the functioning of lipid-tethered morphogens in patterning tissues in situ.

The trajectory of this work has led us to explore the fine structure of the plasma membrane, providing for the first time an in vivo picture of lipidic assemblies providing a new understanding of how membrane rafts may be created, an understanding of the role of specialized endocytic mechanisms for the establishment of developmental gradients and the regulation of membrane tension.