Cellular Contractility
The broad objective of this project is to understand the molecular mechanisms that drive contractility of actin microfilaments in non-muscle cells. The actin cytoskeleton is an essential, dynamic scaffold that defines cellular shape during directed migration, mitosis, and morphogenesis. In all of these processes, reorganization of the actin network is driven by contractile forces produced by a motor protein, non-muscle myosin II, and is governed by multiple regulatory factors including kinases, phosphatases, and small GTPases of the Rho superfamily. Aside from their roles in normal cell behavior, misregulation of the signaling pathways that control contractility may result in human diseases such as hypertension, inflammatory disorders, oncogenic transformation, and tumor metastasis.Drosophila gastrulation as a model for cellular contractility
Studies of Drosophila embryogenesis have identified many evolutionarily conserved molecules that regulate cytoskeletal dynamics during morphogenesis, including mediators of contractility. The process of gastrulation, in particular, has proven to be a superb genetic model for epithelial sheet remodeling. One of the hallmarks of gastrulation is the invagination of a subset of epithelial cells along the ventral midline to form a structure called the ventral furrow. Furrow formation is driven by concerted cellular shape changes in which apical constriction of the actin network by myosin II has the net effect of driving the internalization of the mesodermal precursor cells. Genetic analysis of this pathway has identified several components that are thought to act sequentially in the following order:
1) an extracellular protein, Folded gastrulation (Fog), is secreted from the apical domain of the epithelial cells at the ventral midline;
2) Fog acts as an autocrine signal by binding to its receptor and signals through a heterotrimeric G protein complex containing the Gα12/13 subunit, Concertina (Cta);
3) Cta activates a guanine nucleotide exchange factor, RhoGEF2, which in turn activates the small G protein Rho1;
4) Rho1 activates myosin II at the apical domain via Rho kinase (DROK) thus producing contraction.
Mutations in several of these components interfere with the timing or execution of normal gastrulation and also disrupt epithelial remodeling of other tissues during later stages of development. Overexpression of several of these molecules have also been implicated in tumor progression and cancer cell metastasis.
We are studying the cortical signaling network involved in activation of the Fog/RhoGEF2/Rho pathway. We have identified a G-protein coupled receptor for Fog and are currently working to understand how it triggers the cellular contractions that drive morphogenesis during Drosophila development.