Regulation of single cell migration in vivo

About This Grant

Project Summary: Cell migration is a critical aspect of normal development, as cells are often not born in the location of function, and migrate long distances to their final destination. But this process is often co-opted in disease states such as cancer. Much of our understanding regarding cell migration stems from work in 2D cell culture models, in which many types of cells exhibit a net forward movement through cell protrusion at the front and cell retraction at the back. Central to this form of migration is the ability of the cell to physically attach to its underlying substrate through the formation of focal adhesions. in vitro 2D and 3D approaches offer numerous advantages to dissect focal adhesion biology in terms of high-resolution image acquisition, control over matrix properties, and quantitatively assessing biophysical properties. While these studies have been immensely valuable, despite the years of research, it is still unclear what the organization and dynamic regulation of focal adhesions are during single cell migration in complex in vivo systems. Furthermore, pharmacological inhibitors have been developed against components of focal adhesion machinery for the treatment of disease without a clear understanding of how focal adhesions form and function during cell migration in animals. To meet this need, we developed a system in which we can directly visualize the formation and dynamics of focal adhesion structures of highly migratory single cells on a relatively planar surface of the zebrafish larval skin. Our recently published work challenges dogma established by in vitro studies, showing that phosphorylation of a key focal adhesion component, Paxillin, is greatly reduced in migrating cells in vivo, and that lack of Paxillin phosphorylation promotes focal adhesion disassembly rates and single cell migration in vivo, despite inhibiting cell migration in culture. This contradiction emphasizes the need for additional work in understanding focal adhesion regulation in complex in vivo environments (Aim 1). Furthermore, we found that the expression of the upstream kinase, FAK, is significantly reduced in cells in vivo compared to cells in culture. Given that FAK inhibitors are currently being developed in the clinic under the premise that part of FAK's function is for focal adhesion regulation, it is important to definitively determine whether FAK activity is required for focal adhesion regulation during single cell migration in vivo (Aim 2), and how Paxillin promotes cell migration in the absence of FAK phosphorylation (Aim 3). Identifying new proteins that interact with Paxillin in vivo will also begin to unravel why focal adhesion regulation is different in vivo versus in culture. Thus, our work has the potential to re-define the roles for focal adhesion proteins during single cell migration in vivo.