Mechanisms of cytoskeletal crosstalk during cellular motility

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The ability of cells to alter their shape is critical to the ontogeny of most organisms. Within tissues, for example, changes in cellular morphology drive tissue remodeling during morphogenesis and are essential for wound repair. At the level of the individual cell, cycles of shape change allow some cell types to migrate during embryogenesis, immune function, and (more insidiously) during metastasis. Cellular morphology is dictated by the cytoskeleton - the network of actin filaments and microtubules. The long-term goal of this project is to understand the principles and mechanisms underlying cellular morphology at the molecular level by studying the pathways that regulate and integrate cytoskeletal dynamics. Importantly, the networks of actin and microtubules do not act in isolation, rather there is an unprecedented degree of cross-talk, both regulatory interactions and mechanical interactions. Microtubule plus end-tracking proteins (or +TIPs) are a class of molecules that selectively localize to the tips of growing and shrinking microtubules. Since their discovery in 1999, +TIPs have been implicated in almost every microtubule-dependent cellular function including regulation of microtubule dynamic instability, organelle and chromosomal transport, assembly of the mitotic spindle, establishment of cellular polarity, and cell migration. In this proposal, we focus on +TIPs with a particular emphasis on actin-microtubule cross-talk as this represents a relatively unexplored functional interface between the two cytoskeletal networks. Our core hypothesis is that microtubule plus ends are dynamic platforms that deliver information to cortical regulatory networks governing cell shape and also act as sites of structural integration between actin and microtubules. We will test these ideas using novel assays we have developed with cultured Drosophila cell lines as this model system is amenable to high-resolution light microscopy, biochemical analyses, and gene inhibition using RNAi. The results of these studies will contribute to a basic understanding about the network of cellular components that mediate changes in cellular shape during processes such as morphogenesis and cell migration. The goal of this proposal is to understand the mechanistic basis of cellular morphogenesis and motility. The proper execution of cellular shape changes is essential for embryonic development - if they are not synchronized during development, or fail to occur at all, this can result in congenital birth defects. Like wise, cellular motility underlies processes such as wound healing and immune response. Improper cell motility is also an underlying cause of atherosclerosis, inflammation, and metastasis.