Coordinating cell adhesion and the cytoskeleton are critical for shaping tissues and organs during development and homeostasis. We established a model to study this during Drosophila morphogenesis, using a highly multidisciplinary approach. Proteins on which we focus also play key roles in mammalian development and cancer metastasis. Understanding mechanisms coordinating adhesion and the cytoskeleton thus advances both basic science and clinical applications. Having identified proteins mediating adhesion and regulating actin, we face a new challenge: how do cells use these molecular machines to carry out the diverse cell behaviors shaping development. In the last four years we defined roles for Canoe/afadin as an adherens junction (AJ)-actin linker in four central developmental events and began to place it in a protein network regulating morphogenesis. We also defined roles in morphogenesis of two key actin regulators: Ena/VASP proteins and Dia-class formins. We found Ena and Dia physically interact and functionally cooperate in complex, non-additive ways, and explored how Abelson kinase integrates upstream signals and coordinates activity of multiple actin regulators. These data underlie our Aims, which explore new cell biological paradigms.
Aim 1 Determine how Rap1 and Canoe and their network of interactors work together and separately to regulate establishment and maintenance of apical-basal polarity and columnar cell shape. Our data reveal that Canoe and Rap1 are critical regulators of AJ:actin linkage during morphogenesis, and demonstrate they play unexpected roles in initiation and maintenance of cell polarity. Our working hypothesis is that they do so as part of a regulatory network including AJ proteins, the apical polarity protein Bazooka/Par3, the actomyosin cytoskeleton, and unidentified effectors. We will define how they work individually and together in two key events: apical-basal polarity establishment and maintenance and establishing columnar cell shape. Successful completion of this Aim will provide novel mechanistic insights into how diverse cell behaviors are controlled by overlapping networks of junctional, cytoskeletal and polarity proteins.
Aim 2 Define mechanisms by which actin dynamics are coordinately regulated during morphogenesis. Our data suggest Dia and Ena cooperatively regulate actin in non-additive ways, and Abl is a scaffold integrating multiple cytoskeletal regulators. Our working hypothesis is that direct Ena:Dia interaction modulates their action at barbed ends, producing diverse cell behaviors, and that the Abl acts as a scaffold via multiple partially redundant interactions, and uses both Ena and Abi as effectors. We will use a multidisciplinary approach to study Ena and Dia cooperation in vitro, in model cells, and in embryos, and will define how Abl and effectors coordinately regulate the cytoskeleton. Successful completion of this Aim will provide novel mechanistic insights into how actin regulators cooperate via physical interaction and how they are coordinately regulated by scaffolding proteins to produce actin structures with distinct dynamics and functions to drive morphogenesis.
To form tissues and organs, cells must adhere to one another, and must act together, by coordinating their cytoskeletons. Disruptions of this process because certain birth defects, contribute to blistering skin diseases and some forms of congenital heart disease, and also play a role in cancer metastasis. We have developed a model system to explore how cell adhesion and the cytoskeleton are normally regulated, to allow better understanding of what goes wrong in human disease.
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