CAREER: Molecular mechanisms of epithelial and mesenchymal plasticity: the reversible regulation of cell polarity and cell adhesion

University Of Nevada Las Vegas, Las Vegas NV

Investigators

Abstract

The complexity and diversity of animal body structures arise from the combinations of just two tissue types: the attached, static epithelial cells (forming skin and gut lining); and the detached, often migratory mesenchymal cells (forming muscle and blood cells). Epithelial cells, form the stable building blocks for organ formation, while mesenchymal cells provide tissue dynamics and mobility in embryos. This project aims to understand the “plasticity” of epithelial-mesenchymal transition (EMT), the fundamental cellular process that transforms epithelial cells to mesenchymal cells. By connecting epithelial state to mesenchymal state, EMT is essential for generating diverse cell types during development and wound healing. In the past, EMT was thought to be a binary switch, but recent studies have pointed to a more fluid model: Cells transition back and forth along a spectrum with intermediate states exhibiting partial epithelial and mesenchymal traits. Importantly, such plasticity is central to the normal function of EMT both in embryos and adults; it allows cells to access the optimal states to grow, migrate, and construct tissues and organs. How cells are stabilized in these intermediate states is poorly known. This project will reveal the mechanisms that achieve and maintain intermediate EMT states. The project will also provide research opportunities for undergraduate students with the goal of facilitating access to STEM field careers. In collaboration with local high school teacher leaders, this project will bring cellular and developmental biology to high school classrooms by providing summer workshops for high school teachers from Clark County School District. At the core of EMT transition is the regulation of cell polarity and cell adhesion, two defining features of epithelial cells. The investigators' central hypothesis is that the reversibility of cell state is achieved by regulating polarity and cell adhesion at the level of protein subcellular localization. The investigators' previous work points to two mechanisms that may confer plasticity in fly mesoderm EMT. The first mechanism requires EMT master transcription factor Snail to promote the loss of polarity protein Par-3 from junctional cortex. Since Par-3 plays a central role in the assembly of cell adhesion, such a mechanism weakens cell adhesion but preserves adhesion proteins for use on demand. The second mechanism is a myosin-dependent mechanosensitive mechanism that rebuilds adhesion junctions using the adhesion proteins preserved from the disassembly. The investigators will identify the molecular players in these two mechanisms by: 1) Testing whether Snail promotes disassociation of Par-3 from junctional cortex via reducing Par-3 protein clustering and enhancing Par-3 phosphorylation; 2) Dissecting the mechanosensitive strengthening of cell adhesions by characterizing two new components the PI identified recently: junctional myosin for its role in directly clustering junction complexes and a conserved casein kinase for its role as a novel mechanosensitive junction effector; 3) Identifying targets of the Snail transcription factor and the intermediate players that mediate Snail’s action on junctional Par-3 through a non-biased genetic screen. The project will take advantage of the live imaging expertise, the machine-learning-based quantitative tools, new reagents and assays developed in the lab to acquire new insight into the mechanisms and players in EMT plasticity. This award is funded by the Cellular Dynamics and Function Cluster of the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.