Biophysics and Cell Biology of Meso-scale Gap Closure - PROJECT SUMMARY Background: Gap closure is a critical step in wound healing and the maintenance of tissue homeostasis during embryogenesis. Current studies of gap closure focus on epithelial cells with strong adhesion strength and junctional actin cytoskeletons and have identified lamellipodia-mediated cell crawling and “purse-string”-like contractile actin rings as two major mechanisms for gap closure. At the molecular level, ERK and p53 activations are known to regulate the migration and proliferation of tissues. Recent new findings, including our own data, suggest that tissue fluidity, the tissue mechanical property that reflects the frequency of cell intercalations, plays a major role in gap closure. It is still unclear how tissue fluidity is patterned spatiotemporally during gap closure, how it is regulated within the cells and by the microenvironment, and what are its molecular regulators. We have discovered that by introducing epithelial-mesenchymal transition (EMT) to epithelial cells and generating a meso- scale gap in the order of magnitude of millimeter, tissues with partial EMT status demonstrate a coordinated collective migration pattern that is distinct from both random cell crawling and purse-string-like contraction. This coordinated gap closure will serve as a novel model system to study the fundamental mechanisms for gap closure from biophysics, cell and molecular biology perspectives. Recent Progress by the PI: In the past 7 years, the PI has established his lab and built a productive research team at UMass Amherst. Since joining UMass, the PI’s group has published 26 journal articles and engaged 8 graduate students, 2 postdoctoral fellows, and more than 20 undergraduate researchers with diverse backgrounds, including bioengineering, molecular and cell biology, neuroscience, and biophysics. With strong collaborations with cell biologists, biophysicists, and bioinformatic experts, the PI’s lab has developed several bioengineering tools to define cell microenvironment, including micropatterning, traction force microscopy, DNA- based fluorescence sensors for intercellular force measuring, mechanical strain gradient generation device, and single cell RNA sequencing expertise. Leveraging those tools, the PI’s lab has investigated how mechanical cues such as geometrical confinement, substrate mechanics, and external mechanical strains regulate cell rearrangement and migration. Overview of Future Research Plans: To fully understand the mechanism of this novel gap closure process, our first goal is to track and rigorously characterize cell kinematics, proliferation/growth pattern, force distribution, and tissue fluidity during the gap closure of tissues undergoing EMT. We will study how force and tissue fluidity patterns are regulated by environmental factors such as gap geometry, 3D curvature, extracellular matrix properties, and external mechanical strains. Further, we aim to combine spatial transcriptomics and molecular biology techniques to identify the molecular mechanisms for coordinated gap closure and molecular regulators of tissue fluidity. Together, those fundamental studies will deepen our understanding of the wound healing process and guide the design of novel medical devices to accelerate the wound healing process.
