Regulation of apical constriction by the RhoGEF protein Plekhg5

SUMMARY Epithelial morphogenesis involves cell shape changes, cell rearrangements, and spatially regulated cell division. It is a crucial process that is employed both during embryo development and in adult homeostasis. Dysregulated epithelial morphogenesis is associated with a range of human diseases, such as neural tube defects, highlighting the importance of this process. Despite this, our understanding of molecular control of epithelial remodeling is quite limited. In vitro cell culture models often do not capture epithelial morphogenesis in a precise and faithful manner. Hence usage of animal models is required to address detailed molecular mechanisms that regulate epithelial morphogenesis. In this project, we focus on a specific event during epithelial morphogenesis, namely apical constriction, a process whereby apical cell surface is actively reduced under the control of Rho signaling. We will investigate in depth an activator of Rho GTPases, the RhoGEF Plekhg5, in modulation of apical constriction. Our previous studies reveal that plekhg5 is necessary for apical constriction to make bottle-shaped cells during Xenopus gastrulation and sufficient to induce apical constriction ectopically in other epithelial cells. We further demonstrate that plekhg5 modulates dynamic apical actomyosin organization to reduce apical cell area, and it does so efficiently in part due to self-association of Plekhg5 protein to facilitate formation of a signaling platform. We plan to build upon these and other preliminary data to explore several additional hypotheses. In aim 1, we will test the hypothesis that apical constriction involves sequential events of junctional recruitment of Plekhg5, activation of Rho signaling, post-translational modification of Plekhg5, junctional release of modified Plekhg5, and translocation of Plekhg5 to the apical cortex to regulate actomyosin dynamics. In aim 2, we will examine the hypothesis that multiple regulators of actomyosin act downstream of Plekhg5 and activated Rho to regulate apical constriction of the bottle cells. In aim 3, we will investigate the hypothesis that human PLEKHG5 variants of uncertain significance can be studied in Xenopus to reveal differential effects of these variants on protein levels, localization, dimerization, activation of Rho, and/or interaction with other partners. Results from our studies will help uncover detailed mechanisms underlying the function of the RhoGEF gene plekhg5. The data will also provide deeper insight into general strategies that RhoGEF genes use to control biological processes during embryonic development. It will additionally present Xenopus as an attractive model to use for functional and mechanistic interrogation of human variants with uncertain significance. Project Number: 1R01GM164517-01 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of General Medical Sciences (NIGMS) | Principal Investigator: CHENBEI CHANG | Institution: UNIVERSITY OF ALABAMA AT BIRMINGHAM, BIRMINGHAM, AL | Award Amount: $445,358 | Activity Code: R01 | Study Section: Development - 2 Study Section[DEV2] View on NIH RePORTER: https://reporter.nih.gov/project-details/11341527