Cellular Basis of Incisor Asymmetry

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Project Summary Morphogenesis is the biological process by which cells, tissues, and organs acquire the shape that is critical to their function during embryonic development, and it can be repurposed during regeneration of tissues after damage in a mature organism. Work on embryonic explants has revealed that differences in cellular morphologies and mechanical cell-cell interactions, both controlled by signaling molecules, likely drive tissue- specific shapes in multiple epithelial tissues including the symmetric murine molar. Nevertheless, a deeper understanding of the basic principles and cellular behaviors that regulate morphogenesis is required to leverage these processes for future regenerative therapies that can mitigate the effects of aging and disease. I will use the early developmental stages of the murine incisor to study how cell behaviors drive directional growth and morphogenesis. Murine incisor development is highly asymmetric, and the mechanisms regulating this process have remained elusive. Prior studies have shown that perturbations in Sonic Hedgehog (Shh) signaling result in abnormal incisor morphology, and that Shh-dependent cell movement drives tooth bud invagination in the symmetrical molar. Through this proposal, I will test the hypothesis that modulation of the Shh signaling cascade drives changes in cellular morphology and behavior that determine the asymmetric morphogenic development of the incisor. I will measure and quantify localized cellular and tissue morphological changes such as cell shape, nuclear position, and tooth curvature, as well as dynamic cell behaviors such as differential proliferation, oriented cell division, and cell intercalation, using high resolution live imaging and our novel software program, MARGARITA. This will establish a foundational atlas of cell morphologies and behaviors responsible for the epithelial bending events driving early development of the asymmetric incisor (Aim 1). Next, pharmacological perturbation of Shh signaling in incisor explants and spatiotemporal modulation of Shh expression in genetic mutants will determine to what extent the modulation of this signal transduction pathway affects cellular morphology during incisor development (Aim 2). These findings will provide significant insights into basic tooth and developmental biology, which have the potential to be applied towards future dental regenerative therapies. Current strategies to restore missing dentition (i.e., implants, dentures) can lead to significant bone resorption or may fail due to limited osseointegration. Thus, biologically regenerating teeth using morphogenesis-driven techniques has the potential to significantly improve restorative dentistry. These research goals will be conducted in conjunction with a comprehensive training plan designed to develop my career as a dentist-scientist. Training includes structured mentorship from two highly qualified sponsors, as well as scientific and technical training through meetings, seminars, journal clubs, and classes at UCSF, which offers both an outstanding research environment and an excellent dental school for clinical training.