Chromatin modifier Polycomb Repressive Complex 2 as a regulator of dental epithelial progenitor cells

Project Summary/Abstract Understanding the mechanisms of dental epithelial progenitor cell fate decisions will help to lay the long-term groundwork for clinical applications of stem cell biology in human dentition. In the continuously growing mouse incisor, cycling progenitor cells orchestrate incisor epithelium renewal during both homeostasis and injury- induced regeneration. The swift and well-orchestrated balance of progenitor cell self-renewal and differentiation into either enamel-producing ameloblasts or non-ameloblasts supports the continuous growth of the tooth. However, the mechanisms that control these rapid fate decisions remain unclear. To understand mechanisms of cell fate decisions, this proposal will examine how Polycomb Repressive Complex 2 (PRC2), through trimethylation of lysine 27 on Histone 3, represses gene expression to drive fate commitment of progenitor cells. This proposal will establish the role of PRC2 catalytic subunit Enhancer of Zeste Homolog 2 (EZH2) in the incisor epithelium and its specific chromatin targets during progenitor differentiation. Aim 1 will examine how EZH2 contributes to incisor epithelial progenitor cell fate decisions during homeostasis and injury-induced regeneration. This will be achieved by determining how loss of Ezh2 in progenitor cells affects cell fate decisions, such as changes to differentiation, self-renewal or apoptosis. Aim 2 will elucidate the specific targets of EZH2 in progenitor cells during homeostasis and injury-induced regeneration. Chromatin states of incisor epithelial cells during both conditions will be determined using state-of-the-art single-cell Assay for Transposase Accessible Chromatin sequencing (scATACseq) and Cleavage Under Targets and Release Using Nuclease (CUT&RUN) technologies. These analyses will show whether PRC2 targets in the incisor epithelium are similar to those in other self-renewing tissues. They will also identify the dental epithelial tissue-specific targets that contribute to ameloblast and non-ameloblast fates. This research plan will be conducted in conjunction with a comprehensive training plan designed to develop the applicant’s career as a dentist-scientist. The training includes structured mentorship from a highly qualified clinician-scientist sponsor, as well as scientific and technical training through attending seminars, journal clubs, classes, laboratory meetings, conferences, and more. Research and training will take place at the University of California, San Francisco, which offers both an outstanding research environment and an excellent dental school for clinical training.