How To Make a Mouth: Oral Epithelia Require Locoregional Mitotic Diversity in Morphogenesis and in Maintenace

Oral epithelia (OE) frequently renew and function to protect the oral cavity against constant challenge from microbes, toxins, and injury. Despite increasing evidence that differentiation pathways are frequently mutated in oral squamous cell carcinomas (OSCCs), little is known about what regulates OE development and maintenance. Work from our lab in skin has shown that proper orientation of mitotic spindles (oriented cell divisions, OCDs) is essential for development; yet, whether OCDs play any role in OE is unknown. The first aim was to characterize OE development to assess if known OCD gene LGN (Gpsm2) promoted OCDs in OE. Apically localized LGN was found to direct perpendicular divisions that promoted E16.5 OE stratification. Surprisingly, in dorsal tongue (DT), LGN was alternatively localized and promoted planar OCDs. Loss of LGN disrupted the 3D morphogenesis of DT filiform papillae but was dispensable for hair folliculogenesis. Thus, LGN demonstrated tissue-specific functions in ectoderm and its appendage development by spatiotemporally controlling OCDs. The next aim was to assess adult OE under homeostatic conditions, searching for evidence of OE stem/progenitor cell (OESC) heterogeneity. I adopted lineage tracing and genetic label retention strategies, which identified frequently and infrequently dividing cells (FDC/IDCs) in the hard palate. Using lineage tracing, I found evidence of FDCs that often oriented their divisions perpendicularly. However, using label retention assays, I also identified IDCs with characteristics indicative of stemness, including less proliferation and more planar OCDs. With these initial experiments, I provided preliminary evidence of OESC heterogeneity in adult OE, including slower-cycling reserve OESCs and more rapidly dividing active OESCs. The final aim was to test the role of OCDs in oral tumorigenesis. This project aim was to create a novel mouse model of OSCC, LSL-p53R172H or LSL-p53R270H mice, which express p53 gain-on-function “hotspot” mutations (p53GOF) when crossed to an epithelial-specific cre (K14-cre). To accomplish this goal, a large pilot study was performed and demonstrated significantly decreased oral tumor latency in both K14-p53GOF compared to p53WT or heterozygous p53GOF mice. This aim has generated a new model of OSCC that will be used for testing the role of OCDs during OSCC initiation.Doctor of Philosoph