Notch signaling in the embryonic ectoderm promotes periderm cell fate and represses mineralization of vibrissa hair follicles

The Notch signaling pathway is a critical means to regulate cell fate choice in animals. Appropriate regulation of this pathway is also required for human face formation as both loss and gain of function mutations of Notch signaling can cause syndromes with craniofacial abnormalities. Here we examine the consequences of manipulation of Notch signaling in the early mouse embryonic ectoderm by either removing the transcriptional effector Rbpj or expressing a constitutively active form of the Notch1 intracellular domain. Loss of Rbpj resulted in cleft secondary palate but strikingly was also associated with the ectopic mineralization of vibrissa follicles. In contrast, activation of Notch signaling resulted in multiple embryonic defects including a fully penetrant bilateral cleft lip and palate. Further, single cell RNA-seq data indicated a switch from a basal epithelial cell identity towards periderm when Notch signal transduction was elevated. These cell fate changes were accompanied by misregulation of genes and pathways known to impact human and mouse orofacial clefting including Grhl3, Irf6, and Wnt pathway. Together, these findings provide insight into human craniofacial conditions caused by misregulated Notch activity. SUMMARY STATEMENTOur studies demonstrate that Notch signaling in the embryonic ectoderm stimulates periderm cell fate while also repressing transformation of the inner root sheath of whisker follicles into mineralized tissue.