UC Davis

During craniofacial development, defective growth and fusion of the upper lip and/or palate can cause orofacial clefts (OFCs), which are among the most common structural birth defects in humans. Cranial neural crest (NC) cells and orofacial epithelial cells are two major cell types that interact with various cell lineages and play key roles in orofacial development. NC cells are a temporary population of multipotent stem cells that generate a diverse array of cell types during embryonic development. However, the mechanism that drives the fate determination of cranial NC cells remains unclear. Using single-cell RNA sequencing, I reconstructed developmental trajectories of the post-migratory cranial NC cells, and traced the differentiation of cranial NC cells in mouse embryos. My results indicate that early facial prominences appear to be built by undifferentiated, fast-dividing NC cells. The proliferation activity of the post-migratory cranial NC cells continues during the morphogenesis of the facial primordia. Wnt signaling plays essential roles in embryonic development and cancer. I studied the role canonical Wnt signaling plays in the NC development. Lrp5 and Lrp6 are single-span transmembrane co-receptors in the canonical Wnt signaling pathway. Conditional inactivation of Lrp6/Lrp5 in the NC cells results in craniofacial and cardiovascular defects. Mechanistic studies suggest that Lrp6/Lrp5-mediated Wnt signaling is essential for NC cell expansion and maintenance of their multipotency to generate diverse NC derivatives. Conditional inactivation of the Wnt secretion protein Wls in the mesenchymal cells disrupts dorsal MNP patterning and directional outgrowth, resulting in midfacial hypoplasia and midline clefts, including median cleft lip and bifid nose. Based on single cell transcriptomic profiles and cis-regulatory sequence analyses, I revealed crucial gene regulatory networks modulated by Wnt signaling that maintain proper MNP patterning and midfacial morphogenesis.