Cell cycle arrest of a craniofacial epithelial population shapes faces in mice and humans

The mechanisms that shape human facial features and lead to abnormalities if disrupted are complex and multilayered. Orofacial clefting (OFC), the most common craniofacial disorder, results from a failed fusion of facial prominences, partly driven by persisting of cephalic epithelia. Here, we characterize an epithelial cell population, the zippering lambda (ZL), which is cell cycle-arrested and mediates facial prominence fusion in mice and humans. We find uninhibited cell cycle progression in the ZL of Pbx1/2 and p63 mutant mice with OFC. A comparison of ZL-enriched genes with human OFC whole-genome sequencing datasets identifies Zinc-finger homeobox 3 (ZFHX3) variants in affected individuals. Notably, the deletion of Zfhx3 in cephalic epithelia initiates murine OFC. Zfhx3 and Pbx1 genetically interact, and their protein products cooperatively downregulate cell cycle inhibitors in embryonic facial development. Taken together, we reveal a facial patterning mechanism that links cell cycle arrest to developmental tissue fusion.