AP-2α and AP-2β cooperatively function in the craniofacial surface ectoderm to regulate chromatin and gene expression dynamics during facial development

Abstract

The facial surface ectoderm is essential for normal development of the underlying cranial neural crest 32 cell populations, providing signals that direct appropriate growth, patterning, and morphogenesis. Despite 33 the importance of the ectoderm as a signaling center, the molecular cues and genetic programs 34 implemented within this tissue are understudied. Here we show that removal of two members of the AP-2 35 transcription factor family, AP-2α and AP-2ß, within the early embryonic ectoderm of the mouse leads to 36 major alterations in the craniofacial complex. Significantly, there are clefts in both the upper face and 37 mandible, accompanied by fusion of the upper and lower jaws in the hinge region. Comparison of ATAC38 seq and RNA-seq analyses between controls and mutants revealed significant changes in chromatin 39 accessibility and gene expression centered on multiple AP-2 binding motifs associated with enhancer 40 elements within these ectodermal lineages. In particular, loss of these AP-2 proteins affects both skin 41 differentiation as well as multiple signaling pathways, most notably the WNT pathway. We also 42 determined that the mutant clefting phenotypes that correlated with reduced WNT signaling could be 43 rescued by Wnt1 ligand overexpression in the ectoderm. Collectively, these findings highlight a 44 conserved ancestral function for AP-2 transcription factors in ectodermal development and signaling, and 45 provide a framework from which to understand the gene regulatory network operating within this tissue 46 that directs vertebrate craniofacial development.