Identifying transcriptional interplay between skin and oral ectoderm during mandibular patterning - PROJECT SUMMARY: Development of the mouth is complex, requiring the proper segmentation of epithelial domains along the dorsoventral axis into oral, dental, and skin lineages. Congenital defects impacting structures derived from these lineages are common and can be severely debilitating for those afflicted, thus necessitating a precise understanding of their underlying genetic control. Knockout (KO) mouse models have begun to identify genetic programs responsible for driving individual epithelial lineages. However, despite these efforts, if and how these programs (oral, dental, skin) intersect and their functional influence on one another remains poorly understood. We found that in the mandibular ectoderm SHH, Sox2, Pitx1 and Pitx2 are strongly expressed on the dorsal, oral/dental-fated side, while WNT, Tfap2a and Tfap2b are strongly expressed on the ventral, skin-fated side. While expression domains initially overlapped at E9.5, they formed complementary expression domains at E11.5, coincident with the specification of oral/dental or skin fates. Highlighting the functional significance of these partitioned networks, early ectodermal double KO of Tfap2a/Tfap2b (Tfap2- LOF) led to a ventral expansion of the oral/dental domain, including associated transcription factors, signaling pathways, and structures, such as an ectopic incisor. Conversely, KO of Pitx2, associated with arrest of the dental lineage, led to a dorsal expansion of the skin domain, including associated transcription factors and signaling pathways. Our overall objective with this proposal is to determine how interactions between different groups of transcription factors—namely, SOX2/PITX1/PITX2 and TFAP2A/TFAP2B—drive the specification of oral/dental or skin fates, respectively, within the mandibular ectoderm. In Aim 1, we will determine how these domain specific transcription factors, including SOX2, PITX1, and PITX2 in the dorsal oral/dental epithelium and TFAP2A and TFAP2B in the ventral, aboral, skin epithelium counteract one another, to both strengthen and refine these domains. In Aim 2, we will identify how TFAP2 programs a ventral/skin identity, including regulation of this program at a chromatin level. Finally, in Aim 3, we will identify the cellular and molecular underpinnings associated with the expanded dorsal domains, including communication between epithelium and underlying mesenchyme, and the involvement of SHH and WNT in defining odontogenic competence of the underlying mesenchyme, in Tfap2-LOF embryos. Collectively, using a strong set of in vivo animal models, explant, and genome wide assays, these studies will fill a critical knowledge-gap in our current understanding of epithelial patterning along the dorsal-ventral axis of the mandible. The Principal Investigators of this MPI study have complementary expertise in relevant areas for this proposal. They will collaborate with Dr. Kenny, an expert in gene regulatory networks and genome wide assays. Collectively, the experimental design and approach, the PIs, and the environment outlined provide the catalyst to improve oral and craniofacial health.
