Grhl3 modulates epithelial structure formation of the circumvallate papilla during mouse development

Grainyhead-like 3 (Grhl3) is a transcription factor involved in epithelial morphogenesis. In the present study, we evaluated the developmental role of Grhl3 in structural formation of the circumvallate papilla (CVP), which undergoes dynamic morphological changes during organogenesis. The specific expression pattern of Grhl3 was examined in the CVP-forming region, specifically in the apex and epithelial stalk from E13.5 to E15.5 using in situ hybridization. To determine the role of Grhl3 in epithelial morphogenesis of the CVP, we employed an in vitro tongue culture method, wherein E13.5 tongue were isolated and cultured for 2 days after knocking down of Grhl3. Knockdown of Grhl3 resulted in significant changes to the epithelial structure of the CVP, such that the apical region of the CVP was smaller in size, and the epithelial stalks were more deeply invaginated. To define the mechanisms underlying these morphological alterations, we examined cell migration, proliferation, and apoptosis using phalloidin staining, immunohistochemistry against Ki67, ROCK1, and E-cadherin, and a TUNEL assay, respectively. These results revealed an increase in proliferation, a reduction in apoptosis, and an altered pattern of cytoskeletal formation in the CVP-forming epithelium, following Grhl3 knockdown. In addition, there were changes in the specific expression patterns of signaling and apoptosis-related molecules such as Axin2, Bak1, Bcl2, Casp3, Casp8, Ctnnb1, Cnnd1, Gli3, Lef1, Ptch1, Rock1, Shh, and Wnt11, which could explain the altered cellular and morphological events. Based on these results, we propose that developmental stage-specific Grhl3 plays a significant role in CVP morphogenesis not by just disruption of epithelial integrity but by regulating epithelial cell proliferation, apoptosis, and migration via Shh, Wnt, and apoptosis signaling during mouse embryogenesis.