Title: Regulation of Tgfb3 Expression in the Prefusion Palatal Epithelium
Adam Rice (Presenter)
University of Michigan School of Dentistry
Vesa Kaartinen, University of Michigan School of Dentistry
Objectives: The original aim of our study was to determine whether elements regulating transforming growth factor beta 3 (Tgfb3) located in the intraflagellar transport 43 gene (Ift43) are sensitive to canonical Wnt/β-catenin (Ctnnb1) signaling. We addressed this through palatal epithelium-specific deletion of Ctnnb1 and observation of palatal phenotype and Tgfb3-reporter activity during palate fusion.
Methods: We generated β-catenin/keratin 14-Cre knockout mice expressing a lacZ reporter within the Tgfb3 gene. Embryos were harvested at E13.5 (prefusion), E14.0 (during fusion) and at E14.5 (postfusion), and embryonal heads were processed for paraffin embedding. We analyzed expression of Tgfb3 in tissue sections and whole mount samples using β-galactodase staining and in situ hybridization. We also analyzed whole mount samples for expression of Sonic hedgehog (Shh) with in situ hybridization.
Results: While deletion of Ctnnb1 resulted in noticeable craniofacial and hind limb abnormalities, such as narrow snout, highly arched and narrow palate, lack of palatal rugae, and missing or malformed digits, cleft palate was not observed. Also, Tgfb3 reporter activity was not grossly influenced by Ctnnb1 deletion, suggesting that, at least in our outbred genetic background, canonical Wnt/β-catenin signaling is dispensable for Tgfb3 expression. This was further confirmed through analysis of endogenous Tgfb3 expression using in situ hybridization. In concordance with the lack of visible palatal rugae, the expression pattern and levels of Shh were altered in palatal epithelial-specific Ctnnb1 mutants.
Conclusions: Our current results show that epithelium-specific Ctnnb1 mutants do not exhibit cleft palate and that loss of canonical Wnt signaling does abrogate Tgfb3 expression in medial edge epithelial cells of prefusion palatal shelves. In contrast, our results imply that canonical Wnt signaling is required for appropriate Shh expression in the developing palatal epithelium.