Id2 Play a Role During Murine Palatal Fusion

Transforming growth factor (TGF)-b3 is an important contributor to the regulation of murine medial edge epithelium (MEE) disappearance during palatal fusion. TGF-b3 null mutant mice (TGF-b3-/-) have a phenotype characterized by cleft palate. Overexpression of Smad2 in the MEE is capable of rescuing the cleft palate in TGF-b3-/- mice, however the downstream effects of activated Smad2 have not yet been determined. The Inhibitor of DNA binding (Id) 2 protein is negative regulator of basic helix-loop-helix transcription factors and involved in cellular differentiation and proliferation. We have reported that Id2 was present in the tips of palatal shelves and that the distribution of Id2 was consistent with phosphorylated Smad2. In this study, we examined gene expression of Id2 and Smad2 in MEE using real-time PCR. Objective: To examine the temporal expression levels of Id2 and Smad2 in the MEE during murine palatal fusion. Methods: Palatal tissues were dissected at specific stages of development and the RNA isolated. The RNA was converted to cDNA and amplified using quantitative real-time PCR. The quantities of mRNA were compared between different developmental stages. Results:In the critical stages of palatogenesis associated with palatal shelf adherence and breakdown of the midline seam Id2 was expressed at a high level specifically in the MEE. The Id2 expression level had temporal changes in quantity that were comparable to the Smad2 expression level. The sites of expression and timing of expression suggest that Ids could mediate downstream effects of TGF- signaling related to palatogenesis. Conclusion: Id2 may be a downstream target of TGF-3/Smad2 signaling pathway and play an important role in the regulation of MEE disappearance during murine palatal fusion. Supported by NIDCR grant R01 DE16296.