Spatiotemporal Expression and Functional Analysis of miRNA-22 in the Developing Secondary Palate

Objective: Normal development of the embryonic orofacial region requires precise spatiotemporal coordination between numerous genes. MicroRNAs represent small, single-stranded, non-coding molecules that regulate gene expression. This study examines the role of microRNA-22 (miR-22) in murine orofacial ontogeny.

Methods: Spatiotemporal and differential expression of miR-22 (mmu-miR-22-3p) within the developing secondary palate was determined by in situ hybridization and quantitative real-time PCR, respectively. Bioinformatic approaches were used to predict potential mRNA targets of miR-22 and analyze their association with cellular functions indispensable for normal orofacial ontogeny. An in vitro palate organ culture system was used to assess the role of miR-22 in secondary palate development.

Results: There was a progressive increase in miR-22 expression from GD12.5 to GD14.5 in palatal processes. On GD12.5 and GD13.5, miR-22 was expressed in the future oral, nasal, and medial edge epithelia. On GD14.5, miR-22 expression was observed in the residual midline epithelial seam (MES), the nasal epithelium and the mesenchyme, but not in the oral epithelium. Inhibition of miR-22 activity in palate organ cultures resulted in failure of MES removal. Bioinformatic analyses revealed potential mRNA targets of miR-22 that may play significant roles in regulating apoptosis, migration, and/or convergence/extrusion, developmental processes that modulate MES removal during palatogenesis.

Conclusions: Results from the current study suggest a key role for miR-22 in the removal of the MES during palatogenesis and that miR-22 may represent a potential contributor to the etiology of cleft palate.