Immunohistochemical and 3D analysis of the human fetal palate

Objectives: Hard palate development occurs between 7-12 weeks post conception with the fusion of the epithelial lined maxillary prominences creating a midline epithelial seam. The failure of fusion or seam removal in hard palate leads to cleft palate or cyst formation. The mechanism of soft palate formation is less well defined. Evidence exists supporting both fusion and the alternative mechanism of merging. The aim of this study is to densely sample the late embryonic-early fetal period between 54-84days post-conception to determine the mechanism and timing of palate closure. Methods: 28 human fetal heads aged 54-74days were serially sectioned and subjected to immunohistochemistry. Several archival specimens had the coverslips removed and were used for IHC. Seven fetal heads aged 67-84days underwent MRI and microCT with phosphotungstic acid contrast agent. Qualitative analysis of 3-dimensional shape changes during palatal development was completed using a 3D slicer program. Results: We confirm the presence of an epithelial seam extending throughout the soft palates in 57-day specimens suggesting fusion. Cytokeratin antibody staining confirmed the epithelial character of the cells in the midline seam and that there was no difference in the intensity of staining in the endodermal versus ectodermally-derived epithelium. There was surprisingly no E-Cadherin antibody staining in the midline seam although positive signal was found in the dental lamina and dorsal surface of the tongue. MF-20 antibody staining identified the facial musculature including palatine muscles controlling movement of the soft palate. The midline seam in the soft palate is rapidly degraded prior to 64days, however MRI and PTA-microCT imaging revealed the hard palate midline seam is almost completely intact until at least 84-days. Conclusions: The epithelial character of the midline seam in the hard and soft palate has similar cytokeratin antibody staining. There is a difference in E-Cadherin staining which, may be tied to epithelial-mesenchymal transformation that takes place in the midline epithelial seam. The 3D-imaging results were superior with PTA staining and revealed the complex anatomy of the oropharynx. PTA staining can be used in the future to comprehensively document the fusion process as well as muscular development in the soft palate.Dentistry, Faculty ofGraduat