JAPANESE JOURNAL OF ORAL & MAXILLOFACIAL SURGERY

Vol. 55 No. 2       2009

ISSN: 0021-5163      UBIC: 151-J

ABSTRACT

During morphogenesis of the secondary palate, medial edge epithelium (MEE) is formed by fusion of the opposing epithelia covering the tips of the palatal shelves. Thereafter, MEE disappears from the mesenchymal tissue at the appropriate time, and palatal fusion is completed. While this developmental phenomenon has long been known, the mechanisms underlying MEE disappearance remain to be elucidated. Previous studies have shown that MEE loss is due to factors such as apoptosis, shedding of periderm into the body cavity, epithelialmesenchymal transformation, and macrophage phagocytosis. The present study focused on the role of cell migration. ICR mouse fetuses (E14) were studied. Frontal sections were prepared, and those in stages from contact of the palatal shelves to the start of MEE disappearance were analyzed. For each specimen, 5-µm continuous sections were prepared, and the secondary palate (from the tip of the soft palate to the site of fusion of the nasal septum) was stained using hematoxylin and eosin (HE) at 10-µm intervals. We used 3-dimensional stomatognathic reconstruction software (TRY/3D-SRF). The outline of epithelial tissue, mesenchymal tissue, and apoptotic bodies were extracted to reconstruct 3-dimensional images. Each of the extracted data were superimposed and examined. The results showed that when palatal shelves carne in contact, a multilayer epithelial seam was formed, and many apoptotic bodies were observed. In addition, once the epithelia came in contact, an epithelial triangle was formed on the side of the nasal and oral cavities, and the width of the central MEE narrowed. This phenomenon was attributed to epithelial cell migration. Furthermore, epithelial disappearance did not occur sequentially from the anterior region of the hard palate to the soft palate in a unidirectional manner, but occurred simultaneously wherever contact was made. At the same time, apoptosis relating to epithelial disappearance occurred regularly throughout the palatal region. Migrating bodies that were shed into the oral and nasal cavity were seen regularly, and this appears to be one of the ways of effectively eliminating epithelia. Keywords: ICR mice, morphogenesis of secondary palate, medial edge epithelium, apoptosis, cell migration.

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