Changes in cell distribution during mouse secondary palate closure in vivo and in vitro: I. Epithelial cells

The distribution of epithelial cells around the perimeter of mouse secondary palatal shelves was observed before and after shelf reorientation in vivo and in vitro. Changes in shelf perimeter, cells per micrometer, and cell layering were measured for each of three shelf regions: anterior and posterior presumptive hard and presumptive soft palate at developmental stages which were 30, 24, and 18 hr prior to expected in vivo elevation, after in vivo elevation, and during the course of in vitro elevation. Pronounced increases in numerical cell density and cell layering accompanying shelf reorientation were noted in the superior nasal and mid-oral portions of the shelf perimeter in all three shelf regions with greatest changes noted in the posterior hard palate region. These changes were not attributable to cell division or to perimeter changes. The localized nature of the changes in cell distribution suggest that the underlying mechanisms may also be localized.