Three-dimensional ultrastructure and histomorphology of mouse circumvallate papillary taste buds before and after birth using focused ion beam-scanning electron microscope tomography.

Early taste buds are formed from placode cells. Placode cells differentiate into Type I-Ⅲ cells at birth; however, the ultrastructure of these first taste cells remain elusive. Here, we used focused ion beam-scanning electron microscopy (FIB-SEM) to analyze taste buds on the dorsal surface of the circumvallate papilla on embryonic day (E) 18.5 and postnatal day (P) 1.5. The taste buds on E18.5 existed as a mass of immature cells. One of the immature cells extended the cell process to the surface of the epithelium from the taste bud mass. Cytoplasm of this cell contained many mitochondria and vesicles in the apical region. The taste buds at P1.5 had small taste pores and had an onion-shaped structure. Most of the cells in the taste buds extended toward the taste pores. Some of the cells in the taste buds were Type II-like cells with glycogen in their cytoplasm. In this study, it was shown in three dimensions that immature cells extend to the surface of epithelium before the formation of the taste pore. Subsequently, the formation of taste pores and maturation of taste buds progress simultaneously.