Distribution of vimentin in the developing chick taste bud during the perihatching period.

The tissue environment within which taste bud cells develop has not been wholly elaborated. Previous studies of taste bud development in vertebrates, including the avian chick, have suggested that taste bud cells could arise from one, or several tissue sources (e.g. crest-mesenchyme, local ectoderm or endoderm). Thus, molecular markers which are present in gemmal as well as interfacing (peribud epithelium; mesenchyme-epithelium) regions, and their degree of expression during stages of taste bud development, are of special interest. The intermediate filament protein, vimentin, occurs in mesenchymal and mesodermally-derived (e.g. endothelial, fibroblast) cells as well as highly proliferating epithelium (e.g. tumors). The present study in chick gustatory tissue utilized antibodies against vimentin and the avidin-biotin-peroxidase technique to evaluate vimentin immunoreactivity (IR) within a timeframe which includes: 1) early stages of the taste bud primordium [embryonic days (E)17-E18)]; 2) the beginning of an accelerated bud cell proliferation at the time of initial, taste bud pore opening [around E19]; 3) attaining the adult complement of taste buds [around posthatch (H) day 1], and 4) completed organogenesis (H 17). During this time span, vimentin-IR was characterized in a region including and sometimes bridging taste bud and subepithelial connective tissue, whereas non-gustatory surrounding epithelium and salivary glands were vimentin-immuno-negative. Intragemmally, the proportion of vimentin-IR cells as related to total taste bud cells peaked at E19. These results indicate that vimentin expression, in part, is related to the onset of taste bud cell proliferation and suggest that mesenchyme could be one source of taste bud cells. Secondly, fibronectin, an extracellular matrix component of the epithelial basement membrane interface with mesenchyme, was expressed at or near the apical surfaces of taste bud cells projecting into the bud lumen, and in the basal gemmal region suggesting the possible role of fibronectin as a chemotactic anchor for differentiating and migrating taste bud receptor cells. Lastly, neuron-specific enolase-IR indicates that axonal varicosities are already present intragemmally at E17-E18, that is, during the incipient period of identifiable taste bud primordia.