Diversity in cell motility reveals the dynamic nature of the formation of zebrafish taste sensory organs

Taste buds are sensory organs in jawed vertebrates, composed of distinct cell types that detect and transduce specific taste qualities. Taste bud cells differentiate from oropharyngeal epithelial progenitors localized mainly in proximity of the forming organs. Despite recent progress in elucidating the molecular interactions required for taste bud cell development and function, the cell behaviour underlying the organ assembly is poorly defined. Here, we used time-lapse imaging to observe the formation of taste buds in live zebrafish larvae. We found that tg(fgf8a.dr17) expressing cells form taste buds and get rearranged within the forming organs. In addition, differentiating cells move from the epithelium to the forming organs and can be displaced between developing organs. During organ formation, taste bud tg(fgf8a.dr17) and Type-II cells are displaced in random, directed or confined mode relative to the taste bud they join or are maintained. Finally, ascl1a activity in the 5-HT/Type-III cell is required to direct and maintain tg(fgf8a.dr17) expressing cells into the taste bud. We propose diversity in displacement modes of differentiating cells as a key mechanism for the highly dynamic process of taste bud assembly.