The mouse tongue possesses three types of gustatory papillae: large circumvallate papillae (CVP), foliate papillae (FOP) and fungiform papillae (FFP). Although CVP is the largest papilla and contain a high density of taste buds, little is known about CVP development. Their transition from placode to dome-shape is particularly ambiguous. Understanding this phase is crucial since dome-shaped morphology is essential for proper localization of the imminent nerve fibers and taste buds. Here, we report actomyosin-dependent apical and basal constriction of epithelial cells during dynamic epithelial folding. Furthermore, actomyosin-dependent basal constriction requires focal adhesion kinase to guide dome-shape formation. Sonic hedgehog (Shh) is closely associated with the differentiation or survival of the neurons in CVP ganglion and cytoskeletal alteration in trench epithelial cells which regulate CVP morphogenesis. Our results demonstrate the CVP morphogenesis mechanism from placode to dome-shape by actomyosin-dependent cell shape change and suggest roles that Shh may play in trench and stromal core formation during CVP development.

Taste stem/progenitor cells from posterior mouse tongues have been used to generate taste bud organoids. However, the inaccessible location of taste receptor cells is observed in conventional organoids. In this study, we established a suspension-culture method to fine-tune taste bud organoids by apicobasal polarity alteration to form the accessible localization of taste receptor cells. Compared to conventional Matrigel-embedded organoids, suspension-cultured organoids showed comparable differentiation and renewal rates to those of taste buds in vivo and exhibited functional taste receptor cells and cycling progenitor cells. Accessible taste receptor cells enabled the direct application of calcium imaging to evaluate the taste response. Moreover, suspension-cultured organoids can be genetically altered. Suspension-cultured taste bud organoids harmoniously integrated with the recipient lingual epithelium, maintaining the taste receptor cells and gustatory innervation capacity. We propose that suspension-cultured organoids may provide an efficient model for taste research, including taste bud development, regeneration, and transplantation. Supplementary Information The online version contains supplementary material available at 10.1007/s00018-022-04242-0.

Taste receptor cells are taste bud epithelial cells that are dependent upon the innervating nerve for continuous renewal and are maintained by resident tissue stem/progenitor cells. Transection of the innervating nerve causes degeneration of taste buds and taste receptor cells. However, a subset of the taste receptor cells is maintained without nerve contact after glossopharyngeal nerve transection in the circumvallate papilla in adult mice. Here, we revealed that injury caused by glossopharyngeal nerve transection triggers the remaining differentiated K8-positive taste receptor cells to dedifferentiate and acquire transient progenitor cell-like states during regeneration. Dedifferentiated taste receptor cells proliferate, express progenitor cell markers (K14, Sox2, PCNA) and form organoids in vitro. These data indicate that differentiated taste receptor cells can enter the cell cycle, acquire stemness, and participate in taste bud regeneration. We propose that dedifferentiated taste receptor cells in combination with stem/progenitor cells enhance the regeneration of taste buds following nerve injury.

Tissue regeneration after injury involves the dedifferentiation of somatic cells, a natural adaptive reprogramming process that leads to the emergence of injury-responsive cells with fetal-like characteristics in the intestinal epithelium. However, there is no direct evidence that adaptive reprogramming involves a shared molecular mechanism with direct cellular reprogramming. Here, we induced dedifferentiation of intestinal epithelial cells through forced partial reprogramming in vivo using Yamanaka factors (Oct4, Sox2, Klf4, and c-Myc: OSKM). The OSKM-induced dedifferentiation showed similar molecular features of intestinal regeneration, including a rapid transition from homeostatic cell types to injury-responsive-like cell types. These injury-responsive-like cells, sharing a gene signature of revival stem cells and atrophy-induced villus epithelial cells, actively assisted tissue regeneration following ionizing radiation-induced acute tissue damage. In contrast to normal intestinal regeneration, which involves epi-mesenchymal crosstalk through induction of Ptgs2 (encoding Cox2) upon injury, the OSKM expression promotes the autonomous production of prostaglandin E2 via epithelial Ptgs1 (encoding Cox1) expression. These results indicate that prostaglandin synthesis is a common mechanism for intestine epithelial regeneration, but involves a different enzyme (Ptgs1 for Cox1) when partial reprogramming is directly applied to the intestinal epithelium.

Background: Taste buds are a complex organ and require a plethora of growth factors for their development, homeostasis, and regeneration. Taste bud organoids provide a platform for understanding their development, disease and regeneration.Methods: In this study, we focused on identifying the localization of receptors involved during taste bud development in taste bud organoids, either in an extracellular matrix scaffold (Matrigel) or in the absence of a scaffold with suspension culture.Results: Compared to Matrigel-cultured organoids, suspension organoids showed stable expression of nerve growth factor receptor (NGFR) cells, which are important for innervation. Transporters for glucose metabolism, such as GLUT1, GLUT2, and the insulin receptor (IGF1R), were observed in suspension-cultured organoids. Furthermore, immunostaining for downstream phosphorylated signaling molecules indicated that the NGFR and IGFR pathways were functional and active in the organoids.Conclusion: Based on these results, suspension-cultured organoids may provide an efficient model for mimicking in vivo taste buds compared to conventional Matrigel organoids.