Mash1-expressing cells could differentiate to type III cells in adult mouse taste buds.

The gustatory cells in taste buds have been identified as paraneuronal; they possess characteristics of both neuronal and epithelial cells. Like neurons, they form synapses, store and release transmitters, and are capable of generating an action potential. Like epithelial cells, taste cells have a limited life span and are regularly replaced throughout life. However, little is known about the molecular mechanisms that regulate taste cell genesis and differentiation. In the present study, to begin to understand these mechanisms, we investigated the role of Mash1-positive cells in regulating adult taste bud cell differentiation through the loss of Mash1-positive cells using the Cre-loxP system. We found that the cells expressing type III cell markers-aromatic L-amino acid decarboxylase (AADC), carbonic anhydrase 4 (CA4), glutamate decarboxylase 67 (GAD67), neural cell adhesion molecule (NCAM), and synaptosomal-associated protein 25 (SNAP25)-were significantly reduced in the circumvallate taste buds after the administration of tamoxifen. However, gustducin and phospholipase C beta2 (PLC beta2)-markers of type II taste bud cells-were not significantly changed in the circumvallate taste buds after the administration of tamoxifen. These results suggest that Mash1-positive cells could be differentiated to type III cells, not type II cells in the taste buds.