[Development and cell dynamics of PLCbeta2 positive cells in mouse taste buds]

Taste buds, the sensory end organs for the sense of taste, consist of taste sensing cells, supportive cells and basel cells. Taste bud cells are heterogeneous in terms of morphology as well as functional profiles. Although the lineage of mammalian taste bud cells is largely unknown, it is generally accepted that undifferentiated epithelial basal cells surrounding taste buds enter the taste buds to form and maintain this specialized corpuscle. To analyze taste bud formation during development, we conducted morphological observations and examined differentiation marker expression. Thickening of epithelia starts at 13 dpc foetus and immunohistochemistry against a neural marker, PGP 9.5, revealed that the change of epithelial morphology precedes neural projection observed at 14 dpc foetus. Taste sensing cells appear 6 days after birth indicated by expression of the single transduction component phospholipase Cbeta2 (PLCbeta2) as differentiation marker. To further investigate the maintenance and cell lineage in the taste buds in adults, we injected 5'bromo-2'deoxyuridine (BrdU) solution to young growing mice for a week. BrdU label retaining cells (LRCs) could be observed even 8 weeks after injection. LRCs were examined the differentiation by PLCbeta2 and proliferative activity by Ki-67. The results suggested two possibilities. (1) Part of PLCbeta2 positive cells retain proliferative activity and multipotentiality, or (2) precursor cells (stem cells) stay in the taste buds and produce at least part of the taste sensing cells through proliferation and differentiation processes.