Figure 7.

Summary and a model for taste epithelial cell loss and regeneration following irradiation injury. In the first several days following irradiation, taste progenitors arrest the cell cycle (black and white boxes) and their contribution of new cells to taste buds is interrupted (blue box). During this time, the number of both type II (blue squares and circles) and type III (red triangles) cells trend downward, and are significantly reduced by day 7 following radiation. We propose that this loss is due to natural attrition of aged taste cells, which are not replaced by the mitotically arrested progenitor cells. As progenitors resume proliferation, new taste precursor cells enter buds, but these cells require an additional 3–5 d to differentiate (gray box), after which taste cell numbers recover to control values (pink box). Unexpectedly, a second wave of loss of type II taste cells only occurs at 21 dpi (black open circle), which may reflect synchronous, albeit naturally timed death of the cohort of type II cells generated by the burst of proliferative activity ∼14 d prior. The data from Figures 1 and 5 are shown as percentage of controls for this summary diagram.