Using an asynchronously growing cell population, we investigated how X-irradiation at different stages of the cell cycle influences individual cell–based kinetics. To visualize the cell-cycle phase, we employed the fluorescent ubiquitination-based cell cycle indicator (Fucci). After 5 Gy irradiation, HeLa cells no longer entered M phase in an order determined by their previous stage of the cell cycle, primarily because green phase (S and G2) was less prolonged in cells irradiated during the red phase (G1) than in those irradiated during the green phase. Furthermore, prolongation of the green phase in cells irradiated during the red phase gradually increased as the irradiation timing approached late G1 phase. The results revealed that endoreduplication rarely occurs in this cell line under the conditions we studied. We next established a method for classifying the green phase into early S, mid S, late S, and G2 phases at the time of irradiation, and then attempted to estimate the duration of G2 arrest based on certain assumptions. The value was the largest when cells were irradiated in mid or late S phase and the smallest when they were irradiated in G1 phase. In this study, by closely following individual cells irradiated at different cell-cycle phases, we revealed for the first time the unique cell-cycle kinetics in HeLa cells that follow irradiation.

Necrotizing sialometaplasia is a rare lesion that mimics malignant neoplasm, which is characterized by salivary gland metaplasia, necrosis, and inflammation. We present a case of necrotizing sialometaplasia that presented as an ugly ulcer at the junction of the soft and hard palates; the lesion was clinically suspected to be a malignant lesion. A 62‐year‐old man was referred to our department with a complaint of severe pain during swallowing. A crater‐like ulcer lesion was observed extending from the maxillary tuberosity to the soft palate. Histopathological diagnosis of necrotizing sialometaplasia was confirmed on biopsy. This lesion was spontaneously relieved.