The effect of chalone on the cell cycle in the epidermis during wound healing

A cut was made on the ear conch of mouse and an extract containing epidermal chalone was injected subcutaneously 2 days later. The time changes after the chalone administration in the number of cells labeled with ³H-thymidine, in the number of grains on labeled cells and in the number of mitoses within the regenerating epidermis surrounding the wound were investigated by means of autoradiography (ARG). Grain counts decreased temporarily in early phase (0–2 h) after chalone injection. This decrease in grain count resulted in a decrease in the number of labeled cells on the ARG of a short exposure but not in that on the ARG of a long exposure. A decrease in the number of labeled cells on the ARG of a long exposure was evident at 6 h when the grain counts reverted to a level similar to the control without chalone. The number of mitoses reached a minimum at 2 h and then recovered quickly, indicating a rapid disappearance of the inhibition of cells in G 2 from entering M phase. Mitoses decreased again thereafter, presumably as a result caused by inhibition of cells in the preceding S phase from completing DNA synthesis. The extract made similarly from liver or kidney affected neither the mitotic nor the DNA synthetic activities.These results indicate that the epidermal chalone or chalones inhibit the epidermal cell proliferation in, at least, 3 different processes of the cell cycle; the DNA synthesis in S phase, the transition from G 1 to S phase and the transition from G 2 to M phase.