Circadian rhythm of DNA synthesis and mitotic activity in tongue keratinocytes

Tongue keratinocytes have a high mitotic index (MI) with an evident circadian variation. Our study set out to compare and contrast two phases of the cell cycle: DNA synthesis (S-phase), with immunocytochemical detection by bromodeoxyuridine (BrdU), and mitosis (M-phase), by the colchicine-arrest of metaphase method, exploring both the dorsal and ventral surfaces of the mouse tongue throughout a circadian period. Adult male mice standardized for light periodicity used for MI experiment were injected intraperitoneally with colchicine. Other animals were injected intraperitoneally with 5-BrdU for S-phase determination. Animals given both treatments were divided into six groups and killed at 4 h intervals until 20:00 h. Tongue samples were processed for hist ology and immune-histochemistry. S and M indices were expressed as labelled nuclei or colchicine metaphases, respectively, per 1000 nuclei. Peak MI occurred at 12:00, with the minimum value at 20:00 on dorsal and ventral tongue surfaces. Peak S-phase was at 04.00, whereas the minimum value was at 16:00 for both surfaces. These results show that the proliferative activity of the tongue epithelium is of similar intensity and temporal distribution on both surfaces. (C) 2001 Academic Press.