Circadian rhythm of DNA synthesis and mitotic activity in tongue keratinocytes.

ABSTRACT

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 inmunocytochemical 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 2000 h. Tongue samples were processed for histology and immuno-histochemistry. S and M indices were expressed as labelled nuclei or colchicine metaphases, respectively, per 1000 nuclei. Peak MI occurred at 1200, with the minimum value at 2000 on dorsal and ventral tongue surfaces. Peak S-phase was at 0400, whereas the minimum value was at 1600 for both surfaces. These results show that the proliferative activity of the tongue epithelium is of similar intensity and temporal distribution on both surfaces.