Perturbation of cell cycle progression in mouse epidermis prior to the regenerative response

Cell kinetic perturbations that resulted in a wave of increased cell division during the 6--8 hr lag period prior to regenerative DNA replication in mouse epidermis were examined. The epidermis was stimulated to proliferate by adhesive tape stripping, and flow cytometric DNA measurements of isolated epidermal basal cells, counting of mitoses, of Colcemid arrested metaphases and of labeled mitoses among basal cells in histologic sections were made. The results showed that mitotic peaks that occur in the pre-replicative period subsequent to tape stripping can be explained by a delay in cell progression through the S phase, followed by subsequent release and partial synchrony in further cell cycle progression. Early peaks of mitoses in epidermis stimulated to proliferate should therefore not, without further evidence, be assumed to originate from cells triggered into division from a resting G2 compartment. The results also indicate an initial delayed cell progression through the G2 phase, whereas the mitotic duration seemed to be initially reduced, indicating that the DNA synthesis phase and the G2 phase are parts of the epidermal cell cycle that may be most vulnerable to various types of influences.