Epidermal DNA synthesis in organ culture explants. A study of hairless mouse ear epidermis.

Explants of split mouse ear were incubated in organ culture for up to 48 h, and the cell proliferation was studied by the addition of Thymidine-methyl-3-H (3HTdR) to the medium during different time periods, mainly for the first 14 h of incubation. Cultures were started at 0900, 2130 and 2300. In all cases the labelling index remained stable for 6-8 h, and then increased. The mean grain count, however, was falling and so was the epidermal DNA-specific uptake of 3HTdR. Based on the experimental results, calculations can be made of the flux of cells through S. It is concluded that the increasing LI is not due to inherent diurnal variation in cell proliferation, and is not a sign of real growth but caused instead by a complete block of the cell exit from S, probably combined with periods of an increased entrance rate into S. Other methodological factors, however, may also contribute to the increasing LI. Hence, this system is not suited for the measurement of factors that influence epidermal DNA synthesis.