On the Non-Random Distribution of Dividing Cells

Abstract

The interpretation of results from experiments involving the measurement of the uptake of labelled thymidine in organ cultured skin is difficult since the tissue studied is not homogeneous. Results have been expressed in terms of dry weight, wet weight, surface area, protein content and DNA content. Ideally one would like to know the exact number of cells in the basal layer of the epidermis, but there is no suitable method yet available for such determination. In an attempt to reduce the variability of the results of measurement of changes in the rate of DNA synthesis in response to experimental manipulation, the following strategy was adopted. Explants of skin were cultured in the presence of ¹⁴C-thymidine for 5 h, washed, incubated in the presence of the test substances for periods up to 30 h and then incubated in the presence of ³H-thymidine for the final 5 h of culture [6]. The effect of the test substance on the ratio of ³H: ¹⁴C-thymidine could then be compared to the ratio obtained from comparable control cultures. In this way it was hoped that the uncertainty in the measurements of the dividing cell population could be eliminated.