Measurement of S phase duration in human epidermis using cyclin immunostaining and 3H-thymidine pulse labelling

Cyclin/PCNA (proliferating cell nuclear antigen) is a nuclear protein strongly associated with DNA replication sites. Under methanol fixation, cyclin immunostaining might serve as a specific marker for S-phase cells. Associated with single labelling with 3H-thymidine, this immunodetection represents an easy method for measuring S-phase duration. Its application to six samples of normal human epidermis allowed us to measure an S phase of 9.7 +/- 0.3 h, a result in fair agreement with a previous estimate of 10.2 h obtained from a classical double-labelling technique with two different concentrations of 3H-thymidine.