The development of methods and tools suitable for functional analysis of keratinocytes placed in an in vitro context is of
great importance for characterizing properties associated with their normal state, for detecting abnormalities related to
pathological states, or for studying the effects of extrinsic factors. In the present chapter, we describe the use of the
intracellular fluorescent dye carboxyfluorescein succinimidyl ester (CFSE) to monitor cell division in mass cultures of normal
human keratinocytes. We detail the preparation of CFSE-labeled keratinocyte samples and the identification by flow cytometry
of cell subpopulations exhibiting different cycling rates in a mitogenic culture context. In addition, we show that the CFSE-based
division-tracking approach enables the monitoring of keratinocyte responsiveness to growth modulators, which is here exemplified
by the cell-cycling inhibition mediated by the growth factor TGF-β1. Finally, we show that keratinocyte subpopulations, separated
according to their mitotic history using CFSE fluorescence tracking, can be sorted by flow cytometry and used for further
functional characterization, including determination of clone-forming efficiency.