The Journal of investigative dermatology
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To anticipate daily environmental changes, most organisms developed endogenous timing systems, the so-called circadian (∼24 hours) clocks. Circadian clocks exist in most peripheral tissues and govern a huge variety of cellular, metabolic, and physiological processes. Recent studies have suggested daytime-dependent variations in epidermal functions such as barrier recovery and pH homeostasis. ⋯ Furthermore, temperature was identified to be a potent time cue (Zeitgeber) for the epidermal oscillator. Temperature cycles entrain HaCaT keratinocytes, leading to the identification of rhythmic expression of several genes involved in epidermal physiology such as cholesterol homeostasis and differentiation. Thus, we present HaCaT keratinocytes as an excellent model to study the regulation of keratinocyte physiology by the circadian clock in a simple yet robust in vitro system.