Low-level expression of KLF4 induces epithelial turnover without overt hyperplasia. Transgenic animals carrying the reverse tetracycline-responsive transcriptional activator (rtTA) under control of the MMTV promoter (i.e., MMTV-rtTA) were crossed with tetracycline response element (TRE)-KLF4 transgenic mice, and bitransgenic offspring were induced with dox (upper panels). Paraffin sections of skin were analyzed by immunostaining. Control animals were administered sucrose-water without dox. As an additional control, animals expressing KLF4 under control of a K14-rtTA transgene were induced and analyzed in parallel (lower panels). Closed arrows indicate the DEJ, and open arrows indicate follicle epithelium. Scale bars, 50μ.