Figure 4

Histological comparison of skin epidermis from Involucrin-c-MycER ^TAM transgenic mice following activation, inactivation, and reactivation of c-MycER ^TAM (c-Myc). Paraffin-embedded fixed sections of skin from Involucrin-c-MycER ^TAMmice were examined histologically by H&E staining. In the absence of 4-OHT (inactive c-Myc) the epidermis shows normal histology (Normal). Activation of c-Myc in skin treated topically with 4-OHT daily for 14 days induced hyperplasia, dysplasia and angiogenesis within papillomatous lesions (c-Myc on). Subsequent inactivation of c-Myc for 5 days following 4-OHT withdrawal led to redifferentiation of suprabasal keratinocytes as evidenced by the appearance of the granular cells and loss of dysplasia (c-Myc on-off). Reactivation of c-Myc for 5 days restored the papillomatous phenotype (c-Myc on-off-on). Scale bar: 100 μm