Publisher Summary Site-directed gene targeting in the mouse has led to marked advances in understanding the function played by gene products in mammalian development, as well as in adult homeostasis and pathophysiology. Terminally differentiated keratinocytes forming the cornified layer are lost daily from the surface of the skin and are replaced continuously by newly differentiating cells. Hair follicles that develop through a series of mesenchymal-epithelial interactions during embryogenesis are also dynamic structures that are mainly composed of keratinocytes and whose outer root sheath (ORS) is contiguous with the basal layer of the epidermis. The phenotypic analysis of mice in which a target gene is ablated in adult mouse skin can be investigated by macroscopic examination and histological analysis. The active form of tamoxifen, 4-hydroxytamoxifen, can also be administered, but as it is less soluble and more costly, but not more potent in the mouse, it is recommended to use tamoxifen, which is converted to 4-hydroxytamoxifen in the liver.
