Fig. 2. Fate of Notch1-activated cells in the epidermal lineages. (A,C) At E12.5, lacZ is first activated in the AER of the fore- and hind limb buds (A, arrows) and the epidermis between the dorsal and ventral surface (C, arrows). (B) Nuclear -VLLS staining demonstrating Notch1 activation in suprabasal nuclei of the epidermis at E12.5 (arrows). (D,E) N1::cre marks only supra-basal cells in the epidermis at E14.5 (D) and at E16.5 (E), where the majority of supra-basal cells in the skin are labeled, but most of the follicular epidermis remains negative. (F) In adult skin, staining was mostly absent in the epidermis; lacZ-labeled cells were present only in the differentiated cells of the hair follicle and the bulge (arrowhead, and high magnification inset). (G) Germ-line-deleted R26R mice label all keratinocytes. (H) Notch1 is not required for skin development because N1^-/-; Rosa26-lacZ^tg/+ cells efficiently contribute to all epidermal structures in adult mice. Dashed line (B-E) delineates epidermis and dermis. Magnification: A, 40x; B,C,D,E, 20x; F,G,H, 10x.