Fig. 6. Following the caudal to rostral and deep to superficial development of the whisker pad vasculature (E), embryonic microvascular endothelial cells of the whisker pad only express the ß4 integrin subunit in the caudal and deep vasculature in the whisker pad from an E19.5 p.c. animal. Sections from the caudal region (A,B) are shown immunostained with s100 (green) and either MEC 13.3 to PECAM-1 (A: red) or with 346-11A to ß4 (B: red). Neighboring sections from a more rostral region are shown immunostained with MEC 13.3 to PECAM-1 (C) or 346-11A to ß4 (D). The majority of the vasculature was ß4 negative, however, some larger caliber vessels deeper in the tissue were ß4 positive (arrowheads). (E) Schematic representation of the whisker pad showing six whisker follicles along the caudal to rostral axis, where the filled arrowhead indicates a whisker and the open arrowhead indicates a hair follicle. Intense ß4 labeling is present on basal keratinocytes of the epidermis (e), hair follicles (f) and whisker follicles (wf). Scale bars: 100 µm.