Isolation of embryonic hair follicle progenitors. (A) P-cadherin is up-regulated at sites of hair follicle morphogenesis. This differential expression was used to isolate PCAD+ hair progenitors and PCAD− interfollicular basal cells by FACS (figs. S2 and S3). Scale bar, 40 μm. (B) Summary of cytospin analyses for epidermal markers K1, K5, and β4-integrin. (C) The differential activity of the Wnt reporter gene TOPGAL was assessed by chemiluminescence. β-gal, β-galactosidase; WT, wild type. (D) Semi-quantitative RT-PCR shows differential expression of known placode mRNAs. K5 and K14 are known to be down-regulated, but still expressed, in hair germs (15). Abbreviations are as follows: epi, epidermis; der, dermis; Pc, hair placode; HG, hair germ; HF, hair follicle; β4, β4-integrin.