Issues

The cover photograph shows cross sections of three hair follicles reflecting the excessive growth of hair-follicle cells in mice lacking Patched1 (Ptch1) gene activity in cells of the outer layer of the skin (K14Cre:Ptch1^lox/lox mice). Cells in the outer layer of hair follicles always express keratin 14 protein (green), and only a small number of these cells normally express insulin-like growth factor binding protein 2 (IGFBP2; red). In Ptch1-null mice, however, all cells of the hair-follicle outer layer express IGFBP2; areas of overlapping expression of keratin 14 and IGFBP2 in these mice are shown in light yellow (nuclei are counterstained in blue). This increased expression of IGFBP2 is responsible for the excessive production of hair-follicle progenitor cells, which eventually leads to the development of basal cell carcinoma. See articles by Villani et al. (beginning on page 1222), Rudin and Peacock (beginning on page 1213), and Ivy (beginning on page 1217) for more information.