Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): E16.5 transgenic mouse embryo expressing the green fluorescent protein (GFP), used as a reporter, under the control of the keratin 17 (K17) gene promoter. GFP fluorescence distinctly occurs at future sites of epithelial appendages within developing skin, including hair and nail, correctly reflecting the regulation of endogenous K17. At right is a series of magnified views of the trunk surface from E12.5 to E16.5 transgenic embryos (top to bottom), illustrating the appearance of two successive waves of GFP-positive hair placodes within developing skin. (See related article on p. 7249.)