About the cover: Cover is based on an image showing smooth muscle actin (red) and beta III tubulin (green) double immunohistochemical labelling of human lung epithelial tubule at week 10 of development. Smooth muscle is positioned immediately underneath the airway epithelium, encircling the tubule, with beta III tubulin-positive neuronal tissue located outside the smooth muscle layers. For more information, see article by Burns and colleagues beginning on page 269.