Closing Time: In this micrograph of dorsal closure in a fruit-fly embryo, the protein actin is marked red, prominent around the gap in the epithelial cells. The microtubules that give shape to cells are green, and epithelial cells with their microtubules destroyed are blue. Damian Brunner
One of the steps in fruit-fly development is similar to the healing of wounds. Until recently, scientists believed that when fruit-fly bodies take form during a process called dorsal closure, long strings of the protein actin behaved like the drawstring of a purse, pulling together the epithelial cells that eventually form the fly’s skin.