Fig. 3. Persistence of segmental grooves is affected by dorsal closure. (A-D) Wild type and zipper mutants, which are defective in dorsal closure, at stage 15 and oriented such that the ventral midline is at the bottom. (A) Wild-type embryo stained with anti-Engrailed (black). (B) Wild-type embryo as seen by scanning electron microscopy (SEM). The ventral epidermis is almost flat (black arrow), whereas shallow grooves are still present laterally (white arrow). (C) Brightfield image of a zipper mutant embryo stained with anti-Engrailed (black). Note that grooves persist ventrally (black arrow). (D) Persistent ventral grooves can also be seen by SEM (black arrow). Moreover, lateral grooves appear deeper (white arrow) than in the wild type.