A scanning electron-microscopic study of apical contacts in the eye during postembryonic development of Drosophila melanogaster.

The apical surface of the ommatidium plays a major role during development of the compound eye. Cell-cell contacts leading to induction seem to be initiated at this surface. The pupal eye of Drosophila was examined, using scanning electron microscopy, from a few hours after eversion of the imaginal disc (19 h after pupariation, 25 degrees C) until shortly after the onset of the corneal secretion (46 h after pupariation, 25 degrees C). At 19 h, the primary pigment cells are in the process of encircling the cone cells. At this time, tufts formed by the cone cell microvilli are the most prominent feature of the eye's surface. Shortly thereafter, the interommatidial cells become more prominent. Their surfaces are raised to form ridges that enclose primary pigment cells and cone cells. From 21 h onwards and lasting for 5-6 h, the interommatidial cells form slim cytoplasmic extensions that spread over the surfaces of the surrounding cells. These extensions contact neighbouring interommatidial or primary pigment cells, but also non-adjacent cells such as cone cells. The fates of these interommatidial cells presumably are determined during that time. The cell-cell interactions may play a role in determining cell fates, for example by providing positional information.