ROTATION OF PHOTORECEPTOR CLUSTERS IN THE DEVELOPING DROSOPHILA EYE REQUIRES THE NEMO GENE

The Drosophila eye consists of a reiterative hexagonal array of photor eceptor cell clusters, the ommatidia. During normal morphogenesis, the clusters in the dorsal or ventral halves of the disc rotate 90 degree s in opposite directions, forming mirror images across a dorsoventral equator. In the mutant nemo (nmo), there is an initial turning of appr oximately 45 degrees, but further rotation is blocked. Genetic mosaic analysis indicates that the nmo gene acts upon each cluster as a whole ; normal nmo function in one or more photoreceptor cells appears to be sufficient to induce full rotation. The nmo gene sequence encodes a s erine/threonine protein kinase homolog, suggesting that the kinase is required to initiate the second step of rotation. In another mutant, r oulette, excessive rotation through varying angles occurs in many omma tidia. This defect is suppressed by nmo, indicating that nmo acts upst ream in a rotation-regulating pathway.