Fig. 1. Ommatidial rotation during PCP establishment in Drosophila eye. (A) Schematic presentation of ommatidial rotation in 3rd instar larval eye disc. Photoreceptors differentiate behind the morphogenetic furrow (MF, vertical yellow line). Five-cell preclusters are first organized in the AP axis. As photoreceptors become specified in the precluster, the group of cells simultaneously undergoes a 90° rotation towards the equator (horizontal yellow line). Green cells highlight R3/R4 precursors, and red marks future R1/R6 (stained with anti-Bar in C,D). (B) Tangential section of adult eye with ommatidia having completed 90° rotation (equator: yellow line). Right panel shows schematic presentation with dorsal and ventral chiral forms indicated with black and red arrows, respectively. (C,D) Larval eye disc with differentiating ommatidial preclusters posterior to MF, stained with neuronal marker Elav (blue; labeling all photoreceptor nuclei), Bar (red; R1and R6; also indicated in red in A) and Boss (green; labeling R8 in the center of the cluster). (C) Whole disc; (D) a higher magnification of a ventral area. White bars in D indicate the degree of rotation of the respective cluster. Anti-Bar-staining is detected from about a 30° angle to the posterior margin of disc, where all clusters acquire a 90° angle from their original position.