A In wild type, photoreceptor neurons (ELAV, magenta) differentiate clustered around central R8 cells (SENSELESS, green). Arrowhead indicates column 0 within the morphogenetic furrow, anterior to the left. B. Reduced N function causes recruitment of additional neurons (ELAV, magenta). Not all label with the R8 marker Senseless(green). Many are associated with large clusters of R8 cells (arrows). Additional neurons are also recruited by ommatidia that contain single R8 cells, however (arrowhead). Such recruitment reflects N function after R8 cell patterns has been finalized in column 0. C. Ectopic non-R8 neurons are EGFR dependent. When egfr function is reduced in addition to N, the only extra neurons are R8's. D-F. Ectopic expression on N-DN does little to interfere with normal neurogenesis, or with ectopic neurogenesis in response to activated RasV12.