Fig. 4. Disruption of the retina upon depletion of Pros26.4 (A) Scanning-electron micrograph of a wild-type eye highlights the regular array of the ommatidia. (B) A tangential section through a wild-type eye reveals the crystalline-like structure of the retina. In each ommatidium, seven photoreceptor cells are discernible by the centrally located, darkly stained rhabdomeres. (C) Eye imaginal discs from wild-type third instar larvae contain few apoptotic cells as visualized by Acridine Orange staining (bright dots, examples are marked by arrows). (D) Depletion of Pros26.4 within the differentiating eye field by respective overexpression of the dsS4 construct (gmr-Gal4>UAS-dsS4) results in a graded fusion of the ommatidia from posterior (arrowhead) to anterior (left). (E) Underlying is a degeneration of retinula cells as seen in tangential sections of the eye. Whereas the ommatidial array is still visible at the anterior (left half, compare with B), the tissue is completely deranged at the posterior side and ommatidial structure is no longer discernible (arrowhead). (F) Larvae of the same genotype show a dramatic increase in cell death in their eye imaginal discs as visualized with Acridine Orange (bright dots, examples marked by arrows). (G) Only remnants of the head remain after knock-down of Pros26.4 within the developing eye (ey-Gal4>UAS-dsS4): parts of the antenna (an, 3rd antennal segment; ar, arista) are present and a fully developed labrum (lb) with pedipalpi (pd) that arise from different imaginal discs. (H) Cell death can be rescued to almost wild-type pattern by overexpressing baculoviral p35 protein in larval eye discs with reduced Pros26.4 activity (compare with C and F). Posterior is on the right side in all pictures except for G) which shows a frontal view.