Drosophila Crumbs Is Required to Inhibit Light-Induced Photoreceptor Degeneration

Kevin Johnson, Ferdi Grawe, Nicola Grzeschik, Elisabeth Knust
2002 Current Biology  
Heinrich-Heine-Universitä t Dü sseldorf of Crumbs expression in the adult eye. Immunohistochemistry revealed that Crumbs protein is found in a Universitä tsstrasse 1 40225 Dü sseldorf circumferential stripe at the apical sides of the photoreceptor cells, bordering the ZA, which is visualized as a Germany circumferential belt by anti-Armadillo staining ( Figures 1A-1C) . Within the apical domain, Crumbs is localized to the apical stalk membrane, which connects the ZA Summary with the rhabdomeres
more » ... ( Figure 1E ; also see Figure 2G for the demonstration of the stalk membrane). The rhab-Mutations in the human transmembrane protein CRB1 domeres are also apical derivatives containing highly are associated with severe forms of retinal dystrophy, pleated stacks of microvilli, rich in F-actin, that carry retinitis pigmentosa 12 (RP12), and Leber's congenital the photosensitive pigment rhodopsin and the photoamaurosis (LCA) [1-3]. The Drosophila homolog, transduction complexes. crumbs, is required for polarity and adhesion in embryonic epithelia [4-6] and for correct formation of adherens junctions and proper morphogenesis of photo-Loss of crb in the Eye Leads to Gradual, receptor cells [7, 8]. Here, we show that mutations in Light-Induced Retinal Degeneration Drosophila crumbs result in progressive, light-induced Since, in Drosophila, hereditary retinal degenerations retinal degeneration. Degeneration is prevented by exare light dependent in several cases [12], we analyzed pression of p35, an inhibitor of apoptosis, or by reducmosaic eyes containing large crb mutant clones of flies tion of rhodopsin levels through a vitamin A-deficient kept under constant illumination. The Drosophila eye is diet. In the dark, rhabdomeres survive but exhibit morcomposed of about 800 ommatidia, cylindrical, barrelphogenetic defects. We demonstrate that it is the exlike structures, containing eight photoreceptor cells in tracellular portion of the Crumbs protein that is essentheir center that are arranged in a stereotypic manner tial to suppress light-induced programmed cell death, (Figures 2A, 2E, and 2G). When flies carrying crb 11A22 while proper morphogenesis depends on the intracelmosaic eyes are kept in constant light for 7 days, the lular part. We conclude that human and Drosophila retina shows massive degeneration (Figure 2B). This Crumbs proteins are functionally conserved to prevent phenotype strictly depends on continous exposure to light-dependent photoreceptor degeneration. This exlight, since, in flies kept under standard laboratory conperimental system is now ideally suited to study the ditions, i.e., in artificial low light, no degeneration of genetic and molecular basis of RP12-and LCA-related photoreceptors occurred. crb mosaic flies raised under retinal degeneration. these conditions show a slightly variable, mutant phenotype. Their rhabdomeres are thicker and shorter com-Results and Discussion pared to wild-type and are often found in close contact with other rhabdomeres of the same ommatidium (Fig-Drosophila embryos mutant for crumbs (crb) fail to mainures 2C, 2F, and 2H). Serial cross-sections (Figures 2C tain a proper zonula adherens (ZA), a belt-like adhesive and 2D) and horizontal sections stained with FITC-phalstructure encircling the apex of epithelial cells [9, 10]. loidin, which highlights the F-actin bundles of the rhab-As a consequence, cells lose contact with each other domeres (Figure 1D), reveal that the rhabdomeres fail and undergo programmed cell death (PCD) in several to reach the basal lamina and extend from the distal epithelia. The human homolog CRB1 displays a similar pole near the lens to only about one third of the normal overall organization to the Drosophila protein [1], and length. In addition, the stalk membrane is reduced in its cytoplasmic tail can functionally substitute for the fly length (Figures 2F and 2H). However, the tightly stacked protein in the Drosophila embryo [11]. Mutations in "semicristalline" internal structure of the rhabdomere is CRB1 are associated with progressive degeneration of unaffected. The catacomb-like rhabdomere base [13] is the retina in patients suffering from RP12 or LCA [1-3]. also unaffected in mutant photoreceptor cells. In many RP12 is characterized by an early onset of retinal degenommatidia, ZAs are visible in the distal regions of the eration and the loss of vision in patients before the age cells ( Figures 2F and 2H) . Control of morphogenesis of 20 years, while LCA, the earliest and most severe seems to be cell autonomous, since ommatidia comform of retinal dystrophy, causes blindness at birth or posed of wild-type and mutant cells only exhibit defects during the first months of life. This connection of strucin the mutant cells (Figures 1F and 2C ). tural and functional preservation prompted us to assay To analyze the temporal course of degeneration, eyes crumbs mosaic eyes for any phenotype relating to retinal carrying mutant clones were sectioned at different time degeneration. points after light exposure. Eyes kept for only 1 day in constant illumination do not show any sign of photoreceptor degeneration but only exhibit the morphoge-
doi:10.1016/s0960-9822(02)01180-6 pmid:12361571 fatcat:to7thfth5zhblirzf2yuz2poge