title: Carotenoid replacement in Drosophila: freeze-fracture electron microscopy.
abstract: Because of the consequent lack of photopigment chromophore, carotenoid/ retinoid (vitamin A) deprivation during the larval period of Drosophila leads to decreased rhodopsin in adult photoreceptors. Decreased density of P-face particles in photoreceptor membrane (rhabdomeric microvilli) is a prominent ultrastructural feature of this rhodopsin deficiency. When adults are fed carotenoid, the rhabdomeric P-face particle density-which reflects the concentration of rhodopsin-increases halfway to the replete control level during the first 12 hours, and is fully restored by 2 days. Based on freeze-fracture replicas, there is a continuity of membrane between rhabdomeric microvilli and the parent retinula cell. That confluence is relevant to turnover of photoreceptive membrane. Microvillar and retinula cell P-face particle densities covary. The relevance of the demonstration of rapid recovery from chromophore depletion is discussed in relation to hypotheses that the chromophore and/or related retinoids regulate opsin gene transcription, and/or post-translational processing and deployment from the endoplasmic reticulum to the rhabdomere.
authors.affiliation: Department of Biology, Saint Louis University, MO 63103-2010, USA.
authors.forename: W S
authors.initials: WS
authors.lastname: Stark
authors.forename: R H
authors.initials: RH
authors.lastname: White
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000494:pharmacology*; D004331:Drosophila melanogaster; D005614:Freeze Fracturing / Q000379:methods; D007814:Larva; D008854:Microscopy, Electron / Q000379:methods; D008871:Microvilli / Q000187:drug effects / Q000648:ultrastructure; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D012176:Retinoids / Q000494:pharmacology; D012243:Rhodopsin / Q000378:metabolism
chemical_list: D012176:Retinoids; D002338:Carotenoids; D012243:Rhodopsin