BAS1: A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis.
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The Arabidopsis bas1-D mutation suppresses the long hypocotyl phenotype caused by mutations in the photoreceptor phytochrome B (phyB). The adult phenotype of bas1-D phyB-4 double mutants mimics that of brassinosteroid biosynthetic and response mutants. bas1-D phyB-4 has reduced levels of brassinosteroids and accumulates 26-hydroxybrassinolide in feeding experiments. The basis for the mutant phenotype is the enhanced expression of a cytochrome P450 (CYP72B1). bas1-D suppresses a phyB-null allele, but not a phyA-null mutation, and partially suppresses a cryptochrome-null mutation. Seedlings with reduced BAS1 expression are hyperresponsive to brassinosteroids in a light-dependent manner and display reduced sensitivity to light under a variety of conditions. Thus, BAS1 represents one of the control points between multiple photoreceptor systems and brassinosteroid signal transduction. (+info)
Parietal eye of the lizard: neuronal photoresponses and feedback from the pineal gland.
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The parietal eye of the lizard responds to illumination by sending afferent impulses to the pineal gland during daylight, the photophase. The pineal gland has efferently conducting neurons which are especially sensitive to norepinephrine and whose feedback to the parietal eye enhances its photo responsiveness. During the scotophase, at night, the eye generates afferent impulses to the cessation of light and the pineal efferents are most sensitive to serotonin. Thus, the photo-and chemoresponses of this system of interacting neurons are nearly reversed during the two phases of the daily photoperiod of the lizard. (+info)
Retinal asymmetry in birds.
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Vertebrate sensory systems are generally based on bilaterally symmetrical sense organs. It is evident, nevertheless, that birds preferentially use either their left or right eye for viewing novel or familiar stimuli [1], and perform visual discrimination tasks under monocular viewing conditions better with one eye than with the other [2] [3]. Because of the nearly complete contralateral decussation of the optic nerves in birds [4], it has been assumed that this division of labour is due solely to cerebral hemispheric specialisation, generated as a result of uneven photostimulation of the eyes of the developing embryo during the last three or four days before hatching [5] [6]. Here, however, we present evidence that in the European starling, Sturnus vulgaris, even the retinae are morphologically asymmetrical in terms of photoreceptor distribution. This is the first evidence for such asymmetry in any bird and suggests that retinal photoreceptor composition should be assessed during studies involving the lateralisation of visually mediated behaviours. (+info)
The use of adenovirus-mediated gene transfer to develop a rat model for photoreceptor degeneration.
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PURPOSE: To investigate the effects of recombinant adenovirus-mediated downregulation of cathepsin S (CatS) on the retinal pigment epithelium and/or neural retina in vivo. METHODS: The expression of green fluorescent protein (gfp) after subretinal injection of a recombinant adenovirus, Ad.gfp, into rat eyes was first established by in vivo fundus fluorescence photography and fluorescence microscopy. The autofluorescent debris accumulation in Ad.CatSAS (recombinant adenovirus carrying the antisense CatS gene)injected rat eyes was monitored by fluorescence microscopy, and the antisense CatS RNA expression was demonstrated by in situ hybridization. Changes in the retinal morphology were assessed by light microscopy. ResuLTS. The gfp expression was present in 30% to 90% of the injection area at 3 days and was absent 9 days after Ad.gfp injection. In Ad.CatSAS-injected eyes, the expression of antisense CatS RNA was demonstrated by in situ hybridization. Autofluorescent debris accumulation was significantly higher in Ad.CatSAS-injected eyes than in control eyes. The shortening of photoreceptor outer segments in Ad.CatSAS-injected eyes coincided with intense autofluorescent debris accumulation. The number of layers of photoreceptor cells decreased with time and were 11, 9, and 8 at 7, 14, and 28 days after Ad.CatSAS injection, respectively. In control eyes, the number of layers of photoreceptor cells (14) remained unchanged. CONCLUSIONS: These results demonstrate that recombinant adenovirus-mediated transient modulation of gene expression in retinal pigment epithelial (RPE) cells could induce changes in the retina, and, in spite of the low expression of endogenous CatS in RPE cells, this enzyme plays an important role in maintenance of normal retinal function. (+info)
Investigation of the organization of rhodopsin in the sheep photoreceptor membrane by using cross-linking reagents.
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The organization of rhodopsin in the photoreceptor membrane of sheep rod outer segments was investigated by using a variety of bifunctional reagents. Of the nine reagents used, seven gave oligomeric opsin species, whereas two, copper phenanthroline and dithiobisphenyl azide, failed to cross-link the protein. In general, the cross-linked species obtained showed diminishing yields from dimer to tetramer, together with some higher-molecular-weight aggregates. It is proposed that the patterns of cross-linking arise as a result of collision complexes and best describe a monomeric organization for native rhodopsin. No significant differences between the patterns obtained with dark-adapted bleached or regenerated protein states were observed. This interpretation is discussed in relation to the postulated mechanism of action of rhodopsin. (+info)
Photoreceptor pigment that induces differentiation in the slime mold Physarum polycephalum.
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An extract of small molecules (molecular weight less than 500) of the slime mold Physarum polycephalum undergoes a shift in ultraviolet-visible absorption spectrum upon illumination. This illumination also confers on the extract the ability to induce sporulation when injected into a starved, unilluminated slime mold. The spectral shift and appearance of the sporulation-inducing activity both occur regardless of whether the illumination is carried out on an intact slime mold or on the plasmodium-free extract itself. Thin-layer chromatography resolves the slime mold extract into four major visible fractions. One of these has high sporulation-inducing activity after illumination in vitro. (+info)
SPACRCAN, a novel human interphotoreceptor matrix hyaluronan-binding proteoglycan synthesized by photoreceptors and pinealocytes.
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The interphotoreceptor matrix is a unique extracellular complex occupying the interface between photoreceptors and the retinal pigment epithelium in the fundus of the eye. Because of the putative supportive role in photoreceptor maintenance, it is likely that constituent molecules play key roles in photoreceptor function and may be targets for inherited retinal disease. In this study we identify and characterize SPACRCAN, a novel chondroitin proteoglycan in this matrix. SPACRCAN was cloned from a human retinal cDNA library and the gene localized to chromosome 3q11.2. Analysis of SPACRCAN mRNA and protein revealed that SPACRCAN is expressed exclusively by photoreceptors and pinealocytes. SPACRCAN synthesized by photoreceptors is localized to the interphotoreceptor matrix where it surrounds both rods and cones. The functional protein contains 1160 amino acids with a large central mucin domain, three consensus sites for glycosaminoglycan attachment, two epidermal growth factor-like repeats, a putative hyaluronan-binding motif, and a potential transmembrane domain near the C-terminal. Lectin and Western blotting indicate an M(r) around 400,000 before and 230,000 after chondroitinase ABC digestion. Removal of N- and O-linked oligosaccharides reduces the M(r) to approximately 160,000, suggesting that approximately 60% of the mass of SPACRCAN is carbohydrate. Finally, we demonstrate that SPACRCAN binds hyaluronan and propose that associations between SPACRCAN and hyaluronan may be involved in organization of the insoluble interphotoreceptor matrix, particularly as SPACRCAN is the major proteoglycan present in this matrix. (+info)
Arabidopsis phytochromes C and E have different spectral characteristics from those of phytochromes A and B.
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The red/far-red light absorbing phytochromes play a major role as sensor proteins in photomorphogenesis of plants. In Arabidopsis the phytochromes belong to a small gene family of five members, phytochrome A (phyA) to E (phyE). Knowledge of the dynamic properties of the phytochrome molecules is the basis of phytochrome signal transduction research. Beside photoconversion and destruction, dark reversion is a molecular property of some phytochromes. A possible role of dark reversion is the termination of signal transduction. Since Arabidopsis is a model plant for biological and genetic research, we focussed on spectroscopic characterization of Arabidopsis phytochromes, expressed in yeast. For the first time, we were able to determine the relative absorption maxima and minima for a phytochrome C (phyC) as 661/725 nm and for a phyE as 670/724 nm. The spectral characteristics of phyC and E are strictly different from those of phyA and B. Furthermore, we show that both phyC and phyE apoprotein chromophore adducts undergo a strong dark reversion. Difference spectra, monitored with phycocyanobilin and phytochromobilin as the apoprotein's chromophore, and in vivo dark reversion of the Arabidopsis phytochrome apoprotein phycocyanobilin adducts are discussed with respect to their physiological function. (+info)