Effects of cyclic adenosine 3,5-monophosphate on photoreceptor disc shedding and retinomotor movement. Inhibition of rod shedding and stimulation of cone elongation.

As a test of the hypothesis that cyclic nucleotides play a role in the regulation of retinomotor movements and disc shedding in the photoreceptor-pigment epithelial complex, we have used an in vitro eyecup preparation that sustains both disc shedding and cone retinomotor movements, Eyecups were prepared in white light from animals in which both shedding and cone movement had been blocked by 4 d of constant-light treatment. In eyecups incubated for 3 h in light, disc shedding was negligible and cones remained in the light-adapted (contracted) position. In eyecups incubated in darkness, however, a massive shedding response (dominated by rod photoreceptors) was induced, and at the same time cone photoreceptors elongated to their dark-adapted position. In eyecups incubated in light dbcAMP promoted cone elongation and thus mimicked darkness; the dbcAMP effect was potentiated by the phosphodiesterase inhibitors papaverine and 3-isobutylmethylxanthine. In eyecups incubated in darkness, on the other hand, both phosphodiesterase inhibitors and dbcAMP reduced the phagosome content of the pigment epithelium. The effects of dbcAMP on the cone elongation and rod shedding appear to be specific in that dbcGMP, adenosine, and adenosine 5-monophosphate had no significant effect. Our results suggest that cAMP plays a role in the regulation of both retinomotor movements and disc shedding

Greasing the protein biosynthesis machinery of photoreceptor neurons: Role for postprenylation processing of proteins

Daily phagocytosis of outer segments (OS) places extraordinary demands on protein biosynthesis and trafficking in photoreceptor neurons. While the members and roles of the phototransduction pathway in the OS are well characterized, details about protein trafficking are just beginning to emerge. Phosphodiesterase6 (PDE6), the effector enzyme in phototransduction cascade, serves as an example of the steps multimeric proteins must pass through to achieve their functional state in the OS. Genetic model systems have recently provided snapshots of various steps in the pathway, as experimental difficulties such as an inability to maintain ciliated photoreceptor outer segments or express functional PDE6 holoenzyme in vitro necessitate in vivo studies. We will highlight the significant findings, their implications to blinding diseases, as well as discuss the gaps requiring further investigation

Interaction of retinitis pigmentosa GTPase regulator (RPGR) with RAB8A GTPase: implications for cilia dysfunction and photoreceptor degeneration

Defects in biogenesis or function(s) of primary cilia are associated with numerous inherited disorders (called ciliopathies) that may include retinal degeneration phenotype. The cilia-expressed gene RPGR (retinitis pigmentosa GTPase regulator) is mutated in patients with X-linked retinitis pigmentosa (XLRP) and encodes multiple protein isoforms with a common N-terminal domain homologous to regulator of chromosome condensation 1 (RCC1), a guanine nucleotide exchange factor (GEF) for Ran GTPase. RPGR interacts with several ciliopathy proteins, such as RPGRIP1L and CEP290; however, its physiological role in cilia-associated functions has not been delineated. Here, we report that RPGR interacts with the small GTPase RAB8A, which participates in cilia biogenesis and maintenance. We show that RPGR primarily associates with the GDP-bound form of RAB8A and stimulates GDP/GTP nucleotide exchange. Disease-causing mutations in RPGR diminish its interaction with RAB8A and reduce the GEF activity. Depletion of RPGR in hTERT-RPE1 cells interferes with ciliary localization of RAB8A and results in shorter primary cilia. Our data suggest that RPGR modulates intracellular localization and function of RAB8A. We propose that perturbation of RPGR–RAB8A interaction, at least in part, underlies the pathogenesis of photoreceptor degeneration in XLRP caused by RPGR mutations

Cryptochrome Genes Are Highly Expressed in the Ovary of the African Clawed Frog, Xenopus tropicalis

Cryptochromes (CRYs) are flavoproteins sharing high homology with photolyases. Some of them have function(s) including transcription regulation in the circadian clock oscillation, blue-light photoreception for resetting the clock phase, and light-dependent magnetoreception. Vertebrates retain multiple sets of CRY or CRY-related genes, but their functions are yet unclear especially in the lower vertebrates. Although CRYs and the other circadian clock components have been extensively studied in the higher vertebrates such as mice, only a few model species have been studied in the lower vertebrates. In this study, we identified two CRYs, XtCRY1 and XtCRY2 in Xenopus tropicalis, an excellent experimental model species. Examination of tissue specificity of their mRNA expression by real-time PCR analysis revealed that both the XtCRYs showed extremely high mRNA expression levels in the ovary. The mRNA levels in the ovary were about 28-fold (XtCry1) and 48-fold (XtCry2) higher than levels in the next abundant tissues, the retina and kidney, respectively. For the functional analysis of the XtCRYs, we cloned circadian positive regulator XtCLOCK and XtBMAL1, and found circadian enhancer E-box in the upstream of XtPer1 gene. XtCLOCK and XtBMAL1 exhibited strong transactivation from the XtPer1 E-box element, and both the XtCRYs inhibited the XtCLOCK:XtBMAL1-mediated transactivation, thereby suggesting this element to drive the circadian transcription. These results revealed a conserved main feedback loop in the X. tropicalis circadian clockwork and imply a possible physiological importance of CRYs in the ovarian functions such as synthesis of steroid hormones and/or control of estrus cycles via the transcription regulation

Rhodopsin Mutant P23H Destabilizes Rod Photoreceptor Disk Membranes

Mutations in rhodopsin cause retinitis pigmentosa in humans and retinal degeneration in a multitude of other animals. We utilized high-resolution live imaging of the large rod photoreceptors from transgenic frogs (Xenopus) to compare the properties of fluorescently tagged rhodopsin, Rho-EGFP, and RhoP23H-EGFP. The mutant was abnormally distributed both in the inner and outer segments (OS), accumulating in the OS to a concentration of ∼0.1% compared to endogenous opsin. RhoP23H-EGFP formed dense fluorescent foci, with concentrations of mutant protein up to ten times higher than other regions. Wild-type transgenic Rho-EGFP did not concentrate in OS foci when co-expressed in the same rod with RhoP23H-EGFP. Outer segment regions containing fluorescent foci were refractory to fluorescence recovery after photobleaching, while foci in the inner segment exhibited recovery kinetics similar to OS regions without foci and Rho-EGFP. The RhoP23H-EGFP foci were often in older, more distal OS disks. Electron micrographs of OS revealed abnormal disk membranes, with the regular disk bilayers broken into vesiculotubular structures. Furthermore, we observed similar OS disturbances in transgenic mice expressing RhoP23H, suggesting such structures are a general consequence of mutant expression. Together these results show that mutant opsin disrupts OS disks, destabilizing the outer segment possibly via the formation of aggregates. This may render rods susceptible to mechanical injury or compromise OS function, contributing to photoreceptor loss

Dysfunction of Heterotrimeric Kinesin-2 in Rod Photoreceptor Cells and the Role of Opsin Mislocalization in Rapid Cell Death

Loss of kinesin-2 function causes rapid death of rod photoreceptors. The cell death is dependent on the expression of opsin, which first accumulates along the route to the outer segment, but not on signaling by opsin-arrestin complexes or by light activation; the key element appears to be the accumulation of excessive protein in the wrong place

Light pollution: The possible consequences of excessive illumination on retina

Light is the visible part of the electromagnetic radiation within a range of 380-780 nm; (400-700 on primates retina). In vertebrates, the retina is adapted to capturing light photons and transmitting this information to other structures in the central nervous system. In mammals, light acts directly on the retina to fulfill two important roles: (1) the visual function through rod and cone photoreceptor cells and (2) non-image forming tasks, such as the synchronization of circadian rhythms to a 24 h solar cycle, pineal melatonin suppression and pupil light reflexes. However, the excess of illumination may cause retinal degeneration or accelerate genetic retinal diseases. In the last century human society has increased its exposure to artificial illumination, producing changes in the Light/Dark cycle, as well as in light wavelengths and intensities. Although, the consequences of unnatural illumination or light pollution have been underestimated by modern society in its way of life, light pollution may have a strong impact on people's health. The effects of artificial light sources could have direct consequences on retinal health. Constant exposure to different wavelengths and intensities of light promoted by light pollution may produce retinal degeneration as a consequence of photoreceptor or retinal pigment epithelium cells death. In this review we summarize the different mechanisms of retinal damage related to the light exposure, which generates light pollution.Fil: Contin, Maria Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Benedetto, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Quinteros Quintana, María Luz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Guido, Mario Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; Argentin

Rural waste generation: a geographical survey at local scale

"The paper examines the per capita waste generation rates from from rural areas of Neamț County (Romania) using thematic cartography. Geographical approach of this issue is difficult because the lack of a geostatistic database at commune scale. Spatial analysis of waste indicators reveals several disparities between localities. Comparability of data between communes located in various geographical conditions must be carrefully made according to local waste management systems. Several dysfunctionalities are outlined in order to compare these results, on the one hand, between localities and on the one hand, between recent years. Geographical analysis of waste generation rates is imperative for a proper monitoring of this sector. Data from 2009, 2010 and 2012 shows that rural waste management is in a full process of change towards a more organized, stable and efficient system." (author's abstract