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  • Opsin-like immunoreactivity in the circadian pacemaker neurons and photoreceptors of the eye of the opisthobranch mollusc Bulla gouldiana.

    27 November 2018

    Circadian pacemaker cells in the eyes of the opisthobranch mollusc Bulla gouldiana generate a near 24-h rhythm in the frequency of optic nerve impulses. Previous electrophysiological studies suggest that these basal retinal neurons are intrinsically photosensitive and transduce light signals that shift the phase of their pacemaker mechanism. To test whether the pacemaker neurons contain opsin-like proteins, several polyclonal antibodies that recognize opsins of vertebrate photoreceptors have been tested on histological sections of the eye and on the neurons in primary cell culture. The antibodies label both the pacemaker cells and the large distal photoreceptors that surround the lens. Immunoblot analyses of the proteins of the eye have identified a single band at 62+/-4 kDa. These opsin antibodies may label the photopigment used in the entrainment of the circadian pacemaker.

  • The regulation of circadian clocks by light in fruitflies and mice.

    27 November 2018

    A circadian clock has no survival value unless biological time is adjusted (entrained) to local time and, for most organisms, the profound changes in the light environment provide the local time signal (zeitgeber). Over 24 h, the amount of light, its spectral composition and its direction change in a systematic way. In theory, all of these features could be used for entrainment, but each would be subject to considerable variation or 'noise'. Despite this high degree of environmental noise, entrained organisms show remarkable precision in their daily activities. Thus, the photosensory task of entrainment is likely to be very complex, but fundamentally similar for all organisms. To test this hypothesis we compare the photoreceptors that mediate entrainment in both flies and mice, and assess their degree of convergence. Although superficially different, both organisms use specialized (employing novel photopigments) and complex (using multiple photopigments) photoreceptor mechanisms. We conclude that this multiplicity of photic inputs, in highly divergent organisms, must relate to the complex sensory task of using light as a zeitgeber.

  • Circadian rhythms: Something to cry about?

    27 November 2018

    Recent studies suggest that a class of proteins known as cryptochromes have an evolutionarily conserved role in the entrainment of circadian rhythms to the night-day cycle. While the evidence reported is intriguing, the notion that cryptochromes have the same role in all species requires further investigation.

  • A novel rod-like opsin isolated from the extra-retinal photoreceptors of teleost fish.

    27 November 2018

    We have isolated a novel opsin from the pineal complex of Atlantic salmon (Salmo salar) and from the brain of the puffer fish (Fugu rubripes). These extra-retinal opsins share approximately 74% identity at the nucleotide and amino acid level with rod-opsins from the retina of these species. By PCR, we have determined that the novel rod-like opsin is not expressed in the salmon retina, and the retinal rod-opsin is not expressed in the salmon pineal. Phylogenetic analysis suggests that the rod-like opsins arose from a gene duplication event approximately 205 million years ago, a time of considerable adaptive radiation of the bony fish. In view of the large differences in the coding sequences of the pineal/brain rod-like opsins, their extra-retinal sites of expression, and phylogenetic position we have termed these novel opsins 'extra-retinal rod-like opsins' (ERrod-like opsins). We speculate that the differences between retinal rod-opsins and ERrod-like opsins have arisen from their differing photosensory roles and/or genetic drift after the gene duplication event in the Triassic.

  • The persistence of cone photoreceptors within the dorsal retina of aged retinally degenerate mice (rd/rd): implications for circadian organization.

    27 November 2018

    Rod- and cone-opsin specific antibodies were used in an attempt to immunolabel remaining photoreceptor cells in the mutant rd (retinal degeneration) mouse retina. We identified a region-specific distribution in the pattern of photoreceptor degeneration, with the dorsal retina showing markedly less photoreceptor degeneration than the ventral retina. All rod and cone immunoreactive cells disappeared in the ventral retina by 100-120 days of age. By contrast, both cone and a small number of rod immunopositive cells were identified in the dorsal retina at this time. By 200 days all rod immunoreactive cells had disappeared. At 360 days numerous cone immunoreactive cells remained within a restricted region of the dorsal retina. As rd mice show unattenuated circadian responses to light, these remaining photoreceptor cells within the dorsal retina become candidates for the regulation of circadian physiology by light.

  • In silico characterisation and chromosomal localisation of human RRH (peropsin)--implications for opsin evolution.

    27 November 2018

    BACKGROUND: The vertebrate opsins are proteins which utilise a retinaldehyde chromophore in their photosensory or photoisomerase roles in the visual/irradiance detection cycle. The majority of the opsins, such as rod and cone opsins, have a very highly conserved gene structure suggesting a common lineage. Exceptions to this are RGR-opsin and melanopsin, whose genes have very different intron insertion positions. The gene structure of another opsin, peropsin (retinal pigment epithelium-derived rhodopsin homologue, RRH) is unknown. RESULTS: By in silico analysis of the GenBank database we have determined that the human RRH comprises 7 exons spanning approximately 16.5 kb and is localised to chromosome 4q25 in the following gene sequence: cen-EGF-RRH-IF-qter - a position that excludes this gene as a candidate for the RP29 autosomal recessive retinitis pigmentosa locus. A comparison of opsin gene structures reveals that RRH and RGR share two common intron (introns 1 and 4) insertion positions which may reflect a shared ancestral gene. CONCLUSION: The opsins comprise a diverse group of genes which appear to have arisen from three different lineages. These lineages comprise the "classical opsin superfamily" which includes the rod and cone opsins, pinopsin, VA-opsin, parapinopsin and encephalopsin; the RRH and RGR group; and the melanopsin line. A common lineage for RRH and RGR, together with their sites of expression in the RPE, indicates that peropsin may act as a retinal isomerase.

  • Transplanted suprachiasmatic nucleus determines circadian period.

    27 November 2018

    The pacemaker role of the suprachiasmatic nucleus in a mammalian circadian system was tested by neural transplantation by using a mutant strain of hamster that shows a short circadian period. Small neural grafts from the suprachiasmatic region restored circadian rhythms to arrhythmic animals whose own nucleus had been ablated. The restored rhythms always exhibited the period of the donor genotype regardless of the direction of the transplant or genotype of the host. The basic period of the overt circadian rhythm therefore is determined by cells of the suprachiasmatic region.

  • Annual rhythms that underlie phenology: biological time-keeping meets environmental change.

    27 November 2018

    Seasonal recurrence of biological processes (phenology) and its relationship to environmental change is recognized as being of key scientific and public concern, but its current study largely overlooks the extent to which phenology is based on biological time-keeping mechanisms. We highlight the relevance of physiological and neurobiological regulation for organisms' responsiveness to environmental conditions. Focusing on avian and mammalian examples, we describe circannual rhythmicity of reproduction, migration and hibernation, and address responses of animals to photic and thermal conditions. Climate change and urbanization are used as urgent examples of anthropogenic influences that put biological timing systems under pressure. We furthermore propose that consideration of Homo sapiens as principally a 'seasonal animal' can inspire new perspectives for understanding medical and psychological problems.

  • Opsins and melanopsins.

    27 November 2018

  • Best daze of your life

    27 November 2018