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Neurobiology: bright blue times.

27 November 2018

Regulation of mammalian circadian behavior by non-rod, non-cone, ocular photoreceptors.

27 November 2018

Circadian rhythms of mammals are entrained by light to follow the daily solar cycle (photoentrainment). To determine whether retinal rods and cones are required for this response, the effects of light on the regulation of circadian wheel-running behavior were examined in mice lacking these photoreceptors. Mice without cones (cl) or without both rods and cones (rdta/cl) showed unattenuated phase-shifting responses to light. Removal of the eyes abolishes this behavior. Thus, neither rods nor cones are required for photoentrainment, and the murine eye contains additional photoreceptors that regulate the circadian clock.

Regulation of the mammalian pineal by non-rod, non-cone, ocular photoreceptors.

27 November 2018

In mammals, ocular photoreceptors mediate an acute inhibition of pineal melatonin by light. The effect of rod and cone loss on this response was assessed by combining the rd mutation with a transgenic ablation of cones (cl) to produce mice lacking both photoreceptor classes. Despite the loss of all known retinal photoreceptors, rd/rd cl mice showed normal suppression of pineal melatonin in response to monochromatic light of wavelength 509 nanometers. These data indicate that mammals have additional ocular photoreceptors that they use in the regulation of temporal physiology.

Zebrafish melanopsin: isolation, tissue localisation and phylogenetic position.

27 November 2018

Photoreception is best understood in retinal rods and cones, but it is not confined to these cells. In non-mammals, intrinsically photosensitive cells have been identified within several structures including the pineal, hypothalamus and skin. More recently novel light sensitive cells have been identified in the inner/basal retina of both teleosts and rodents. Melanopsin has been proposed as the photopigment mediating many of these non-rod, non-cone responses to light. However, much about the melanopsin gene family remains to be clarified including their potential role as photopigments, and taxonomic distribution. We have isolated the first orthologue of melanopsin from a teleost fish and show expression of this gene in a sub-set of retinal horizontal cells (type B). Zebrafish melanopsin, and orthologues of this gene, differ markedly from the vertebrate photopigment opsins. The putative counterion is not a glutamate but a tyrosine, the putative G-protein binding domain in the third cytoplasmic loop is not conserved, and they show low levels of amino acid identity (approximately 27%) to both the known photopigment opsins and to other members of the melanopsin family. Mouse melanopsin is only 58% identical to Xenopus, and 68% identical to zebrafish. By contrast, the photosensory opsin families show approximately 75% conservation. On the basis of their structure, genomic organisation, discrete evolutionary lineage, and their co-expression with other opsins, the melanopins are not obvious photosensory opsins. They might represent a separate branch of photopigment evolution in the vertebrates or they may have a non-direct photosensory function, perhaps as a photoisomerase, in non-rod, non-cone light detection.

Structure and evolution of the teleost extraretinal rod-like opsin (errlo) and ocular rod opsin (rho) genes: is teleost rho a retrogene?

27 November 2018

In Teleost fish examined to date the ocular rod opsin gene, rho, is intronless, unlike the rod opsin genes of other vertebrate classes which possess a five exon/four intron structure. We have examined in silico the structure of rho (which is expressed uniquely in the retina) and the closely related extraretinal rod-like opsin (exo-rhodopsin) gene, errlo (which is expressed uniquely in the pineal), in the puffer-fish, Fugu rubripes (Takifugu rubripes). Whilst the ocular rho is intronless in common with other Teleosts, the pineal errlo has the five exon/four intron structure common to the rod opsin gene of other vertebraes. A comparison of the sequence surrounding the errlo and rho loci indicates that the errlo locus is syntenic with RHO, the human rod opsin gene, rather than rho. We suggest that the intronless rho may have arisen through an ancient retrotransposition of a mature mRNA originating from errlo. This duplication event has occurred early in the evolution of the Actinopterygii (ray-finned fish) since the rho of the primitive Actinopterygians such as sturgeon, bowfin, and gar is also intronless. Since it appears that the intron containing errlo is the ancestral opsin gene that gave rise to the intronless rho in the Teleostei, errlo is therefore the true orthologue of the rod opsin gene in other vertebrate classes. We suggest that loss of expression of errlo in the retina could be related to the metabolic and physiological advantages, such as a reduction in splicing events during RNA processing, that may be conferred through possession of an additional, intronless rod opsin gene in the form of rho.

Retinal projections in mice with inherited retinal degeneration: implications for circadian photoentrainment.

27 November 2018

The availability of naturally occurring and transgenic retinal mutants has made the mouse an attractive experimental model to address questions regarding photoentrainment of circadian rhythms. However, very little is known about the retinal cells and the retinal projections to the nuclei of the murine circadian timing system. Furthermore, the effect of inherited retinal degeneration on these projections is not understood. In this report, we have used pseudorabies virus as a neuroanatomical tract tracer in mice to address a series of questions: Which retinal cells mediate circadian responses to light? What is the nature of the retinohypothalamic projection? What is the impact of the inherited retinal disorder, retinal degenerate (rd/rd), on the structures of the photoentrainment pathway? Our results show that a class ofretinal ganglion cell, morphologically similar to the type III ganglion cells of the rat, appears to project to central circadian structures of the mouse. They are few in number and sparsely distributed throughout the retina. The low number and broad distribution of these specialized retinal ganglion cells may be an adaptive mechanism to integrate environmental irradiance without compromising the spatial resolution required for vision. In addition, viral infection of conelike and rodlike photoreceptors and amacrinelike cells suggest that these cells may mediate or contribute to circadian responses to light. Inherited retinal degeneration has no obvious effect on the anatomy of the retinal cells or their projections to the circadian axis. These anatomical findings are consistent with our previous findings showing that aged rd/rd mice are capable of regulating their circadian rhythms by light with unattenuated sensitivity.

Light perception in the vertebrate brain: an ultrastructural analysis of opsin- and vasoactive intestinal polypeptide-immunoreactive neurons in iguanid lizards.

27 November 2018

Recent biochemical and immunocytochemical evidence indicates that a population of circadian and reproductive rhythm-entraining photoreceptors lies in the basal diencephalon of iguanid lizards. Here, we report the results of correlated light and electron microscopy of opsin-immunoreactive cells in the basal brain, and we discuss their ultrastructural relationship to known photoreceptors. Cerebrospinal fluid (CSF)-contacting bipolar neurons in the lizards Anolis carolinensis and Iguana iguana were immunolabeled with antisera generated against vertebrate retinal opsins and vasoactive intestinal polypeptide (VIP). Within the brain, opsin-immunoreactive cells were found exclusively in the ependyma of the basal region of the lateral ventricles (adjacent to nucleus paraolfactorius/nucleus ventromedialis and neostriatum/paleostriatum). Cells in the same anatomical location and with the same morphology were labeled with anti-VIP antisera. These cells possessed a dendritic process that extended toward the lateral ventricle, ending in a bulbous terminal that protruded into the ventricle. Axonal processes travelled ventrally and caudally. The entire cell, including the axonal process, exhibited opsin-like and VIP-like immunoreactivity. By light microscopy, opsin-like immunostaining appeared punctate, with immunoreactivity greatest in the bulbous terminal. Opsin- and VIP-immunostained thick sections were resectioned, and individual cells observed by light microscopy were then characterized using electron microscopy. We found that all immunostained cells were morphologically similar and that they were morphologically distinct from neighboring nonimmunoreactive cells. CSF-contacting opsin- and VIP-immunoreactive cells lacked the membranous stacks characteristic of retinal photoreceptors but were ciliated and contained numerous large electron-dense vesicles. Multiple synaptic contacts were made on the soma and putative dendritic processes of opsin- and VIP-immunoreactive CSF-contacting neurons. Our results provide the first ultrastructural characterization of opsin-immunostained encephalic CSF-contacting neurons in a vertebrate animal, and they indicate that these putative photoreceptors share structural features with pineal photoreceptors and with certain invertebrate extraretinal photoreceptors, but they are morphologically and biochemically distinct from visual photoreceptors of the retina.

Cloning of opsin cDNAs from the brain of Anolis carolinensis

27 November 2018

Purpose. We have previously shown that a range of different anti-opsin antibodies labelled CSF-contacting neurons in the septal area of the brain of the lizard Anolis carolinensis. This makes these cells strong candidates for the deep brain photoreceptors that mediate circadian responses to light in this species. In an attempt to characterize these putative photoreceptors and their transduction machinery we have started to isolate cDNA clones encoding their opsin(s). Methods. Initially, we used degenerate opsin primers in reverse transcription PCR with RNA from Anolis brain. The amplified DNA was subcloned and sequenced. Subsequently, a λgt11 cDNA library was constructed with Anolis brain mRNA. This library was screened with the PCR-amplified cDNA, as well as a chicken pineal opsin cDNA. Results. An 0.4 kb PCR product was obtained. Sequence analysis showed it to be identical with the rhodopsin-like gene previously cloned from an Anolis genomic library by Kawamura and Yokoyama (Gene 1995;149:267-270). Screening of the library with both probes gave several positive clones, the analysis of which is in progress. Conclusions. The detection of a message for the putative Anolis pineal opsin in the brain indicates that it is expressed in the deep brain photoreceptor as well as (or possibly instead of) in the pineal organ. We intend to further investigate this by cDNA cloning from pineal and ocular photoreceptors, as well as screening for other transduction genes.

Characterization of a putative novel opsin from atlantic salmon

27 November 2018

Purpose. To investigate the structural characteristics of a putative novel opsin family. Methods. We have initiated a screen of salmon ocular opsins. Degenerate PCR primers were designed against evolutionarily conserved structural domains of opsins. cDNA was synthesized from ocular RNA. Opsin cDNAs were amplified using opsin specific degenerate primers. cDNAs were subsequently subcloned and sequenced. 5′ and 3′ RACE PCR was used to isolate the complete coding region. Phylogenetic trees of cloned opsins were generated using commercially available software (PAUP). Results. Within opsin families, opsins from different species show amino acid identity of 65-95%. Between families, they show amino acid identity of 40-50%. During our screen we isolated an opsin cDNA partial clone (tentatively called salopsin) whose deduced translation (153 amino acids) showed approximately 40% identity to all other vertebrate opsin families, including pinopsin. Salopsin contains a Schiff base lysine for chromophore binding, a cysteine involved in an intramolecular disulfide bond, and three hydrophobic domains corresponding to the expected transmembrane domains of other opsins. Additionally, salopsin contains differences in conserved residues within suggested transducin interacting domains, and a deletion of two amino acids within the second intradiskal loop. In the various phylogenetic trees generated, salopsin was placed as either a third clade at the long wavelength/short wavelength duplication event, or as a separate clade preceding it. Salopsin was never placed within another opsin family. Conclusions. Based upon the amino acid identity of salopsin (≈ 40%) to all other vertebrate opsin families, we propose that it may form a novel opsin family. Salopsin has several structural features common to vertebrate opsins yet contains differences in functionally important residues. Finally, phylogenetic analysis places salopsin as a separate early clade in vertebrate opsin evolution. We have begun further studies to determine the structural features and functional importance of salopsin.

Developmental pathways towards mood disorders in adult life: Is there a role for sleep disturbances?

27 November 2018

INTRODUCTION: Mood disorders are among the most prevalent and serious mental disorders and rank high among to the leading global burdens of disease. The developmental psychopathology framework can offer a life course perspective on them thus providing a basis for early prevention and intervention. Sleep disturbances, are considered risk factors for mood disorders across childhood, adolescence and adulthood. Assuming that sleep disturbances may play a pivotal role in the pathogenesis of mood disorders from a life course point of view, we reviewed the data on developmental pathways towards mood disorders in adult life in relation to sleep disturbances. METHOD: From February 2017, a systematic search was conducted in PubMed, PsycINFO and Embase electronic databases for literature on developmental pathways to mood disorders in adult life in relation to sleep disturbances and to 1) pre-natal stress, 2) early brain developmental processes, and 3) temperaments, character and attachment style. RESULTS: Eleven, 54 and 15 articles were respectively selected. CONCLUSIONS: Experimental and clinical studies revealed that exposure to prenatal/early life stress results in sleep disturbances such as poor sleep and altered circadian regulation phases and may predict or even precipitate mood disorders in adulthood. Chronic sleep disruption may interfere with neuronal plasticity, connectivity and the developing brain thus contributing to the development of mood disorders. In addition sleep and circadian dysregulations have been shown to be related to those temperaments, character and attachment styles which are considered precursors of mood disorders. Sleep and circadian behaviours may serve as early targets regarding mood disorders.