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PubMed1991

The cyclophilin homolog ninaA is a tissue-specific integral membrane protein required for the proper synthesis of a subset of Drosophila rhodopsins.

Mutations in the Drosophila ninaA gene cause dramatic reductions in rhodopsin levels, leading to impaired visual function. The ninaA protein is a homolog of peptidyl-prolyl cis-trans isomerases. We find that ninaA is unique among this family of proteins in that it is an integral membrane protein, and it is expressed in a cell type-specific manner. We have used transgenic animals misexpressing different rhodopsins in the major class of photoreceptor cells to demonstrate that ninaA is required for normal function by two homologous rhodopsins, but not by a less conserved member of the Drosophila rhodopsin gene family. This demonstrates in vivo substrate specificity in a cyclophilin-like molecule. We also show that vertebrate retina contains a ninaA-related protein and that ninaA is a member of a gene family in Drosophila. These data offer insights into the in vivo role of this important family of proteins.

Amino Acid Isomerases↗
PubMed1993

Diethylene glycol distearate (DGD): a versatile embedding medium for retinal cytochemistry.

Embedment in diethylene glycol distearate (DGD) was shown to be highly desirable and versatile for retinal cytochemical studies, including in situ hybridization, immuno- and lectin cytochemistry. This method allows for preservation of fine tissue detail as well as good reaction sensitivity. It appears to be more suitable than most other methods currently used for light microscopic retinal cytochemistry.

Animals↗
PubMedDate not supplied

Structure and photobleaching process of chicken iodopsin.

Iodopsin, a dominant cone pigment in a chicken retina, has an absorption spectrum in longer wavelength region than rhodopsin. To account for this red-shift of iodopsin, we had proposed a structural model from retinal analogue experiments, in which iodopsin would have a relatively long distance between the protonated Schiff base nitrogen and the counterion. This was confirmed by a resonance Raman spectroscopy. The photochemical properties of iodopsin were studied and compared with those of rhodopsin, which revealed the following differences. The regeneration rate of iodopsin with 11-cis-retinal was 240 times faster than rhodopsin. Meta-iodopsin II, the signalling state of iodopsin, decayed about 100 times faster than meta-rhodopsin II. The Km value of meta-iodopsin II and rhodopsin kinase was lower than meta-rhodopsin II. These results are in consistent with rapid adaptation and low photosensitivity of cones relative to those of rods.

Amino Acid Sequence↗
PubMedDate not supplied

Changes in structure of the chromophore in the photochemical process of bovine rhodopsin as revealed by FTIR spectroscopy for hydrogen out-of-plane vibrations.

The hydrogen out-of-plane bending (HOOP) vibrations were studied in the difference Fourier transform infrared spectra of lumirhodopsin and metarhodopsin I by use of a series of specifically deuterated retinal derivatives of bovine rod outer segments. The 947 cm-1 band of lumirhodopsin and the 950 cm-1 band of metarhodopsin I were assigned to the mode composed of both 11-HOOP and 12-HOOP vibrations. This result suggests that the perturbation near C12-H of the retinal in the earlier intermediate, bathorhodopsin (Palings, van den Berg, Lugtenburg and Mathies, Biochemistry, 28 (1989) 1498-1507), is extinguished in lumirhodopsin and metarhodopsin I. Unphotolyzed rhodopsin and metarhodopsin I exhibited the 14-HOOP bands in the 12-D derivatives at 901 and 886 cm-1, respectively. Lumirhodopsin, however, did not show the 14-HOOP in the 12-D derivatives. The result suggests a change in geometrical alignment of the C14-H bond in lumirhodopsin with respect to the N-H bond of the Schiff base.

Animals↗
PubMed1990

Rod photoreceptor development in vitro: intrinsic properties of proliferating neuroepithelial cells change as development proceeds in the rat retina.

We describe a reaggregated cell culture system in which retinal neuroepithelial cells from embryonic rats proliferate extensively and give rise to rod photoreceptors on the same schedule in vitro as they do in vivo. Both the proliferative potential of the embryonic neuroepithelial cells and the timing of their differentiation into rods are not changed by the presence of a 50-fold excess of neonatal neural retinal cells, although many more of the embryonic cells develop into rods in these circumstances. In such mixed-age cultures, dividing neonatal cells proliferate much less and give rise to rods much sooner than do dividing embryonic cells, suggesting that the dividing cells at the two ages are intrinsically different. These and other findings suggest that both cell-cell interactions and an intrinsic program in neuroepithelial cells determine cell fate in the developing rat retina.

Aging↗
PubMed1992

Histidine residues regulate the transition of photoexcited rhodopsin to its active conformation, metarhodopsin II.

The biologically active photoproduct of rhodopsin, metarhodopsin II (M II), exists in a pH-sensitive equilibrium with its precursor, metarhodopsin I (M I). Increasing acidity favors M II, with the midpoint of the pH titration curve at pH 6.4. To test the long-standing proposal that histidine protonation regulates this conformational transition, we characterized mutant rhodopsins in which each of the 6 histidines was replaced by phenylalanine or cysteine. Only mutants substituted at the 3 conserved histidines showed abnormal M I-M II equilibria. Those in which His-211 was replaced by phenylalanine or cysteine formed little or no M II at either extreme of pH, whereas mutants substituted at His-65 or at His-152 showed enhanced sensitivity to protons. The simplest interpretation of these results is that His-211 is the site where protonation strongly stabilizes the M II conformation and that His-65 and His-152 are sites where protonation modestly destabilizes the M II conformation.

Amino Acid Sequence↗
PubMed1993

Circadian regulation of iodopsin gene expression in embryonic photoreceptors in retinal cell culture.

A circadian clock regulates a number of diverse physiological functions in the vertebrate eye. In this study, we show that mRNA for the red-sensitive cone pigment, iodopsin, fluctuates with a circadian rhythm in chicken retina. Transcript levels increase in the late afternoon just prior to the time of cone disc shedding. Furthermore, iodopsin mRNA levels are regulated similarly by a circadian oscillator in primary cultures of dispersed embryonic chick retina. Nuclear run-on experiments show that the circadian regulation of iodopsin transcript abundance occurs at the level of gene transcription. Our results provide a demonstration of clock-regulated gene expression in a vertebrate preparation maintained in cell culture.

Animals↗
PubMed1991

Molecular determinants of visual pigment function.

Mutagenesis studies and comparisons of natural variants of rhodopsin and related visual pigments have led to new insights concerning photoreceptor function. The studies identify domains important for receptor folding, the residues that set the wavelength of absorption for the ligand 11-cis retinal, and residues, that when mutated, trigger the cell death of photoreceptors.

Amino Acid Sequence↗
PubMedDate not supplied

Toward optimizing lighting as a countermeasure to sleep and circadian disruption in space flight.

Light is being used as a pre-launch countermeasure to circadian and sleep disruption in astronauts. The effect of light on the circadian system is readily monitored by measurement of plasma melatonin. Our group has established an action spectrum for human melatonin regulation and determined the region of 446-477 nm to be the most potent for suppressing plasma melatonin. The aim of this study was to compare the efficacy of 460 and 555 nm for suppressing melatonin using a within-subjects design. Subjects (N=12) were exposed to equal photon densities (7.18 x 10(12) photons/cm2/s) at 460 and 555 nm. Melatonin suppression was significantly stronger at 460 nm (p<0.02). An extension to the action spectrum showed that 420 nm light at 16 and 32 microW/cm2 significantly suppressed melatonin (p<0.04 and p<0.002). These studies will help optimize lighting countermeasures to circadian and sleep disruption during spaceflight.

Adult↗
PubMed2005

Circadian gene expression patterns of melanopsin and pinopsin in the chick pineal gland.

The directly light-sensitive chick pineal gland contains at least two photopigments. Pinopsin seems to mediate the acute inhibitory effect of light on melatonin synthesis, whereas melanopsin may act by phase-shifting the intrapineal circadian clock. In the present study we have investigated, by means of quantitative RT-PCR, the daily rhythm of photopigment gene expression as monitored by mRNA levels. Under a 12-h light/12-h dark cycle, the mRNA levels of both pigments were 5-fold higher in the transitional phase from light to dark than at night, both in vivo and in vitro. Under constant darkness in vivo and in vitro, the peak of pinopsin mRNA levels was attenuated, whereas that of melanopsin was not. Thus, whereas the daily rhythm of pinopsin gene expression is dually regulated by light plus the intrapineal circadian oscillator, that of melanopsin appears to depend solely on the oscillator.

Adaptation, Ocular↗
PubMed2006

Oxidative-induced retinal degeneration is attenuated by epigallocatechin gallate.

The aim of this investigation was to determine whether an ingredient of green tea, epigallocatechin gallate (EGCG) could attenuate oxidative stress-induced degeneration of the retina as occurs in age-related macular degeneration (AMD) and glaucoma. Initial in vitro studies on brain membranes showed that EGCG was approximately 10 times more potent than trolox (vitamin E analogue) at attenuating lipid peroxidation caused by the nitric oxide donor, sodium nitroprusside (SNP). Subsequent immunohistochemical studies revealed that following an intraocular injection of SNP retinal photoreceptors are affected. This was supported by electroretinogram (ERG) recordings which showed both the a- and b-wave amplitudes to be significantly reduced. RT-PCR and Western blotting techniques showed that SNP caused a significant decrease in photoreceptor-specific markers (RET-P1, rhodopsin kinase), an increase in the cell death marker caspase-3, and no change in the ganglion cell specific markers, neurofilament (NF-L) and Thy-1. Importantly, when EGCG was co-injected, the detrimental effects to the retina caused by SNP were significantly blunted. The conclusion reached from this study is that EGCG is a powerful antioxidant and when injected into the eye with SNP attenuated the detrimental influence of SNP to retinal photoreceptors. Since oxidative stress has been implicated in retinal diseases like AMD and glaucoma this study provides "proof of principle" for the idea that daily intake of EGCG may help individuals suffering from retinal diseases where oxidative stress is implicated.

Animals↗
PubMed2005

Non-image-forming ocular photoreception in vertebrates.

It has been accepted for a hundred years or more that rods and cones are the only photoreceptive cells in the retina. The light signals generated in rods and cones, after processing by downstream retinal neurons (bipolar, horizontal, amacrine and ganglion cells), are transmitted to the brain via the axons of the ganglion cells for further analysis. In the past few years, however, convincing evidence has rapidly emerged indicating that a small subset of retinal ganglion cells in mammals is also intrinsically photosensitive. Melanopsin is the signaling photopigment in these cells. The main function of the inner-retina photoreceptors is to generate and transmit non-image-forming visual information, although some role in conventional vision (image detection) is also possible.

Animals↗
PubMed2005

Cephalochordate melanopsin: evolutionary linkage between invertebrate visual cells and vertebrate photosensitive retinal ganglion cells.

Animal photoreceptor cells can be classified into two distinct types, depending on whether the photopigment is borne on the membrane of a modified cilium (ciliary type) or apical microvilli (rhabdomeric type) [1]. Ciliary photoreceptors are well known as vertebrate rods and cones and are also found in several invertebrates. The rhabdomeric photoreceptor, in contrast, is a predominant type of invertebrate visual cell, but morphologically identifiable rhabdomeric photoreceptors have never been found in vertebrates. It is hypothesized that the rhabdomeric photoreceptor cell had evolved to be the photosensitive retinal ganglion cell for the vertebrate circadian photoentrainment [2, 3 and 4] owing to the fact that some molecules involved in cell differentiation are common among them [5]. We focused on the cephalochordate amphioxus because it is the closest living invertebrate to the vertebrates, and interestingly, it has rhabdomeric photoreceptor cells for putative nonvisual functions [6]. Here, we show that the amphioxus homolog of melanopsin [7, 8 and 9], the circadian photopigment in the photosensitive retinal ganglion cells of vertebrates, is expressed in the rhabdomeric photoreceptor cells of the amphioxus and that its biochemical and photochemical properties, not just its primary structure, are considerably similar to those of the visual rhodopsins in the rhabdomeric photoreceptor cells of higher invertebrates. The cephalochordate rhabdomeric photoreceptor represents an evolutionary link between the invertebrate visual photoreceptor and the vertebrate circadian photoreceptor.

Animals↗
PubMed2005

Melanopsin-dependent photoreception provides earliest light detection in the mammalian retina.

BACKGROUND: The visual system is now known to be composed of image-forming and non-image-forming pathways. Photoreception for the image-forming pathway begins at the rods and cones, whereas that for the non-image-forming pathway also involves intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin. In the mouse retina, the rod and cone photoreceptors become light responsive from postnatal day 10 (P10); however, the development of photosensitivity of the ipRGCs remains largely unexplored. RESULTS: Here, we provide direct physiological evidence that the ipRGCs are light responsive from birth (P0) and that this photosensitivity requires melanopsin expression. Interestingly, the number of ipRGCs at P0 is over five times that in the adult retina, reflecting an initial overproduction of melanopsin-expressing cells during development. Even at P0, the ipRGCs form functional connections with the suprachiasmatic nucleus, as assessed by light-induced Fos expression. CONCLUSIONS: The findings suggest that the non-image-forming pathway is functional long before the mainstream image-forming pathway during development.

Animals↗
PubMed2005

Retinal development: second sight comes first.

Mammals are functionally blind at birth because responses to rod and cone photoreceptor activation are immature. Recent studies show that the newborn retina is nevertheless sensitive to light. Indeed, intrinsically photosensitive retinal ganglion cells are present from birth and already make functional connections with the suprachiasmatic nucleus, the site of the central circadian clock.

Animals↗
PubMed2006

Melanopsin regulates visual processing in the mouse retina.

The discovery of melanopsin-dependent inner retinal photoreceptors in mammals has precipitated a fundamental reassessment of such non-image forming (NIF) light responses as circadian photoentrainment and the pupil light reflex. By contrast, it remains unclear whether these new photoreceptors also play a role in classical image-forming vision. The retinal ganglion cells that subserve inner retinal photoreception (ipRGCs) project overwhelmingly to brain areas involved in NIF responses, indicating that, in terms of central signaling, their predominant function is non-image forming. However, ipRGCs also exhibit intraretinal communication via gap junction coupling, which could allow them to modulate classical visual pathways within this tissue. Here, we explore this second possibility by using melanopsin knockout (Opn4-/-) mice to examine the role of inner retinal photoreceptors in diurnal regulation of retinal function. By using electroretinography in wild-type mice, we describe diurnal rhythms in both the amplitude and speed of the retinal cone pathway that are a function of both prior light exposure and circadian phase. Unexpectedly, loss of the melanopsin gene abolishes circadian control of these parameters, causing significant attenuation of the diurnal variation in cone vision. Our results demonstrate for the first time a melanopsin-dependent regulation of visual processing within the retina, revealing an important function for inner retinal photoreceptors in optimizing classical visual pathways according to time of day.

Animals↗