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PubMed2001

Pinopsin mRNA levels are significantly elevated in the pineal glands of chickens carrying a null mutation in guanylate cyclase-1.

The purpose of this study was to determine if the absence of guanylate cyclase-1 (RetGC1, GC1), a key visual phototransduction cascade enzyme that is expressed in both retinal photoreceptors and pinealocytes, disrupts light regulation of pinopsin mRNA levels in the chicken pineal gland. In this series of experiments, we compared levels of pinopsin and tryptophan 5-hydroxylase mRNA in the pineal glands of GUCY1*B (*B) and normal chickens housed under either cyclic light or constant dark conditions. The *B chicken carries a null mutation in the gene encoding guanylate cyclase-1 that results in blindness in these animals at hatching. The results of our experiments show (1) that the amount of pinopsin mRNA in *B pineal is significantly higher than the amount in normal pineal in both light and dark conditions, (2) that light induces an increase in pinopsin mRNA levels in *B pineal, (3) that the relative magnitude of the light-induced increase in pinopsin mRNA in *B pineal is not significantly different from that observed in normal pineal, and (4) that the changes in the regulation of pinopsin mRNA levels in *B pineal gland are not accompanied by changes in the circadian expression of tryptophan 5-hydroxylase mRNA. These results show that the absence of guanylate cyclase-1 expression in the *B pineal gland leads to a significant increase in basal levels of pinopsin mRNA in this gland but does not alter the magnitude of the increase in pinopsin mRNA levels that is observed as a result of light stimulation.

Animals↗
PubMed2001

Serine 85 in transmembrane helix 2 of short-wavelength visual pigments interacts with the retinylidene Schiff base counterion.

Short-wavelength cone visual pigments (SWS1) are responsible for detecting light from 350 to 430 nm. Models of this class of pigment suggest that TM2 has extensive contacts with the retinal binding pocket and stabilizes interhelical interactions. The role of TM2 in the structure-function of the Xenopus SWS1 (VCOP, lambda(max) = 427 nm) pigment was studied by replacement of the helix with that of bovine rhodopsin and also by mutagenesis of highly conserved residues. The TM2 chimera and G78D, F79L, M81E, P88T, V89S, and F90V mutants did not produce any significant spectral shift of the dark state or their primary photointermediate formed upon illumination at cryogenic temperatures. The mutant G77R (responsible for human tritanopia) was completely defective in folding, while C82A and F87T bound retinal at reduced levels. The position S85 was crucial for obtaining the appropriate spectroscopic properties of VCOP. S85A and S85T did not bind retinal. S85D bound retinal and had a wild-type dark state at room temperature and a red-shifted dark state at 45 K and formed an altered primary photointermediate. S85C absorbed maximally at 390 nm at neutral pH and at 365 nm at pH >7.5. The S85C dark state was red shifted by 20 nm at 45 K and formed an altered primary photointermediate. These data suggest that S85 is involved in a hydrogen bond with the protonated retinylidene Schiff base counterion in both the dark state and the primary photointermediate.

Amino Acid Sequence↗
PubMed2005

Amino acid residues responsible for the meta-III decay rates in rod and cone visual pigments.

Vertebrate retinas have two types of photoreceptor cells, rods and cones, which contain visual pigments with different molecular properties. These pigments diverged from a common ancestor, and their difference in molecular properties originates from the difference in their amino acid residues. We previously reported that the difference in decay times of G protein-activating meta-II intermediates between the chicken rhodopsin and green-sensitive cone (chicken green) pigments is about 50 times. This difference only originates from the differences of two residues at positions 122 and 189 (Kuwayama, S., Imai, H., Hirano, T., Terakita, A., and Shichida, Y. (2002) Biochemistry 41, 15245-15252). Here we show that the meta-III intermediates exhibit about 700 times difference in decay times between the two pigments, and the faster decay in chicken green can be converted to the slower decay in rhodopsin by replacing the residues in chicken green with the corresponding rhodopsin residues. However, the inverse directional conversion did not occur when the two residues in rhodopsin were replaced by those of chicken green. Analysis using chimerical mutants derived from these pigments has demonstrated that amino acid residues responsible for the slow rhodopsin meta-III decay are situated at several positions throughout the C-terminal half of rhodopsin. Considering that rhodopsins evolved from cone pigments, it has been suggested that the molecular properties of rhodopsin have been optimized by mutations at several positions, and the chicken green mutants at two positions could be rhodopsin-like pigments transiently produced in the course of molecular evolution.

Amino Acid Sequence↗
PubMed1994

Sequence divergence of the red and green visual pigments in great apes and humans.

We have determined the coding sequences of red and green visual pigment genes of the chimpanzee, gorilla, and orangutan. The deduced amino acid sequences of these pigments are highly homologous to the equivalent human pigments. None of the amino acid differences occurred at sites that were previously shown to influence pigment absorption characteristics. Therefore, we predict the spectra of red and green pigments of the apes to have wavelengths of maximum absorption that differ by < 2 nm from the equivalent human pigments and that color vision in these nonhuman primates will be very similar, if not identical, to that in humans. A total of 14 within-species polymorphisms (6 involving silent substitutions) were observed in the coding sequences of the red and green pigment genes of the great apes. Remarkably, the polymorphisms at 6 of these sites had been observed in human populations, suggesting that they predated the evolution of higher primates. Alleles at polymorphic sites were often shared between the red and green pigment genes. The average synonymous rate of divergence of red from green sequences was approximately 1/10th that estimated for other proteins of higher primates, indicating the involvement of gene conversion in generating these polymorphisms. The high degree of homology and juxtaposition of these two genes on the X chromosome has promoted unequal recombination and/or gene conversion that led to sequence homogenization. However, natural selection operated to maintain the degree of separation in peak absorbance between the red and green pigments that resulted in optimal chromatic discrimination. This represents a unique case of molecular coevolution between two homologous genes that functionally interact at the behavioral level.

Amino Acid Sequence↗
PubMed2003

A broad role for melanopsin in nonvisual photoreception.

The rod and cone photoreceptors that mediate visual phototransduction in mammals are not required for light-induced circadian entrainment, negative masking of locomotor activity, suppression of pineal melatonin, or the pupillary light reflex. The photopigment melanopsin has recently been identified in intrinsically photosensitive retinal ganglion cells (RGCs) that project to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and olivary pretectal nucleus, suggesting that melanopsin might influence a variety of irradiance-driven responses. We have found novel projections from RGCs that express melanopsin mRNA to the ventral subparaventricular zone (vSPZ), a region involved in circadian regulation and negative masking, and the sleep-active ventrolateral preoptic nucleus (VLPO) and determined the subsets of melanopsin-expressing RGCs that project to the SCN, the pretectal area (PTA), and the IGL division of the lateral geniculate nucleus (LGN). Melanopsin was expressed in the majority of RGCs that project to the SCN, vSPZ, and VLPO and in a subpopulation of RGCs that innervate the PTA and the IGL but not in RGCs projecting to the dorsal LGN or superior colliculus. Two-thirds of RGCs containing melanopsin transcript projected to each of the SCN and contralateral PTA, and one-fifth projected to the ipsilateral IGL. Double-retrograde tracing from the SCN and PTA demonstrated a subpopulation of RGCs projecting to both sites, most of which contained melanopsin mRNA. Our results suggest that melanopsin expression defines a subset of RGCs that play a broad role in the regulation of nonvisual photoreception, providing collateralized projections that contribute to circadian entrainment, negative masking, the regulation of sleep-wake states, and the pupillary light reflex.

Animals↗
PubMed1994

Molecular and biochemical analyses of iodopsin in rd chick retina.

PURPOSE: The results of previous immunocytochemical and electrophysiological studies of retinas of rd (retinal degeneration) chicks suggest that the iodopsin cone visual pigment may be defective in this mutant. The goal of this study was to determine if the primary structure and synthesis of this protein is normal in this animal model of inherited retinal degeneration. METHODS: Northern cDNA sequence and western analyses were used to study rd/rd iodopsin. cDNAs encoding rd/rd iodopsin were obtained by screening an rd/rd cDNA retinal expression library and by reverse transcription PCR. Western blots were probed with either R4 or COS-1, two different monoclonal antibodies that have been shown to specifically recognize chicken iodopsin. RESULTS: Hybridization of the +/+, +/rd, and rd/rd poly(A)+ RNA with an iodopsin cDNA probe revealed the presence of a single 1.5 kb band in each of the samples, all of which were labeled with equal intensity. No significant differences were found between the published nucleic acid sequences for normal chicken iodopsin cDNA and that determined for rd/rd iodopsin cDNA. Antibody-dependent differences in the staining intensity of the 34 kDa band containing iodopsin were observed on western blots of +/+, +/rd, and rd/rd retinal protein. R4 stained the 34 kDa band in each sample with equal intensity. COS-1 labeling of the 34 kDa band in the rd/rd sample was less intense than that observed in the +/+ and +/rd samples. CONCLUSIONS: Based on the results of the cDNA sequence and northern blot experiments, the authors conclude that the gene encoding iodopsin and transcription of this gene are normal in the rd mutant. The results of the western blot analyses of rd/rd iodopsin suggest that post-translational processing of iodopsin may be abnormal in this mutant.

Animals↗
PubMed1998

Transgenic mice expressing a functional human photopigment.

PURPOSE: Changes in retinal photopigments represent a fundamental step in the evolution of visual systems, in that addition of new pigment types or alterations in the spectral absorption properties of existing pigments modify visual capacities and thus open new visual worlds. To provide a tool that would allow direct examination of the changes caused by the presence of novel photopigments, this study was designed to determine whether a gene encoding a human cone photopigment introduced into the mouse genome would be expressed in a cone-specific manner and would support phototransduction. METHODS: Mice transgenic for the human long wavelength-sensitive (L) photopigment were generated by microinjection of fertilized mouse eggs. RNA expression in different tissues was monitored by reverse transcription-polymerase chain reaction analysis. Photopigment protein was localized in retinal cross sections and wholemounts by antibody staining. Light transduction of the cone photopigments was assessed by flicker photometric electroretinography (ERG). RESULTS: The human transgene was expressed specifically in the mouse cones in quantities comparable to those of the mouse middle wavelength-sensitive (M) pigment gene. Immunocytochemical analysis showed that the human L pigment was abundantly synthesized in most mouse cones, was translocated to the outer segments, and caused no detectable cone degeneration. Electroretinographic spectral sensitivity analysis showed that the human L pigment was efficient in eliciting an electrical response. The degree of expression of the transgene in the two founders correlated well with the spectral responsivity of the ERG. CONCLUSIONS: The human L photopigment transduces light efficiently in mouse cones, implying that all protein domains necessary for efficient interaction with intracellular transport and signal transduction machineries in mouse cones have been conserved through evolution. The expression of the human L photopigment gene in both classes of cone of the mouse retina indicates that the transgene did not have the regulatory elements necessary for restricting its expression to mouse M cones or that such elements are not recognized in mouse UV-sensitive cones.

Animals↗
PubMed2005

Progressive cone dystrophy with deutan genotype and phenotype.

PURPOSE: To study the electroretinographic signals originating in the long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cone pathways by means of large-field and multifocal cone type-specific electroretinograms (ERGs) in a patient with progressive cone dystrophy. METHODS: A 65-year-old male patient with colour vision disturbances (age at onset 10 years), loss of visual acuity (14 years), and central visual field defects (40 years) was investigated. Large-field flicker-ERG responses to stimuli that exclusively modulated the L-cones or the M-cones, or the two simultaneously (both in-phase and in counter-phase), were measured. Short-wavelength-sensitive (S) cones were not modulated. Multifocal ERGs (mfERGs) were also recorded, with a pattern-reversing display that modulated only the L- or the M-cones at equal cone contrasts and average quantal catches. Genetic analysis of L- and M-pigment genes was performed on genomic DNA isolated from peripheral venous blood. RESULTS: The patient showed a normal rod-driven ERG but reduced cone-driven electroretinographic amplitudes with normal implicit times in the International Society for Clinical Electrophysiology of Vision (ISCEV) standard ERG. The large-field flicker-ERG responses to pure L-cone modulation were significantly above noise level but were substantially reduced in comparison with both normal trichromatic subjects and (otherwise normal) deuteranopes. The L-cone driven electroretinographic implicit times and phases were within normal limits. The M-cone driven electroretinographic responses were not detectable. A model fit of all the L- and M-cone driven flicker-ERG data revealed that the responses were exclusively driven by the L-cones. Consistently, the cone type-specific mfERGs showed severely reduced but detectable responses to L-cone-isolating stimuli. The M-cone driven multifocal-ERG responses were undistinguishable from noise. The L- and M-pigment gene array consisted of only a single L-pigment gene. The complete coding sequence of this gene was determined and showed no abnormality. CONCLUSIONS: This patient exhibits a coincidence of progressive cone dystrophy and deuteranopia. The molecular genetic data of the L/M-pigment gene array is consistent with the deutan phenotype. It cannot be excluded that the rearrangement of the X-chromosome pigment gene array is responsible for the cone dystrophy in this patient. It is, however, suggested that the dichromacy and the cone dystrophy have different and independent genetic origins.

Aged↗