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PubMed2000

Detection of female carriers of congenital color-vision deficiencies by visual pigment gene analysis.

PURPOSE: Congenital color-vision deficiencies are frequent among males, 4.7-8.0%, suggesting that female carriers are present at a frequency of 9-15%. The purpose of this study was to determine whether carriers could be detected by analysis of the visual pigment genes. METHODS: DNA from 29 males with congenital color-vision deficiencies, from their mothers, and from 117 randomly-selected females was analyzed. The most upstream genes, the downstream genes, and the most downstream genes in the red/green pigment gene arrays were amplified separately by PCR. Exon 5 of each gene was analyzed by single-strand conformation polymorphisms (SSCP). RESULTS: Analysis of the visual pigment genes suggests that one of the 29 mothers examined is a female protan and two others are carriers of both protan and deutan defects. The remaining 26 mothers were confirmed to be carriers of congenital color-vision deficiencies. Unusual patterns were observed in 15 (13%) of the randomly-selected females; among them, 5 appeared to be protan carriers and at least 4 to be deutan carriers. CONCLUSIONS: Female carriers of congenital color-vision deficiencies can be detected by analysis of the visual pigment genes. Since the proportion of females showing unusual patterns was slightly higher than expected, some must be false-positives and require more detailed examination.

Color Perception↗
PubMed2006

Light-evoked FOS induction within the suprachiasmatic nuclei (SCN) of melanopsin knockout (Opn4-/-) mice: a developmental study.

The aims of this study were to address three related questions: (1) Do the photosensitive ganglion cells of the mouse convey light information to the suprachiasmatic nuclei (SCN) at P0? (2) Do the differentiating rods and cones contribute to light-evoked FOS induction within the murine SCN at P4? (3) How does light-evoked FOS induction within the SCN of melanopsin knockout (Opn4-/-) mice differ at P4 and P14? Our approaches took advantage of the published descriptions of murine ocular development, melanopsin knockout (Opn4-/-) mouse, and light-induced expression of FOS (the phosphoprotein product of immediate early gene c-fos) within the SCN as a marker of retinohypothalamic tract competence. Collectively, our results show that photosensitive melanopsin-dependent retinal ganglion cells provide light information to the murine SCN on the day of birth, and possibly beforehand, and that developing rods and cones fail to provide light information to the SCN during early postnatal life. On the basis of previous publications and data presented here, we suggest that at ages around P14 the rods and cones might be capable of fully compensating for the loss of melanopsin-photosensitive ganglion cells if exposure to light is of sufficiently long duration. These results are related to the broader context of recent findings and the potential role(s) of a neonatal photoreceptor.

Animals↗
PubMed2004

Extraocular photoreception and circadian entrainment in nonmammalian vertebrates.

In mammals both the regulation of circadian rhythms and photoperiodic responses depend exclusively upon photic information provided by the lateral eyes; however, nonmammalian vertebrates can also rely on multiple extraocular photoreceptors to perform the same tasks. Extraocular photoreceptors include deep brain photoreceptors located in several distinct brain sites and the pineal complex, involving intracranial (pineal and parapineal) and extracranial (frontal organ and parietal eye) components. This review updates the research field of the most recent acquisitions concerning the roles of extraocular photoreceptors on circadian physiology and behavior, particularly photic entrainment and sun compass orientation.

Animals↗
PubMed1991

Polarized sorting of rhodopsin on post-Golgi membranes in frog retinal photoreceptor cells.

We have isolated a subcellular fraction of small vesicles (mean diameter, 300 nm) from frog photoreceptors, that accumulate newly synthesized rhodopsin with kinetics paralleling its appearance in post-Golgi membranes in vivo. This fraction is separated from other subcellular organelles including Golgi and plasma membranes and synaptic vesicles that are sorted to the opposite end of the photoreceptor cell. The vesicles have very low buoyant density in sucrose gradients (rho = 1.09 g/ml), a relatively simple protein content and an orientation of rhodopsin expected of transport membranes. Reversible inhibition of transport by brefeldin A provides evidence that these vesicles are exocytic carriers. Specific immunoadsorption bound vesicles whose protein composition was indistinguishable from the membranes sedimented from the subcellular fraction. Some of these proteins may be cotransported with rhodopsin to the rod outer segment; others may be involved in vectorial transport.

Animals↗
PubMed1992

Protein translocation across the ER requires a functional GTP binding site in the alpha subunit of the signal recognition particle receptor.

The signal recognition particle (SRP)-mediated translocation of proteins across the RER is a GTP dependent process. Analysis of the primary amino acid sequence of one protein subunit of SRP (SRP54), as well as the alpha subunit of the SRP receptor (SR alpha), has indicated that these proteins contain predicted GTP binding sites. Several point mutations confined to the GTP binding consensus elements of SR alpha were constructed by site specific mutagenesis to define a role for the GTP binding site in SR alpha during protein translocation. The SR alpha mutants were analyzed using an in vitro system wherein SR alpha-deficient microsomal membranes were repopulated with SR alpha by in vitro translation of wild-type or mutant mRNA transcripts. SRP receptors containing SR alpha point mutants were analyzed for their ability to function in protein translocation and to form guanylyl-5'-imidodiphosphate (Gpp[NH]p) stabilized complexes with the SRP. Mutations in SR alpha produced SRP receptors that were either impaired or inactive in protein translocation. These SRP receptors were likewise unable to form Gpp(NH)p stabilized complexes with the SRP. One SR alpha point mutant, Thr 588 to Asn 588, required 50- to 100-fold higher concentrations of GTP relative to the wild-type SR alpha to function in protein translocation. This mutant has provided information on the reaction step in protein translocation that involves the GTP binding site in the alpha subunit of the SRP receptor.

Animals↗
PubMed1998

Coordination of an array of signaling proteins through homo- and heteromeric interactions between PDZ domains and target proteins.

The rapid activation and feedback regulation of many G protein signaling cascades raises the possibility that the critical signaling proteins may be tightly coupled. Previous studies show that the PDZ domain containing protein INAD, which functions in Drosophila vision, coordinates a signaling complex by binding directly to the light-sensitive ion channel, TRP, and to phospholipase C (PLC). The INAD signaling complex also includes rhodopsin, protein kinase C (PKC), and calmodulin, though it is not known whether these proteins bind to INAD. In the current work, we show that rhodopsin, calmodulin, and PKC associate with the signaling complex by direct binding to INAD. We also found that a second ion channel, TRPL, bound to INAD. Thus, most of the proteins involved directly in phototransduction appear to bind to INAD. Furthermore, we found that INAD formed homopolymers and the homomultimerization occurred through two PDZ domains. Thus, we propose that the INAD supramolecular complex is a higher order signaling web consisting of an extended network of INAD molecules through which a G protein-coupled cascade is tethered.

Animals↗
PubMed2002

The intraflagellar transport protein, IFT88, is essential for vertebrate photoreceptor assembly and maintenance.

Approximately 10% of the photoreceptor outer segment (OS) is turned over each day, requiring large amounts of lipid and protein to be moved from the inner segment to the OS. Defects in intraphotoreceptor transport can lead to retinal degeneration and blindness. The transport mechanisms are unknown, but because the OS is a modified cilium, intraflagellar transport (IFT) is a candidate mechanism. IFT involves movement of large protein complexes along ciliary microtubules and is required for assembly and maintenance of cilia. We show that IFT particle proteins are localized to photoreceptor connecting cilia. We further find that mice with a mutation in the IFT particle protein gene, Tg737/IFT88, have abnormal OS development and retinal degeneration. Thus, IFT is important for assembly and maintenance of the vertebrate OS.

Animals↗
PubMed1998

Kinetics of recovery of the dark-adapted salamander rod photoresponse.

The kinetics of the dark-adapted salamander rod photocurrent response to flashes producing from 10 to 10(5) photoisomerizations (Phi) were investigated in normal Ringer's solution, and in a choline solution that clamps calcium near its resting level. For saturating intensities ranging from approximately 10(2) to 10(4) Phi, the recovery phases of the responses in choline were nearly invariant in form. Responses in Ringer's were similarly invariant for saturating intensities from approximately 10(3) to 10(4) Phi. In both solutions, recoveries to flashes in these intensity ranges translated on the time axis a constant amount (tauc) per e-fold increment in flash intensity, and exhibited exponentially decaying "tail phases" with time constant tauc. The difference in recovery half-times for responses in choline and Ringer's to the same saturating flash was 5-7 s. Above approximately 10(4) Phi, recoveries in both solutions were systematically slower, and translation invariance broke down. Theoretical analysis of the translation-invariant responses established that tauc must represent the time constant of inactivation of the disc-associated cascade intermediate (R*, G*, or PDE*) having the longest lifetime, and that the cGMP hydrolysis and cGMP-channel activation reactions are such as to conserve this time constant. Theoretical analysis also demonstrated that the 5-7-s shift in recovery half-times between responses in Ringer's and in choline is largely (4-6 s) accounted for by the calcium-dependent activation of guanylyl cyclase, with the residual (1-2 s) likely caused by an effect of calcium on an intermediate with a nondominant time constant. Analytical expressions for the dim-flash response in calcium clamp and Ringer's are derived, and it is shown that the difference in the responses under the two conditions can be accounted for quantitatively by cyclase activation. Application of these expressions yields an estimate of the calcium buffering capacity of the rod at rest of approximately 20, much lower than previous estimates.

Animals↗
PubMed1956

The nature of the gecko visual pigment.

Retinal extracts of the Australian gecko, Phyllurus milii (White), have revealed the presence of a photosensitive pigment, unusual for terrestrial animals, because of its absorption maximum at 524 mmicro. This pigment has an absorption spectrum which is identical in form with that of other visual chromoproteins. It is not a porphyropsin, for bleaching revealed the presence, not of retinene(2), but of retinene(1) as a chromophore. Photolabile pigments with characteristics similar to those of the Phyllurus visual pigment were also detected in retinal extracts of six other species of nocturnal geckos. The presence of this retinal chromoprotein adequately accounts for the unusual visual sensitivity curve described by Denton for the nocturnal gecko. This pigment may have special biological significance in terms of the unique phylogenetic position of geckos as living representatives of nocturnal animals which retain some of the characteristics of their diurnal ancestors. The occurrence of this retinene(1) pigment, intermediate in spectral position between rhodopsin and iodopsin, is interpreted in support of the transmutation theory of Walls. The results and interpretation of this investigation point up the fact that, from a phylogenetic point of view, too great an emphasis on the duplicity theory may serve to detract attention from the evolutionary history of the retina and the essential unitarianism of the visual cells.

Animals↗
PubMed1988

Fenretinide does not block visual pigment formation in the rat.

Abnormal retinal function has been reported in patients receiving the synthetic retinoid fenretinide. In this study, the vitamin A deprived rat was used as a model to test the possibility that fenretinide is interfering with the vitamin A transport system and/or blocking the normal uptake of 11-cis retinal into the visual pigment. Assessing retinal function by electroretinogram measurements and visual pigment formation by competition studies, our data demonstrate normal uptake of vitamin A and normal visual pigment formation in the rat after treatment with the drug.

Animals↗
PubMed2002

A branch-and-bound algorithm for the inference of ancestral amino-acid sequences when the replacement rate varies among sites: Application to the evolution of five gene families.

MOTIVATION: We developed an algorithm to reconstruct ancestral sequences, taking into account the rate variation among sites of the protein sequences. Our algorithm maximizes the joint probability of the ancestral sequences, assuming that the rate is gamma distributed among sites. Our algorithm probably finds the global maximum. The use of 'joint' reconstruction is motivated by studies that use the sequences at all the internal nodes in a phylogenetic tree, such as, for instance, the inference of patterns of amino-acid replacement, or tracing the biochemical changes that occurred during the evolution of a given protein family. RESULTS: We give an algorithm that guarantees finding the global maximum. The efficient search method makes our method applicable to datasets with large number sequences. We analyze ancestral sequences of five gene families, exploring the effect of the amount of among-site-rate-variation, and the degree of sequence divergence on the resulting ancestral states. AVAILABILITY AND SUPPLEMENTARY INFORMATION: http://evolu3.ism.ac.jp/~tal/ CONTACT: tal@ism.ac.jp

Algorithms↗
PubMed1994

Stability of YACs containing ribosomal or RCP/GCP locus DNA in wild-type S. cerevisiae and RAD mutant strains.

About 2% of human YAC clones, including tandemly repeated segments color vision pigment DNA, ribosomal DNA and alphoid DNA have been reported to be inherently unstable in yeast hosts, producing more stable deletion products. YACs containing color vision red pigment gene DNA or 1.5 rDNA tandem repeat units were transformed into hosts bearing lesions at the RAD1, RAD6, RAD51, or RAD52 loci. YACs susceptible to deletion during outgrowth of wild-type cells (or in preliminary experiments, in RAD6 transformants) were stable for up to 100 generations or more in the other strains. Thus both the RAD1 and RAD51/RAD52 epistatic pathways are apparently involved in the instability of YACs containing tandem repeat loci, presumably during recombination-based deletion formation; and a yeast host disarmed in these pathways will likely maintain YACs intact that are otherwise unstable.

Animals↗
PubMed2002

The molecular basis of dichromatic color vision in males with multiple red and green visual pigment genes.

We investigated the genotypic variation in 50 red-green color vision deficient males (27 deuteranopes and 23 protanopes) of middle European ancestry who possess multiple genes in the X-linked photopigment gene array. We have previously shown that only the first two genes of the array are expressed and contribute to the color vision phenotype. Therefore, the hypothesis is that the first two genes possessed by multigene-dichromats encode pigments of identical or nearly identical spectral sensitivity: one gene normal (R or G) and the other a hybrid (G/R or R/G). The spectral sensitivities of the encoded pigments were inferred from published in vitro and in vivo data. The color vision phenotype was assessed by standard anomaloscopy. Most genotypes (92%) included hybrid genes whose sequence and position and whose encoded pigment correlated exactly with the phenotype. However, one and possibly two of the protanopes had gene arrays consistent with protanomaly rather than protanopia, since two spectrally different pigments may be encoded by their arrays. Two of the deuteranopes had only R- and G-photopigment genes, without any detectable G/R-hybrid genes or any as-of-yet identified point mutation or coding/promoter sequence deletions. Further, an unexpectedly high number of multigene-deuteranopes (11%) had the C203R mutation in their most upstream G-pigment gene, suggesting a founder effect of middle European origin for this mutation. About half of the protanopes possessed an upstream R/G-hybrid gene with different exon 2 coding sequences than their downstream G-pigment gene(s), which is inconsistent with published data implying that a single amino acid substitution in exon 2 can confer red-green color discrimination capacity on multigene-protans by altering the optical density of the cones.

Color Perception↗
PubMed1997

Visual pigment gene structure and expression in human retinae.

We determined the genotypes of the X-chromosome-linked red/green color vision genes by a novel PCR/SSCP-based method and assessed expression by mRNA analysis in retinae of 51 unselected post mortem eye specimens from Caucasian males of unknown color vision status. All individuals had a single red (long-wave) pigment gene and one or more (an average of two) green (middle-wave) pigment genes. Four males had 5'green-red3' hybrid genes in addition to normal red and green pigment genes. These findings are consistent with earlier studies on human visual pigment gene structure using Southern blotting and with a recent study using pulsed-field electrophoresis. We interpret claims of much larger numbers of red, green and green-red hybrid genes to be technical artifacts. The ratio of expressed red to green pigment retinal mRNA varied widely (1-10 with a mode of 4) and was not correlated with that of red to green pigment genes. In one individual with a green-red hybrid gene in addition to normal red and green pigment genes, the normal red pigment gene and the hybrid gene were both expressed, but the normal green gene was not. This person presumably had deuteranomalous color vision. Two with green-red hybrid genes expressed the normal red and green pigment genes, but not the hybrid genes. These two individuals presumably had normal color vision. We interpret the failure to express their green-red hybrid genes to be caused by their location at a more distal position in the visual pigment gene array.

Color Vision Defects↗
PubMed2001

Regulatory mechanism for the stability of the meta II intermediate of pinopsin.

Pinopsin is a chicken pineal photoreceptive molecule with a possible role in photoentrainment of the circadian clock. Sequence comparison among members of the rhodopsin family has suggested that pinopsin might have properties more similar to cone visual pigments than to rhodopsin, but the lifetime of the physiologically active intermediate (meta II) of pinopsin is rather similar to that of metarhodopsin II, which is far more stable than meta II intermediates of cone visual pigments [Nakamura, A. et al., (1999) Biochemistry 38, 14738-14745]. In the present study, we investigated the amino acid residue(s) contributing to this unique property of pinopsin by using site-directed mutagenesis to pinopsin-specific structural features, (i) Ser171, (ii) Asn184, and (iii) the second extracellular loop two-amino acids shorter than that of cone visual pigments. The meta II stability of the 171/184 double mutant of pinopsin (S171R/N184D) is almost the same as that of wild-type pinopsin. In contrast, the meta II lifetime is markedly shortened (one third) by introduction of the third mutation (replacement of a six-amino acid stretch, 188-193, by the corresponding eight residues of chicken green-sensitive cone pigment) to the 171/184 double mutant of pinopsin. Consistently, meta II of the green-sensitive pigment mutant, in which the eight-amino acid stretch is inversely replaced by the corresponding six residues of pinopsin, is more stable than meta II of the wild-type pigment. These results strongly suggest that the specific sequence and/or the number of residues at amino acids 188-193 in pinopsin play an important role in the stabilization of the meta II intermediate.

Amino Acid Substitution↗
PubMed1991

Total synthesis of a gene for octopus rhodopsin and its preliminary expression.

To carry out systematic structure-function studies of octopus rhodopsin, photoreceptor protein of octopus visual cells, by means of specific amino-acid replacements, we have totally synthesized a DNA duplex of 1,365 base pairs that encodes the entire octopus rhodopsin of 455 amino acids [Ovchinnikov et al. (1988) FEBS Lett. 232, 69-72] by introducing codons preferred in Escherichia coli. Total synthesis simplifies site-specific mutagenesis in all parts of the gene by replacement of short restriction fragments by their newly synthesized counterparts containing the required nucleotide alterations. Thirty unique restriction sites were introduced in the octopus rhodopsin gene, which was assembled on a plasmid in two steps. Five cartridge genes of 344, 296, 320, 212, and 317 base pairs capable of being expressed independently were first constructed by using 48 synthetic oligonucleotides ranging in size from 54 to 73 nucleotides. The entire gene was constructed by consecutive linkage of cartridge genes. These cartridge genes were designed to correspond to the transmembrane helical unit of octopus rhodopsin, resulting in easy construction of various chimeric rhodopsins. The nucleotide sequences were confirmed by sequencing the cartridges as well as the entire gene. These synthetic genes were cloned into an expression vector carrying the trp promoter of E. coli, and were preliminarily expressed in vitro and in vivo.

Amino Acid Sequence↗
PubMed1996

Gene conversion and natural selection in the evolution of X-linked color vision genes in higher primates.

During higher primate evolution, gene conversion seems to have occurred often between the red and green photo-pigment genes, which are tandemly linked on the X chromosome. To understand this phenomenon better, intron 4 sequences of the red and green pigment genes of a male human (an Asian Indian), a male chimpanzee, and a male baboon were amplified by PCR and sequenced. The data show that the intron 4 sequences between the two genes have been strongly or completely homogenized in the three species studied. Apparently recent gene conversion events have occurred in introns 4 of the red and green pigment genes in humans and chimpanzees. Two or more conversion events may have occurred at different times in introns 4 of the two pigment genes in baboons. The divergence between the two genes is significantly lower in intron 4 than in exons 4 and 5 in each species, contrary to the usual situation that introns evolve faster than exons. It is most likely that strong natural selection for maintaining the distinct functions of exons 4 and 5 of the red and green pigment genes has acted against sequence homogenization of these exons.

Animals↗
PubMed1998

The "five-sites" rule and the evolution of red and green color vision in mammals.

Amino acid changes S180A (S-->A at site 180), H197Y, Y277F, T285A, and A308S are known to shift the maximum wavelength of absorption (lambda max) of red and green visual pigments toward blue, essentially in an additive fashion. To test the generality of this "five-sites" rule, we have determined the partial amino acid sequences of red and green pigments from five mammalian orders (Artiodactyla, Carnivora, Lagomorpha, Perissodactyla, and Rodentia). The result suggests that cat (Felis catus), dog (Canis familiaris), and goat (Capra hircus) pigments all with AHYTA at the five critical sites have lambda max values of approximately 530 nm, whereas rat (Rattus norvegicus) pigment with AYYTS has a lambda max value of approximately 510 nm, which is accurately predicted by the five-sites rule. However, the observed lambda max values of the orthologous pigments of European rabbit (Oryctolagus cuniculus), white-tailed deer (Odocoileus virginianus), gray squirrel (Sciurus carolinensis), and guinea pig (Cavia procellus) are consistently more than 10 nm higher than the predicted values, suggesting the existence of additional molecular mechanisms for red and green color vision. The inferred amino acid sequences of ancestral organisms suggest that the extant mammalian red and green pigments appear to have evolved from a single ancestral green-red hybrid pigment by directed amino acid substitutions.

Amino Acid Sequence↗