Incorporation of tritium of 3H-5-uridine into DNA

Neuron, 2001

Vision Research, 1997

Deuteranomalous trichromacy is the most common form of inherited color-vision deficiency. A modern description of its cause is a single abnormality: the normal middle-wave cone photopigment (M) is replaced by a shifted middle-wave pigment (M') that is shared by all deuteranomalous trichromats. This explanation, however, fails to account for the individual differences in color vision observed even within the subgroup of deuteranomals with good chromatic discrimination. An ensemble of color matches is used here to test whether these individual differences reflect differences in the wavelength of peak sensitivity (2~,J of individual deuteranomals' cone photopigments. The results show variation in both the 2~~~a nd the effective optical density of thehcone pigments. The individual differences found in A max are in accord with recent mo]ecu]ar biological research that shows individual differences in the genes thought to encode deuteranomalous photopigments.

To analyze the human red, green, and red-green hybrid cone pigments in vivo, we studied 41 male dichromats, each of whose X chromosome carries only a single visual pigment gene (singlegene dichromats). This simplified arrangement avoids the difficulties of complex opsin gene arrays and overlapping cone spectral sensitivities present in trichromats and of multiple genes encoding identical or nearly identical cone pigments in many dichromats. It thus allows for a straightforward correlation between each observer's spectral sensitivity measured at the cornea and the amino acid sequence of his visual pigment. For each of the 41 singlegene dichromats we determined the amino acid sequences of the X-linked cone pigment as deduced from its gene sequence. To correlate these sequences with spectral sensitivities in vivo, we determined the Rayleigh matches to different red/green ratios for 29 single-gene dichromats and measured psychophysically the spectral sensitivity of the remaining green (middle wavelength) or red (long wavelength) cones in 37 single-gene dichromats. Cone spectral sensitivity maxima obtained from subjects with identical visual pigment amino acid sequences show up to a ϳ3 nm variation from subject to subject, presumably because of a combination of inexact (or no) corrections for variation in preretinal absorption, variation in photopigment optical density, optical effects within the photoreceptor, and measurement error. This variation implies that spectral sensitivities must be averaged over multiple subjects with the same genotype to obtain representative values for a given pigment. The principal results of this study are that (1) ϳ54% of the single-gene protanopes (and ϳ19% of all protanopes) possess any one of several 5Јred-3Јgreen hybrid genes that encode anomalous pigments and that would be predicted to produce protanomaly if present in anomalous trichromats; (2) the alanine/serine polymorphism at position 180 in the red pigment gene produces a spectral shift of ϳ2.7 nm; (3) for each exon the set of amino acids normally associated with the red pigment produces spectral shifts to longer wavelengths, and the set of amino acids normally associated with the green pigment produces spectral shifts to shorter wavelengths; and (4) changes in exons 2, 3, 4, and 5 from green to red are associated with average spectral shifts to long wavelengths of ϳ1 nm (range, Ϫ0.5 to 2.5 nm), ϳ3.3 nm (range, Ϫ0.5 to 7 nm), ϳ2.8 nm (range, Ϫ0.5 to 6 nm), and ϳ24.9 nm (range, 22.2-27.6 nm).

Vision Research, 1971

The Journal of general physiology, 1996

A B S TRACT Mthough a given retina typically contains several visual pigments, each formed from a retinal chromophore bound to a specific opsin protein, single photoreceptor cells have been thought to express only one type of opsin. This design maximizes a cell's sensitivity to a particular wavelength band and facilitates wavelength discrimination in retinas that process color. We report electrophysiological evidence that the ultraviolet-sensitive cone of salamander violates this rule. This cell contains three different functional opsins. The three opsins could combine with the two different chromophores present in salamander retina to form six visual pigments. Whereas rods and other cones of salamander use both chromophores, they appear to express only one type of opsin per cell. In visual pigment absorption spectra, the bandwidth at half-maximal sensitivity increases as the pigment's wavelength maximum decreases. However, the bandwidth of the UV-absorbing pigment deviates from this trend; it is narrow like that of a red-absorbing pigment. In addition, the UV-absorbing pigment has a high apparent photosensitivity when compared with that of red-and blue-absorbing pigments and rhodopsin. These properties suggest that the mechanisms responsible for spectrally tuning visual pigments separate two absorption bands as the wavelength of maximal sensitivity shifts from UV to long wavelengths.

Vision Research, 1995

Individual differences in abnormal color vision are well known. A fundamental unresolved problem is the great variation in color vision even among those classified as having the same color-vision defect. Several physiological hypotheses have been proposed to account for this variation but little consideration has been given to how (and how much) color matching and discrimination are affected by the posited physiological mechanisms. Advances in molecular genetics have renewed interest in this problem, which is at the foundation of the relation between genotype and phenotype. We report here theoretical Rayleigh ranges (chromatic discrimination) and quantal matches for deuteranomalous trichromats with photopigments in the red]green range that vary in their separation and optical density. The results show there is relatively little loss of discrimination with pigments of normal optical density separated by as little as 2-3 nm. With pigments separated by 4 nm or less, however, optical density can strongly influence discrimination when varied independently in the two types of cone. Moderately lower (or higher) optical density in only one cone-type affects discrimination by altering the shape of the cone's relative spectral sensitivity function. The lack of correlation between Rayleigh-match midpoint and range, which is reported in the literature, may be accounted for by independent variation in pigment separation and optical density. Anomalous trichromacy Color matching Rayleigh matching Cone photopigments Optical density Color discrimination

The Journal of Physiology, 1991

1. Photosensitivities of visual pigments were determined by measuring early receptor currents (ERCs) in voltage-clamped photoreceptors from larval salamanders. 2. As expected from previous work of others, the ERC elicited by a brief flash consisted of a rapid inward component followed by a larger and slower outward component. The magnitude of the outward component corresponded to the movement of about 0O18 electronic charge across the membrane per photoisomerization. 3. The time course of the ERC was independent of the flash intensity, the flash wavelength and the magnitude of the response. The outward component of the cone ERC declined about twice as rapidly as the outward component of the rod ERC. 4. The amplitude of the ERC decreased as successive flashes bleached the cell's pigment. Using the proportional relation between the size of the ERC and the number of pigment molecules photoisomerized, photosensitivities of the native A2 pigments in rods, red-sensitive cones, blue-sensitive cones and UV-sensitive cones were determined. Calculated solution photosensitivities for rhodopsin, red-sensitive and blue-sensitive cone pigments were not significantly different and the average value for all three pigments at their respective absorption maxima was (7 3 + 1-6) x 10-um2 molecule-'. A value of 44 0 x 10-9 #m2 molecule-' was obtained in a single UV-sensitive cone. 5. Substitution of the native dehydroretinal chromophore in the red-sensitive cone pigment with 11-cis-retinal increased the solution photosensitivity to (9X6±+062) x 10-9 /Im2 molecule-'. 6. We conclude that cone pigments have large molecular absorption cross-sections and high quantum efficiencies of photoisomerization. These properties seem well suited for the receptive molecules of a highly sensitive, miniaturized transducer.

Experimental Eye Research, 1990

We have determined the pattern of RNA labeling (uridine incorporation) in the normal retina of the domestic cat. One eye in each of eight cats was labeled by injecting [3H]uridine into the vitreous cavity. Two of the labeled eyes had the lens and vitreous removed 10 days before labeling. Three additional animals received intravenous (i.v.) injections of C3H]uridine. All animals were injected 4 hr into the light period and fixed 24 hr later: then the retinas were divided into quadrants (ST = superior temporal, SN superior nasal, IT = inferior temporal, and IN = inferior nasal). The ST quadrant contains the area centralis and the SN quadrant the optic nerve head. Autoradiograms were prepared from plastic sections 1 ,um thick taken near the centre of each quadrant. In animals receiving intravitreal r3H]uridine. the ganglion cells and the inner and outer nuclear layers (INL; ONL) were heavily labeled ; the synaptic layers and the retinal pigment epithelium (RPE) were very lightly labeled. Amacrines were the heaviest labeled cells in the INL: cones were more heavily labeled than rods in the ONL. This finding indicates that amacrines and cone photoreceptors may be synthesizing RNA more actively than other retinal neurons. In animals receiving intravenous [3H]uridine the pattern of labeling was the same as above except that the RPE was heavily labeled. Because cells in the ST quadrant appeared to be more heavily labeled than the same cell types in the other retinal quadrants, silver grains over the ONL in each quadrant were counted as grains pm-2 or grains per rod nucleus. In all cases rod nuclei in the ST quadrant are about twice as heavily labeled as in the SN, IT and IN quadrants (P < 0.001, Student's f-tests). In addition, in three animals with i.v. injections, rods in the ST quadrant of the right eye are more heavily labeled than in the ST quadrant of the lefi eye (P < 0005, Student's t-tests). Because of the 24-hr incubation period and the nuclear location of the labeling, the species of RNA being observed in this study is probably small nuclear RNA (&&'A). Our results show that there are large differences in uridine labeling of diierent regions of the retina, with the highest labeling in the quadrant containing the area centralis (the region of high visual acuity). In addition, the right eyes have a higher labeling with uridine than the left eyes. These data indicate regional and interocular differences in retinal metabolism.

Biophysical Journal, 1994

The basic precondition for color vision is the presence of at least two receptor types with different spectral sensitivities. The sensitivity of a receptor is mostly defined by the opsin-based visual pigment expressed in it. We show here, through behavioral experiments, that the nymphalid butterfly Heliconius erato, although it expresses short and medium wavelength opsins and only one long wavelength opsin, discriminates colors in the long-wavelength range (590 nm, 620 nm and 640 nm), whereas another nymphalid, Vanessa atalanta, despite having color vision, is unable to do so. In the eyes of H. erato we identified filtering pigments very close to the rhabdom which differ between ommatidia and produce the yellow and red ommatidial reflection seen under orthodromic illumination. The eyes of V. atalanta lack the filtering pigments, and reflect a homogeneous orange. We hypothesize that the filtering pigments found in the eyes of H. erato may shift the spectral sensitivity peak of the long wavelength receptors in some ommatidia towards longer wavelengths. The comparison of the signals between the two new receptor types makes color discrimination in the red range possible. To our knowledge, this is the first behavioral proof of color vision based on receptors expressing the same opsin.