Short Single Cones Research Articles

Molecular Cloning and characterization of the putative ultraviolet-sensitive visual pigment of goldfish

A cDNA full length encoding a putative ultraviolet (UV)-sensitive visual pigment of goldfish was isolated. The deduced amino acid sequence shows 64% identity to those of human blue and chicken violet, and less identity (40–49%) to those of other vertebrate visual pigments. The mRNA is localized in the miniature short single cone cells, which are known to have a sensitivity maximum in the near UV-region.

Temporal and spatial patterns of opsin gene expression in zebrafish (Danio rerio).

In zebrafish, the first class of cone photoreceptor to become morphologically distinct is the ultraviolet-sensitive short single cone, at 4 days postfertilization, whereas the last class, the red- and green-sensitive double cone, becomes distinct at 10 days postfertilization. We have examined the time course of visual pigment gene expression in zebrafish using whole-mount in situ hybridization. Within the retina, opsins may be detected as early as 40 h postfertilization with the ultraviolet and rod visual pigments being expressed before the blue- (48 h) and red- (60 h) sensitive pigments. In the pineal, red-sensitive opsin is expressed at 48 h postfertilization. Visual pigment expression provides a useful tool for investigations of early cell fate in zebrafish.

Zebrafish ultraviolet visual pigment: absorption spectrum, sequence, and localization.

In many vertebrates, UV-sensitive photoreceptors have been identified by microspectrophotometry and UV-visual sensitivity has been identified by behavioral studies, but as yet no vertebrate UV-sensitive pigment gene has been isolated. We have sequenced a cDNA clone that hybridizes to short single cone cells in the zebrafish (Brachydanio rerio). These cells, which make up 25% of the cone population in zebrafish retinae, are UV-sensitive (lambda max approximately 360 nm). The visual pigment encoded by this gene is unusual in that its amino acid sequence is more homologous to the rod pigment rhodopsin (up to 89%) than to other cone pigments (35-83%). Like all other vertebrate visual pigments, it contains a lysine residue at position 296, the presumptive retinal binding site, and a glutamate residue at position 113. However, it is unique in possessing a lysine residue at position 126, which may account for the UV-sensitivity of the pigment.

Landolt's club in the retina of catfish, Heteropneustes fossilis: a new finding in Teleostei

The visual cells in the retina of the freshwater catfish, Heteropneustes fossilis comprise rods, long single cones, short single cones and Landolt's clubs.

Landolt's club in the retina of catfish, Heteropneustes fossilis: a new finding in Teleostei

The visual cells in the retina of the freshwater catfish, Heteropneustes fossilis comprise rods, long single cones, short single cones and Landolt's clubs.

Green-sensitive cone photoreceptors are selectively labeled by Procion yellow dye in goldfish retina

Selective labeling of intravitreal Procion yellow dye by presumed blue-sensitive cone photoreceptors has been demonstrated in primate retina. To determine whether Procion yellow is selective for this cone type in an unrelated vertebrate species, labeling by this dye was studied in goldfish retina, where cone pigment type can be directly inferred from photoreceptor morphology. At low vitreal concentrations of the dye (less than 0.4%), only cone outer segments were labeled. At vitreal concentrations of 0.4-0.5%, the inner segments of short-double cones and a subset of long single cones (presumed green-sensitive cones) were selectively stained. At still higher vitreal concentrations (0.6-0.7%), the inner segments of short-single cones and miniature short-single cones (presumed blue-sensitive cones) showed evidence of Procion label, but were not as heavily labeled. The inner segments of long-double cones and a subset of long-single cones (presumed red-sensitive cones) did not label at any of these concentrations. These results show that Procion yellow is not a selective marker for blue-sensitive cones in the goldfish retina. In addition, stained rod and cone nuclei were observed at each dye concentration, including those concentrations at which no inner segments were labeled.

A short-wavelength sensitive cone mechanism in juvenile yellow perch, Perca flavescens

The retinal cone mosaic of adult yellow perch, Perca flavescens, consists of square units each having a central single cone surrounded by four identical twin cones. No cones are present at the corners of the square units. However, the cone types and organization of the retinal mosaic in juvenile P. flavescens has not been thoroughly described. We report here the presence of small, single cones at the corner positions of the square units in juvenile P. flavescens. Not every corner, nor every unit has these cones, and their distribution over the retina is not uniform. Microspectrophotometry places the visual pigment absorbance maximum of these short single cones in the region of 400 nm. Electrophysiological measurements of spectral sensitivity demonstrate a short-wavelength mechanism in juveniles that is absent, as are the small corner cones, in adults. Possible advantages of such a mechanism to juvenile perch are discussed.

Photoreceptors of a cyprinid fish, the roach: morphological and spectral characteristics

Structure-function studies were undertaken on cones in the retina of the cyprinid fish, the roach,Rutilus rutilus, in order to provide a basis for analysis of colour information by post-receptoral neurones. Measurements were made with two main aims: (i) To determine by microspectrophotometry the absorbance spectra of the photopigments present within the retina, and correlate these with the morphological types of photoreceptor; (ii) To characterize the morphologies of the photoreceptors at both light and electron microscopical levels and determine their relative abundance in the retina. In addition to red-, green-, and blue-sensitive cones, an ultra-violet-sensitive photoreceptor has been found in a sub-population of miniature short single cones. Possible relevance of this finding to vertebrate vision is discussed.

Cytodifferentiation of photoreceptors in larval goldfish: delayed maturation of rods.

This study describes the differentiation of photoreceptors in larval goldfish retina. The earliest photoreceptors to differentiate were cones; 3H-fucose labeled cone but not rod outer segments in larval as well as adult goldfish. All major cone types known to be present in the adult goldfish retina (double cones, long and short single cones) were found in the larval retina by 2 days after hatching. The cones matured rapidly; within a few days they had well-developed outer segments and synaptic pedicles that were smaller, but otherwise similar to those in adults. Rods were slower to mature. Their outer segments were at first short, wide, and misshapen; only as they grew longer and narrower did they become straight and properly aligned. Rod spherules were first seen in fish older than 1 month; immature rods contained perinuclear synaptic ribbons and invaginating processes penetrated the cell body. These results suggest that the influence of rods and cones on visual function in larval goldfish may be quite different from the adult.

Growth rate and number of dopamine cells in a defined peripheral zone of the goldfish retina

Histologic examination of the retina in comet goldfish 11 cm long (nose to base of tail) reveals at least six distinct varieties of cones. Unequal double cones (DC) comprise long (LD) and short (SD) members which differ in form as well as length. Long single (LS) cones are similar in length and form to SD cones. Although evidence indicates that there are two subpopulations of LS cones, normally they are structurally indistinguishable. Short single (SS) cones have short, broad outer segments and ellipsoids and virtually no myoids. Miniature long single (MLS) cones have the same shape as LS cones, but they are shorter and more slender and their nuclei project farther into the outer nuclear layer. Miniature short single (MSS) cones have the same shape as SS cones, but they are shorter and more slender and their nuclei are found with those of MLS cones. The average cone densities, relative to SS = 1.0, are: DC (pairs) ≅ 2.0, LS (total) ≅ 1.4–2.0, MSS ≅ 0.4–0.8, and MLS < 0.1. The form, dimensions, and densities of cones do not vary systematically with location in the retina.An irregular mosaic is discernible. In the fundus, this is fundamentally a rhombic array of SS cones separated by 20–28 μm (1000–2500 SS/mm2). Double cones form the sides of rhombi whose centers are occupied by SS cones. MSS cones lie at the corners of the rhombi, while LS cones are scattered. The location of MLS cones in the mosaic has not been determined. In the far periphery the double cones form rows instead of rhombi, but otherwise the mosaic is the same.Microspectrophotometric measurement of visual pigments, accompanied by microscopic identification of the cones containing them, reveals a strong correlation between structure (cone type) and function (visual pigment). The LD and some LS cones contain the red-sensitive pigment (λmax ≅ 625nm). The SD and other LS cones contain the green-sensitive pigment (λmax ≅ 530nm). The probable ratio of LS (red):LS (green) ≅ 2:1. The SS cones contain the blue-sensitive pigment (λmax ≅ 455nm). The pigment contained in the MSS and MLS cones has not been determined.

Larval and adult visual pigments of the zebrafish, Brachydanio rerio

Photoreceptors of adult and larval zebrafish were assayed by microspectrophotometry to characterize their visual pigments, and to determine when the visual pigments first appear during development. Short single cone outer segments contained a pigment with a λ max near 417 nm. Long single cones and long members of double cone outer segments contained a pigment with a λ max near 480 nm. Short members of double cone outer segments contained a pigment with a λ max near 556 nm. Rod outer segments contained a rhodopsin with a λ max near 501 nm. All four visual pigment types found in adult photoreceptors were present in the earliest measurable larval photoreceptors.

Ontogeny of the photoreceptors in the embryonic retina of the viviparous guppy, Poecilia reticulata P. (Teleostei). An electron-microscopical study.

Ultrastructural analyses of retinal development in the guppy embryo show that at midgestation all types of photoreceptors are differentiated in the fundus, and at birth differentiation extends over the whole retina. Formation of discs of outer segments is more rapid in rods than in cones. Double cones differentiate simultaneously with long single cones and are formed by the adhesion of two primordial inner segments; short single cones develop last. Wherever cones are differentiated, they are arranged in an adult-type square mosaic. The rods in the embryo, as opposed to the adult, are likewise regularly arranged within the mosaic unit. These results are at variance with the generally held opinion that adult teleosts which possess duplex retinae have larvae with pure cone retinae, and that rods, double cones and mosaics appear in late larval life or only at metamorphosis. In the double cones of the guppy embryo subsurface cisternae develop along the adjoining primordial inner segments. Additionally, regularly distributed subsurface cisternae are formed in the regions of intimate contact of long single cones with double cones and rods. We suggest that the early development of rods and double cones, and a square-mosaic with regular distribution of rods and subsurface cisternae, provide the newly born with a fully functional optical apparatus, especially suited to perception of movements. This is necessary for its survival against predatory, especially maternal, attacks.

The outer retina and tapetum lucidum of the snook Centropomus undecimalis (Teleostei).

The snook Centropomus undecimalis is a nocturnal fish inhabiting turbid estuaries, bays, and inshore waters. Its retina is duplex, containing rods and short single, long single, and double cones. Cones are arranged in a square mosaic; the rods are extremely numerous and outer segments are short and staggered in depth. Ellipsoid mitochondria undergo morphological alterations along the vitreo–scleral axis including the appearance of elongate cristae and the development of electron-dense matrices which nearly obscure the cristae. Peripheral mitochondria give off tubular elements in the calycal processes. Pigment epithelial cells have long processes which extend vitread to the cone ellipsoids and contain tapetal spheres (0.3 to 0.5 μm). The processes form a diffusely reflecting tapetum about 80 μm thick. In the scotopic eye the tapetum is uncovered when the retinal pigment retreats into the cell bases. The reflecting material is a triglyceride, largely glyceryl tridocosahexaenoate. Its high refractive index (n = 1.50) and the close packing of the spheres cause light to be backscattered. Reflection from the white lipid tapeta is about 50%; quantal catch in the retina because of the tapetum is enhanced by a factor of about 1.5.

Visual receptor pigments in the african cichlid fish, Haplochromis burtoni

The retinal receptors of the African cichlid fish, Haplochromis burtoni, are arranged in a mosaic of square arrays which have four double cones around a central cone. Microspectrophotometric measurement of spectral absorbance reveals that the short single cones contain the blue photopigment, P455, while the larger double cones contain “red-green” pigment pairs of P562 and P523. Rods are interspersed throughout the cone array and contain rhodopsin, P500. Spectral shape, pigment absorbance and the λ max of photo-products are characteristic of A 1 based pigments. The retinal receptors of H. burtoni appear to be well matched to important visual recognition tasks.

Color receptor identities of goldfish cones.

Goldfish retinas were exposed to spectral lights, then incubated with nitroblue tetrazolium chloride. Diformazan deposits revealed that five morphologically distinct cone types were segregated into three color classes: red long double and long single cones, green short double and long single cones, and blue short single and miniature short single cones.

Cone structure and visual pigment content in the retina of the goldfish

Histologic examination of the retina in comet goldfish 11 cm long (nose to base of tail) reveals at least six distinct varieties of cones. Unequal double cones (DC) comprise long (LD) and short (SD) members which differ in form as well as length. Long single (LS) cones are similar in length and form to SD cones. Although evidence indicates that there are two subpopulations of LS cones, normally they are structurally indistinguishable. Short single (SS) cones have short, broad outer segments and ellipsoids and virtually no myoids. Miniature long single (MLS) cones have the same shape as LS cones, but they are shorter and more slender and their nuclei project farther into the outer nuclear layer. Miniature short single (MSS) cones have the same shape as SS cones, but they are shorter and more slender and their nuclei are found with those of MLS cones. The average cone densities, relative to SS = 1.0, are: DC (pairs) ≅ 2.0, LS (total) ≅ 1.4–2.0, MSS ≅ 0.4–0.8, and MLS < 0.1. The form, dimensions, and densities of cones do not vary systematically with location in the retina. An irregular mosaic is discernible. In the fundus, this is fundamentally a rhombic array of SS cones separated by 20–28 μm ( 1000–2500 SS/mm 2 ). Double cones form the sides of rhombi whose centers are occupied by SS cones. MSS cones lie at the corners of the rhombi, while LS cones are scattered. The location of MLS cones in the mosaic has not been determined. In the far periphery the double cones form rows instead of rhombi, but otherwise the mosaic is the same. Microspectrophotometric measurement of visual pigments, accompanied by microscopic identification of the cones containing them, reveals a strong correlation between structure (cone type) and function (visual pigment). The LD and some LS cones contain the red-sensitive pigment ( λ max ≅ 625nm ). The SD and other LS cones contain the green-sensitive pigment ( λ max ≅ 530nm ). The probable ratio of LS (red):LS (green) ≅ 2:1. The SS cones contain the blue-sensitive pigment ( λ max ≅ 455nm ). The pigment contained in the MSS and MLS cones has not been determined.

The chromatic organization of the goldfish cone mosaic

Responses of individual goldfish cones to spectral lights were monitored using reduction of Nitro-blue tetrazolium chloride as an indicator of response magnitude. Red sensitive cones (long double, some long single and miniature long single cones), green sensitive cones (short double and some long single cones) and blue sensitive cones (short single and miniature short single cones) were identified in flat mounts of whole retinae. Cone patterning, densities and dimensions were examined in whole mounts and thin sections. The total chromatic composition of the retina was found to be 45% red cones, 35% green cones and 20% blue cones.

Studies on the eyes of New Zealand parrot-fishes (Labridae).

An investigation was made of the pigment epithelium and photoreceptor layer of the eyes of New Zealand parrot-fishes Pesudolabrus miles , P. celidotus and P. pittensis (Labridae). Eyes were studied by light and electron microscopy, and characteristics of the retinal pigments were investigated. The pigment epithelium contains numerous melanosomes in the basal region of the cell and red cylinders within the processes. Melanosomes and cylinders are dispersed slightly vitread during light- adaptation. The photoreceptors comprise long single cones, short single cones, double cones and rods. The cones possess a lateral sac connected to the outer segment, and well-developed calycal processes arising from the ellipsoid. Rods are without a lateral sac and have fewer and less regularly arranged calycal processes. The membranes of rod lamellae stacks are more widely spaced than those of cones and are deeply dissected by a few longitudinal fissures. Cones form a regular mosaic of squares throughout the depth of the retina scleral to the external limiting membrane. Rods are numerous and distributed throughout the cone mosaic with no particular patterns. Cones undergo only very limited radial movements, and long single cones are always buried in the pigment epithelium where they are surrounded by red pigment. Rods shorten in darkness and come to lie inside the pigment epithelium. The red material in the cylinders is apparently a new pigment; it absorbs strongly below 560 nm, and prevents all but red light from reaching the long single cones and the rods when extended. Several features and consequences of this organization are discussed.