David Hunt

Evolution of the eyes of vipers with and without infrared-sensing pit organs

Publisher: Oxford University Press (OUP)

Date: 10-03-2019

DOI: 10.1093/BIOLINNEAN/BLZ003

Enhanced retinal longwave sensitivity using a chlorophyll-derived photosensitiser in Malacosteus niger, a deep-sea dragon fish with far red bioluminescence

Publisher: Elsevier BV

Date: 08-1999

DOI: 10.1016/S0042-6989(98)00332-0

Abstract: Through partial bleaching of both visual pigment extracts and cell suspensions we show that the deep-sea stomiid Malacosteus niger, which produces far red bioluminescence, has two visual pigments within its retina which form a rhodopsin orphyropsin pigment pair with lambda max values around 520 and 540 nm, but lacks the very longwave sensitive visual pigments (lambda max > 550 nm) observed in two other red light producing stomiids. The presence of only a single opsin gene in the M. niger genome was confirmed by molecular and cladistic analysis. To compensate for its apparently reduced longwave sensitivity compared to related species, the outer segments of M. niger contain additional pigments, which we identify as a mixture of defarnesylated and demetallated derivatives of bacteriochlorophylls c and d, that are used as a photosensitiser to enhance its sensitivity to longwave radiation.

Retinal Amino Acid Neurochemistry of the Southern Hemisphere Lamprey, Geotria australis

Publisher: Public Library of Science (PLoS)

Date: 13-03-2013

DOI: 10.1371/JOURNAL.PONE.0058406

Shortwave visual sensitivity in tree and flying squirrels reflects changes in lifestyle

Publisher: Elsevier BV

Date: 02-2006

DOI: 10.1016/J.CUB.2006.01.045

The rod opsin pigments from two marsupial species, the South American bare-tailed woolly opossum and the Australian fat-tailed dunnart

Publisher: Elsevier BV

Date: 12-2003

DOI: 10.1016/J.GENE.2003.09.016

Abstract: Rod visual pigment genes have been studied in a wide range of vertebrates including a number of mammalian species. However, no marsupials have yet been examined. To correct this omission, we have studied the rod pigments in two marsupial species, the nocturnal and frugivorous bare-tailed woolly opossum, Caluromys philander, from Central and South America, and the arhythmic and insectivorous fat-tailed dunnart, Sminthopsis crassicaudata, from Australia. Phylogenetic analysis establishes that the cloned opsin sequences are orthologues of rod opsin genes from other vertebrate species. The deduced amino acid sequences show that both possess glutamate at residue 122, a feature of rod opsins, and the corresponding gene follows the typical vertebrate rod opsin pattern of five exons separated by four introns. Compared to other vertebrates, a stretch of five residues near the C-terminus is deleted in the rod opsin of both marsupials and all eutherian mammals. From microspectrophotometric measurements, the pigments in the two species show an 8 nm difference in peak absorbance the molecular basis for this spectral shift is discussed and two candidate substitutions are identified.

Ultraviolet-sensitive vision in long-lived birds

Publisher: The Royal Society

Date: 28-07-2010

DOI: 10.1098/RSPB.2010.1100

Abstract: Long-term exposure to ultraviolet (UV) light generates substantial damage, and in mammals, visual sensitivity to UV is restricted to short-lived diurnal rodents and certain marsupials. In humans, the cornea and lens absorb all UV-A and most of the terrestrial UV-B radiation, preventing the reactive and damaging shorter wavelengths from reaching the retina. This is not the case in certain species of long-lived diurnal birds, which possess UV-sensitive (UVS) visual pigments, maximally sensitive below 400 nm. The Order Psittaciformes contains some of the longest lived bird species, and the two species examined so far have been shown to possess UVS pigments. The objective of this study was to investigate the prevalence of UVS pigments across long-lived parrots, macaws and cockatoos, and therefore assess whether they need to cope with the accumulated effects of exposure to UV-A and UV-B over a long period of time. Sequences from the SWS1 opsin gene revealed that all 14 species investigated possess a key substitution that has been shown to determine a UVS pigment. Furthermore, in vitro regeneration data, and lens transparency, corroborate the molecular findings of UV sensitivity. Our findings thus support the claim that the Psittaciformes are the only avian Order in which UVS pigments are ubiquitous, and indicate that these long-lived birds have UV sensitivity, despite the risks of photodamage.

Phototactic tails: Evolution and molecular basis of a novel sensory trait in sea snakes

Publisher: Wiley

Date: 15-02-2019

DOI: 10.1111/MEC.15022

Abstract: Dermal phototaxis has been reported in a few aquatic vertebrate lineages spanning fish, hibians and reptiles. These taxa respond to light on the skin of their elongate hind-bodies and tails by withdrawing under cover to avoid detection by predators. Here, we investigated tail phototaxis in sea snakes (Hydrophiinae), the only reptiles reported to exhibit this sensory behaviour. We conducted behavioural tests in 17 wild-caught sea snakes of eight species by illuminating the dorsal surface of the tail and midbody skin using cold white, violet, blue, green and red light. Our results confirmed phototactic tail withdrawal in the previously studied Aipysurus laevis, revealed this trait for the first time in A. duboisii and A. tenuis, and suggested that tail photoreceptors have peak spectral sensitivities between blue and green light (457-514 nm). Based on these results, and an absence of photoresponses in five Aipysurus and Hydrophis species, we tentatively infer that tail phototaxis evolved in the ancestor of a clade of six Aipysurus species (comprising 10% of all sea snakes). Quantifying tail damage, we found that the probability of sustaining tail injuries was not influenced by tail phototactic ability in snakes. Gene profiling showed that transcriptomes of both tail skin and body skin lacked visual opsins but contained melanopsin (opn4x) in addition to key genes of the retinal regeneration and phototransduction cascades. This work suggests that a nonvisual photoreceptor (e.g., Gq rhabdomeric) signalling pathway underlies tail phototaxis, and provides candidate gene targets for future studies of this unusual sensory innovation in reptiles.

Avian Visual Pigments: Characteristics, Spectral Tuning, and Evolution

Publisher: University of Chicago Press

Date: 2007

DOI: 10.1086/510141

Abstract: Birds are highly visual animals with complex visual systems. In this article, we discuss the spectral characteristics and genetic mechanisms of the spectral tuning of avian visual pigments. The avian retina contains a single type of rod, four spectrally distinct types of single cone, and a single type of double cone photoreceptor. Only the single cones are thought to be involved in color discrimination double cones are thought to be involved in achromatic visual tasks, such as movement detection and pattern recognition. Visual pigment opsin protein genes in birds are orthologous to those in other vertebrates and have a common origin early in vertebrate evolution. Mechanisms of spectral tuning in the different classes of avian cone visual pigments show similarities in most instances to those in other vertebrates. The exception is the ultraviolet/violet (SWS1) class of pigments phylogenetic evidence indicates that the ancestral vertebrate SWS1 pigment was ultraviolet sensitive (UVS), with different molecular mechanisms accounting for the generation of violet-sensitive (VS) pigments in different vertebrate classes. In birds, however, UVS visual pigments have re-evolved from an ancestral avian VS pigment by using a novel molecular mechanism not seen in other vertebrate classes. This has occurred independently in four of the 14 avian orders examined to date, although the adaptive significance of this is currently unknown.

Functional characterization, tuning, and regulation of visual pigment gene expression in an anadromous lamprey

Publisher: Wiley

Date: 26-04-2007

DOI: 10.1096/FJ.06-8057COM

Abstract: L reys are one of the two surviving groups of jawless vertebrates, whose ancestors arose more than 540 million years ago. Some species, such as Geotria australis, are anadromous, commencing life as ammocoetes in rivers, migrating downstream to the sea, and migrating back into rivers to spawn. Five photoreceptor types and five retinal cone opsin genes (LWS, SWS1, SWS2, RhA, and RhB) have previously been identified in G. australis. This implies that the ancestral vertebrates possessed photopic or cone-based vision with the potential for pentachromacy. Changes in the morphology of photoreceptors and their spectral sensitivity are encountered during differing aquatic phases of the l rey lifecycle. To understand the molecular basis for these changes, we characterized the visual pigments and measured the relative levels of opsin expression over two lifecycle phases that are accompanied by contrasting ambient light environments. By expressing recombinant opsins in vitro, we show that SWS1, SWS2, RhA, and RhB visual pigments possess lambda(max) values of 359, 439, 497, and 492 nm respectively. For the LWS visual pigment, we predict a lambda(max) value of 560 nm based on key spectral tuning sites in other vertebrate LWS opsins. Quantitative reverse transcriptase-polymerase chain reaction reveals that the retinal opsin genes of G. australis are differentially regulated such that the visual system switches from a broad sensitivity across a wide spectral range to a much narrower sensitivity centered around 490-500 nm on transition from marine to riverine conditions. These quantitative changes in visual pigment expression throughout the lifecycle may directly result from changes in the lighting conditions of the surrounding milieu.

Spectral tuning and evolution of primate short-wavelength-sensitive visual pigments

Publisher: The Royal Society

Date: 22-06-2011

DOI: 10.1098/RSPB.2011.0782

Abstract: The peak sensitivities ( λ max ) of the short-wavelength-sensitive-1 (SWS1) pigments in mammals range from the ultraviolet (UV) (360–400 nm) to the violet (400–450 nm) regions of the spectrum. In most cases, a UV or violet peak is determined by the residue present at site 86, with Phe conferring UV sensitivity (UVS) and either Ser, Tyr or Val causing a shift to violet wavelengths. In primates, however, the tuning mechanism of violet-sensitive (VS) pigments would appear to differ. In this study, we examine the tuning mechanisms of prosimian SWS1 pigments. One species, the aye-aye, possesses a pigment with Phe86 but in vitro spectral analysis reveals a VS rather than a UVS pigment. Other residues (Cys, Ser and Val) at site 86 in prosimians also gave VS pigments. Substitution at site 86 is not, therefore, the primary mechanism for the tuning of VS pigments in primates, and phylogenetic analysis indicates that substitutions at site 86 have occurred at least five times in primate evolution. The sole potential tuning site that is conserved in all primate VS pigments is Pro93, which when substituted by Thr (as found in mammalian UVS pigments) in the aye-aye pigment shifted the peak absorbance into the UV region with a λ max value at 371 nm. We, therefore, conclude that the tuning of VS pigments in primates depends on Pro93, not Tyr86 as in other mammals. However, it remains uncertain whether the initial event that gave rise to the VS pigment in the ancestral primate was achieved by a Thr93Pro or a Phe86Tyr substitution.

Molecular, Cellular and Functional Changes in the Retinas of Young Adult Mice Lacking the Voltage-Gated K+ Channel Subunits Kv8.2 and K2.1

Publisher: MDPI AG

Date: 05-05-2021

DOI: 10.3390/IJMS22094877

Abstract: Cone Dystrophy with Supernormal Rod Response (CDSRR) is a rare autosomal recessive disorder leading to severe visual impairment in humans, but little is known about its unique pathophysiology. We have previously shown that CDSRR is caused by mutations in the KCNV2 (Potassium Voltage-Gated Channel Modifier Subfamily V Member 2) gene encoding the Kv8.2 subunit, a modulatory subunit of voltage-gated potassium (Kv) channels. In a recent study, we validated a novel mouse model of Kv8.2 deficiency at a late stage of the disease and showed that it replicates the human electroretinogram (ERG) phenotype. In this current study, we focused our investigation on young adult retinas to look for early markers of disease and evaluate their effect on retinal morphology, electrophysiology and immune response in both the Kv8.2 knockout (KO) mouse and in the Kv2.1 KO mouse, the obligate partner of Kv8.2 in functional retinal Kv channels. By evaluating the severity of retinal dystrophy in these KO models, we demonstrated that retinas of Kv KO mice have significantly higher apoptotic cells, a thinner outer nuclear cell layer and increased activated microglia cells in the subretinal space. Our results indicate that in the murine retina, the loss of Kv8.2 subunits contributes to early cellular and physiological changes leading to retinal dysfunction. These results could have potential implications in the early management of CDSRR despite its relatively nonprogressive nature in humans.

Shedding Light on Serpent Sight: The Visual Pigments of Henophidian Snakes

Publisher: Society for Neuroscience

Date: 10-06-2009

DOI: 10.1523/JNEUROSCI.0517-09.2009

The visual pigments of a deep-sea teleost, the pearl eye Scopelarchus analis

Publisher: The Company of Biologists

Date: 15-08-2007

DOI: 10.1242/JEB.006064

Abstract: The eyes of deep-sea fish have evolved to function under vastly reduced light conditions compared to those that inhabit surface waters. This has led to a bathochromatic shift in the spectral location of maximum absorbance(λmax) of their rod (RH1) pigments and the loss of cone photoreceptors. There are exceptions to this, however, as demonstrated by the deep-sea pearl eye Scopelarchus analis. Here we show the presence of two RH1 pigments (termed RH1A and RH1B) and a cone RH2 pigment. This is therefore the first time that the presence of a cone pigment in a deep-sea fish has been confirmed by molecular analysis. The λmaxvalues of the RH1A and RH1B pigments at 486 and 479 nm, respectively, have been determined by in vitro expression of the recombinant opsins and show the typical short-wave shifts of fish that live in deep water compared to surface dwellers. RH1B, however, is expressed only in more adult fish and lacks key residues for phosphorylation, indicating that it may not be involved in image formation. In contrast, the RH2 pigment has additional residues near the C terminus that may be involved in phosphorylation and does not show temporal changes in expression. The distribution of these pigments within the multiple retinae of S. analis is discussed.

Evolution and spectral tuning of visual pigments in birds and mammals

Publisher: The Royal Society

Date: 12-10-2009

DOI: 10.1098/RSTB.2009.0044

Abstract: Variation in the types and spectral characteristics of visual pigments is a common mechanism for the adaptation of the vertebrate visual system to prevailing light conditions. The extent of this ersity in mammals and birds is discussed in detail in this review, alongside an in-depth consideration of the molecular changes involved. In mammals, a nocturnal stage in early evolution is thought to underlie the reduction in the number of classes of cone visual pigment genes from four to only two, with the secondary loss of one of these genes in many monochromatic nocturnal and marine species. The trichromacy seen in many primates arises from either a polymorphism or duplication of one of these genes. In contrast, birds have retained the four ancestral cone visual pigment genes, with a generally conserved expression in either single or double cone classes. The loss of sensitivity to ultraviolet (UV) irradiation is a feature of both mammalian and avian visual evolution, with UV sensitivity retained among mammals by only a subset of rodents and marsupials. Where it is found in birds, it is not ancestral but newly acquired.

Into the blue: Gene duplication and loss underlie color vision adaptations in a deep-sea chimaera, the elephant shark Callorhinchus milii

Publisher: Cold Spring Harbor Laboratory

Date: 04-02-2009

DOI: 10.1101/GR.084509.108

Abstract: The cartilaginous fishes reside at the base of the gnathostome lineage as the oldest extant group of jawed vertebrates. Recently, the genome of the elephant shark, Callorhinchus milii , a chimaerid holocephalan, has been sequenced and therefore becomes the first cartilaginous fish to be analyzed in this way. The chimaeras have been largely neglected and very little is known about the visual systems of these fishes. By searching the elephant shark genome, we have identified gene fragments encoding a rod visual pigment, Rh1 , and three cone visual pigments, the middle wavelength-sensitive or Rh2 pigment, and two isoforms of the long wavelength-sensitive or LWS pigment, LWS1 and LWS2 , but no evidence for the two short wavelength-sensitive cone classes, SWS1 and SWS2 . Expression of these genes in the retina was confirmed by RT-PCR. Full-length coding sequences were used for in vitro expression and gave the following peak absorbances: Rh1 496 nm, Rh2 442 nm, LWS1 499 nm, and LWS2 548 nm. Unusually, therefore, for a deep-sea fish, the elephant shark possesses cone pigments and the potential for trichromacy. Compared with other vertebrates, the elephant shark Rh2 and LWS1 pigments are the shortest wavelength-shifted pigments of their respective classes known to date. The mechanisms for this are discussed and we provide experimental evidence that the elephant shark LWS1 pigment uses a novel tuning mechanism to achieve the short wavelength shift to 499 nm, which inactivates the chloride-binding site. Our findings have important implications for the present knowledge of color vision evolution in early vertebrates.

Enzyme Sequence and Its Relationship to Hyperbaric Stability of Artificial and Natural Fish Lactate Dehydrogenases

Publisher: Public Library of Science (PLoS)

Date: 30-04-2008

DOI: 10.1371/JOURNAL.PONE.0002042

Visual opsin expression and morphological characterization of retinal photoreceptors in the pouched lamprey ( Geotria australis ,

Publisher: Wiley

Date: 30-12-2020

DOI: 10.1002/CNE.25092

Abstract: L reys are extant members of the agnathan (jawless) vertebrates that erged ~500 million years ago, during a critical stage of vertebrate evolution when image-forming eyes first emerged. Among l rey species assessed thus far, the retina of the southern hemisphere pouched l rey, Geotria australis, is unique, in that it possesses morphologically distinct photoreceptors and expresses five visual photopigments. This study focused on determining the number of different photoreceptors present in the retina of G. australis and whether each cell type expresses a single opsin class. Five photoreceptor subtypes were identified based on ultrastructure and differential expression of one of each of the five different visual opsin classes (lws, sws1, sws2, rh1, and rh2) known to be expressed in the retina. This suggests, therefore, that the retina of G. australis possesses five spectrally and morphologically distinct photoreceptors, with the potential for complex color vision. Each photoreceptor subtype was shown to have a specific spatial distribution in the retina, which is potentially associated with changes in spectral radiance across different lines of sight. These results suggest that there have been strong selection pressures for G. australis to maintain broad spectral sensitivity for the brightly lit surface waters that this species inhabits during its marine phase. These findings provide important insights into the functional anatomy of the early vertebrate retina and the selection pressures that may have led to the evolution of complex color vision.

Cone visual pigments in two species of South American marsupials

Publisher: Elsevier BV

Date: 03-2009

DOI: 10.1016/J.GENE.2008.12.006

Abstract: Marsupials are largely confined to Australasia and to Central and South America. The visual pigments that underlie the photosensitivity of the retina have been examined in a number of species from the former group where evidence for trichromatic colour vision has been found, but none from the latter. In this paper, we report the cone opsin sequences from two nocturnal South American marsupial species, the gray short-tailed opossum, Monodelphis domestica, and the big-eared opossum, Didelphis aurita. Both are members of the Order Didelphimorphia (American opossums). For both species, only two classes of cone opsin were found, an SWS1 and an LWS sequence, and in vitro expression showed that the peak sensitivity of the SWS1 pigment is in the UV. Analysis of the Monodelphis genome confirms the absence of other classes of cone visual pigment genes. The SWS1 and LWS genes with 4 and 5 introns respectively, show the same exon-intron structure as found for these genes in all other vertebrates. The SWS1 gene shows a conserved synteny with flanking genes. The LWS gene is X-linked, as in all therian mammals so far examined, with a locus control region 1.54 kb upstream.

Detecting gene conversion: primate visual pigment genes.

Publisher: The Royal Society

Date: 22-09-1992

DOI: 10.1098/RSPB.1992.0114

Abstract: The effects of gene conversion can be detected in the DNA sequences of multigene families. We develop a permutation test of the significance of patterns of sequence mismatches, and apply it to the sequences of the red- and green-sensitive visual pigment genes of human and the diana monkey. Whereas conventional tests of the rate of sequence ergence are equivocal, the permutation test convincingly excludes ergence in the absence of gene conversion (p = 10(-6)).

The Molecular Evolution of Avian Ultraviolet- and Violet-Sensitive Visual Pigments

Publisher: Oxford University Press (OUP)

Date: 07-06-2007

DOI: 10.1093/MOLBEV/MSM109

Abstract: The shortwave-sensitive SWS1 class of vertebrate visual pigments range in lambda(max) from the violet (385-445 nm) to the ultraviolet (UV) (365-355 nm), with UV-sensitivity almost certainly ancestral. In birds, however, the UV-sensitive pigments present in a number of species have evolved secondarily from an avian violet-sensitive (VS) pigment. All avian VS pigments expressed in vitro to date encode Ser86 whereas Phe86 is present in all non-avian ultraviolet sensitive (UVS) pigments. In this paper, we show by site directed mutagenesis of avian VS pigments that Ser86 is required in an avian VS pigment to maintain violet-sensitivity and therefore underlies the evolution of avian VS pigments. The major mechanism for the evolution of avian UVS pigments from an ancestral avian VS pigment is undoubtedly a Ser90Cys substitution. However, Phe86, as found in the Blue-crowned trogon, will also short-wave shift the pigeon VS pigment into the UV whereas Ala86 and Cys86 which are also found in natural avian pigments do not generate short-wave shifts when substituted into the pigeon pigment. From available data on avian SWS1 pigments, it would appear that UVS pigments have evolved on at least 5 separate occasions and utilize 2 different mechanisms for the short-wave shift.

Cone dystrophy phenotype associated with a frameshift mutation (M280fsX291) in the  -subunit of cone specific transducin (GNAT2)

Publisher: BMJ

Date: 11-2003

DOI: 10.1136/BJO.87.11.1317

Abstract: To describe the phenotype of a three generation consanguineous Pakistani family containing six in iduals with autosomal recessive cone dystrophy caused by mutation in GNAT2. Five of the six affected in iduals underwent an ophthalmological examination, electrodiagnostic testing, fundus photography, autofluorescence imaging, and detailed psychophysical testing. All five examined patients had a history of nystagmus from infancy, photophobia, defective colour vision, and poor visual acuity. The nystagmus in three of the in iduals had lessened with time. Fundus examination revealed an abnormal foveal appearance, without frank atrophy or pigmentation. Electroretinography (ERG) revealed absent ISCEV cone flicker ERGs with some preservation of responses to short wavelength stimulation. Rod ERGs showed no definite abnormality, but maximal (mixed rod-cone) response a-wave litudes were mildly subnormal. Rudimentary residual colour vision was detected in three in iduals. There is clinical evidence of progressive visual acuity reduction in two older in iduals. Mutation in the alpha-subunit of cone specific transducin (GNAT2) is characterised by an infantile onset cone dystrophy. Some affected in iduals may show deterioration of visual acuity with time.

Visual pigments of the platypus: A novel route to mammalian colour vision

Publisher: Elsevier BV

Date: 03-2007

DOI: 10.1016/J.CUB.2007.01.037

How parrots see their colours: novelty in the visual pigments ofPlatycercus elegans

Publisher: The Company of Biologists

Date: 12-2013

DOI: 10.1242/JEB.094136

Abstract: Intraspecific differences in retinal physiology have been demonstrated in several vertebrate taxa and are often subject to adaptive evolution. Nonetheless, such differences are currently unknown in birds, despite variations in habitat, behaviour and visual stimuli that might influence spectral sensitivity. The parrot Platycercus elegans is a species complex with extreme plumage colour differences between (and sometimes within) subspecies, making it an ideal candidate for intraspecific differences in spectral sensitivity. Here, the visual pigments of P. elegans were fully characterised through molecular sequencing of five visual opsin genes and measurement of their absorbance spectra using microspectrophotometry. Three of the genes, LWS, SW1 and SWS2, encode for proteins similar to those found in other birds however, both the RH1 and RH2 pigments had polypeptides with carboxyl termini of different lengths and unusual properties that are unknown previously for any vertebrate visual pigment. Specifically, multiple RH2 transcripts and protein variants (short, medium and long) were identified for the first time that are generated by alternative splicing of downstream coding and non-coding exons. Our work provides the first complete characterisation of the visual pigments of a parrot, perhaps the most colourful order of birds, and moreover suggests more variability in avian eyes than hitherto considered.

Autosomal dominant cone–rod retinal dystrophy (CORD6) from heterozygous mutation of GUCY2D , which encodes retinal guanylate cyclase 1 1The authors have no proprietary interests in the materials menti

Publisher: Elsevier BV

Date: 2000

DOI: 10.1016/S0161-6420(99)00038-X

Abstract: To describe the clinical features of autosomal dominant cone-rod retinal dystrophy (CRD) in a British family mapping to chromosome 17p12-p13 (CORD6), with a heterozygous mutation (Glu837Asp/ Arg838Ser) of GUCY2D. A prospective, clinical family survey. Ten affected members of a family with autosomal dominant CRD. Full clinical examinations were undertaken. Selected affected family members underwent electrophysiologic evaluation, scotopic static perimetry, dark adaptometry, and color vision assessment. Clinical appearance and electroretinographic responses. Typical clinical and electroretinographic features of childhood-onset CRD were recorded. In addition, moderate myopia and pendular nystagmus were seen in affected in iduals. Color vision assessment in the youngest affected in idual showed no color discrimination on a tritan axis, but retention of significant red-green discrimination. Electronegative electroretinogram responses were seen on electrophysiology in the only young family member examined. The phenotype associated with GUCY2D CRD is clinically distinct from that associated with other dominant CRD loci. Unusual electroretinographic responses may indicate that this mutation of GUCY2D is associated with early defects in photoreceptor synaptic transmission to second-order neurons.

The role of voltage-gated ion channels in visual function and disease in mammalian photoreceptors

Publisher: Springer Science and Business Media LLC

Date: 13-07-2021

DOI: 10.1007/S00424-021-02595-2

Abstract: Light activation of the classical light-sensing retinal neurons, the photoreceptors, results in a graded change in membrane potential that ultimately leads to a reduction in neurotransmitter release to the post-synaptic retinal neurons. Photoreceptors show striking powers of adaptation, and for visual processing to function optimally, they must adjust their gain to remain responsive to different levels of ambient light intensity. The presence of a tightly controlled balance of inward and outward currents modulated by several different types of ion channels is what gives photoreceptors their remarkably dynamic operating range. Part of the resetting and modulation of this operating range is controlled by potassium and calcium voltage-gated channels, which are involved in setting the dark resting potential and synapse signal processing, respectively. Their essential contribution to visual processing is further confirmed in patients suffering from cone dystrophy with supernormal rod response (CDSRR) and congenital stationary night blindness type 2 (CSNB2), both conditions that lead to irreversible vision loss. This review will discuss these two types of voltage-gated ion channels present in photoreceptors, focussing on their structure and physiology, and their role in visual processing. It will also discuss the use and benefits of knockout mouse models to further study the function of these channels and what routes to potential treatments could be applied for CDSRR and CSNB2.

Spectral Tuning of Shortwave-sensitive Visual Pigments in Vertebrates†

Publisher: American Society for Photobiology

Date: 14-03-2007

DOI: 10.1562/2006-06-27-IR-952

SPLICE: A technique for generating in vitro spliced coding sequences from genomic DNA

Publisher: Future Science Ltd

Date: 12-2007

DOI: 10.2144/000112588

Abstract: We describe a rapid and cost-effective technique for the in vitro removal of introns and other unwanted regions from genomic DNA to generate a single sequence of continuous coding capacity, where tissues required for RNA extraction and complementary DNA synthesis are unavailable. Based on an overlapping fusion-PCR strategy, we name this procedure SPLICE (for swift PCR for ligating in vitro constructed exons). As proof-of-principle, we used SPLICE successfully to generate a single piece of DNA containing the coding region of a five-exon gene, the short-wavelength-sensitive 1 (SWS1) opsin gene, from genomic DNA extracted from the brown lemur, Eulemur fulvus, in only two short rounds of PCR. Where the genomic structure and sequence is known, this technique may be universally applied to any gene expressed in any organism to generate a practical unit for investigating the function of a particular gene of interest. In this report, we provide a detailed protocol, experimental considerations, and suggestions for troubleshooting.

Cone monochromacy and visual pigment spectral tuning in wobbegong sharks

Publisher: The Royal Society

Date: 19-09-2012

DOI: 10.1098/RSBL.2012.0663

Abstract: Much is known regarding the evolution of colour vision in nearly every vertebrate class, with the notable exception of the elasmobranchs. While multiple spectrally distinct cone types are found in some rays, sharks appear to possess only a single class of cone and, therefore, may be colour blind. In this study, the visual opsin genes of two wobbegong species, Orectolobus maculatus and Orectolobus ornatus , were isolated to verify the molecular basis of their monochromacy. In both species, only two opsin genes are present, RH1 (rod) and LWS (cone), which provide further evidence to support the concept that sharks possess only a single cone type. Examination of the coding sequences revealed substitutions that account for interspecific variation in the photopigment absorbance spectra, which may reflect the difference in visual ecology between these species.

X-Linked Cone Dysfunction Syndrome with Myopia and Protanopia

Publisher: Elsevier BV

Date: 08-2005

DOI: 10.1016/J.OPHTHA.2005.02.021

Abstract: To perform a detailed clinical, psychophysical, and molecular assessment of members of 4 families with an unusual X-linked cone dysfunction syndrome associated with myopia. Affected and unaffected members of 4 British nonconsanguineous families. Subjects underwent both detailed clinical examination and psychophysical testing. After informed consent was obtained, blood s les were taken for DNA extraction, and molecular genetic analysis was performed. The strategy for molecular analysis was to lify the coding regions of the long and middle wavelength-sensitive cone opsin genes and the upstream locus control region by polymerase chain reaction and to examine these fragments for mutations by sequencing of DNA. The phenotype was almost identical in all 4 families, consisting of moderate to high myopia, astigmatism, moderately reduced acuity, and normal fundi. Electroretinography showed abnormal cone but normal rod responses. Psychophysical testing showed a selective impairment of long cones in combination with well-preserved middle cone and short cone function. There was no evidence to suggest that the phenotype was progressive. Molecular analysis of the X-linked opsin gene array in the 4 families indicated that affected males have inherited the same X-chromosome from their mother. In 2 families, a long/middle hybrid gene was detected. In a third family, the commonly described deleterious Cys203Arg amino acid substitution was identified in both the long and middle opsin genes. In the fourth family, the only abnormality was absence of a middle opsin exon 2 the cause of the protanopia in this family is uncertain. The X-linked cone dysfunction syndrome associated with myopia and dichromacy described here has many similarities to Bornholm eye disease, a condition previously mapped to Xq28. Except for the Cys203Arg substitution in one family, no alterations in the opsin gene array were identified that could underlie the cone dysfunction. It is therefore possible that the cone dysfunction may have a genetic origin different from that of the dichromacy.

The influence of ontogeny and light environment on the expression of visual pigment opsins in the retina of the black bream, Acanthopagrus butcheri

Publisher: The Company of Biologists

Date: 05-2008

DOI: 10.1242/JEB.012047

Abstract: The correlation between ontogenetic changes in the spectral absorption characteristics of retinal photoreceptors and expression of visual pigment opsins was investigated in the black bream, Acanthopagrus butcheri. To establish whether the spectral qualities of environmental light affected the complement of visual pigments during ontogeny, comparisons were made between fishes reared in: (1) broad spectrum aquarium conditions (2) short wavelength-reduced conditions similar to the natural environment or (3) the natural environment (wild-caught). Microspectrophotometry was used to determine the wavelengths of spectral sensitivity of the photoreceptors at four developmental stages: larval, post-settlement, juvenile and adult. The molecular sequences of the rod (Rh1) and six cone (SWS1, SWS2A and B, Rh2Aα and β, and LWS) opsins were obtained and their expression levels in larval and adult stages examined using quantitative RT-PCR. The changes in spectral sensitivity of the cones were related to the differing levels of opsin expression during ontogeny. During the larval stage the predominantly expressed opsin classes were SWS1, SWS2B and Rh2Aα, contrasting with SWS2A, Rh2Aβ and LWS in the adult. An increased proportion of long wavelength-sensitive double cones was found in fishes reared in the short wavelength-reduced conditions and in wild-caught animals, indicating that the expression of cone opsin genes is also regulated by environmental light.

Evolution of the shut-off steps of vertebrate phototransduction

Publisher: The Royal Society

Date: 2018

DOI: 10.1098/RSOB.170232

Abstract: Different isoforms of the genes involved in phototransduction are expressed in vertebrate rod and cone photoreceptors, providing a unique ex le of parallel evolution via gene duplication. In this study, we determine the molecular phylogeny of the proteins underlying the shut-off steps of phototransduction in the agnathan and jawed vertebrate lineages. For the G-protein receptor kinases (GRKs), the GRK1 and GRK7 isions arose prior to the ergence of tunicates, with further expansion during the two rounds of whole-genome duplication (2R) subsequently, jawed and agnathan vertebrates retained different subsets of three isoforms of GRK. For the arrestins, gene expansion occurred during 2R. Importantly, both for GRKs and arrestins, the respective rod isoforms did not emerge until the second round of 2R, just prior to the separation of jawed and agnathan vertebrates. For the triplet of proteins mediating shut-off of the G-protein transducin, RGS9 erged from RGS11, probably at the second round of 2R, whereas Gβ5 and R9AP appear not to have undergone 2R expansion. Overall, our analysis provides a description of the duplications and losses of phototransduction shut-off genes that occurred during the transition from a chordate with only cone-like photoreceptors to an ancestral vertebrate with both cone- and rod-like photoreceptors.

Blue cone monochromatism: a phenotype and genotype assessment with evidence of progressive loss of cone function in older individuals

Publisher: Springer Science and Business Media LLC

Date: 16-04-2004

DOI: 10.1038/SJ.EYE.6701391

The evolution of early vertebrate photoreceptors

Publisher: The Royal Society

Date: 12-10-2009

DOI: 10.1098/RSTB.2009.0099

Abstract: Meeting the challenge of s ling an ancient aquatic landscape by the early vertebrates was crucial to their survival and would establish a retinal bauplan to be used by all subsequent vertebrate descendents. Image-forming eyes were under tremendous selection pressure and the ability to identify suitable prey and detect potential predators was thought to be one of the major drivers of speciation in the Early Cambrian. Based on the fossil record, we know that hagfishes, l reys, holocephalans, elasmobranchs and lungfishes occupy critical stages in vertebrate evolution, having remained relatively unchanged over hundreds of millions of years. Now using extant representatives of these ‘living fossils’, we are able to piece together the evolution of vertebrate photoreception. While photoreception in hagfishes appears to be based on light detection and controlling circadian rhythms, rather than image formation, the photoreceptors of l reys fall into five distinct classes and represent a critical stage in the dichotomy of rods and cones. At least four types of retinal cones s le the visual environment in l reys mediating photopic (and potentially colour) vision, a s ling strategy retained by lungfishes, some modern teleosts, reptiles and birds. Trichromacy is retained in cartilaginous fishes (at least in batoids and holocephalans), where it is predicted that true scotopic (dim light) vision evolved in the common ancestor of all living gnathostomes. The capacity to discriminate colour and balance the tradeoff between resolution and sensitivity in the early vertebrates was an important driver of eye evolution, where many of the ocular features evolved were retained as vertebrates progressed on to land.

Discovery Projects - Grant ID: DP0343933

Start Date: 06-2003

End Date: 01-2006

Amount: $285,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0662985

Start Date: 2006

End Date: 03-2010

Amount: $210,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0878206

Start Date: 2008

End Date: 12-2011

Amount: $345,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0558844

Start Date: 2005

End Date: 01-2008

Amount: $330,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP110103294

Start Date: 2011

End Date: 12-2013

Amount: $375,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0209452

Start Date: 2002

End Date: 12-2004

Amount: $345,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP140102117

Start Date: 2014

End Date: 06-2017

Amount: $380,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0562497

Start Date: 12-2005

End Date: 02-2009

Amount: $105,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE180100056

Start Date: 2018

End Date: 03-2019

Amount: $621,198.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE140100116

Start Date: 03-2014

End Date: 03-2015

Amount: $400,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP180101688

Start Date: 01-2018

End Date: 12-2023

Amount: $371,347.00

Funder: Australian Research Council