Memoria de actividades: Año 2005

Purpose: In Bornholm eye disease, a defect in the splicing of transcripts from a variant OPN1LW opsin gene leads to a depletion in spliced transcript levels and, consequently, a reduction in photopigment in photoreceptors expressing the variant gene. Methods: Myopic and age-matched control subjects were drawn from the Western Australian Pregnancy Cohort (Raine) Study and the Norfolk Island Eye Study groups. The OPN1LW opsin gene was amplified using long-range PCR methodology and was fully sequenced. Expression of variant opsins was evaluated using quantitative PCR (qPCR). RNA secondary structure changes arising from identified variants were predicted by modeling. Results: Forty-two nucleotide sites were found to vary across the 111 subjects studied. Of these, 15 had not been previously reported, with three present only in myopic individuals. Expression of these variants in transfected human embryonic kidney (HEK293T) cells demonstrated that splicing efficiencies were not affected. However, gene transcripts from two of the three variants were significantly depleted. RNA secondary structure modeling predicted that these single nucleotide changes could affect RNA stability. Conclusions: None of the variants identified in myopic individuals appeared to alter the efficiency of transcript splicing. However, two resulted in a significant reduction in the number of spliced and unspliced transcripts, indicating an overall reduction in steady-state transcript stability. Such a change would be expected to result in a reduced amount of photopigment, and this may be a contributing factor in the development of myopia.</p

Visual pigments in a palaeognath bird, the emu Dromaius novaehollandiae : implications for spectral sensitivity and the origin of ultraviolet vision

A comprehensive description of the spectral characteristics of retinal photoreceptors in palaeognaths is lacking. Moreover, controversy exists with respect to the spectral sensitivity of the short-wavelength-sensitive-1 (SWS1) opsin-based visual pigment expressed in one type of single cone: previous microspectrophotometric (MSP) measurements in the ostrich (Struthio camelus) suggested a violet-sensitive (VS) SWS1 pigment, but all palaeognath SWS1 opsin sequences obtained to date (including the ostrich) imply that the visual pigment is ultraviolet-sensitive (UVS). In this study, MSP was used to measure the spectral properties of visual pigments and oil droplets in the retinal photoreceptors of the emu (Dromaius novaehollandiae). Results show that the emu resembles most other bird species in possessing four spectrally distinct single cones, as well as double cones and rods. Four cone and a single rod opsin are expressed, each an orthologue of a previously identified pigment. The SWS1 pigment is clearly UVS (wavelength of maximum absorbance [λmax] = 376 nm), with key tuning sites (Phe86 and Cys90) consistent with other vertebrate UVS SWS1 pigments. Palaeognaths would appear, therefore, to have UVS SWS1 pigments. As they are considered to be basal in avian evolution, this suggests that UVS is the most likely ancestral state for birds. The functional significance of a dedicated UVS cone type in the emu is discussed.9 page(s

Enhanced short-wavelength sensitivity in the blue-tongued skink Tiliqua rugosa

Despite lizards using a wide range of colour signals, the limited variation in photoreceptor spectral sensitivities across lizards suggests only weak selection for species-specific, spectral tuning of photoreceptors. Some species, however, have enhanced short-wavelength sensitivity, which probably helps with the detection of signals rich in ultraviolet and short wavelengths. In this study, we examined the visual system of Tiliqua rugosa, which has an ultraviolet/blue tongue, to gain insight into this species' visual ecology. We used electroretinograms, opsin sequencing and immunohistochemical labelling to characterize whole-eye spectral sensitivity and the elements that shape it. Our findings reveal that T. rugosa expresses all five opsins typically found in lizards (SWS1, SWS2, RH1, RH2 and LWS) but possesses greatly enhanced short-wavelength sensitivity compared with other diurnal lizards. This enhanced short-wavelength sensitivity is characterized by a broadening of the spectral sensitivity curve of the eye towards shorter wavelengths while the peak sensitivity of the eye at longer wavelengths (560 nm) remains similar to that of other diurnal lizards. While an increased abundance of SWS1 photoreceptors is thought to mediate elevated ultraviolet sensitivity in a couple of other lizard species, SWS1 photoreceptor abundance remains low in this species. Instead, our findings suggest that short-wavelength sensitivity is driven by multiple factors which include a potentially red-shifted SWS1 photoreceptor and the absence of short-wavelength-absorbing oil droplets. Examining the coincidence of enhanced short-wavelength sensitivity with blue tongues among lizards of this genus will provide further insight into the co-evolution of conspecific signals and whole-eye spectral sensitivity

Pushing the limits of photoreception in twilight conditions: the rod-like cone retina of the deep-sea pearlsides

Most vertebrates have a duplex retina comprising two photoreceptor types, rods for dim-light (scotopic) vision and cones for bright-light (photopic) and color vision. However, deep-sea fishes are only active in dim-light conditions; hence, most species have lost their cones in favor of a simplex retina composed exclusively of rods. Although the pearlsides, Maurolicus spp., have such a pure rod retina, their behavior is at odds with this simplex visual system. Contrary to other deep-sea fishes, pearlsides are mostly active during dusk and dawn close to the surface, where light levels are intermediate (twilight or mesopic) and require the use of both rod and cone photoreceptors. This study elucidates this paradox by demonstrating that the pearlside retina does not have rod photoreceptors only; instead, it is composed almost exclusively of transmuted cone photoreceptors. These transmuted cells combine the morphological characteristics of a rod photoreceptor with a cone opsin and a cone phototransduction cascade to form a unique photoreceptor type, a rod-like cone, specifically tuned to the light conditions of the pearlsides' habitat (blue-shifted light at mesopic intensities). Combining properties of both rods and cones into a single cell type, instead of using two photoreceptor types that do not function at their full potential under mesopic conditions, is likely to be the most efficient and economical solution to optimize visual performance. These results challenge the standing paradigm of the function and evolution of the vertebrate duplex retina and emphasize the need for a more comprehensive evaluation of visual systems in general

Maurolicus_spp_OpsinGeneConversionTree_RAxML

rh2 opsin gene conversion phylogeny based on a ML reconstruction using RAxM

Maurolicus_spp_GalphaTransducinTree_RAxML

Vertebrate Gα transducin gene phylogeny based on a ML reconstruction using RAxM

Maurolicus_spp_OpsinDatasetAlignment

Sequence alignment for gene coding region (CDS) inferred vertebrate opsin gene phylogen