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

Lampreys are extant members of the agnathan (jawless) vertebrates that diverged ~500 million years ago, during a critical stage of vertebrate evolution when image-forming eyes first emerged. Among lamprey species assessed thus far, the retina of the southern hemisphere pouched lamprey, 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.

Modeling binary and graded cone cell fate patterning in the mouse retina.

Nervous systems are incredibly diverse, with myriad neuronal subtypes defined by gene expression. How binary and graded fate characteristics are patterned across tissues is poorly understood. Expression of opsin photopigments in the cone photoreceptors of the mouse retina provides an excellent model to address this question. Individual cones express S-opsin only, M-opsin only, or both S-opsin and M-opsin. These cell populations are patterned along the dorsal-ventral axis, with greater M-opsin expression in the dorsal region and greater S-opsin expression in the ventral region. Thyroid hormone signaling plays a critical role in activating M-opsin and repressing S-opsin. Here, we developed an image analysis approach to identify individual cone cells and evaluate their opsin expression from immunofluorescence imaging tiles spanning roughly 6 mm along the D-V axis of the mouse retina. From analyzing the opsin expression of ~250,000 cells, we found that cones make a binary decision between S-opsin only and co-expression competent fates. Co-expression competent cells express graded levels of S- and M-opsins, depending nonlinearly on their position in the dorsal-ventral axis. M- and S-opsin expression display differential, inverse patterns. Using these single-cell data, we developed a quantitative, probabilistic model of cone cell decisions in the retinal tissue based on thyroid hormone signaling activity. The model recovers the probability distribution for cone fate patterning in the mouse retina and describes a minimal set of interactions that are necessary to reproduce the observed cell fates. Our study provides a paradigm describing how differential responses to regulatory inputs generate complex patterns of binary and graded cell fates.

Soluble opsin is present in human vitreous.

The purpose of this research project was to evaluate if intravitreal opsins are present in human vitreous liquid which is, so far, unknown. Therefore a pilot study was conducted including 22 vitreal samples which were harvested at the beginning of a standard 23-gauge three-port pars plana vitrectomy for macular pucker, diabetic vitreous hemorrhage or vitreal floater removal as well as macular hole closure or vitreomacular traction relief from the central vitreous body. No adverse events or serious side effects occurred. All samples were immediately stabilized by human albumin and arginine and subsequently frozen. Short-wavelength cone opsin concentrations were analyzed by enzyme immune essay (EIA) with anti-proteolytic 400 mM arginine, pH 8.7, in the antigen capture phase. Intravitreal short-wavelength cone opsins were detected in all analyzed samples and respective concentrations ranged at levels of 157 pg/ml ± 73 pg/ml (MV ± SD; range: 27 pg/m-286 pg/ml). Eyes with MP/MH/DVH/VMT and VF exhibited intravitreal short-wavelength cone opsin concentrations of 189 pg/ml ± 68 pg/ml (range: 72 pg/ml-286 pg/ml)/96 pg/ml ± 39 pg/ml (range: 50 pg/ml-138 pg/ml)/126 pg/ml ± 88 pg/ml (range: 27 pg/ml-198 pg/ml)/224 pg/ml and 121 pg/ml. Further studies will quantify the intravitreal opsin pattern of all visual opsins and compare these concentrations between different vitreoretinal diseases. This in turn might offer a better pathophysiological understanding and new diagnostic and therapeutic strategies for various eye pathologies. As a hypothesis, soluble opsins might be a biomarker for retinal damage comparable to creatinine for kidney damage.

Comparative retinal morphology of the platypus.

The purpose of this study is to identify evolutionary origin and fate of anatomic features of the duck-billed platypus eye. Eyes from the duck-billed platypus and four key evolutionary basal vertebrates (Pacific hagfish, north hemisphere sea lamprey, and Australian and South American lungfishes) were prepared for light microscopy. In addition to a standard panel of stains, tissues were immunostained against a variety of rod and cone opsins. Finally, published opsin sequences of platypus and several other vertebrate species were aligned and compared with immunohistochemical results. A complete scleral cartilage similar to that seen in birds, reptiles and amphibians encloses the platypus eye. This feature is present in sharks and rays, and in extant relatives of tetrapods, the lungfishes. The choroid lacks a tapetum. The retina is largely avascular and is rod-dominated, with a minority of red- and blue- cone immunoreactive photoreceptors. Like marsupials and many nonmammalian vertebrates, cones contain clear inner segment droplets. Double cones were present, a feature not found in eutherian mammals or marsupials. Evaluation of opsins indicates that red and blue immunoreactive cone opsins, but not rhodopsin, are present in the most basal of the extant species examined, the Pacific hagfish. Rhodopsin appears in the Australian and South American lungfishes, establishing emergence of this pigment in an extant relative of tetrapods. Unlike eyes of eutherian mammals, the platypus eye has retained morphologic features present in early tetrapods such as amphibians and their evolutionarily basal sister group, the lungfishes. These include scleral cartilage, double cones and cone droplets. In the platypus, as in other mammals, rod rhodopsin is the predominant photoreceptor pigment, at expense of the cone system.

Expressions of rod and cone photoreceptor-like proteins in human epidermis.

Previous reports have suggested the existence of photoreceptors for visible radiation at the surface of the human body. Rhodopsin is a well-known photosensitive protein found in the rod cells of the retina and detects light/dark contrast. Cone opsins are also photosensitive receptors in the cone cells of the retina and detect colour. Here, we describe immunochemical studies using anti-rhodopsin and anti-opsin antibodies on human skin. Both mouse retina and human epidermis showed clear immunoreactivity with each antibody. Interestingly, immunoreactivity against longer-wavelength opsin antibody was observed in the basal layer of the epidermis, while immunoreactivity against rhodopsin and shorter-wavelength opsin was observed in the upper layer. PCR analysis confirmed the expression of rhodopsin-like and opsin-like genes in human retina and the skin. These results suggest that a series of proteins, which play a crucial role in visual perception, are expressed in human epidermis.