Feeding ecology of two planktonic sculpins, Comephorus baicalensis and Comephorus dybowskii (Comephoridae), in Lake Baikal

Planktonic sculpins (Comephorus baicalensis and Comephorus dybowskii) are endemic to Lake Baikal, and their migration behavior is characterized by their strange movements, which occur only vertically. We investigated their detailed food sources at each growth stage by stable isotope analyses in combination with stomach content analysis. At all growth stages, both fishes and amphipods were the main diet for C. baicalensis, whereas amphipods alone were the main diet for C. dybowskii. Our results indicate that the relationship between the two species shifts from a competitive interaction to a predator–prey interaction with the growth stages of C. baicalensis.     

The relationship of ocular morphology to feeding modes and activity periods in shallow marine teleosts from New Zealand

Synopsis Thirty one species of shallow water teleosts were captured from the NE coast of New Zealand. Ocular morphology was assessed in terms of eye size, pupil shape, theoretical sensitivity and acuity based on retinal morphology, and regional distribution of photoreceptors within the retina. Eye size was relatively or absolutely larger in carnivores than herbivores. Diurnal planktivores and nocturnal species of small body size maximise vision by having relatively large eyes. Anterior aphakic spaces were present in most of the species examined, and 25% of the species also had posterior aphakic spaces. Theoretical sensitivity was generally higher among nocturnal than diurnal species, however, a number of benthic and pelagic carnivores showed retinal specialization for enhanced sensitivity. Diurnal species displayed high spatial acuity, with maximum acuity occurring in carnivorous species. Crepuscular species had either high or low acuity, whereas that of nocturnal species was generally lower than in diurnal species. Ten species displayed regional variation in rod density, with crepuscular and nocturnal species showing streaks of high rod density in the retina. Eleven species of carnivores displayed regional variation in cone density, with highest density usually occurring in the caudal part of the retina. In most of the species with areas of high cone density, there was a forward visual axis that coincided with the location of the aphakic space, suggestive of accomodation along that axis.     

Morphometry of the Gill Respiratory Area in Comephorus dybowskii and Some Other Endemic Cottoidei of Lake Baikal

Abstract Morphometric investigations of the gill apparatus in the small golomyanka, Comephorus dybowskii, revealed a unique structure and a very small gill respiratory area (GRSA) compared with other endemic Cottoidei of Lake Baikal: from 5.5 to about 7 times smaller than in the pelagic waterside sculpins. Cottocomephorus grewingki and C. inermis, and about 3 times smaller than in groundling deep-water Cotinella boulengeri. This is an extremely small GRSA considering no accessory respiratory organs are present. Scanning electron microscopic observations revealed numerous chloride cells in the epithelium of golomyanka gill lamellae but not in the sculpin lamellae. Chloride cells probably restrict gas exchange in the lamellae considerably. The results suggest that golomyankas have a small oxygen requirement.     

Ontogeny of the photoreceptors in the embryonic retina of the viviparous guppy,Poecilia reticulata P. (Teleostei)

Summary Ultrastructural analyses of retinal development in the guppy embryo show that at midgestation all types of photoreceptors are differntiated 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.This work was in part subsidized by a grant from the Medical Research Council of Ireland to Y.W.K.     

Retinal pigmentation, visual acuity and brightness levels.

This study investigates the hypothesis that the degree of retinal pigmentation in the human eye is adaptive as it relates to the maintenance of visual acuity in optically stressful environments, deserts and snowfields. Eighty-four subjects were examined, an estimation of their degree of retinal pigmentation made by ophthalmoscopic examination and their binocular visual acuity tested over ten levels of brightness. The general level of retinal pigmentation did not influence mean visual acuity within the levels of brightness used in this study. The hypothesis was, therefore, rejected, but with the proviso that this study should be extended to even higher levels of brightness than were obtained here. There was no difference in mean pupil size at various levels of illumination between individuals grouped by degree of retinal pigmentation.     

Deuterium enrichment of vitamin A at the C20 position slows the formation of detrimental vitamin A dimers in wild-type rodents

Degenerative eye diseases are the most common causes of untreatable blindness. Accumulation of lipofuscin (granular deposits) in the retinal pigment epithelium (RPE) is a hallmark of major degenerative eye diseases such as Stargardt disease, Best disease, and age-related macular degeneration. The intrinsic reactivity of vitamin A leads to its dimerization and to the formation of pigments such as A2E, and is believed to play a key role in the formation of ocular lipofuscin. We sought a clinically pragmatic method to slow vitamin A dimerization as a means to elucidate the pathogenesis of macular degenerations and to develop a therapeutic intervention. We prepared vitamin A enriched with the stable isotope deuterium at carbon twenty (C20-D(3)-vitamin A). Results showed that dimerization of deuterium-enriched vitamin A was considerably slower than that of vitamin A at natural abundance as measured in vitro. Administration of C20-D(3)-vitamin A to wild-type rodents with no obvious genetic defects in vitamin A processing, slowed A2E biosynthesis. This study elucidates the mechanism of A2E biosynthesis and suggests that administration of C20-D(3)-vitamin A may be a viable, long-term approach to retard vitamin A dimerization and by extension, may slow lipofuscin deposition and the progression of common degenerative eye diseases.     

The eyes of a patrolling butterfly: visual field and eye structure in the Orange Sulphur, Colias eurytheme (Lepidoptera, Pieridae)

Sensory information plays a critical role in determining an animal's behavior on both proximate and evolutionary timescales. Butterflies, like many other insects, use vision extensively over their lifetimes, and yet relatively little work has been published to date on their visual capabilities. We describe the visual system of a pierid butterfly, Colias eurytheme, with the ultimate goal of better understanding its role in shaping the behavior of this animal. We made several measurements: visual field dimensions, eye surface area, interommatidial angle (Deltaphi), facet diameter (D), and eye parameter (p). C. eurytheme had a large visual field and considerable regional variation in visual acuity, as inferred by Deltaphi and D. When compared to females, males had larger eye surface areas, smaller Deltaphi, and larger D in all regions except ventrally. Both sexes had proportionally large eye surface areas compared to other butterflies. Minimum p in males was small, indicating that some regions of their eyes may operate close to the diffraction limit. Finally, we found that both eye surface area and D scaled positively, but with negative allometry to body size. We discuss the relevance of these visual characteristics to the biology and behavior of C. eurytheme.     

A study of the intestinal microbiomes of the Lake Baikal oilfishes (Cottoidei,Comephoridae)

A comparative analysis of the intestinal microbiomes of some representatives of the Lake Baikal endemic family Comephoridae—the big oilfish Comephorus baicalensis (Pallas, 1776) and the little oilfish C. dybowski (Korotneff, 1904)—has been performed for the first time. The phylotype Akkermansia (phylum Verrucomicrobia) was detected in the C. dybowski microbiome, while Alistipes, Bacteroides, Chryseobacterium, Prevotella (Bacteroidetes), and Peptoniphilus (Firmicutes), were found in the C. baicalensis microbiome. Their presence in the intestine is associated with an elevated lipid uptake or an increase in the human and animal body weight. It is hypothesized that these microorganisms are involved in the lipid metabolism of the oilfish and determine their morphophysiological adaptations to pelagic life.     

Melanopsin and mechanisms of non-visual ocular photoreception

In addition to rods and cones, the mammalian eye contains a third class of photoreceptor, the intrinsically photosensitive retinal ganglion cell (ipRGC). ipRGCs are heterogeneous irradiance-encoding neurons that primarily project to non-visual areas of the brain. Characteristics of ipRGC light responses differ significantly from those of rod and cone responses, including depolarization to light, slow on- and off-latencies, and relatively low light sensitivity. All ipRGCs use melanopsin (Opn4) as their photopigment. Melanopsin resembles invertebrate rhabdomeric photopigments more than vertebrate ciliary pigments and uses a G(q) signaling pathway, in contrast to the G(t) pathway used by rods and cones. ipRGCs can recycle chromophore in the absence of the retinal pigment epithelium and are highly resistant to vitamin A depletion. This suggests that melanopsin employs a bistable sequential photon absorption mechanism typical of rhabdomeric opsins.     

C20-D3-vitamin A slows lipofuscin accumulation and electrophysiological retinal degeneration in a mouse model of Stargardt disease

Stargardt disease, also known as juvenile macular degeneration, occurs in approximately one in 10,000 people and results from genetic defects in the ABCA4 gene. The disease is characterized by premature accumulation of lipofuscin in the retinal pigment epithelium (RPE) of the eye and by vision loss. No cure or treatment is available. Although lipofuscin is considered a hallmark of Stargardt disease, its mechanism of formation and its role in disease pathogenesis are poorly understood. In this work we investigated the effects of long-term administration of deuterium-enriched vitamin A, C20-D(3)-vitamin A, on RPE lipofuscin deposition and eye function in a mouse model of Stargardt's disease. Results support the notion that lipofuscin forms partly as a result of the aberrant reactivity of vitamin A through the formation of vitamin A dimers, provide evidence that preventing vitamin A dimerization may slow disease related, retinal physiological changes and perhaps vision loss and suggest that administration of C20-D(3)-vitamin A may be a potential clinical strategy to ameliorate clinical symptoms resulting from ABCA4 genetic defects.     

A Functional Kinase Homology Domain Is Essential for the Activity of Photoreceptor Guanylate Cyclase 1

Phototransduction is carried out by a signaling pathway that links photoactivation of visual pigments in retinal photoreceptor cells to a change in their membrane potential. Upon photoactivation, the second messenger of phototransduction, cyclic GMP, is rapidly degraded and must be replenished during the recovery phase of phototransduction by photoreceptor guanylate cyclases (GCs) GC1 (or GC-E) and GC2 (or GC-F) to maintain vision. Here, we present data that address the role of the GC kinase homology (KH) domain in cyclic GMP production by GC1, the major cyclase in photoreceptors. First, experiments were done to test which GC1 residues undergo phosphorylation and whether such phosphorylation affects cyclase activity. Using mass spectrometry, we showed that GC1 residues Ser-530, Ser-532, Ser-533, and Ser-538, located within the KH domain, undergo light- and signal transduction-independent phosphorylation in vivo. Mutations in the putative Mg²⁺ binding site of the KH domain abolished phosphorylation, indicating that GC1 undergoes autophosphorylation. The dramatically reduced GC activity of these mutants suggests that a functional KH domain is essential for cyclic GMP production. However, evidence is presented that autophosphorylation does not regulate GC1 activity, in contrast to phosphorylation of other members of this cyclase family.     

Accumulation of the Raf-1 kinase inhibitory protein (Rkip) is associated with Cep290-mediated photoreceptor degeneration in ciliopathies

Primary cilia regulate polarized protein trafficking in photoreceptors, which are dynamic and highly compartmentalized sensory neurons of retina. The ciliary protein Cep290 modulates cilia formation and is frequently mutated in syndromic and non-syndromic photoreceptor degeneration. However, the underlying mechanism of associated retinopathy is unclear. Using the Cep290 mutant mouse rd16 (retinal degeneration 16), we show that Cep290-mediated photoreceptor degeneration is associated with aberrant accumulation of its novel interacting partner Rkip (Raf-1 kinase inhibitory protein). This effect is phenocopied by morpholino-mediated depletion of cep290 in zebrafish. We further demonstrate that ectopic accumulation of Rkip leads to defective cilia formation in zebrafish and cultured cells, an effect mediated by its interaction with the ciliary GTPase Rab8A. Our data suggest that Rkip prevents cilia formation and is associated with Cep290-mediated photoreceptor degeneration. Furthermore, our results indicate that preventing accumulation of Rkip could potentially ameliorate such degeneration.     

Lipids and fatty acids of two pelagic cottoid fishes (Comephorus spp) endemic to Lake Baikal

Matured females of two Lake Baikal endemic fish species, Comephorus baicalensis and Comephorus dybowski, have been investigated for lipid of the whole body and specific tissues (liver, muscles, ovaries), phospholipid classes and fatty acids of neutral and polar lipids. Total lipid in the body (38.9% fresh weight), liver (23.5%) and muscles (14.5%) of C. baicalensis were greater than those of C. dybowski (4.7, 8.7 and 2.6%, respectively); only their ovaries were similar (5.3 and 5.6% lipid, respectively). In both species, phosphatidylcholine and phosphatidylethanolamine were the major phospholipids, ranging from 60.7 to 75.1% of total phospholipid and 14.5–25.7%, respectively. In most cases, monounsaturated fatty acids (MUFA) were the major fatty acid group in C. baicalensis, whereas polyunsaturated fatty acids (PUFA) were the major group in C. dybowski. The MUFA 18:1(n-9) prevailed over other fatty acids in C. baicalensis and varied from 19% in polar lipids of muscles to 56.1% in neutral lipids of muscles. In polar lipid of C. dybowski, the PUFA 22:6(n-3) prevailed over other fatty acids in muscles and ovaries, while 16:0 dominated polar liver lipids and neutral lipids of all tissues. Other major fatty acids included 16:1(n-7), 18:1(n-7), and 20:5(n-3). Values of the (n-3)/(n-6) fatty acid ratio for neutral lipids of C. baicalensis (0.5–0.9) are well below the range of values characteristic either for marine or freshwater fish, while these values for polar lipids (1.6–1.8) are in the range typical of freshwater fish. Neutral lipid fatty acid ratios in C. dybowski (2.5–3.1) allow it to be assigned to freshwater fish, but polar lipids (2.8–3.7) leave it intermediary between freshwater and marine fish.     

In-vivo labeling of (3H)D-aspartate uptake sites in monkey retina

Summary Following prolonged topical application of (³H)D-aspartate in vivo, selective labeling of three distinct cell classes was observed in light-microscopic radioautographs from squirrel monkey retina. Müller (glial) cell bodies and their processes were intensely and consistently labeled in all preparations. Moderately labeled perikarya were occasionally detected in the area of bipolar cells, within the inner nuclear layer. These were particularly numerous in sections from the central retina where an intense diffuse labeling of the inner plexiform layer was also prominent. Finally, moderate to dense accumulations of label were observed over the cell bodies, internal segments and fiber processes of cone photoreceptors. These results strongly suggest that cones, as well as a sub-population of bipolar cells, use glutamate and/or aspartate as neurotransmitter(s) in monkey retina.     

Eye and optic lobe metamorphosis in the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae)

Nearly nothing is known about the transition that visual brain regions undergo during metamorphosis, except for Drosophila in which larval eyes and the underlying neural structure are strongly reduced. We have studied the larvae of the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae), which are sophisticated visually oriented predators characterized by six elaborate stemmata on each side of the head and an associated large optic lobe. We used general neurohistological staining and 3D reconstruction to determine how the eyes and optic lobe of T. marmoratus change morphologically during metamorphosis. We find that in third (last) instar larvae, the adult neuropils are already forming de novo dorsally and slightly anteriorly to the larval neuropils, while the latter rapidly degenerate. Larval eyes are eventually reduced to distinct areas with dark pigmentation. This complete reorganization, which may be an evolutionarily conserved trait in holometabolous insects, occurs despite the considerable costs that must apply to such a visually complex animal. Our findings are consistent with the concept that stemmata are homologous to the most posterior ommatidia of hemimetabolous insects, an idea also recently supported by molecular data.     

New species of Myxosporidia (Myxosporea: Cnidosporidia) from cottids (Abyssocottidae) and the oilfishes (Comephorus spp.) of Baikal Lake

Two new species of Myxosporidia, Myxidium baicalensis sp. n., Myxidium donecae sp. n. are described from the gall bladder of fishes from Baikal. Myxidium baicalensis sp. n. parasitising gobies Cyphocottus megalops, Asprocottus platycephalus, and other host species, while Myxidium donecae sp. n. parasitising Baikal oil fishes Comephorus baicalensis and C. dybowski.     

Interaction of transducin with uncoordinated 119 protein (UNC119): implications for the model of transducin trafficking in rod photoreceptors

The key visual G protein, transducin undergoes bi-directional translocations between the outer segment (OS) and inner compartments of rod photoreceptors in a light-dependent manner thereby contributing to adaptation and neuroprotection of rods. A mammalian uncoordinated 119 protein (UNC119), also known as Retina Gene 4 protein (RG4), has been recently implicated in transducin transport to the OS in the dark through its interaction with the N-acylated GTP-bound transducin-α subunit (Gα(t1)). Here, we demonstrate that the interaction of human UNC119 (HRG4) with transducin is dependent on the N-acylation, but does not require the GTP-bound form of Gα(t1). The lipid specificity of UNC119 is unique: UNC119 bound the myristoylated N terminus of Gα(t1) with much higher affinity than a prenylated substrate, whereas the homologous prenyl-binding protein PrBP/δ did not interact with the myristoylated peptide. UNC119 was capable of interacting with Gα(t1)GDP as well as with heterotrimeric transducin (G(t)). This interaction of UNC119 with G(t) led to displacement of Gβ(1)γ(1) from the heterotrimer. Furthermore, UNC119 facilitated solubilization of G(t) from dark-adapted rod OS membranes. Consistent with these observations, UNC119 inhibited rhodopsin-dependent activation of G(t), but had no effect on the GTP-hydrolysis by Gα(t1). A model for the role of UNC119 in the IS→OS translocation of G(t) is proposed based on the UNC119 ability to dissociate G(t) subunits from each other and the membrane. We also found that UNC119 inhibited activation of G(o) by D2 dopamine receptor in cultured cells. Thus, UNC119 may play conserved inhibitory role in regulation of GPCR-G protein signaling in non-visual tissues.     

Sponge Transgenic Mouse Model Reveals Important Roles for the MicroRNA-183 (miR-183)/96/182 Cluster in Postmitotic Photoreceptors of the Retina

MicroRNA-183 (miR-183), miR-96, and miR-182 comprising the miR-183/96/182 cluster are highly expressed in photoreceptor cells. Although in vitro data have indicated an important role for this cluster in the retina, details of its in vivo biological activity are still unknown. To observe the impact of the miR-183/96/182 cluster on retinal maintenance and light adaptation, we generated a sponge transgenic mouse model that disrupted the activities of the three-component microRNAs simultaneously and selectively in the retina. Although our morphological and functional studies showed no differences between transgenic and wild type mice under normal laboratory lighting conditions, sponge transgenic mice displayed severe retinal degeneration after 30 min of exposure to 10,000 lux light. Histological studies showed that the outer nuclear layer thickness was dramatically reduced in the superior retina of transgenic mice. Real time PCR experiments in both the sponge transgenic mouse model and different microRNA stable cell lines identified Arrdc3, Neurod4, and caspase-2 (Casp2) as probable downstream targets of this cluster, a result also supported by luciferase assay and immunoblotting analyses. Further studies indicated that expression of both the cluster and Casp2 increased in response to light exposure. Importantly, Casp2 expression was enhanced in transgenic mice, and inhibition of Casp2 partially rescued their light-induced retinal degeneration. By connecting the microRNA and apoptotic pathways, these findings imply an important role for the miR-183/96/182 cluster in acute light-induced retinal degeneration of mice. This study demonstrates a clear involvement of miRs in the physiology of postmitotic cells in vivo.