Retinula Cells Research Articles

Disconnected mutants show disruption to the central projections of proprioceptive neurons inDrosophila melanogaster

We used a P[GAL4] enhancer-trap line, C161, in conjunction with the UAS-lacZ reporter construct to visualize the central projections of a defined set of thoracic and abdominal sensory neurons in a disconnected (disco) mutant background. The results show defects in the organization of sensory axons in the larval and adult central nervous system. The defects are indicative of problems with axon growth and development and include (a) poor axon fasciculation, (b) aberrant axon growth, (c) excessive terminal branching, and (d) ectopic innervation. Sensory neuron identity appears to be normal. The defects are comparable to those previously described for larval photoreceptor and adult retinular cells in disco mutants and extend the known effects of this mutation. Reduced larval and adult viability are likely to result from locomotory defects related to the disruption of the sensory system.

Disconnected mutants show disruption to the central projections of proprioceptive neurons in Drosophila melanogaster

We used a P[GAL4] enhancer-trap line, C161, in conjunction with the UAS-lacZ reporter construct to visualize the central projections of a defined set of thoracic and abdominal sensory neurons in a disconnected (disco) mutant background. The results show defects in the organization of sensory axons in the larval and adult central nervous system. The defects are indicative of problems with axon growth and development and include (a) poor axon fasciculation, (b) aberrant axon growth, (c) excessive terminal branching, and (d) ectopic innervation. Sensory neuron identity appears to be normal. The defects are comparable to those previously described for larval photoreceptor and adult retinular cells in disco mutants and extend the known effects of this mutation. Reduced larval and adult viability are likely to result from locomotory defects related to the disruption of the sensory system. © 1998 John Wiley & Sons, Inc. J Neurobiol 36: 337–347, 1998

Morphogenesis and pattern formation in the retina of the crayfish Procambarus clarkii.

Pattern formation and ommatidial differentiation in the crayfish retina were analyzed using confocal, light and electron microscopy. Optic primordia first appear in the embryo as round elevations covered by a surface epithelial layer. Retinal differentiation begins with a wave of mitotic activity that moves across this epithelium from lateral to medial. Ommatidial cell clusters are visible at the surface along a transition zone, which lies at the interface of the medial undifferentiated retina and the lateral patterned retina. This zone is 8-10 cells wide and composed of small uniform cell profiles. Lateral to the transition zone the initial ommatidial cell clusters form staggered rows across the surface. Each first row cluster contains eight retinula cells surrounded by four cone, two corneagenous and two distal pigment cells. Ommatidial clusters in the first nine rows show significant changes in their organization, which are visible at the surface of the retina. In row 10 the retinula cells recede from the surface and the cone cells close in above them creating a constant cell pattern at the surface. Rhabdome development begins distally and extends downward as the retinula cluster recedes from the surface. Movement of the retinula cells inward and enlargement of the cone and corneagenous cells at the surface creates a two-tiered organization characteristic of each ommatidium. Comparison of retinal pattern formation and differentiation in the crayfish with retinal morphogenesis in Drosophila and other insects show several similarities between the two arthropod groups.

Fine Structure of the Compound Eye of Mallada basalis (Neuroptera: Chrysopidae)

The morphology of the compound eye of the lacewing Mallada basalis (Walker) was investigated by scanning and transmission electron microscopy. The optical superposition eye is composed of ≈600 ommatidia that are identical in both sexes. The length of an ommatidiumis ≈100 μm. Each ommatidium contains a lens covered with small corneal nipples, 4 cone cells forming a crystalline cone and tract, 2 principal pigment cells that encompass the crystalline cone, and 8 retinula cells (numbers 1–8). Each ommatidium is surrounded by 12 accessory pigment cells, some of which are located in the center of a triangle formed by 3 adjacent ommatidia. Thus, accessory pigment cells belong to part of 3 different ommatidia. The proximal part of the ommatidium is tightly enclosed by the tracheae. In dark adaptation, 7 retinula cells (numbers 1–7) are arranged in a circle at the tip of the crystalline tract. The rhabdomere of retinula cell number 7 lies at the proximal end of the crystalline tract, and number 8 lies at the distal end of the rhabdom column. All 8 retinula cells penetrate the basement membrane and continue as 8 axons. Each ommatidium shows the fused-type rhabdom that is of great advantage to spectral sensitivity. The fine structure of the ommatidia is further discussed in detail.

Compound eye ultrastructures in six species of ecologically diverse stag-beetles (Coleoptera, Scarabaeoidea, Lucanidae)

The structural organizations of the compound eyes of six Japanese stag-beetles, i. e. Aesalus asiaticus (abbr. Aa) and Platycerus acuticollis (Pa) of the subfamily Aesalinae, Figulus boninensis (Fb) of the Figulinae, Nipponodorcus rubrofemoratus (Nr) of the Dorcinae, Lucanus maculifemoratus (Lm) and L. gamunus (Lg), both of Lucanidae, were examined by light and electron microscopy. The results of this study formed the basis for a comparison between eye structures on the one hand and beetle ecology, activity, and phylogeny on the other. In Pa, instead of a true cone, some electron dense material was seen in each cone cell ; this suggests that the typical "eucone condition" had been replaced by an acone type of eye or a transitional condition between the eucone and acone types. The eyes of all other species were of the eucone type. The retinae of both Aa and Pa exhibited typically photopic organization, but those of Nr and Lm were clearly representatives of the scotopic type. The retinae of Fb and Lg were intermediate in nature. The retinula cells numbered eight in Aa, Pa, and most of the ommatidia of Fb ; in the other species they varied in number from eight to 11. Consequently, the rhabdom itself exhibited variations depending on the number of the retinula cells. With 88%, the ratio of rhabdom to cytoplasmic area in transverse sections of the retinula cells, was largest in Lm and Nr, while in Aa and Pa it measured a mere 5-6%. The differences appear to parallel the degree to which the species are active in day or at night.

Compound Eye Fine Structure in Paralomis multispina Benedict, an Anomuran Half-Crab From 1200 m Depth (Crustacea; Decapoda; Anomura).

Fully grown, unsexed specimens of the anomuran half-crab Paralomis multispina Benedict were obtained from a depth of 1200 m, and the eyes of three individuals were prepared for light and electron microscopy. In their outer appearance the compound eyes of Paralomis resemble those of common shallow-water half-crabs (e.g., Petrolisthes), but facets in Paralomis were about 3 times larger in diameter (i.e., 60 {mu}m) and at least twice as long. Interommatidial angles ranged from 3{deg} to 5{deg}. The proximal width of the crystalline cone in Paralomis was 10 times that of its equivalent in the Petrolisthes eye, and the rhabdom--although only twice as long--had a radius that was 7 times greater distally and 4 times greater proximally. A clear-zone between cones and rhabdom was not developed, and cross sections of crystalline cones revealed rounded rather than square profiles. A distal retinula cell (R8) was absent, and all regular retinula cells (R1-R7) protruded microvilli of about 0.11 {mu}m diameter in many (and not only two) directions. A maximum rhabdom occupation ratio of 85% was found in the Paralomis retinula, whereas in the shallow-water half-crabs the comparable figure was 35%. Paralomis featured a wide, rhabdomless space between basement membrane and proximal rhabdom ends; the space was occupied by reflecting cells. Primary screening pigment cells and their dark granules were present; secondary screening pigment cells, however, were replaced by reflecting cells. The anatomical modifications in the Paralomis eye are consistent with habitat-related adaptations seen in the eyes of other benthic and slow-moving deep-water crustaceans, but not with those of euphausiids. We conclude that the eye of Paralomis functions as an apposition eye, designed to maximize photon capture, especially from point sources (i.e., bioluminescence) rather than extended sources. We estimate that the Paralomis eye is at least 150 times more sensitive to light than the eye of shallow-water Petrolisthes.

Steroids Modulate the Excitability of Crayfish (Procambarus digueti) Photoreceptors: Long- and Short-Term Actions

Short- and long-term actions of the steroids corticosterone, progesterone, and ecdysterone were analyzed upon excitability of crayfish retinular cells. The three hormones showed short-term actions, particularly during photoreceptor dark adaptation; effects were found to be dependent on the hour of the day. Corticosterone and progesterone had similar effects, i.e., resembled dark-adapted conditions; ecdysterone actions were opposite and resembled light adaptation. Long-term effects were opposed to short-term effects in all cases. Possible mechanisms underlying these effects are discussed.

Effect of Formoguanamine on Structure and Function of the Compound Eye of the Butterfly, Papilio xuthus

Abstract Formoguanamine hydrochloride (FG) is known as a potent chemical to induce blindness in chick eyes by disrupting the pigment epithelium and visual cells in the retina. In this study, we examined the effect of FG on the structure and function of the compound eyes of the butterfly, Papilio xuthus (Lepidoptera, Insecta). We administrated 2 mg FG per 1 g body weight of the pupa at about the first one third of the whole pupal period, because accomplishment of morphogenesis of the compound eye occurs in the last half of the pupal period. As a result, unusual membranous structures such as trophospongium-like structures and myeloid bodies were observed in the cytoplasm of the retinular cells besides the normal rhabdom. This result suggests that FG treatment influences on some steps in the formation of rhabdom membranes. However, the amount of chromophore, 3-hydroxyretinal and the responses to white light recorded by the ERG method from FG-treated specimens were not different from the control animals.

1015 Axon patterning requires DN-cadherin, a novel neuronal adhesion receptor, in the drosophila embryonic CNS

Stemmata of strepsipteran insects represent the smallest arthropod eyes known, having photoreceptors which form fused rhabdoms measuring an average size of 1.69 × 1.21 × 1.04 μm and each occupying a volume of only 0.97–1.16 μm3. The morphology of the stemmata of the extremely miniaturized first instar larva of Stylops ovinae (Strepsiptera, Stylopidae) was investigated using serial-sectioning transmission electron microscopy (ssTEM). Our 3D reconstruction revealed that, despite different proportions, all three stemmata maintain the same organization: a biconvex corneal lens, four corneagenous cells and five photoreceptor (retinula) cells. No pigment-containing cell-types were found to adjoin the corneagenous cells. Whereas the retinula cells are adapted to the limited space by having laterally bulged median regions, containing mitochondria and the smallest nuclei yet reported for arthropods (1.37 μm3), special adaptations are found in the corneagenous cells which have cell volumes down to 1 μm3. The corneagenous cells lack nuclei and pigment granules and bear only a few mitochondria (up to three) or none at all. Morphological adaptations due to miniaturization are discussed in the context of photoreceptor function and the visual needs of the larva.

Vitamin A, visual pigments, and visual receptors in Drosophila.

The fly visual system has served for decades as a model for receptor spectral multiplicity and vitamin A utilization. A diverse armamentarium of structural techniques has dovetailed with convenient electrophysiology, photochemistry, genetics, and molecular biology in Drosophila to facilitate recent progress, which is reviewed here. New data are also presented. Ultrastructure of retinula cells of carotenoid-deprived flies shows that organelles associated with protein biosynthesis, i.e., rough endoplasmic reticulum and Golgi apparatus, are present, while organelles associated with rhabdomere turnover, i.e., multivesicular bodies (MVBs), are rare. Ultrastructure and morphometry suggest that retinoic acid-rearing stimulates membrane export and rhabdomere buildup, even though functional rhodopsin is missing. Confocal microscopy suggests that RH4, one of the ultraviolet rhodopsins, may reside in the previously-described pale fluorescent R7 cells with RH3 in the yellow fluorescent R7 cells.

Molecular and immunological characterization of a Gq protein from ventral and lateral eye of the horseshoe crabLimulus polyphemus

GTP binding proteins of the Gq family have been implicated in phototransduction in rhabdomeral photoreceptors. In this study we used molecular and immunochemical techniques to characterize a GTP-binding protein alpha subunit of the Gq family in ventral and lateral photoreceptors of the horseshoe crab, Limulus polyphemus. Both ventral photoreceptors and lateral eye retinular cells became strongly labeled with an antibody directed against the common carboxyl tail of two Gq family proteins, G alpha q and G alpha 11. This antibody also labeled a 42 kDa band on Western blots of proteins from ventral photoreceptor cell bodies, ventral photoreceptor axons, lateral eyes and lateral optic nerves. The reverse transcription-polymerase chain reaction (RT-PCR), along with degenerate oligonucleotide primers designed against conserved regions of known G alpha q and G alpha 11 proteins, was used to isolate a cDNA from ventral eye RNA which encodes a protein with high identity to known Gq proteins. Ribonuclease protection assays showed that the corresponding message was expressed in ventral eye, but these assays, as well as Northern blots, failed to detect expression in lateral eye. Therefore, while photoreceptors of both ventral and lateral eyes contain a Gq-like protein, the mRNA encoding the Gq protein in the ventral eye may differ in nucleotide sequence from its lateral eye counterpart.

Cyclophilin-related protein RanBP2 acts as chaperone for red/green opsin.

Cyclophilins are ubiquitous and abundant proteins that exhibit peptidyl prolyl cis-trans isomerization (PPlase) activity in vitro. Their functions in vivo, however, are not well understood. Two new retinal cyclophilin isoforms, types I and II, are highly expressed in cone photoreceptors of the vertebrate retina. Type-II cyclophilin is identical to RanBP2, a large protein that binds the GTPase Ran. Here we report that two contiguous domains in RanBP2, Ran-binding domain 4 (RBD4) and cyclophilin, act in concert as a chaperone for the opsin molecule of the red/green-sensitive visual pigment of a dichromatic vertebrate. In Drosophila, the cyclophilin NinaA is expressed in all photoreceptors and is required for the expression of only a subset of opsins. The molecular basis of these photoreceptor class-specific effects and the functions of NinaA and other cyclophilins in vivo remain unclear. Unlike NinaA, which forms a stable complex with opsin from retinular cells R1-6, we find that the cyclophilin domain of RanBP2 does not bind opsin directly; rather, it augments and stabilizes the interaction between red/green (R/G) opsin and the RBD4 domain. This involves a cyclophilin-mediated modification of R/G opsin, possibly involving proline isomerization. The RBD4-cyclophilin supradomain of RanBP2, therefore, is a form of vertebrate chaperone of defined substrate specificity, which may be involved in the processing and/or transport of long-wavelength opsin in cone photoreceptor cells.

The early stages of ommatidial development in the flour beetle Tribolium castaneum (Coleoptera; Tenebrionidae)

Using electron microscopy, the first stages of ommatidial development in the flour beetle Tribolium castaneum were analysed in relation to the cellular architecture of the adult compound eye and were compared to the corresponding patterning process in the fruit fly Drosophila melanogaster. The ommatidia of the slightly horse-shoe shaped beetle compound eye contain six peripheral and two central retinula cells. The rhabdomere of the posteriorly located central photoreceptor cell is restricted to the distal half of the rhabdom whilst that of the anterior one is restricted to its proximal half. The development of the compound eye takes place in an external eye imaginal disc. Most stages of ommatidial development, as known from Drosophila, i.e. arc-like cell groups, five-cell clusters, immature eight-cell clusters and symmetrical eight-cell clusters, are very precisely conserved between the two species. Two major differences exist: 1. In Tribolium, the cone cell precursor cells synchronously join to the immature eight-cell cluster. As a consequence, the symmetrical eight-cell cluster immediately transforms into a four-cone-cell cluster. 2. The maturing ommatidia do not undergo rotation in Tribolium. Overall, no morphological indiation for an equator in the adult Tribolium compound eye could be found. Considering the strong evolutionary conservation of early ommatidial development, homology of photoreceptor cells of distantly related insects is proposed to be inferred from their ontogenetic origin.

Receiver operating characteristic (ROC) analysis of neural code efficacies. I. Graded photoreceptor potentials and data quality.

Nerve cell signals are different in form from the stimuli that evoke them and they exhibit complex spatio-temporal characteristics. This defines a neural coding problem which is addressed by two current theories: Multiple Meaning Theory holds that neural signals contain patterns that make statements about combinations of stimulus properties; the Task Dependence Hypothesis suggests that different features of identical neural signals mediate performance in different behavioral tasks. These coding issues were addressed by investigating the representation of sensory information in the distal nervous system after transduction of visual stimuli into bio-electric signals. The objects of study were light-evoked neural responses which had been intracellularly recorded from single retinula (photoreceptor) cells in Limulus lateral eyes. The efficacies with which sensory information was represented by various candidate neural codes were calculated using receiver operating characteristic (ROC) analyses to provide objective indices. The specific visual problem under investigation was discrimination between light flashes whose intensities differed by a very small amount. A wide range of light adaptation states and relative stimulus intensities were explored. Extremely stringent data quality standards were applied which restricted the investigation to cells whose potentials did not exhibit any statistically significant drift during the hours required for data collection. Seven cellular characterizations were simultaneously monitored to detect drift in a given cell's potentials; these characterizations included the value of the membrane potential and the values of six candidate codes. These codes were: the area under the light-evoked receptor potential (RP), the mean value of the RP, the peak height of the RP, the slope of the onset of the RP, the duration required for the RP to drop from its peak by a given amount, and the duration required for the RP to end. The results were: (1) Light adaptation increases efficacy. (2) Thus, light adaptation trades sensitivity for acuity (as characterized by ROC discriminations). (3) Increasing relative light flash intensity also increases efficacy. (4) The efficacies of the various codes are significantly different and fall in the following order: area > or = peak = mean > or = duration-end = slope = duration-drop. These findings further demonstrate that arbitrary characterizations of stimulus-response relationships are very likely to be incomplete. They particularly indicate that many commonly used and quite conventional neural analysis strategies may substantially under-estimate system performance.

Dawn, diacylglycerol, calcium, and protein kinase C — the retinal wrecking crew. A signal transduction cascade for rhabdom shedding in the Limulus eye

Vertebrate and invertebrate photoreceptors shed their photosensitive membrane on a daily basis. Although we have detailed knowledge of the morphology of the disc shedding and renewal process in vertebrate photoreceptors, and of the turnover of rhabdom in invertebrate photoreceptors, we know relatively little about the molecular mechanisms whereby these processes are triggered by light and/or by circadian efferent input to the retina. We have used the horseshoe crab, Limulus polyphemus, as a model system to unravel the molecular means by which the trigger light is communicated to the intracellular machinery responsible for the daily breakdown of the photosensitive membrane. Phorbol esters, potent and specific activators of protein kinase C (PKC), induce a robust burst of rhabdom shedding when injected subretinally into the compound lateral eye of Limulus. This occurs in the absence of the light trigger normally required to initiate shedding in the lateral eye at dawn, suggesting that PKC may play a role in the light triggering of rhabdom shedding. Diacylglycerol (DAG) analogf were also found to elicit rhabdom shedding in the lateral eye without a light trigger, but an uncharacteristically high concentrations. However, injecting inositol trisphosphate (InsP 3) and DAG analog simultaneously results in a tenfold decrease in the concentration of DAG analog required to initiate a shedding event. Immunohistochemical screening for PKC in the lateral eye shows that two isozymes (PKC βII and PKC ξ) are co-localized to the retinular cell rhabdom. Taken together, these data suggest that light triggers rhabdom shedding at dawn via a classical Ca 2+-sensitive PKC, similar to PKC βII, which is activated synergistically by the light-evoked production of DAG and InsP 3.

Retinal ultrastructure of the dorsal eye region of Pararge aegeria (Linné) (Lepidoptera: Satyridae)

We examined the fine structure of dorsal rim ommatidia of the compound eye of Pararge aegeria (Lepidoptera: Satyridae) and compared them with ommatidia of the large dorsal region described by Riesenberg (1983 Diploma, University of Munich). 1. The ommatidia of the dorsal rim show morphological specializations known to be typical of the perception of polarized light: (a) the dumb-bell-shaped rhabdoms contain linearly aligned rhabdomeres with only 2 orthogonally arranged microvilli orientations. The rhabdoms are composed of the rhabdomeres of 9 receptor cells, 8 of which are radially arranged. The rhabdomeres of receptor cells VI and V5, as well as D2, D4, D6 and D8 are dorsoventrally aligned, whereas the rhabdomeres of the cells H3 and H7 are perpendicular to them. The rhabdomere of the bilobed 9th retinula cell lies basally and is dorsoventrally aligned, where retinula cell VI and V5 are already axonal. (b) There is no rhabdomeric twist, and (c) the rhabdoms are rather short. 2. However, in the ommatidia of the large dorsal region, only 2 retinula cells (H3 and H7) are suitable for perception of polarized light. 3. Lucifer yellow and horse radish peroxidase were used as tracers to visualize the projections of retinula cell axons of the dorsal rim area and the large dorsal region into the optic neuropils (lamina and medulla). Two receptors (VI and V5) from both the dorsal rim area and the large dorsal region, have long visual fibres projecting into the medulla. The 7 remaining retinula cells of both eye regions, including those that meet the structural requirements for detection of polarized light in the large dorsal region, terminate in the lamina (short visual fibres). These results provide a starting point for further studies to reveal the possible neuronal pathways by which polarized light may be processed.

Spatial Resolution Determined by Electrophysiological Measurement of Acceptance Angle in two Species of Benthic Decapod Crustacean

Angular sensitivity functions were determined electrophysiologically for retinula cells in Nephrops norvegicus and Munida rugosa. For such aquatic species it is shown that reliable measurements cannot be obtained unless the eyes are submerged. In both cases, for submerged eyes, there is a significant reduction in retinula cell acceptance angles with light adaptation. In N. norvegicus the change is from 11·3° dark adapted (DA) to 8·85° light adapted (LA). In M. rugosa there is a larger difference, 12·5° (DA)–6·58° (LA). The changes in acceptance angle with adaptational state can be attributed to differences in screening pigment position between light- and dark-adapted eyes. In N. norvegicus only the retinula cell proximal pigment is migratory. The small change in acceptance angle with adaptation is consistent with the fact that the eye uses superposition optics even when light-adapted.

The eyes of a “nobody”,Anoplodactylus petiolatus (Pantopoda; Anoplodactylidae)

The fine structure of the four ocelli ofAnoplodactylus petiolatus was examined using serial longitudinal and transversal sections of the eye hill. Each pigment cup ocellus is composed of a (planconvex) cuticular lens, lens forming hypodermal cells, inverse retinula cells with latticed rhabdom and surrounding tapetum and pigment layers. Within the retinula cells a distal “vitreous” zone, a nucleus zone and a proximal rhabdomeric zone can be distinguished. Retinula cell axons originate proximally. The tapetum cells contain several layers of reflecting crystals. Distally, they have a common microvillous region. The intraretinal “vitreous” zone contains glycogen-like particles in the centre and rough ER in the periphery. Contrary to other Pantopoda vitreous cells, a praeretinal membrane and a vertical lens groove have not been observed inAnoplodactylus. While the presence of four (median) ocelli appears to be a primitive characteristic, the inverse orientation of the retinula cells in combination with a tapetum lucidum represents a highly derived characteristic among arthropod median eyes.

Two opsins from the compound eye of the crab Hemigrapsus sanguineus

The primary structures of two opsins from the brachyuran crab Hemigrapsus sanguineus were deduced from the cDNA nucleotide sequences. Both deduced proteins were composed of 377 amino acid residues and included residues highly conserved in visual pigments of other species, and the proteins were 75 % identical to each other. The distribution of opsin transcripts in the compound eye, determined by in situ hybridization, suggested that the mRNAs of the two opsins were expressed simultaneously in all of the seven retinular cells (R1-R7) forming the main rhabdom in each ommatidium. Two different visual pigments may be present in one photoreceptor cell in this brachyuran crab. The spectral sensitivity of the compound eye was also determined by recording the electroretinogram. The compound eye was maximally sensitive at about 480 nm. These and previous findings suggest that both opsins of this brachyuran crab produce visual pigments with maximal absorption in the blue-green region of the spectrum. Evidence is presented that crustaceans possess multiple pigment systems for vision.

Carotenoid replacement in Drosophila: freeze-fracture electron microscopy.

Because of the consequent lack of photopigment chromophore, carotenoid/ retinoid (vitamin A) deprivation during the larval period of Drosophila leads to decreased rhodopsin in adult photoreceptors. Decreased density of P-face particles in photoreceptor membrane (rhabdomeric microvilli) is a prominent ultrastructural feature of this rhodopsin deficiency. When adults are fed carotenoid, the rhabdomeric P-face particle density-which reflects the concentration of rhodopsin-increases halfway to the replete control level during the first 12 hours, and is fully restored by 2 days. Based on freeze-fracture replicas, there is a continuity of membrane between rhabdomeric microvilli and the parent retinula cell. That confluence is relevant to turnover of photoreceptive membrane. Microvillar and retinula cell P-face particle densities covary. The relevance of the demonstration of rapid recovery from chromophore depletion is discussed in relation to hypotheses that the chromophore and/or related retinoids regulate opsin gene transcription, and/or post-translational processing and deployment from the endoplasmic reticulum to the rhabdomere.