UV-light-dependent binding of a visual arrestin 1 isoform to photoreceptor membranes in a neuropteran (Ascalaphus) compound eye

Arrestins are regulators of the active state of G-protein-coupled receptors. Towards elucidating the function of different arrestin subfamilies in sensory cells, we have isolated a novel arrestin 1, Am Arr1, from the UV photoreceptors of the neuropteran Ascalaphus macaronius. Am Arr1 forms a phylogenetic clade with antennal and visual Arr1 isoforms of invertebrates. Am Arr1 undergoes a light-dependent binding cycle to photoreceptor membranes, as reported earlier only for members of the arrestin 2 subfamily. This suggests a common control mechanism for the active state of invertebrate rhodopsins and G-protein-coupled receptors of antennal sensory cells. Furthermore, it implies that a strict correlation of distinct arrestin isoforms to distinct functions is not a general principle for invertebrate sensory cells.     

Cell clones and pattern formation: On the lineage of photoreceptor cells in the compound eye ofDrosophila

Summary The generalogical relationships of photoreceptor cells within the compound eye ofDrosophila have been studied using cell labelling, with either³H-thymidine or recessive mutations, during the third larval stage. It has been found that photoreceptor and secondary pigment cells arise from different precursor cells. Under the present experimental conditions, precursors of receptor cells give rise to about 8 elements which differentiate as R cells of two different groups. One of the cells differentiates as R7 and the remaining as any one of the R1 to R6. The last cells behave initially as equivalent, and can differentiate within the same or within different, but neighbouring, ommatidia. The class of R1 to R6 cell in which each one of these elements differentiates, seems to depend on the time of its origin. The implications of these findings for the formation of the ommatidial pattern are discussed.     

Raman-atomic force microscopy of the ommatidial surfaces of Dipteran compound eyes

The ommatidial lens surfaces of the compound eyes in several species of files (Insecta: Diptera) and a related order (Mecoptera) were analyzed using a recently developed Raman-atomic force microscope. We demonstrate in this work that the atomic force microscope (AFM) is a potentially useful instrument for gathering phylogenetic data and that the newly developed Raman-AFM may extend this application by revealing nanometer-scale surface chemistry. This is the first demonstration of apertureless near-field Raman spectroscopy on an intact biological surface. For Chrysopilus testaceipes Bigot (Rhagionidae), this reveals unique cerebral cortex-like surface ridges with periodic variation in height and surface chemistry. Most other Brachyceran flies, and the "Nematoceran" Sylvicola fenestralis (Scopoli) (Anisopodidae), displayed the same morphology, while other taxa displayed various other characteristics, such as a nodule-like (Tipula (Triplicitipula) sp. (Tipulidae)) or coalescing nodule-like (Tabanus punctifer Osten Sacken (Tabanidae)) morphology, a smooth morphology with distinct pits and grooves (Dilophus orbatus (Say) (Bibionidae)), or an entirely smooth surface (Bittacus chlorostigma MacLachlan (Mecoptera: Bittacidae)). The variation in submicrometer structure and surface chemistry provides a new information source of potential phylogenetic importance, suggesting the Raman-atomic force microscope could provide a new tool useful to systematic and evolutionary inquiry.     

An ectopic macrochaeta in the middle of a compound eye of a field-collected anthomyiid fly

Recording and describing animal ‘monsters’ collected in the field can still contribute to progress in developmental biology despite the uncontrolled conditions the specimen experienced throughout development. Comparison with model organisms and a sound phylogenetic analysis may offer a tentative explanation for the underlying developmental mechanism and suggest new targets for experimental studies. We describe a female specimen of the anthomyiid fly Hydrophoria sp. with an ectopic macrochaeta in the left eye and suggest tentative interpretations, including one in terms of a local expression, or derepression, of a proneural gene. The anthomyiid lineage has been estimated to have split ca. 65 million years ago from the dipteran clade containing Drosophila and ca. 140 million years ago from the clade containing Megaselia.     

Survival of photoreceptor neurons in the compound eye of Drosophila depends on connections with the optic ganglia.

The importance of retinal innervation for the normal development of the optic ganglia in Drosophila is well documented. However, little is known about retrograde effects of the optic lobe on the adult photoreceptor cells (R-cells). We addressed this question by examining the survival of R-cells in mutant flies where R-cells do not connect to the brain. Although imaginal R-cells develop normally in the absence of connections to the optic lobes, we find that their continued survival requires these connections. Genetic mosaic studies with the disconnected (disco) mutation demonstrate that survival of R-cells does not depend on the genotype of the eye, but is correlated with the presence of connections to the optic ganglia. These results suggest the existence of retrograde interactions in the Drosophila visual system reminiscent of trophic interactions found in vertebrates.     

An opsin gene expressed in only one photoreceptor cell type of the Drosophila eye

We have isolated an opsin gene from D. melanogaster that is expressed specifically in photoreceptor cell 8 of the Drosophila compound eye. This opsin is 381 amino acid residues long and is 67% homologous to the ninaE opsin, which is expressed in photoreceptor cells 1-6. The gene is divided into four exons; only one of the intron positions is conserved with that of the ninaE gene.     

The structure of a photoreceptor organelle in the eye of Pterotrachea mutica

Summary The photoreceptor cell of Pterotrachea consists of an elongated cell some 100 m long with recogniseable inner and outer segments. The photoreceptor membranes point towards the light. There are about 300 discs per photoreceptor, a small number of discs arising from a single ciliary base. There are bout 75–100 such bases on each receptor cell. The receptor cells themselves (the inner segments) have four recognisable regions. The vacuolated region, the region of mitochondria, the nuclear region, and the axonal region.The photoreceptor cells are organised in five roughly parallel rows, and separated from one another by pale supporting cells.My thanks are due to Professor J. Z. Young, F. R. S. for his enthusiastic support and help during this work. Dr. R. Bellairs kindly provided electron microscope facilities. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldridge provided excellent technical and photographic assistance.     

Geometrical optics of a galatheid compound eye

The eyes of galatheid squat lobsters (Munida rugosa) are shown to be of the reflecting superposition type. In the dark-adapted state corneal lenses focus light at the level of the rhabdoms and light from more than 1000 facets is redirected to the superposition focus by the reflecting surfaces of the crystalline cones. When the eye is light adapted, apposition optics are used. In this state paraxial light is focused by the corneal lens and the parabolic proximal end of the cone onto the distal end of a rhabdomeric lightguide. The latter transmits light across the clear zone to the rhabdom layer. In the dorsal part of the eye the individual ommatidia become progressively shorter until the cones and rhabdoms are no longer separated by a clear zone. Although formerly considered to be developing ommatidia, they are shown to be retained specifically for scanning the downwelling irradiance.Abbreviations RI refractive index - SEM scanning electron microscope     

Ultrastructure of the compound eye and first optic neuropile of the photoreceptor mutant ora JK84 of Drosophila

Summary The developmental mutant of Drosophila (ora ^JK84) is characterized by nonfunctional photoreceptor cells (R1–6), while the R7/R8 cells are normal. A fundamental question is: Does the near absence of photosensitive membranes inhibit development of the Rl-6 axons and their synapses at the other end of the cell? The retina and first optic neuropile (lamina ganglionaris) were examined with freeze-fracture technique and high voltage electron microscopy. R1–6 have reduced rhabdomere caps; rhabdomeric microvilli have about 50% of the normal diameter and 20% of the normal length. Affected cells exhibit prominent vacuoles which appear to communicate with some highly convoluted microvillar membranes. Almost no P-face particles (putative rhodopsin molecules) are present in the R1–6 rhabdomeres, and particle densities are lower in R7 than previously reported. Near the rhabdomere caps, microvilli of R1–6 are fairly normal, but at more proximal levels they are greatly diminished in length and changed in orientation, while at still more proximal levels they are lost. R1–6, R7, and R8 axons from each ommatidium are bundled into normal pseudocartridges beneath the basement membrane. No abnormalities are found in the lamina ganglionaris, and all synaptic associations as well as the presumed virgin synapses (of R1–6) appear normal. No glial anomalies are present, and R7/R8 axons project through the lamina in the usual fashion. These fine structural findings are correlated with known electrophysiological, biochemical, and behavioral correlates of both sets of photoreceptors (R1–6, and R7/R8).This study was supported substantially by the UW-HVEM Laboratory, in addition to a Faculty Development Award, a UMC Biomedical Research Support Grant N.I.H. RR07053 to W.S.S., and a Hatch Grant, Project 2100 to S.D.C. Freeze fracture was done at the Wisconsin Regional Primate Research Center, N.I.H. Grant RR00167. We thank Professor Hans Ris, Dr. J. Pawley, Dr. D. Neuberger, and Ms. M. Bushlow, HVEM Laboratory, Dept. of Zoology, UW. We also thank Mrs. K. Srivastava, Mr. M.B. Garment, Mr. G. Gaard, and Mr. D. Liu for technical assistance.     

Repetitive spikes in photoreceptor axons of the scorpion eye. Invertebrate eye structure and tetrodotoxin

A graded depolarization accompanied by nerve impulses can be recorded from the scorpion lateral and median eyes in response to light. Electron microscopy shows that axons forming the optic nerve arise directly from the photoreceptors. Thus, photoreceptors must respond both by the generation of a slow receptor potential and the initiation of spikes. The latency of the first spike, and the maximal and mean discharge frequencies were a function of light intensity. Spikes were abolished by tetrodotoxin. Repetitive firing to light therefore appears to be a normal response of scorpion photoreceptors and is the result of regenerative Na influx in the cell membrane.     

An independently evolved Dipteran silk with features common to Lepidopteran silks

Male hilarine flies (Diptera: Empididae: Empidinae) present prospective mates with silk-wrapped gifts. The silk is produced by specialised cells located in the foreleg basitarsus of the fly. In this report, we describe 2.3 kbp of the silk gene from a hilarine fly (Hilara spp.) that was identified from highly expressed mRNA extracted from the prothoracic basitarsus of males. Using specific primers, we found that the silk gene is expressed in the basitarsi and not in any other part of the male fly. The silk gene from the basitarsi cDNA library matched an approximately 220 kDa protein from the silk-producing basitarsus. Although the predicted silk protein sequence was unlike any other protein sequence in available databases, the architecture and composition of the predicted protein had features in common with previously described silks. The convergent evolution of these features in the Hilarini silk and other silks emphasises their importance in the functional requirements of silk proteins.     

Developmental Interactions in the Dipteran Salivary Gland

The dipteran salivary gland is considered from several pointsof view. Its development in relation to chromosomal puffingsuggests that this tissue, perhaps more than any other, representsmajor evidence for differential activation and inactivationof genes during development. From studies of this tissue wehave gained further insight into concepts of tissue and stagespecificity. Factors regulating puffing during development includethe natural hormone, ecdysone, as well as a host of other substancesand environmental factors which affect cellular metabolism. Breakdown of the salivary gland seems ultimately to be controlledby chromsomal puffing. In this case one of the first detectablebiochemical alterations in the gland is the accumulation ofthe enzyme DNase. This enzyme may play a role in digesting thechromosomes themselves, thus accomplishing regulated self-destructionof the cell's synthetic machinery.     

An eye for a tooth

Objective: To propose a possible link between dental extraction and intra‐ocular complications. Background: Several publications in medical literature describe intra‐ocular complications after different dental procedures. Results: Retinal detachment and vitreous hemorrhage following dental extraction with an appropriate anesthesia. Conclusion: Systemic complications following dental treatments should not be neglected and proper medical treatment must be provided as soon as possible.     

Sensitivity and adaptation in R7, an ultraviolet photoreceptor,in theDrosophila retina

Summary Receptor deficient mutants and chromatic adaptation were used to isolate the contribution of R7 to the electroretinogram (ERG) ofDrosophila. R7 was found to be a single-peaked ultraviolet (UV) receptor (Fig. 1). Photoconversion of the UV absorbing rhodopsin (R) to its stable 470–495 nm metarhodopsin (M) was shown to elicit a long-lived negative (depolarizing) afterpotential (Fig. 3) while inactivating R7. Photoreconversion ofM toR reactivates R7 (Fig. 2) and repolarizes the ERG (Fig. 3). The intensities of light needed to elicit afterpotentials by photointerconverting R7 photopigment were found to be about 2 log units greater than for R1-6 photopigment (Fig. 4). Vitamin A deprivation decreases R7 (as well as R8) sensitivity by about 2 log units (through decreased photopigment levels) without changing spectral sensitivity shape (Fig. 5). Vitamin A deprivation further eliminates the light-induced inactivation of R7 allowing experiments designed to characterize the in vivo spectral absorption of R7M. R7M was found to have UV and 495 nm maxima (Fig. 6). No polarization sensitivity was detected in the R7 ERG component. The adaptational properties of R7 are similar to the properties previously established for R1-6 but different from the properties of R8.Supported by NSF grants BMS-74-12817 and BNS 76-11921. I thank M. Chapin, R. Greenberg, K. Hu, A. Ivanyshyn, D. Lakin, G. Pransky, D. Sawyer, J. Walker and W. Zitzmann for technical assistance.     

Patterning of a compound eye on an extinct dipteran wing

We have discovered unexpected similarities between a novel and characteristic wing organ in an extinct biting midge from Baltic amber, Eohelea petrunkevitchi, and the surface of a dipteran's compound eye. Scanning electron microscope images now reveal vestigial mechanoreceptors between the facets of the organ. We interpret Eohelea's wing organ as the blending of these two developmental systems: the formation and patterning of the cuticle in the eye and of the wing. Typically, only females in the genus carry this distinctive, highly organized structure. Two species were studied (E. petrunkevitchi and E. sinuosa), and the structure differs in form between them. We examine Eohelea's wing structures for modes of fabrication, material properties and biological functions, and the effective ecological environment in which these midges lived. We argue that the current view of the wing organ's function in stridulation has been misconstrued since it was described half a century ago.