Photoreceptor membrane breakdown in the spider Dinopis: Localisation of acid phosphatases

Summary The ultrastructural localisation of acid phosphatases (AcPhs) during the normal daily breakdown of rhabdomere membrane in Dinopis has been examined using -glycerophosphate and p-nitrophenyl phosphate as substrates. Results are related to the classification of organelles in the receptors given by Blest, Powell and Kao (1978). Weak and infrequent reactions are obtained in multivesicular bodies (mvbs) and multilamellar bodies (mlbs) derived from them. Residual bodies (rbs) begin to react strongly as they lyse. Source of AcPhs is endoplasmic reticulum which has barely differentiated towards the GERL configuration; it becomes reactive as it is incorporated into secondary lysosomes. GERL tubules, Y-bodies and vesicles respond erratically and weakly, and are also incorporated into rbs. No evidence was found for a significant participation of Golgi bodies in these processes, and acid phosphatase cytochemistry fails to reveal a topographical relationship between GERL in these cells and Golgi saccules. Coated vesicle clusters found in the predawn receptive segments are AcPh-negative; this implies that their previous identification as GERL-derived Nebenkerne carrying hydrolytic enzymes to newly-formed mvbs (Blest, Kao and Powell, 1978) is dubious. Isolation bodies and autophagic vacuoles enclosing other organelles in pathological receptors give strong reactions while adjacent secondary lysosomes derived from rhabdomere membrane and associated GERL give weak ones. It is concluded that rhabdomere-derived rb lysis is more tightly regulated than other autophagic processes, and it is suggested that a high degree of control is necessary in a receptor which may repeat the autophagy of a large mass of transductive membrane at least 60–100 times in the course of its working life.The authors thank Professor D.T. Anderson F.R.S. for the use of field facilities at the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, New South Wales throughout all these studies; Dr. Gary Griffiths (EMBO, Heidelberg) and Dr. Alex Pyliotis (Biochemistry, SGS, Australian National University) for some helpful comments on acid phosphatase histochemistry; Sally J. Stowe for help in the field; and Rod Whitty and the staff on the Electron Microscopy Unit for advice and support. Figure 28 was prepared by Chris Snoek     

Photoreceptor membrane breakdown in the spider Dinopis: The fate of rhabdomere products

Summary Photoreceptor membrane breakdown at dawn in the posterior median eyes of the spider Dinopis is described. Coated and smooth vesicles are shed into the receptor cytoplasm and are assembled into multivesicular bodies of two kinds: (i) Coated vesicles form loosely-assembled multivesicular bodies (mvbs) whose bounding membranes are derived from endoplasmic reticulum. (ii) Smooth vesicles generated by the mass disintegration of membrane aggregate to yield tightly-assembled multivesicular bodies which are not membrane-bound. Both types are either lysed in the inter-rhabdomeral cytoplasm, or degrade via multi-lamellar bodies to residual bodies (rbs) while they are being transported to the intermediate segments. Two systems are associated with lysis. Nebenkerne produced by the rapid differentiation of GERL in the intermediate segments fuse with membrane-bound mvbs or rbs and may inject them with hydrolases. Partially-differentiated rigid tubules (Blest et al., 1978) travel to the receptive segments together with RER from the intermediate segments and also fuse with or engulf mvbs. Both systems may contain pro-enzymes which are activated at their target sites. No evidence of a close or necessary geometrical relationship between GERL and Golgi bodies has been seen, and there is no clear demarcation between RER, smooth ER and GERL which is entering into continuity with or engulfing mvbs. The implications of these findings for hypotheses about the origins of isolation membranes and autolytic systems in invertebrate systems are briefly discussed.The authors thank Professor D.T. Anderson, F.R.S., for our use of field facilities at the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, N.S.W., Andrew & Sally Austin and Sally Stowe for help in the field, and Joanne Maples for technical assistance. Professor T.H. Waterman and Dr. V.B. Meyer-Rochow kindly gave us access to certain of their results prior to publication. We are indebted to Rod Whitty and the Electron Microscopy Unit for advice and support throughout these studies     

Photoreceptor membrane turnover in the crayfish Cherax destructor: electron microscopy and anti-rhodopsin electron-microscopic immunocytochemistry

Summary Examination of the ultrastructure of retinula cells of the Australian crayfish Cherax destructor at different times over a 24-hour cycle, together with patterns of anti-rhodopsin antigenicity, has lead to the formulation of a model of photoreceptor membrane turnover in these animals. Its main features are: (a) the existence of two bursts of rhabdomeral membrane breakdown; one, light-sensitive and synchronous, occurring at dawn, the other, constituting the first part of the membrane replacement phase itself, occurring during the afternoon and night, (b) the desynchronisation of the replacement phase of turnover between animals and to a lesser extent between cells of the same retina, (c) confinement of ultrastructurally detectable signs of photoreceptor membrane processing to the retinula cells themselves, and (d) replacement of a substantial part if not all of the rhabdomeral membrane daily. This model is compatible with many of the observations reported on the American crayfish Procambarus, and utilises the same basic mechanisms that are believed to operate in photoreceptor membrane turnover in many other arthropod compound eyes.     

A new mechanism for transitory,local endocytosis in photoreceptors of a spider,Dinopis

Summary Intermediate segment outgrowths (ISOs) are transitory specialisations of the plasma membrane of intermediate segments of the posterior median photoreceptors of Dinopis. Local regions form outgrowths into the glial partitions separating the receptors and remain connected to their parent intermediate segments by narrow necks. ISOs, only a few m in diameter, are sites of intense endocytosis. Coated pits in their plasma membranes give rise to saccular internalisations. Unusual, slender, endocytotic tubules either pinch off coated vesicles, or become detached to yield a tubular detritus. Products of endocytosis are assembled to yield multivesicular and dense bodies, which are usually surrounded by smooth saccules derived from the endoplasmic reticulum of the intermediate segment. ISOs also contain arrays of tubules, thought to be stacks of haemocyanin molecules. There are usually at least 10 times the number of empty ISOs as full and active outgrowths. The number of active ISOs increases rapidly at dawn to peak at about 3 h after sunrise and then rapidly declines. The present sample suggests that the number of empty ISOs increases steadily throughout the day. Thus, ISOs turn over and are probably rapidly formed and short-lived. The contents of ISOs are observed to be evicted into the intermediate segments, where they presumably join the population of secondary lysosomes and are digested. The cyclical activity of ISOs is greatest after shedding of rhabdomeral membrane at dawn (Blest 1978). ISOs are thought to be concerned with the return to the receptors of a minor fraction of rhabdomeral material lost to extracellular space during shedding of the microvillar membrane.The authors thank Professor D.T. Anderson, F.R.S., for use of field facilities of the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, N.S.W., and Andrew and Sally Austin and Carolyn Lawson-Kerr for help in the field. We are indebted to Rod Whitty and the Electron Microscopy Unit for support during these studies, and to Gary Brown for preparing Figs. 1 and 16     

Ultracytochemical evidence for the presence of GERL in pinealocytes of the Mongolian gerbil (Meriones unguiculatus)

Summary Ultracytochemical reactions for the demonstration of acid phosphatase, glucose-6-phosphatase and thiamine pyrophosphatase, as well as zinc iodide-osmium tetroxide impregnation, revealed the existence of GERL (Golgi apparatus — Endoplasmic Reticulum — Lysosomes) in pinealocytes of the Mongolian gerbil (Meriones unguiculatus). The spatial arrangement of this structure was studied on thick sections using a goniometric stage. Although it was not possible to determine whether GERL in pinealocytes belongs to the Golgi apparatus or to endoplasmic reticulum, it can be concluded that its presence in studied cells signifies that they are considerably more active synthetically than has been believed to date.     

Photoreceptor development in the pineal organ and the eye of Plecoglossus altivelis and Paralichthys olivaceus (Teleostei)

Summary The ontogenetic apperance of pineal photo-receptors was compared with that of retinal photoreceptors in the ayu Plecoglossus altivelis and the lefteye flounder Paralichthys olivaceus, which hatched 10 days and 3 days after fertilization, respectively. Despite the disparity in incubation time, the outer segments (containing membranous lamellae) of the pineal photoreceptors first appeared from 3 to 4 days after fertilization in both species. In contrast, the outer segments of the retinal photoreceptors first became visible 5 to 6 days after fertilization, although a characteristic retinal stratification and the optic tract leaving the ganglion cell layer were already found 4 days after fertilization in both species. The functional significance of these temporal disparities and/or similarities in photoreceptor development are discussed with special reference to the timing of daily rhythmic activities during the early developmental period of the teleosts.The results were presented at the Annual Meeting of the Japanese Society of Scientific Fisheries on April 2, 1990 (Tokyo)     

Identification of Wolbachia-responsive microRNAs in the two-spotted spider mite,Tetranychus urticae

Background

The two-spotted spider mite, Tetranychus urticae, is infected with Wolbachia, which have the ability to manipulate host reproduction and fitness. MicroRNAs (miRNAs) are small non-coding RNAs that are involved in many biological processes such as development, reproduction and host-pathogen interactions. Although miRNA was observed to involve in Wolbachia-host interactions in the other insect systems, its roles have not been fully deciphered in the two-spotted spider mite.

Results

Small RNA libraries of infected and uninfected T. urticae for both sexes (in total four libraries) were constructed. By integrating the mRNA data originated from the same samples, the target genes of the differentially expressed miRNAs were predicted. Then, GO and pathway analyses were performed for the target genes. Comparison of libraries showed that Wolbachia infection significantly regulated 91 miRNAs in females and 20 miRNAs in males, with an overall suppression of miRNAs in Wolbachia-infected libraries. A comparison of the miRNA and mRNA data predicted that the differentially expressed miRNAs negatively regulated 90 mRNAs in females and 9 mRNAs in males. An analysis of target genes showed that Wolbachia-responsive miRNAs regulated genes with function in sphingolipid metabolism, lysosome function, apoptosis and lipid transporting in both sexes, as well as reproduction in females.

Conclusion

Comparisons of the miRNA and mRNA data can help to identify miRNAs and miRNA target genes involving in Wolbachia-host interactions. The molecular targets identified in this study should be useful in further functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1122) contains supplementary material, which is available to authorized users.     

Flexibility in the multi-modal courtship of a wolf spider, Schizocosa ocreata

Male Schizocosa ocreata wolf spiders court females with synchronous visual and seismic displays. We tested whether male S. ocreata modify their courtship in relation to light environment, and associated utility of the visual components. Males were generally more active and more likely to perform the major courtship element (jerky tapping) when in the light. One courtship element (arching) was only observed in the light while another (vertical leg-extend) was only observed in the dark. Courtship in the dark retained visual components, suggesting spiders cannot disengage these components of multi-modal display even when superfluous. Once initiated, there was no evidence that performance rate or time spent in each courtship element differed in the light and in the dark.     

Residual bodies resulting from photosensory membrane degradation are taken up by pigment cells in the eyes of the flyLucilia sp.

Retinae of blowflies (Lucilia sp.) were exposed to light for 12 h and then investigated by routine electron microscopy. Residual bodies and multi-vesicular bodies containing electron-dense structures were found in the photoreceptor cells. These structures appeared indistinguishable from material inside the pigment granules of secondary pigment cells. The residual bodies were found in interdigitations between photoreceptor and pigment cells and were often in close contact with mitochondria. Lamellar bodies and pigment granules were also found in the extracellular space between photoreceptor and pigment cells. In a second set of experiments, a membrane-impermeable reagent [sulfosuccinimidyl-6-(biotinamido) hexanoate] that should covalently biotinylate the surface of the photosensory membrane was introduced into the ommatidial cavity. The marker was detected, 4 h after application, inside the ommatidial cavity, on the rhabdomeric microvilli, and on residual bodies inside the photoreceptor cells, by streptavidin-gold binding on ultrathin sections. After 6 h of exposure to the reagent, pigment granules of the adjacent pigment cells were also labeled. The results suggest that the photosensory membrane is taken up and degraded together with the marker. Residual bodies resulting from this degradative process may thus be transported into the pigment cells; eventually material originating from photosensory membrane degradation may then be involved in pigment granule synthesis.     

Ineffective crypsis in a crab spider: a prey community perspective

Cryptic coloration is assumed to be beneficial to predators because of an increased encounter rate with unwary prey. This hypothesis is, however, very rarely, if ever, studied in the field. The aim of this study was to quantify the encounter rate and capture success of an ambush predator, in the field, as a function of its level of colour-matching with the background. We used the crab spider Misumena vatia, which varies its body colour and can thereby match the colour of the flower it hunts upon. We carried out a manipulative field experiment using a complete factorial design resulting in six different colour combinations of crab spiders and flowers differing in their degree of colour-matching. A rich and diverse set of naturally occurring insects visited the flowers while we continuously video-recorded the spider''s foraging activity. This enabled us to test the crypsis, the spider avoidance and the flower visitor attraction hypotheses, all three supported by previous studies. Flower visitors of different groups either avoided crab spiders independent of colour-matching, such as solitary bees and syrphid flies, or ignored them, such as bumble-bees and honeybees. Moreover, colour-matched spiders did not have a higher encounter rate and capture success compared to the visually apparent ones. Thus, our results support the spider avoidance hypothesis, reject the two other hypotheses and uncovered a fourth behaviour: indifference to predators. Because flower visitors reacted differently, a community approach is mandatory in order to understand the function of background colour-matching in generalist predators. We discuss our results in relation to the size and sociality of the prey and in relation to the functional significance of colour change in this predator.     

Hexagonal columnar liquid crystal in the cells secreting spider silk

The liquid crystallinity of spider dragline silk dope is thought to be important for both the spinning process and the extreme mechanical properties of the final thread. Although the formation of the liquid crystalline units is poorly understood, it has been suggested that spider silk proteins are secreted in a random coil and then aggregate end-to-end into rod-shaped units to form supramolecular liquid crystals. However, evidence presented here from transmission electron microscopy indicates that coat protein of the dragline silk of a Nephila spider is stored as hexagonal columnar liquid crystals within the intracellular secretory vesicles. This implies that this component is already folded into short rods within the gland cells and forms molecular rather than supramolecular liquid crystals.     

Acyltransferase and acid hydrolase activities of the abalone photoreceptor cell

Summary In order to study the synthesis and degradation processes of the photoreceptor membranes in the abalone, Nordotis discus, the localization of acyltransferase and acid hydrolase activities, respectively, were determined at the electron-microscopic level. Acyltransferase activity was localized on the cytoplasmic sides of thick (>10 nm) membranes of the following organelles: a few cisternae at the trans (or concave) side of Golgi apparatus, Golgi and probably related vesicles, short tubules, curved pentalaminar disks and limiting membranes of the phagosomal multivesicular bodies; all organelles were scattered in the peri- to supranuclear cytoplasm. The phospholipids, which are major components of the photoreceptor membrane, are considered to be synthesized by these membranes. Acid phosphatase activity was localized in the lumina of Golgi cisternae and vesicles, lysosomes, and smaller multivesicular and related bodies, but not in multilamellar bodies. The matrices of the larger multivesicular bodies and of the pigment granule complexes showed arylsulfatase activity. Vesiculated and autophagocytosed photoreceptor microvilli seemed to be degraded by acid hydrolases, forming multivesicular and related bodies. Supporting cells also showed acyltransferase and acid hydrolase activities.Abbreviations used in this Paper AcP acid phosphatase - ArS arylsulfatase - AT acyltransferase - ER endoplasmic reticulum - GERL Golgi-endoplasmic reticulum-lysosomal complex - MEB meshwork body - MLB multilamellar body - MVB multivesicular body - VLB vesiculolamellar body     

Alloparental behavior in a captive group of spider monkeys (Ateles geoffroyi) at the Auckland zoo

I studied alloparental behavior in a captive group of spider monkeys at the Auckland Zoo using seven infants as focal subjects and assessed the effects of age, sex, and reproductive status of alloparents on patterns of infant-other interaction. Adult males initiated interactions with infants most often, followed by adult females. Immature individuals interacted with infants infrequently. Infants themselves initiated contact with adult males more often than with other members of the group. Alloparental behavior in spider monkeys differs from that in most other species in that the infant is an active rather than a passive participant in alloparental interactions. I discuss the patterns of infant-other interaction in relation to the social structure and dispersal patterns of Ateles.     

Interrelationships among the plasma membrane,the membrane skeleton and surface form in a unicellular flagellate

Summary Surface isolates or membrane skeletons from surface isolates can maintain the cell and surface form characteristic of euglenoids. We now report that the plasma membrane alone obtained by trypsin or urea digestion of surface isolates can also maintain surface form, but the membrane skeleton is able to produce striking changes in membrane organization. Trypsin digests microtubules, the membrane skeleton and partially digests the major integral membrane protein from surface isolates but does not alter the paracrystalline plasma membrane interior. Extraction of surface isolates with 4M urea leaves an insoluble plasma membrane and a subset of proteins arranged perpendicularly to the membrane surface. To resolve further the relationship between the plasma membrane and the membrane skeleton we have perturbed membrane organization by extraction of surface isolates with NaOH and find that readdition of the extract followed by neutralization restored important features of the membrane skeleton and caused patching of the membrane interior. Biochemically, the reassembled membrane skeleton consisted of 80 and 86 kD polypeptides and other less abundant proteins, and structurally the reassembled membrane skeleton was about the same thickness as the native membrane skeleton. Reassembly of the membrane skeleton appeared to be saturatable in that addition of an excess of extract had no effect on the thickness of the membrane skeletal layer. When the 80 kD protein was depleted from the reassembly mixture by affinity chromatography using Sepharose-bound monoclonal antibodies, the amount of 86 kD protein bound was significantly reduced, suggesting a dependance of 86 kD protein on 80 kD binding. A urea soluble fraction enriched in the 80 and 86 kD proteins was added to alkali-stripped membranes and 170 Å filaments were formed perpendicularly to the membrane surface. From the sum of these experiments we suggest that a) the native amorphous membrane skeleton ofEuglena may consist of a framework of 80 and 86 kD filaments arranged in a brush-like layer, b) the framework can direct plasma membrane organization, but once determined, membrane form remains stable to urea and trypsin but not to alkali, and c) new surface growth can in theory occur as an expansion of the brush-like layer by direct intercalation of filaments enriched in or consisting wholly of 80 and 86 kD proteins.Abbreviations BSA bovine serum albumin - ELISA enzyme linked immunosorbant assay - EF ectoplasmic fracture face - IMPs intramembrane particles - PF protoplasmic fracture face This work was supported by a University of Illinois Fellowship to RRD and NSF grant DCB-8602793 to GBB.     

Ultrastructural changes in strawberry leaves infested by two-spotted spider mites

Ultrastructural changes in strawberry leaves after different periods of feeding by Tetranychus urticae were studied. Electron micrographs indicate that the first detectable changes in cells directly punctured by the mites usually occurred after 3 days of feeding and were confined to the chloroplasts. These organelles show instability of the lamellae and the thylakoid membrane system as well as the envelope. Longer times of mite feeding (6–9 days) caused severe alterations, not only within chloroplast. In heavily injured tissues, misshapen cells contain homogeneous protoplasts in which only remains of necrotic chloroplasts were visible. Mesophyll cells adjacent to directly punctured tissues also exhibited subcellular alterations. Possible mechanisms of plant-tissue responses to mite feeding are discussed.

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Zusammenfassung Ultrastrukturelle Veränderungen wurden in Erdbeerblättern nach verschiedenen Perioden Saugtätigkeit von Tetranychus urticae Koch gesucht. Elektronenmikroskopische Aufnahmen zeigen, dass die ersten sichtbaren Veränderungen in direkt von Milben angestochenen Zellen meist nach 3 Tagen Saugen auftraten und auf die Chloroplasten beschränkt waren. Diese Organellen zeigen eine Instabilität der Lamellen, des Thylakoidmem-bransystems sowie der Umhüllung. Ein längere Zeit dauerndes Saugen der Milben (6–9 Tage) verursachte schwere Veränderungen und zwar nicht bloss in den Chloroplasten. In schwer geschädigten Geweben enthalten deformierte Zellen homogene Protoplasten, in denen nur Reste nekrotischer Chloroplasten sichtbar waren.Mesophyllzellen in der Nachbarschaft von direkt angestochenem Gewebe zeigte ebenfalls subzelluläre Veränderungen. Mögliche Mechanismen der Reaktion des Pflanzengewebes auf Milbensaugen werden diskutiert.

     

The tubular endoplasmic reticulum in the amoebocytes of the shell-regenerating snail,Helix pomatia L.

Summary The tubular endoplasmic reticulum has been studied in the amoebocytes which are present in the connective tissue of the hepatopancreas of the snail, Helix pomatia. The reticulum is similar to that previously described within the glandular cells of the hepatopancreas. Two distinct components are recognizable in the reticulum—central main tubules approximately 100 m in diameter and connecting tubules about 20 m in width. The profile of this tubular network in cross-sections appears as a very regular, apparently crystalline array. The tubules are intimately associated with dense granular material, dense bodies and with mitochondria. The possible function of the tubular endoplasmic reticulum is discussed.This investigation was supported by grants from the Swedish Natural Science Research Council, which are gratefully acknowledged. I am indebted to Miss G. Drugge for her technical assistance.     

Papaya transformed with the Galanthus nivalis GNA gene produces a biologically active lectin with spider mite control activity

Snowdrop (Galanthus nivalis) lectin has previously been shown to have anti-feedant and insecticidal activity towards sap-sucking insects. However, its effectiveness against plant-parasitic mites has not been demonstrated. In this study, the commercial papaya (Carica papaya L.) cultivar Kapoho, which is highly susceptible to mites, was transformed with the snowdrop lectin (G. nivalis agglutin [GNA]) gene. Polymerase chain reaction confirmed the presence of the transgene and six independent transformed lines were selected for expression analysis. Western blot analysis showed that the lines expressed a recombinant protein with a molecular weight similar to that of the native snowdrop lectin. Leaf extracts containing the recombinant GNA protein agglutinated trypsinized rabbit erythrocytes thus, showing the GNA protein to be biologically active. ELISA and indirect measurement from the agglutination assay showed there to be variation in GNA expression among the lines produced. A laboratory bioassay using carmine spider mites (Tetranychus cinnabarinus) suggested improved pest resistance in the transgenic papaya plants. This is the first report that a transgenic plant expressing the GNA gene possesses enhanced resistance to a plant-parasitic mite.     

Persistent social interactions beget more pronounced personalities in a desert-dwelling social spider

The social niche specialization hypothesis predicts that repeated social interactions will generate social niches within groups, thereby promoting consistent individual differences in behaviour. Current support for this hypothesis is mixed, probably because the importance of social niches is dependent upon the ecology of the species. We test whether repeated interactions among group mates generate consistent individual differences in boldness in the social spider, Stegodyphus dumicola. In support of the social niche specialization hypothesis, we found that consistent individual differences in boldness increased with longer group tenure. Interestingly, these differences took longer to appear than in previous work suggesting this species needs more persistent social interactions to shape its behaviour. Recently disturbed colonies were shyer than older colonies, possibly reflecting differences in predation risk. Our study emphasizes the importance of the social environment in generating animal personalities, but also suggests that the pattern of personality development can depend on subtle differences in species'' ecologies.