The Anatomy and Ultrastructure of the Digestive Tract and Salivary Glands of Hishimonus lamellatus (Hemiptera: Cicadellidae)

In recent years, we found that Hishimonus lamellatus Cai et Kuoh is a potential vector of jujube witches'-broom phytoplasma. However, little is known about the anatomy and histology of this leafhopper. Here, we examined histology and ultrastructure of the digestive system of H. lamellatus, both by dissecting and by semi- and ultrathin sectioning techniques. We found that the H. lamellatus digestive tract consists of an esophagus, a filter chamber, a conical midgut and midgut loop, Malpighian tubules, an ileum, and a rectum. Furthermore, both the basal region of the filter chamber epithelium and the apical surface of the midgut epithelium have developed microvilli. We also identify the perimicrovillar membrane, which ensheaths the microvilli of midgut loop enterocyte, and the flame-like luminal membrane, which covers the microvilli of the conical midgut epithelium. In addition, H. lamellatus has the principal and accessory salivary glands. Our observations also showed that the endoplasmic reticulum, mitochondria, and secretory granules were all highly abundant in the secretory cells of the principal salivary glands, while the accessory glands consist of only one ovate or elbow-like acinus. We also briefly contrast the structure of the gut of H. lamellatus with those of other leafhopper species. These results intend to offer help for the future study on the histological and subcellular levels of phytopathogen-leafhopper relationships, including transmission barriers and the binding sites of pathogens and other microorganisms within their leafhopper vectors.

Excretion in the mother's body: modifications of the larval excretory system in the viviparous dermapteran, Arixenia esau

The vast majority of Dermaptera are free-living and oviparous, i.e., females lay eggs within which embryonic development occurs until the larva hatches. In contrast, in the epizoic dermapteran Arixenia esau, eggs are retained within mother's body and the embryos and first instar larvae develop inside her reproductive system. Such a reproductive strategy poses many physiological challenges for a mother, one of which is the removal of metabolic waste generated by the developing offspring. Here, we examine how the Arixenia females cope with this challenge by analyzing features of the developing larval excretory system. Our comparative analyses of the early and late first instar larvae revealed characteristic modifications in the cellular architecture of the Malpighian tubules, indicating that these organs are functional. The results of the electron probe microanalyses suggest additionally that the larval Malpighian tubules are mainly involved in maintaining ion homeostasis. We also found that the lumen of the larval alimentary track is occluded by a cellular diaphragm at the midgut-hindgut junction and that cells of the diaphragm accumulate metabolic compounds. Such an organization of the larval gut apparently prevents fouling of the mother's organism with the offspring metabolic waste and therefore can be regarded as an adaptation for viviparity.

Obligate development of Blastocrithidia papi (Trypanosomatidae) in the Malpighian tubules of Pyrrhocoris apterus (Hemiptera) and coordination of host-parasite life cycles

Blastocrithidia papi is a unique trypanosomatid in that its life cycle is synchronized with that of its host, and includes an obligate stage of development in Malpighian tubules (MTs). This occurs in firebugs, which exited the winter diapause. In the short period, preceding the mating of overwintered insects, the flagellates penetrate MTs of the host, multiply attached to the epithelial surface with their flagella, and start forming cyst-like amastigotes (CLAs) in large agglomerates. By the moment of oviposition, a large number of CLAs are already available in the rectum. They are discharged on the eggs' surface with feces, used for transmission of bugs' symbiotic bacteria, which are compulsorily engulfed by the newly hatched nymphs along with the CLAs. The obligate development of B. papi in MTs is definitely linked to the life cycle synchronization. The absence of peristalsis allow the trypanosomatids to accumulate and form dense CLA-forming subpopulations, whereas the lack of peritrophic structures facilitates the extensive discharge of CLAs directly into the hindgut lumen. The massive release of CLAs associated with oviposition is indispensable for maximization of the infection efficiency at the most favorable time point.

Ultrastructure of the larval Malpighian tubules in Terrobittacus implicatus (Mecoptera: Bittacidae)

The larvae of Bittacidae, a cosmopolitan family in Mecoptera, have an interesting habit of spraying the body surface with soil through the anus after hatching, and each molts. The fine structure of Malpighian tubules, however, remains largely unknown in the larvae of Bittacidae to date. Here, we studied the ultrastructure of the larval Malpighian tubules in the hangingfly Terrobittacus implicatus (Huang & Hua) using scanning and transmission electron microscopy. The larvae of T. implicatus have six elongate Malpighian tubules at the junction of the midgut and hindgut. The tubule comprises a basal lamina, a single-layered epithelium, and a central lumen. The basal plasma membranes of the epithelial cells are conspicuously infolded and generate a labyrinth. The epithelium consists of two types of cells: large principal cells and scattered stellate cells. Mitochondria and cisterns of rough endoplasmic reticulum are numerous in the principal cells but are sparsely distributed in the stellate cells, indicating that the principal cells are active in transport. On the other hand, spherites are only abundant in the principal cells and are likely associated with the soil-spraying habit of the larvae.

Post-embryonic development of the Malpighian tubules in Apis mellifera (Hymenoptera) workers: morphology, remodeling, apoptosis, and cell proliferation

The honeybee Apis mellifera has ecological and economic importance; however, it experiences a population decline, perhaps due to exposure to toxic compounds, which are excreted by Malpighian tubules. During metamorphosis of A. mellifera, the Malpighian tubules degenerate and are formed de novo. The objective of this work was to verify the cellular events of the Malpighian tubule renewal in the metamorphosis, which are the gradual steps of cell remodeling, determining different cell types and their roles in the excretory activity in A. mellifera. Immunofluorescence and ultrastructural analyses showed that the cells of the larval Malpighian tubules degenerate by apoptosis and autophagy, and the new Malpighian tubules are formed by cell proliferation. The ultrastructure of the cells in the Malpighian tubules suggest that cellular remodeling only occurs from dark-brown-eyed pupae, indicating the onset of excretion activity in pupal Malpighian tubules. In adult forager workers, two cell types occur in the Malpighian tubules, one with ultrastructural features (abundance of mitochondria, vacuoles, microvilli, and narrow basal labyrinth) for primary urine production and another cell type with dilated basal labyrinth, long microvilli, and absence of spherocrystals, which suggest a role in primary urine re-absorpotion. This study suggests that during the metamorphosis, Malpighian tubules are non-functional until the light-brown-eyed pupae, indicating that A. mellifera may be more vulnerable to toxic compounds at early pupal stages. In addition, cell ultrastructure suggests that the Malpighian tubules may be functional from dark-brown-eyed pupae and acquire greater complexity in the forager worker bee.

Ultrastructure of fat body cells and Malpighian tubule cells in overwintering Scoliopteryx libatrix (Noctuoidea)

The herald moths, Scoliopteryx libatrix, overwinter in hypogean habitats. The ultrastructure of their fat body (FB) cells and Malpighian tubule (MT) epithelial cells was studied by light microscopy and transmission electron microscopy, and essential biometric and biochemical measurements were performed. The FB was composed of adipocytes and sparse urocytes. The ultrastructure of both cells did not change considerably during this natural starvation period, except for rough endoplasmic reticulum (rER) which became more abundant in March females. In the cells, the reserve material consisted of numerous lipid droplets, glycogen rosettes, and protein granula. During overwintering, the lipid droplets diminished, and protein granula became laminated. The MTs consisted of a monolayer epithelium and individual muscle cells. The epithelial cells were attached to the basal lamina by numerous hemidesmosomes. The apical plasma membrane was differentiated into numerous microvilli, many of them containing mitochondria. Nuclei were surrounded by an abundant rER. There were numerous spherites in the perinuclear part of the cells. The basal plasma membrane formed infoldings with mitochondria in between. Nuclei were located either in the basal or in the central part of the cells. During overwintering, spherites were gradually exploited, and autophagic structures appeared: autophagosomes, autolysosomes, and residual bodies. There were no statistical differences between the sexes in any measured biometric and biochemical variables in the same time frames. The energy-supplying lipids and glycogen, and spherite stores were gradually spent during overwintering. In March, the augmented rER signified the intensification of synthetic processes prior to the epigean ecophase.

Spinosad Induces Antioxidative Response and Ultrastructure Changes in Males of Red Palm Weevil Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae)

The red palm weevil, Rhynchophorus ferrugineus, is of great concern worldwide, especially in the Middle East, where dates are a strategic crop. Despite their ecological hazard, insecticides remain the most effective means of control. A bioinsecticide of bacterial origin, spinosad is effective against several pests, and its efficacy against male R. ferrugineus was assessed in the present study. The antioxidative responses of key enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) to spinosad were investigated in the midgut and testes, and the effects of this insecticide on the cell ultrastructure of the midgut, Malpighian tubules, and testes were also determined. The lethal concentration 50 of spinosad was measured at 58.8 ppm, and the insecticide inhibited the activities of CAT, SOD, and GST in the midgut. However, no significant changes in the activities of these enzymes were observed in the testes. Spinosad treatment resulted in concentration-dependent changes in the cellular organelles of the midgut, Malpighian tubules, and testes of R. ferrugineus, and some of these effects were similar to those exerted by other xenobiotics. However, specific changes were observed as a result of spinosad treatment, including an increase in the number and size of concretions in Malpighian tubule cells and the occasional absence of the central pair of microtubules in the axonemes of sperm tails. This study introduces spinosad for potential use as an insecticide within an integrated control program against male red palm weevils. Additionally, the study provides biochemical and ultrastructural evidence for use in the development of bioindicators.

Malpighian Tubule Cells in Overwintering Cave Crickets Troglophilus cavicola (Kollar, 1833) and T. neglectus Krauss, 1879 (Rhaphidophoridae, Ensifera)

During winter, cave cricket larvae undergo dormancy in subterranean habitats; this dormancy is termed diapause in second year Troglophilus cavicola larvae because they mature during this time, and termed quiescence in T. neglectus, because they mature after dormancy. Here we used electron microscopy to analyze ultrastructural changes in the epithelial cells in the Malpighian tubules (MTs) of T. cavicola during diapause, in order to compare them with previous findings on T. neglectus. Moreover, the autophagosomes were studied with immunofluorescence microscopy in both species. Although the basic ultrastructure of the cells was similar, specific differences appeared during overwintering. During this natural starvation period, the nucleus, rER, the Golgi apparatus and mitochondria did not show structural changes, and the spherites were exploited. The abundances of autophagic structures in both species increased during overwintering. At the beginning of overwintering, in both species and sexes, the rates of cells with autophagic structures (phagophores, autophagosomes, autolysosomes and residual bodies) were low, while their rates increased gradually towards the end of overwintering. Between sexes, in T. cavicola significant differences were found in the autophagosome abundances in the middle and at the end, and in T. neglectus at the end of overwintering. Females showed higher rates of autophagic cells than males, and these were more abundant in T. cavicola. Thus, autophagic processes in the MT epithelial cells induced by starvation are mostly parallel in diapausing T. cavicola and quiescent T. neglectus, but more intensive in diapausing females.

The digestive system of the "stick bug" Cladomorphus phyllinus (Phasmida, Phasmatidae): a morphological, physiological and biochemical analysis

This work presents a detailed morphofunctional study of the digestive system of a phasmid representative, Cladomorphus phyllinus. Cells from anterior midgut exhibit a merocrine secretion, whereas posterior midgut cells show a microapocrine secretion. A complex system of midgut tubules is observed in the posterior midgut which is probably related to the luminal alkalization of this region. Amaranth dye injection into the haemolymph and orally feeding insects with dye indicated that the anterior midgut is water-absorbing, whereas the Malpighian tubules are the main site of water secretion. Thus, a putative counter-current flux of fluid from posterior to anterior midgut may propel enzyme digestive recycling, confirmed by the low rate of enzyme excretion. The foregut and anterior midgut present an acidic pH (5.3 and 5.6, respectively), whereas the posterior midgut is highly alkaline (9.1) which may be related to the digestion of hemicelluloses. Most amylase, trypsin and chymotrypsin activities occur in the foregut and anterior midgut. Maltase is found along the midgut associated with the microvillar glycocalix, while aminopeptidase occurs in the middle and posterior midgut in membrane bound forms. Both amylase and trypsin are secreted mainly by the anterior midgut through an exocytic process as revealed by immunocytochemical data.

Ultrastructure of the excretory organs of Bombus morio (Hymenoptera: Bombini): bee without rectal pads

Bumblebees need to keep bodily homeostasis and for that have an efficient system of excretion formed by the Malpighian tubules, ileum, and rectum. We analyzed the excretory organs of Bombus morio, a bee without rectal pads. In addition, we analyzed the rectal epithelium of Melipona quadrifasciata anthidioides which has rectal pads. The Malpighian tubules exhibited two cell types and the ileum four types. However, comparative analysis of the rectum showed that only cells of the anterior region of the rectal epithelium of B. morio are structurally distinct. We suggest that cells of the Malpighian tubules of B. morio have an excretory feature and that cells of ileum have different functions, such as ion absorption and water, organic compound, and protein secretion. In addition, only the anterior region of the rectum of B. morio showed characteristic absorption. We suggest that Malpighian tubules participate in the excretion of solutes and that the ileum and rectal epithelium are responsible for homeostasis of water and solutes, compensating for the absence of rectal papillae. These results contribute to our understanding of the morphophysiology of the excretory organs of bees without rectal pads.

Structure of the Malpighian tubule cells and annual changes in the structure and chemical composition of their spherites in the cave cricket Troglophilus neglectus Krauss, 1878 (Rhaphidophoridae, Saltatoria)

Periodical changes in the structure of spherites in the Malpighian tubule cells of the cave cricket Troglophilus neglectus were studied to elucidate their role during the cricket's life cycle in natural circumstances. Special interest was given to the dormant overwintering period when we hypothesized that the primary role of spherites is to supply minerals for basic vital processes. The investigation was carried out by light and transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy-loss spectroscopy and energy-filtering TEM. Spherites are present only in the middle Malpighian tubule segment, consisting of Type 1 cells, characterized, among other features, by a round, apically placed nucleus and numerous spherites, and a few Type 2 cells with an elongated nucleus in the centre and sparse spherites. At the beginning of dormancy in November juveniles, minerals are accumulated in spherites and then decline until March. In one-year-old May larvae, spherites are commonly rich in minerals, and from July onwards they are progressively exploited in the adults. Spherite destruction starts with apoptosis in senile October individuals. The findings suggest that the mineral supply of spherites in Malpighian tubules is crucial to supporting vital processes throughout the life cycle of T. neglectus.

The ultrastructural investigation of the midgut in the quill mite Syringophilopsis fringilla (Acari, Trombidiformes: Syringophilidae)

The midgut of the females of Syringophilopsis fringilla (Fritsch) composed of anterior midgut and excretory organ (=posterior midgut) was investigated by means of light and transmission electron microscopy. The anterior midgut includes the ventriculus and two pairs of midgut caeca. These organs are lined by a similar epithelium except for the region adjacent to the coxal glands. Four cell subtypes were distinguished in the epithelium of the anterior midgut. All of them evidently represent physiological states of a single cell type. The digestive cells are most abundant. These cells are rich in rough endoplasmic reticulum and participate both in secretion and intracellular digestion. They form macropinocytotic vesicles in the apical region and a lot of secondary lysosomes in the central cytoplasm. After accumulating various residual bodies and spherites, the digestive cells transform into the excretory cells. The latter can be either extruded into the gut lumen or bud off their apical region and enter a new digestive cycle. The secretory cells were not found in all specimens examined. They are characterized by the presence of dense membrane-bounded granules, 2-4 microm in diameter, as well as by an extensive rough endoplasmic reticulum and Golgi bodies. The ventricular wall adjacent to the coxal glands demonstrates features of transporting epithelia. The cells are characterized by irregularly branched apical processes and a high concentration of mitochondria. The main function of the excretory organ (posterior midgut) is the elimination of nitrogenous waste. Formation of guanine-containing granules in the cytoplasm of the epithelial cells was shown to be associated with Golgi activity. The excretory granules are released into the gut lumen by means of eccrine or apocrine secretion. Evacuation of the fecal masses occurs periodically. Mitotic figures have been observed occasionally in the epithelial cells of the anterior midgut.

Ultrastructural alterations in midgut and Malpighian tubules of Boettcherisca peregrina exposure to cadmium and copper

The effects of Cu and Cd at their at their low concentrations (80microg/g diet) on the morphology and ultrastructure of the midgut and Malpighian tubules of Boettcherisca peregrina larvae were observed by light and transmission electron microscopy. After exposure to both metals, the midgut got darker, shorter, and thicker than in control, and many strumae occurred on the surface of the midgut. Similarly, Malpighian tubules got shorter and thinner. Ultrastructural alterations in the midgut included mitochondrial condensation, swelling, and lysis. The rough endoplasmic reticulum (rER) showed dilation and vesiculation. The microvilli were shortened and disorganized. The stored glycogens increased and many mineral spherites appeared along with lipid droplets decreased. Ultrastructural alterations observed in the Malpighian tubules included rER vesiculation and mitochondria swelling with loss of cristae. Shortened and disordered microvilli, increased numbers of large hydropic vacuoles, and mineral spherites were also observed.

Fine structure of the midgut and Malpighian papillae in Campodea (Monocampa) quilisi Silvestri, 1932 (Hexapoda, Diplura) with special reference to the metal composition and physiological significance of midgut intracellular electron-dense granules

The fine structure of the midgut and the Malpighian papillae in Campodea (Monocampa) quilisi Silvestri, 1932 (Hexapoda, Diplura) specimens was described. We observed the presence of electron-dense granules (EDGs) in the midgut epithelial cells, similar in genesis, structure and aspect to the type A spherocrystals described in the midgut epithelium of Collembola and Diplopoda. Energy-dispersive X-ray microanalysis was used to detect the chemical composition of the granules and to relate it to the concentrations of some potential toxic heavy metals (Pb, Cu, Zn) in soil and litter. Chemical composition of the granules seems strongly influenced by the presence and bioavailability of heavy metals in the external environment. Specimens from a contaminated abandoned mining and smelting area (Colline Metallifere, southern Tuscany) were able to accumulate Fe, Mn, Zn, Pb and Cu in their midgut EDGs. In addition, we observed that C. (M.) quilisi was able to excrete the metal-containing granules into the external medium by the moulting of the intestinal epithelium. This confirms that the process of ionic retention of midgut cells is particularly significant in animals lacking Malpighian tubules.

Ultrastructural and genetic evidence of a reptilian tick, Aponomma hydrosauri, as a host of Rickettsia honei in Australia: possible transovarial transmission

In 1993, a novel rickettsia was isolated from the blood of inhabitants of Flinders Island, Australia, with acute febrile illnesses. This rickettsia was found to be a new species of spotted fever group (SFG) rickettsia, eventually named Rickettsia honei. The suspected ectoparasite vector of this rickettsia has yet to be identified. The purpose of this study was to evaluate the presence of this rickettsial species in a suspected tick vector, Aponomma hydrosauri, by DNA sequencing and electron microscopy (EM). Ticks collected from an Australian blue-tongued lizard on Flinders Island and a copperhead snake in Tasmania were demonstrated to be infected with R. honei by PCR, DNA sequencing, and EM. Rickettsiae were found in ultrathin sections of salivary glands, malpighian tubules, and midgut epithelial cells. In a previous study with a R. honei-infected tick from Flinders Island, rickettsiae were found in the nuclei of midgut epithelial cells, and EM also revealed the presence of rickettsiae in the cytosol of oocytes and immature eggs, suggesting transovarial transmission. These results implicate A. hydrosauri as a possible host of R. honei on Flinders Island and Tasmania and also provide evidence favoring transovarial maintenance of R. honei.

Infection and replication sites of Spiroplasma kunkelii (Class: Mollicutes) in midgut and Malpighian tubules of the leafhopper Dalbulus maidis

Spiroplasma kunkelii distribution and infection mechanisms in the intestines and Malpighian tubules of Dalbulus maidis were investigated by transmission electron microscopy. Spiroplasmas were found between microvilli and in endocytic vesicles of the midgut epithelium. At the basal part, cytoplasmic vesicles contained multiple spiroplasmas with tube-like extensions and spiroplasmas accumulated between the laminae rara and densa of the basal lamina. Tip structures of flask-shaped spiroplasmas pierced the lamina densa that was discontinuous in close proximity to spiroplasmas. Spiroplasmas were found in hemolymph, crossed the basal lamina of Malpighian tubule epithelium and accumulated at high numbers in muscle cells that had cytopathogenic changes. S. kunkelii had perithrochous approximately 8nm diameter structures determined to be fimbriae protruding from the cell surface, and similar structures were adhering to the basal lamina of midgut epithelium and to external lamina of muscle cells. Further, spiroplasmas had pili-like appendages at one or both cell poles and appeared to conjugate. This is the first time that fimbriae and pili have been observed in a mollicutes.

Changes in nuclear phenotype frequencies following sequential cold shocks in Triatoma infestans (Hemiptera, Reduviidae)

The nuclear phenotypes of Malpighian tubule cells in fifth instar nymphs of Triatoma infestans, one of the most important vectors of Chagas disease, were studied following sequential shocks at 0 degrees C, separated by intervals of 8 h and 24 h at 30 degrees C, under conditions of moderate fasting and full nourishment. The insects pertained to colonies reared in the laboratory and originated from domestic specimens collected in the Brazilian states of São Paulo (north) and Minas Gerais (south). Since nuclear phenotypes in this species are affected by single cold shocks, it was expected that these phenotypes could also be changed by sequential shocks. Nuclear phenotypes indicative of mechanisms of cell survival (nuclear fusion and heterochromatin decondensation) and cell death (apoptosis and necrosis) were observed concomitantly in all the conditions tested. Nuclear fusion and heterochromatin decondensation were not found relevant for the presumed acquisition of the cold-hardening response in T. infestans. The decreased frequency of apoptosis and necrosis following sequential cold shocks including under fasting conditions, indicated that tolerance to sequential cold shocks occurred in T. infestans of the mentioned origin.

Magnesium transport through the basal plasma membrane of larval malpighian tubules of Drosophila hydei studied by electron probe X-ray microanalysis

Magnesium besides calcium is the most important excretion product. In the anterior Malpighian tubules of Drosophila, excretion of magnesium takes place via the hindgut by proteoglycan containing concretions. This study reports on magnesium transport through the basal plasma membrane of the principal cells of the proximal segment of the anterior Malpighian tubules. Measurements by electron probe X-ray microanalysis indicate the existence of two antiporters which transfer magnesium in still unknown stoichiometry from the hemolymph space into the cell: Mg/H and Mg/Na.

Membrane dynamics in the malpighian tubules of the house cricket, acheta domesticus

In Acheta domesticus, the Malpighian tubules (Mt) are composed of three morphologically distinct regions (proximal, mid and distal), each consisting of a single cell type. The bulk of the Mt is composed of the midtubule, which shows the greatest response to corticotropin releasing factor-related diuretic peptides (CRF-DP). We know from previous laboratory studies that the second messenger cAMP and its analog dibutyryl cAMP (db-cAMP) cause an approximate doubling in the secretion rate and that this is accompanied by notable ultrastructural changes in the midtubule, especially membrane reorganization in the basal area and extensive vesiculation of the cytoplasm. In this study, we examined the morphological changes in membranes both at the cell surface and internally. By enzymatically removing the basal lamina, we examined the increase in spacing between infolded membranes initiated by db-cAMP stimulation. To examine the intracellular membranes, we used a technique developed for use in invertebrate tissues. This allowed the removal of the cytoplasm for high resolution scanning electron microscopy (HR-SEM) while maintaining the integrity of the lipid constituents of the cell. By using HR-SEM and confocal laser scanning microscopy (CLSM), we gained a unique three-dimensional perspective of the complexity of the internal membrane system of the A. domesticus Mt in both the unstimulated and db-cAMP-stimulated states.

Morphology and ultrastructure of the Malpighian tubules of the Chilean common tarantula (Araneae: Theraphosidae)

Relatively little is known about the morphology and ultrastructure of the Malpighian tubules of spiders (Arachnida: Araneae). Our study represents the first investigation of the Malpighian tubules of a theraphosid spider and is the only study to examine the living Malpighian tubules using confocal laser scanning microscopy. In theraphosid spiders, the Malpighian tubules originate from the stercoral pocket in the posterior portion of the opisthosoma and extend forward toward the prosoma in a dendritic pattern. There are three distinct segments (initial, main, and terminal), all dark brown in appearance. Each segment has distinctive ultrastructural features. Both the terminal and the main segment appear to be composed of at least two cell types with finger-like cytoplasmic protrusions associated with one of these types. The terminal segment, which is most proximal to the stercoral pocket, is the largest in diameter. It is composed of large, cuboidal cells containing many mitochondria and lipid inclusions. The main segment is intermediate in diameter with many mitochondria and secretory vesicles present. The initial segment is relatively thin in comparison to the other segments and is intimately associated with the digestive gland. The cells of the initial segment contain very little cytoplasm, fewer mitochondria, secretory vesicles, and prominent inclusions.

Fluid secretion in Rhodnius upper malpighian tubules (UMT): water osmotic permeabilities and morphometric studies

We have measured the osmotic permeability of the basolateral cell membrane (Poscb) and compared it with the transepithelial permeability (Poste) to calculate the paracellular (Posp) permeability of the upper malpighian tubules (UMT) of the 5th instar of Rhodnius prolixus under several experimental conditions, namely, at rest and after stimulation to secrete with 5-HT, each under control conditions (no treatment), after treatment with pCMBS, and after addition of pCMBS and DTT. Secretion rate is negligible at rest. During stimulation mean secretion rate is 43.5 nl/cm2 sec. Secretion is severely curtailed by pCMBS and fully restored by DTT. Poscb = 9.4 (resting, control); 5.8 (control + pCMBS); 10.7 (control + pCMBS + DTT); 20.6 (stimulated, control); 14.7 (stimulated + pCMBS); 49.1 (stimulated + pCMBS + DTT) (x10?4 cm3/cm2 sec Osm). Calculated Posp are higher than the transcellular permeability, Posc, at rest and after stimulation. Electron micrograph morphometry of UMT sections show that cells significantly decrease their volume after stimulation. Lateral intercellular space (LIS) and basolateral extracellular labyrinth (BEL) are barely discernible at rest. LIS and BEL are widely dilated in stimulated UMT. Thus, ions have restricted access to the deep and narrow basolateral cell membrane indentations at rest, but they have ready access to cell membrane indentations after stimulation, because of the opening of LIS and BEL. These findings are discussed in relation to isosmotic secretion. The rate-limiting step for paracellular movement is located at the smooth septate junctions.

Characterization of transepithelial potential oscillations in theDrosophilaMalpighian tubule

The Malpighian tubule of Drosophila melanogaster is a useful model system for studying the regulation of epithelial ion transport. In acutely isolated tubules, the transepithelial potential (TEP) undergoes large oscillations in amplitude with a period of approximately 30s. The TEP oscillations are diminished by reductions in the peritubular chloride concentration in a manner consistent with their being caused by fluctuations in chloride conductance. The oscillations are eliminated by pretreating tubules with the calcium chelator BAPTA-AM, although removal of peritubular calcium has no effect, suggesting that the oscillations are a result of either the release of calcium from intracellular stores or the entry of calcium from the tubule lumen. Transcripts encoding two calcium-release channels, the ryanodine receptor and the inositol trisphosphate receptor, are detectable in the tubule by reverse transcription–polymerase chain reaction. To identify the cell type responsible for the oscillations, tubules were treated with diuretic hormones known to alter calcium levels in each of the two cell types. Leucokinin-IV, which increases calcium levels in the stellate cells, suppressed the oscillations, whereas cardioacceleratory peptide 2b (CAP2b), which increases calcium levels in the principal cells, had no effect. These data are consistent with a model in which rhythmic changes in transepithelial chloride conductance, regulated by intracellular calcium levels in the stellate cells, cause the TEP oscillations.

Ultrastructural variations in Lethocerus niloticum (Insecta: Hemiptera) caused by pollution in Lake Mariut, Alexandria, Egypt

Water bugs, Lethocerus niloticum (Hemiptera: Belostomatidae), were collected from polluted and unpolluted areas of Lake Mariut to study ultrastructural alterations of different organs as a response to mainly heavy metal water pollution in the lake. Malpighian tubules are described by light, scanning, and transmission electron microscopy. L. niloticum has four Malpighian tubules floating in the hemolymph. Each tubule opens separately into the hindgut, consisting of one type of epithelium cells, and is divided into four regions. Structural changes in cells of the third distinctive region are examined. The most prominent pathological changes are the occurrence of pleomorphic mitochondria, the presence of enlarged irregular laminated concretions, an increase in lysosomes, and lysis of cytoplasm. Indentations of the nucleus and chromatin clumping are observed. These results allowed determination of the impact of pollutants in Malpighian tubule cells of L. niloticum, and thus this insect can be used as a biomonitor.

Chloride channels in apical membrane patches of stellate cells of Malpighian tubules of Aedes aegypti

Stellate cells of Aedes aegypti Malpighian tubules were investigated using patch-clamp methods to probe the route of transepithelial Cl(−) secretion. Two types of Cl(−) channel were identified in excised, inside-out apical membrane patches. The first Cl(−) channel, type I, had a conductance of 24 pS, an open probability of 0.816+/−0.067, an open time of 867+/−114 ms (mean +/− s.e.m., four patches) and the selectivity sequence I(−)>Cl(−)(much greater than) isethionate>gluconate. The I(−)/Cl(−)>>isethionate>gluconate. The I(−)Cl(−) permeability ratio was 1.48, corresponding to Eisenman sequence I. The type I Cl(−) channel was blocked by 2,2′-iminodibenzoic acid (DPC) and niflumic acid (2-[3-(trifluoromethyl)anilo]nicotinic acid). The removal of Ca(2+) from the Ringer's solution on the cytoplasmic side had no effect on channel activity. The second Cl(−) channel, type II, had a conductance of 8 pS, an open probability of 0.066+/−0.021 and an open time of 7.53+/−1.46 ms (mean +/− s.e.m., four patches). The high density and halide selectivity sequence of the type I Cl(−) channel is consistent with a role in transepithelial Cl(−) secretion under control conditions, but it remains to be determined whether these Cl(−) channels also mediate transepithelial Cl(−) secretion under diuretic conditions in the presence of leucokinin.

Ultrastructural changes in the Malpighian tubules of the house cricket, Acheta domesticus, at the onset of diuresis: A time study

The Malpighian tubules (Mt) of insects are responsible for maintaining osmotic homeostasis and eliminating waste from the hemolymph. When stimulated by diuretic factors the tubule cells are able to transport extraordinary volumes of fluid over short periods of time. We have been studying the changes that occur within the cells that accompany and facilitate this phenomenon. We present the ultrastructural changes that occur in the mid-tubule of the house cricket, Acheta domesticus, following exposure to the second messenger analog, dibutyryl cAMP, over the period from 15-420 sec. Vacuolation of the cytoplasm begins as early as 30 sec poststimulation with a significant increase in vacuolation occurring after 120 sec. As expected, there is an increase in the surface area of the basolateral membrane to facilitate the rapid movement of fluid into the cells. Other ultrastructural changes noted to accompany the onset of diuresis include the movement of mitochondria into areas adjacent to transport membranes, the vesiculation of Golgi, mobilization of CaPO(4) spherites, and a direct interaction of these spherites with active mitochondria. We discuss several possible roles for these changes in terms of rapid fluid transport.

Secretion of brochosomes during the ontogenesis of a leafhopper, Oncometopia orbona (F.) (Insecta, Homoptera, Cicadellidae)

Secretion of brochosomes, intricately structured symmetrical protein-lipid particles produced in the specialized Malpighian tubules of the Cicadellidae, was studied during the ontogenesis of Oncometopia orbona (F.). Unlike most other cicadellids, O. orbona displays sexual dimorphism in the production of brochosomes. The Malpighian tubule secretory cells of nymphs, males and young females produce spherical brochosomes of 0.3-1.4 microm in diameter, extruded after molts through the hindgut and spread across the integument as a coating. In females with developing eggs the same cells switch to producing rod-like brochosomes of 3.5-11.0 microm in length, which are used to powder the oviposition sites. The transition involves a dramatic change in morphogenesis of the secretory particles. Both types of brochosomes derive from homogenous condensing Golgi granules and acquire their definitive structure as a result of growth, differentiation of the contents into a wall and a core, and development of a lattice of surface invaginations. Final stages of this process take place in Golgi-derived vacuoles. In the development of rod-like brochosomes the condensing granules coalesce into masses several times larger than nascent spherical type. These giant granules flatten, then become doughnut-shaped and finally break open into a pair of linear particles. Whether the chemical composition differs between the two types of brochosomes remains unknown.

Peroxidase activity in Malpighian tubules of Triatoma infestans Klug

Benzidine and diamino benzidine (DAB) oxidation, typically performed by peroxidases, was demonstrated by light and electron microscopy in peroxisomes, mitochondria and membranous structures which occurred in close contact with urate crystals in Malpighian tubules of nymphs and adults of Triatoma infestans. Peroxisomes were predominantly identified in cells of the distal region of the tubules, which is engaged in excretory mechanisms. DAB oxidation in mitochondria, even in the absence of hydrogen peroxide, may indicate the existence of a mitochondrial peroxidase and possibly a cytochrome c peroxidase. The localization of the extracellular membranous structures appeared restricted to the lumen of the proximal region of the tubules and they were assumed to be remnants of endoplasmic reticulum containing peroxidases.

Quantitative elemental X-ray imaging of frozen-hydrated biological samples

It is shown that quantitative X-ray imaging of planed, frozen-hydrated, biological bulk samples that have not been etched is possible. X-ray imaging represents a better alternative to static beam (selected area) analysis of fractured frozen-hydrated samples. This procedure avoids the undesirable necessity of etching planed frozen-hydrated samples to provide an interpretable electron image. Qualitative oxygen and carbon X-ray images, which can be acquired in a short time, can be used for distinguishing morphological features and remove the requirement for electron images. In test samples of frozen-hydrated albumin, containing salts, analyses by X-ray images compared well with static beam (selected area) analyses from the same samples. An example of an analysis of frozen-hydrated insect Malpighian tubules is given in which the response to ouabain treatment was analysed. In this example X-ray imaging showed that ouabain resulted in a significant increase in cytoplasmic and luminal Na and a significant decrease in cytoplasmic and luminal K. X-ray imaging also showed that there was a significant increase in cellular water content. The presence of a potassium gradient in soybean root nodules was also demonstrated. The use of standard deviation images for processing low count images increases analytical precision but results in underestimates of the true concentrations.

Freezing survival by isolated Malpighian tubules of the New Zealand alpine weta Hemideina maori

The ability of isolated Malpighian tubules from a freeze-tolerant insect, the New Zealand alpine weta (Hemideina maori), to withstand freezing was assessed by measuring post-freeze membrane potentials and rates of fluid secretion. The hemolymph of cold-acclimated Hemideina maori was found to contain relatively high concentrations of the cryoprotectants trehalose (>300 mmol l-1) and proline (41 mmol l-1). Survival of isolated Malpighian tubules was correspondingly high when a high concentration of trehalose was present in the bathing saline. Tubules allowed to recover for 20 min from a 1 h freeze to -5 degrees C in saline containing 400 mmol l-1 trehalose had a basolateral membrane potential of -53 mV compared with a potential of -63 mV in tubules not exposed to a freeze/thaw cycle. Fluid secretion in tubules that had experienced a freeze/thaw cycle in saline containing 400 mmol l-1 trehalose was 9.9+/-2.6 nl h-1 compared with 18.7+/-5.0 nl h-1 (means +/- s.e.m., N=18) in tubules that had not been frozen. Tubules frozen in saline containing a lower concentration of trehalose (200 mmol l-1) or in glucose (400 mmol l-1) showed a similar ability to survive freezing to -5 degrees C. In contrast, freezing for 1 h at -5 degrees C in saline containing 400 mmol l-1 sucrose produced a 57 % decrease in membrane potential and an 88 % decrease in secretion rate. Tubules held in saline lacking high concentrations of sugars showed no survival after freezing to -5 degrees C for 1 h. When frozen to -15 degrees C, tubules appeared to survive best in saline with the highest trehalose concentration (400 mmol l-1). Freezing damage was not simply the result of exposure to cold, since tubules chilled (unfrozen) to -5 degrees C for 1 h were not compromised even when the bathing saline lacked a high sugar concentration. Exposure of tubules to a combination of low temperature and high osmolality mimicked damage caused by actual freezing: the membrane potential showed a 60 % recovery when the test was performed in saline containing trehalose, but showed no recovery in saline containing sucrose.

Ultrastructure of infection, development and gametocyst formation of Ascogregarina taiwanensis (Apicomplexa: Lecudinidae) in its mosquito host, Aedes albopictus (Diptera: Culicidae)

The life history of the protozoan parasite Ascogregarina taiwanensis in mosquito larvae (Aedes albopictus, collected in southern Taiwan) was shown to consist of two consecutive stages--intracellular and extracellular. Light microscopy showed that most trophozoites moved into the Malpighian tubules and developed into giant trophozoites during the first day pupa. The locomotion may be associated with bristle-like ridges of the trophozoite. The stage for sexual reproduction, i.e., the gamete, was then formed by segmentation of the giant trophozoite and twisting off the anucleate extremities of the body. Sexual reproduction occurred via fertilization by fusion of two resulting gametes, presumably two opposed sexes. The fused gametes finally generate the formation of the gametocyst, within which oocysts develop by budding from the cytoplasmic mass. This type of sexual reproduction has not been reported previously in any gregarine protozoa. We here proposed it as a new hypothesis for further elucidation of the protozoan reproduction.

Effect of tryptophan metabolites on fluorescent granules in the Malpighian tubules of eye color mutants of Drosophila melanogaster

Fluorescent granules that are stained with Nile blue sulfate are present in larval Malpighian tubules in the wild type strain of Drosophila melanogaster, Oregon-R. These granules emit a weak blue fluorescence and most of them are about 2 microns or more in diameter. The ommochrome precursor 3-hydroxy-kynurenine (3-HK) is actively transferred into the tubules of Oregon-R. Changes in the fluorescent granules in the Malpighian tubules on administration of ommochrome precursors were investigated in eye color mutants of Drosophila. The fluorescent granules in the tubules of the nonautonomous mutants v;bw and cn bw emit a strong blue fluorescence and most of them are about 1 micron or less in diameter. When v;bw and cn bw larvae were cultured on medium supplemented with kynurenine or 3-HK, respectively, the fluorescence intensity of their granules decreased, and their size increased. These additions resulted in almost equal accumulation of 3-HK to that in Oregon-R. On the other hand, no 3-HK accumulated in the tubules of larvae of the autonomous mutants bw;st, ltd bw and w, which lack the fluorescent granules. These findings indicate that the fluorescent granules are an important intracellular site for uptake or storage of ommochrome precursors in larval Malpighian tubules of Drosophila.

The importance of the Golgi complex for epithelial ion transport in Drosophila Malpighian tubules, studied by electron microscopy, cytochemistry and X-ray microanalysis

The distribution of potassium in the cells of Drosophila Malpighian tubules is not homogeneous. In the microvilli of the apical part of the cell the cytoplasmic potassium content was found to be 2 to 3 times higher than in the neighboring intermediate cytoplasm. Data obtained by electron microscopy, histochemistry and electron probe X-ray microanalysis indicate that glucosaminoglycans (GAGs), synthesized by the Golgi-ER complex, are responsible for potassium accumulation in the apical microvilli. Vesicles bud from the Golgi complex and then move to the apical cell region, where they discharge their contents into the cytoplasm or into the lumen. Budded vesicles also discharge their contents into the hemolymph space between the folds of the basal plasma membrane. GAGs, transformed to proteoglycans (PGs), were identified on the folds of the basal cell surface including basal lamina by reaction with alcian blue. Brefeldin A (BFA) was found to disintegrate Golgi-ER structures to vesicles, whereas budded vesicles vanished. Within the microvilli the K+-content decreased to 32%, the water content to 77%. These data provide evidence that the ER-Golgi complex is involved in the delivery of GAGs (and PGs) into the luminal space and the hemolymph. After disintegration of the Golgi complex, GAGs are missing as temporary ion stores from the vicinity of the membrane transporters.

Tat-induced lesions in transgenic mice do not correlate with the HIV-1 LTR transactivation

The product of the tat gene is the most potent transcriptional trans-activator of the HIV-1 LTR (Human Immunodeficiency Virus type 1 Long Terminal Repeat) and might be predicted to be one of the HIV-1 proteins involved in the pathogenesis of AIDS-associated tumors. Deciphering its role in vivo may imply generation of transgenic mouse models displaying different spectra of tat expression. However, it remains difficult to correlate the mRNA expression, the protein production and the eventual pathological consequences in the animal. Our goal in this work was to elaborate a binary transgenic system allowing such an approach, the correlation of the transgene expression in different tissues and the production of the Tat protein, tested as a trans-activator in vivo, with its pathogenic effects. No direct linkage was evident between the degree of transactivation and pathogenesis. Indeed, only benign lesions were observed in malpighian epithelia, where the production of the Tat protein was clearly evidenced by its transactivating property.

Properties of achetakinin binding sites on malpighian tubule membranes from the house cricket, Acheta domesticus

A biologically active 125I-labeled analogue of AK-II (3'-hydroxyphenyl propionic-Gly-Gly-Gly-Phe-Ser-Pro-Trp-Gly-NH2) was used to investigate the properties of achetakinin binding sites on plasma membranes from Malpighian tubules of Acheta domesticus. With optimized conditions, binding was rapid, reversible, and specific, and saturation studies revealed a single class of binding sites with Kd 0.55 nM and Bmax 39.9 fmol/mg membrane protein. The affinities of achetakinins for binding sites on tubule membranes ranked AK-V > AK III > AK-II > AK-I > or = AK-IV, in general agreement with their potencies in functional assays. However, IC50 values were several orders of magnitude higher than corresponding values for EC50, which suggests a considerable receptor reserve.

An ultrastructural study on the early cellular response to Dirofilaria immitis (Nematoda) in the Malpighian tubules of Aedes aegypti (refractory strains)

Dirofilaria immitis living in Aedes aegypti refractory strains were studied in relation to ultrastructural events in primary cells of Malpighian tubules and to defense mechanisms activated by host-cells. When the microfilaria reaches the Malpighian cells, its intracellular development is blocked by defense mechanisms activated by the host, resulting in lysis of the outermost cuticle of the parasite without melanin involvement. Ultrastructural evidence suggests that lysis is brought about by Malpighian cell products.

Myoendocrine-like cells in invertebrates: occurrence of noncardiac striated secretory-like myocytes in the gut of the ant Formica polyctena

The occurrence of myoendocrine-like cells investing the ampullar draining region of Malpighian tubules and neighboring midgut and hindgut regions of the ant Formica polyctena is reported. These striated muscle cells show small electron-dense endocrine-like granules (130 +/- 0.95 nm) in addition to myofilaments and ordinary organules of the myocytes. Apart from their contractile function, such ultrastructural features suggest a regulatory role for these cells, as is the case of vertebrate myoendocrine cells. As far as we know, the ant secretory myocytes reported here constitute the first description of myoendocrine cells among invertebrates, as well as the first report of secretory, striated muscle cells outside the heart in the animal kingdom.

Insecticidal and cytotoxic effects of natural and hemisynthetic destruxins

The insecticidal and cytotoxic effects of 13 natural and hemisynthetic destruxins have been studied. DE shows insecticidal effects similar to those of DA, while DE and DA are more active than all the other natural compounds and analogues tested. Brominated destruxin is a relatively active analogue displaying particular modalities of cytotoxic effects which reflect a certain originality of its mode of action. The linear molecule resulting from the opening of the DA cycle is not toxic. The most hydrophilic destruxins showing e.g. charged radicals (COO-) appear the least toxic probably because they do not penetrate easily the cellular membranes.

An X-ray microanalysis study of Locusta Malpighian tubule cell function using rubidium

Intracellular distributions of Na, K, Mg, Ca, Cl, P, and S were determined in type 1 Malpighian tubule cells of Locusta using X-ray microanalysis. K showed a gradient of increasing concentration from basal to apical surfaces. No other element showed this distribution. Na was below the detection limit. Three types of dark body were present in cytoplasm; one rich in Ca and P and two rich in K and P. Incubation in Rb-Ringer solution resulted in a dramatic fall in cellular K that was not completely replaced by Rb. The distribution of Rb mimicked that of K. Na levels were significantly increased, but the total intracellular monovalent metal concentration was less than in controls. Other elements were little affected. Rb replaced K in dark bodies. Tubules continued to secrete K-rich urine in Rb-Ringer solution even though intracellular [K] was low. Little Rb+ was secreted and Na+ secretion was unchanged. The possible role of dark bodies as a source of secreted K+ is discussed.

Heat shock activation of telomeric sequences in different tissues of Chironomus thummi

The heat shock transcription factor (HSF) has been found by immunocytochemistry using the Drosophila HSF antibody at T-BRIII, a telomeric heat shock-induced puff in polytene chromosomes of Chironomus thummi salivary glands. Other heat shock-activated loci were also positively stained by the antibody. Neither the telomeres nor other heat shock loci were labeled under control conditions. These results support the presence of a heat shock gene at T-BRIII despite its peculiar location and molecular organization, different from other well-characterized heat shock genes in Diptera. This locus is similarly induced and transcribed under heat shock in Malpighian tubules, another larval polytenic tissue. Transcription from telomeric-associated sequences has also been found in control polytenic and diploid tissues. The meaning of transcription and heat shock activation of telomeric sequences is discussed in relation to the organization of telomeres and compared to possible equivalents in other known heat shock loci.

Electron probe X-ray microanalysis of epithelial cells: aspects of cryofixation

Content and distribution of diffusible ions in epithelial cells were studied by scanning transmission electron microscopy and energy dispersive electron probe X-ray microanalysis of freeze-dried cryosections from trout kidney, rat liver and Malpighian tubules of Drosophila larvae. Cryofixation of small excised kidney and liver samples by rapid immersion into liquid propane resulted in intracellular K/Na-ratios < 1. In contrast, K/Na-ratios > 7 were obtained after in situ cryofixation by means of a cryopunching device which allows tissue pieces to be frozen during excision from the intact organ. Isolated hepatocytes cryofixed in a small droplet of culture medium had a K/Na-ratio of 3.7. After culturing the hepatocytes, the K/Na-ratio increased to 24. Effects of extracellular media of different composition on the intracellular element content were studied. Malpighian tubules of Drosophila larvae were cryofixed by rapid immersion into liquid propane, and the distribution of K across the cells forming the tubules from the basal to the apical cell membrane was measured. An increasing K gradient was found from the intermediate to the apical cytoplasm. The intracellular K distribution was dependent on ions and transport inhibitors present in the fluid surrounding the Malpighian tubules within the larvae. Content and distribution of ions in epithelial cells sensitively depend on the physiological state immediately before cryofixation. Thus, electron probe X-ray microanalysis of cells and cell functions requires careful selection and control of the cell system to be studied.

Use of ultra-thin window detectors for biological microanalysis

Films and bulk samples of Nylon, gelatin, Makrofol, epoxy resin, aminoplastic resin and sodium acetate have been used as models of biological samples. It is shown that the use of ultrathin window (UTW) detectors in scanning transmission and scanning electron microsopes permits the quantitative analysis of light elements, yielding a total element analysis with hydrogen estimated by difference or "guesstimated". Comparison with known concentrations of concentrations obtained by chemical analysis shows that X-ray microanalysis of selections by the peak to continuum ratio model and bulk samples by the phi(pz) model gives sufficiently accurate results for biological purposes. It is also shown that sections may be analysed by the standardless ratio model. The application of UTW detectors to total element analysis by quantitative elemental imaging is demonstrated of bulk biological samples. which have been freeze-substituted, embedded in epoxy resin and surface polished. The possibility of imaging the oxygen content of frozen-hydrated bulk tissue samples which have been surface polished is also demonstrated. This may lead to the imaging of water distribution in frozen-hydrated bulk samples of biological tissues. UTW detectors are also useful for detecting mass loss in organic samples by monitoring the decrease in oxygen counts and for detecting contamination by monitoring the increase in carbon counts. It is also shown that changes in carbon counts are good indicators of folds in sections.

Heterogeneous distribution of elemental contents in the larval Malpighian tubules of Drosophila hydei: X-ray microanalysis of freeze-dried cryosections

The elements Na, Cl and K are distributed heterogeneously in the larval cells of the four Malpighian tubules of Drosophila hydei. Elemental gradients are steeper when they are related to the dry weight in comparison to the weight of water. The high contents of Na, Cl and K in the cytoplasm close to the basal plasma membrane differ significantly from the low values found in the neighboring basal "labyrinth" and in the intermediate cytoplasm. Elemental contents (K, Cl) increase from the intermediate cytoplasm to the apical microvilli and further to the lumen. The K/Na-ratio changes across the cells from 0.9 in the hemolymph to 2 in the basal cytoplasm close to the plasma membrane, to 27 in the microvilli, and 89 in the fluid phase of the lumen. In the lumen, K is accumulated in proteoglycan containing type-II concretions. The water content increases from the distal to the proximal segments of anterior and posterior tubules.

Cell proliferation and rearrangement in the development of the malpighian tubules of the hemipteran, Rhodnius prolixus

The pattern of cell activities resulting in the generation of a simple tubular epithelium, the Malpighian tubules of Rhodnius prolixus, is examined during embryogenesis. The anlage of the tubules is shown to be of ectodermal origin. An evolving pattern of cycling cells in the primordia is revealed using the immunocytochemical localization of a substituted nucleotide, BUdR. A cell unique to each tubule is shown not to enter the cell cycle but to be required for the proliferation of the remaining cells in the tubules. Furthermore, the activity of this cell imposes on each tubule a clear proximo-distal axis.

A new method of preparing the basal membrane of renal tubules for patch clamp, using beetle malpighian tubules

Access to the basal membrane of beetle Malpighian tubules (Onymacris rugatipennis) was achieved by a new method of stripping tubules of the surrounding connective tissue and basement membrane, in a simple squeezing process. We recorded single channel currents in the cell-attached configuration from basal K+ channels. The peeling method described in this paper allows quick and easy preparation of Malpighian tubules for patch clamp studies on the basal membrane.

Expression of bovine superoxide dismutase in Drosophila melanogaster augments resistance of oxidative stress

Superoxide dismutases (SOD) play a major role in the intracellular defense against oxygen radical damage to aerobic cells. In eucaryotes, the cytoplasmic form of the enzyme is a 32-kDa dimer containing two copper and two zinc atoms (CuZn SOD) that catalyzes the dismutation of the superoxide anion (O2-) to H2O2 and O2. Superoxide-mediated damage has been implicated in a number of biological processes, including aging and cancer; however, it is not certain whether endogenously elevated levels of SOD will reduce the pathological events resulting from such damage. To understand the in vivo relationship between an efficient dismutation of O2- and oxidative injury to biological structures, we generated transgenic strains of Drosophila melanogaster overproducing CuZn SOD. This was achieved by microinjecting Drosophila embryos with P-elements containing bovine CuZn SOD cDNA under the control of the Drosophila actin 5c gene promoter. Adult flies of the resulting transformed lines which expressed both mammalian and Drosophila CuZn SOD were then used as a novel model for evaluating the role of oxygen radicals in aging. Our data show that expression of enzymatically active bovine SOD in Drosophila flies confers resistance to paraquat, an O2(-)-generating compound. This is consistent with data on adult mortality, because there was a slight but significant increase in the mean lifespan of several of the transgenic lines. The highest level of expression of the active enzyme in adults was 1.60 times the normal value. Higher levels may have led to the formation of toxic levels of H2O2 during development, since flies that died during the process of eclosion showed an unusual accumulation of lipofuscin (age pigment) in some of their cells. In conclusion, our data show that free-radical detoxification has a minor by positive effect on mean longevity for several strains.

Mass dense vacuoles in Drosophila Malpighian tubules contain zinc, not sodium. A reinvestigation by X-ray microanalysis of cryosections

The intracellular storage of zinc in Malpighian tubules of Drosophila hydei was studied by X-ray microanalysis of freeze-dried cryosections. Mass dense vacuoles in the proximal region of the anterior larval Malpighian tubule cells were found to accumulate zinc, not sodium. The zinc content was enhanced considerably after addition of zinc to the food of the larvae. Zinc-containing vacuoles were also found after pupation. After starvation of larvae in sea water, Na was detected in these vacuoles in addition to Zn. A small increase of Na and a remarkable increase of Zn was found in the vacuoles after injection of Ringer solution with ouabain into the larvae. Similar vacuoles in cells of untreated posterior tubules exhibit only low zinc levels.

Cytoskeletal F-actin patterns in whole-mounted insect Malpighian tubules

The distribution of actin filaments in Malpighian tubules of the fleshfly Sarcophaga bullata (Parker) was investigated before and after metamorphosis by means of the rhodamine phalloidin staining method. The numerous primary cells show a pattern of thick basal actin bundles resembling stress fibres of cultured cells, while the apical microvillar zone shows a bright and homogeneous labelling. The less abundant stellate cells contain no such basal actin bundles and their apical microvillar zone gets only faintly stained. Late larval stages display fingerlike infoldings and an increased actin filament concentration at the apical membrane of the stellate cells. During metamorphosis the Malpighian tubules dedifferentiate and eventually redifferentiate to give rise to adult tubules resembling larval ones. The different types of actin filament organisation in the primary and stellate cells of the Malpighian tubules are discussed.

Fluid secretion and microvillar ultrastructure in mosquito malpighian tubules

The Malpighian tubules of fourth instar larvae, pupae, and female adults of the mosquito Aedes taeniorhynchus were examined with regard to in vitro fluid secretion rate and the ultrastructural features of the microvillar border of the primary cells. In vitro fluid secretion rates were determined after stimulation with 5-hydroxytryptamine. While larval tubules are capable of rapid fluid secretion, the tubules of pupae exhibit very low rates of secretion, indistinguishable from 0 nl/h. The capacity to secrete fluid returns after the pupal-adult molt and is further enhanced after blood feeding. Similar results were obtained in tubules stimulated in vitro with dibutyryl adenosine 3',5'-cyclic monophosphate. Ultrastructural examination of the microvillar border of the primary cells of the Malpighian tubules revealed that the period of reduced secretion capacity in the pupal tubules is correlated with a marked reduction in microvillar volume, microvillar surface area, and mitochondrial content in the microvillar border. The results suggest that microvilli of a certain size and containing extensions of mitochondria are required for rapid fluid transport. The absence of these conditions in pupal tubules cannot be overcome by in vitro stimulation with known secretagogues and therefore represents a physiological limit on transport performance in the pupal tubules of mosquitoes.

Intracellular storage of sodium and magnesium in Drosophila Malpighian tubules. X-ray microanalysis of native cryosections

Using electron probe X-ray microanalysis after cryofixation, cryosectioning and freeze-drying we investigated the content of electron-dark vacuoles in the intermediate cell region of the proximal segment of Malpighian tubules in Drosophila larvae. According to this method these vacuoles store sodium and magnesium in a high correlation (r = 0.98) of 5:1 ratio. Phosphorus, potassium and sulfur are also stored. In the intermediate groundplasm surrounding the vacuoles the element content is different from that in the vacuoles. The significance of vacuolar sodium and magnesium storage for the ionic metabolism is unknown. In addition to Na, Mg, P, K and S the vacuoles also contain 3-OH-kynurenine and other fluorochromes. With the pyroantimonate technique intravacuolar precipitates were demonstrated. X-ray microanalysis of the precipitates revealed sodium and calcium, although following cryofixation calcium was not detectable in the vacuoles by X-ray analysis.