Micromorphology of the malpighian tubules in the louse Pediculus humanus corporis (Anoplura)

The ultrastructure of the Malpighian tubes in human louse Pediculus humanus corporis has been studied. The cells of the Malpighian tubules have the uniform structure: the apical surface is covered with microvilli, the basal plasmatic membrana forms relatively small invaginations. The microvilli are most developed in cells of the proximal department of the Malpighian tubules. Microvilli of the apical surface of the cells do not contain mitochondria which are localized mainly in supranuclear part of the cell. Cells are lined with a homogenous basal membrane.     

Ultrastructure of the malpighian tubules of Schistocerca gregaria

The ultrastructure of the Malpighian tubules of the adult desert locust, Schistocerca gregaria, is described. Male and female adults possess about 233 tubules, which empty proximally into the midgut-ileal region of the alimentary canal by way of 12 ampullae. The tubules vary from 10 mm to 23 mm in length. About one third of them are directed anteriorly, attaching distally at the caeca, while the remainder are directed posteriorly, attaching to other tubules, the rectum or large tracheal trunks adjacent to the hindgut. The Malpighian tubules from all locations examined consist of three ultrastructurally distinct regions: proximal, middle, and distal, referring to their position relative to the midgut. All cell types possess ultrastructural features characteristic of ion transporting tissue, i.e., elaboration of the basal and apical membranes and a close association of these membranes with mitochondria. The distal and proximal segments are short (1.5-1.7 mm) and heavily tracheated, and each is composed of a single, distinct cell type. The middle region is the longest segment of the Malpighian tubule and is composed of two distinct cell types, primary and secondary. Both cell types are binucleate. The more numerous primary cells have large nuclei, contain laminate concretions in membrane-bound vacuoles, and possess large microvilli that contain mitochondria. The secondary cells are smaller and possess smaller nuclei. The microvilli are reduced and lack mitochondria. Secondary cells do not contain laminate concretions. The possible compartmentalization of ion and fluid transport function based on segmentation in the Malpighian tubules is discussed.     

An ultrastructural study of Dirofilaria immitis infection in the Malpighian tubules of Anopheles quadrimaculatus

An ultrastructural study was conducted of the Malpighian tubules of Anopheles quadrimaculatus, both uninfected and following infection with Dirofilaria immitis. The Malpighian tubules in Anopheles are composed of primary and stellate cells. The primary cells are the predominant cell type and are characterized by the presence of membrane-bound, intracellular, mineralized concretions and large apical microvilli containing mitochondria. Following the infective blood meal, the microfilariae enter the primary cells of the Malpighian tubules and reside in the cytoplasm in a clear zone without a delimiting membrane. Cells in infected tubules differ from those in uninfected tubules in that the membranes of the vacuoles surrounding the concretions are disrupted in many specimens. The apical and basal cell membranes and the mitochondria associated with these are not disrupted during the first 6-8 days of infection. These observations differ sharply from those previously described in Aedes taeniorhynchus infected with D. immitis. The observations are consistent with the hypothesis that the extended transport capacity observed in previous physiological studies of An. quadrimaculatus infected with D. immitis are dependent on the prolonged normal ultrastructure of the apical microvilli, mitochondria, and basal membranes.     

Fine structure of the Malpighian tubules in the housefly, Musca domestica

The epithelium of the Malpighian tubules in the housefly is comprised of four distinct cellular types. Type I cells are characterized by the presence of intimate associations between infoldings of basal plasma membrane and mitochondria. On the luminal surface, cytoplasm is extended into microvilli which contain mitochondria. Membrane-bound vacuoles in the cytoplasm seem to progressively accumulate granular material. Type II cells have dilated canaliculi. Microvilli lack mitochondria. The Type III cell has not been reported previously in Malpighian tubules. It has very well-developed granular endoplasmic reticulum which contains intracisternal bundles of tubules. Cytoplasm contains numerous electron dense bodies. Type IV cells occur in the common duct region of the Malpighian tubules. Mitochondria do not extend into the microvilli.     

Post-embryonic development of the Malpighian tubules in <Emphasis Type="Italic">Apis mellifera</Emphasis> (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.     

Anatomy and fine structure of the alimentary canal of the spittlebug Lepyronia coleopterata (L.) (Hemiptera: Cercopoidea)

The alimentary canal of the spittlebug Lepyronia coleopterata (L.) differentiates into esophagus, filter chamber, midgut (conical segment, tubular midgut), and hindgut (ileum, rectum). The filter chamber is composed of the anterior extremity of the midgut, posterior extremity of the midgut, proximal Malpighian tubules, and proximal ileum; it is externally enveloped by a thin cellular sheath and thick muscle layers. The sac-like anterior extremity of the midgut is coiled around by the posterior extremity of the midgut and proximal Malpighian tubules. The tubular midgut is subdivided into an anterior tubular midgut, mid-midgut, posterior tubular midgut, and distal tubular midgut. Four Malpighian tubules run alongside the ileum, and each terminates in a rod closely attached to the rectum. Ultrastructurally, the esophagus is lined with a cuticle and enveloped by circular muscles; its cytoplasm contains virus-like fine granules of high electron-density. The anterior extremity of the midgut consists of two cellular types: (1) thin epithelia with well-developed and regularly arranged microvilli, and (2) large cuboidal cells with short and sparse microvilli. Cells of the posterior extremity of the midgut have regularly arranged microvilli and shallow basal infoldings devoid of mitochondria. Cells of the proximal Malpighian tubule possess concentric granules of different electron-density. The internal proximal ileum lined with a cuticle facing the lumen and contains secretory vesicles in its cytoplasm. Dense and long microvilli at the apical border of the conical segment cells are coated with abundant electron-dense fine granules. Cells of the anterior tubular midgut contain spherical secretory granules, oval secretory vesicles of different size, and autophagic vacuoles. Ferritin-like granules exist in the mid-midgut cells. The posterior tubular midgut consists of two cellular types: 1) cells with shallow and bulb-shaped basal infoldings containing numerous mitochondria, homocentric secretory granules, and fine electron-dense granules, and 2) cells with well-developed basal infoldings and regularly-arranged apical microvilli containing vesicles filled with fine granular materials. Cells of the distal tubular midgut are similar to those of the conical segment, but lack electron-dense fine granules coating the microvilli apex. Filamentous materials coat the microvilli of the conical segment, anterior and posterior extremities of the midgut, which are possibly the perimicrovillar membrane closely related to the nutrient absorption. The lumen of the hindgut is lined with a cuticle, beneath which are cells with poorly-developed infoldings possessing numerous mitochondria. Single-membraned or double-membraned microorganisms exist in the anterior and posterior extremities of the midgut, proximal Malpighian tubule and ileum; these are probably symbiotic.     

Regional specialization in the malpighian tubules of the new zealand glow-worm Arachnocampa luminosa (diptera: Mycetophilidae). The structure and function of type I and II cells

The Malpighian tubules of the glow-worm Arachnocampa luminosa are divided into four morphologically distinct regions (Parts 1--4) each comprised of a different cell type (Types I--IV). The ultrastructure of Type II cells is indicative of a transport function. The basal cell surface is highly invaginated and at the apical surface the lumen is lined with microvilli about 80% of which contain mitochondria. Spherites contained in these cells are formed from small vesicles produced by the Golgi apparatus. They have a central uric acid core enclosed by laminations of phosphates of calcium and magnesium. Cells of Part 2 of the tubule secrete a fluid high in potassium (173 mM) and low in sodium (18 mM). The cell is 30 mV negative and the lumen 44 mV positive to the bathing solution. This is consistent with the proposal of an apical cation pump. The secretion produced by Part 2 of the tubules is modified by the Type I cells by the reabsorption of potassium (162 mM) and the addition of sodium (24 mM) to the primary excretory fluid. Type I cells are 20 mV negative and the lumen 22 mV positive with respect to the bathing medium. From ultrastructural observations, Type I cells exhibit features characteristic of transporting cells thought to have an absorptive function. The basal and apical cell surfaces are extensively folded, and mitochondria are found in bands above the basal infoldings and below the microvilli. Mitochondria do not penetrate the microvilli. On comparative grounds, the fine structure of Type I cells suggest that they reabsorb ions from the tubule lumen. Energy for these processes may come from the breakdown of lipids by microperoxisomes contained within these cells. Alternatively, the fluid produced by Part 2 of the tubule may be modified passively by diffusional processes across Type I cells.     

A structural basis for fluid secretion by malpighian tubules

The Malpighian tubules of Calliphora are described, emphasizing the possible role of surface specializations in solute-linked water transport. The tubules are composed of two cell types, primary and stellate, intermingling along the tubule length. The primary cells have long narrow basal infoldings and a microvillate luminal border, both intimately associated with mitochondria. The stellate cells have shorter and wider basal infoldings and their apical microvilli do not contain mitochondria. Application of the standing gradient hypothesis to this sytem provides a model for urine formation in which the local gradients for osmotic water flow occur within the long narrow channels of the basal infolds and microvilli of the primary cells. Stellate cells may modify the initial secretion by reabsorbing sodium.     

小地老虎变态期间马氏管超微结构与酯酶活性的变化

本实验用光镜和电镜观察了小地老虎Agrotis ypsilon Rottemberg幼虫在变态期间马氏管超微结构的变化及成虫马氏管的重组过程,同时还研究了变态期马氏管酯酶的活性.结果表明:(1)变态期间马氏管外形完整,除至预蛹期隐肾复合体解体外,其余无明显变化.(2)变态期间管壁细胞变化显著.幼虫6龄末期马氏管细胞结构开始变化,主要特点为:细胞质电子密度高,充满了核糖体颗粒,微绒毛萎缩,线粒体从萎缩的微绒毛中退出进入细胞质,基膜内褶破坏.进入预蛹期幼虫马氏管细胞解体:基膜内褶、顶端微绒毛、线粒体及细胞质内的其它细胞器消失,并形成自体吞噬泡,细胞质内仅存细胞核及各种类型的液泡.但是在变态期间因底膜始终存在,故马氏管外形不变;至蛹后期,成虫马氏管细胞在原位重组,基膜内褶由浅变深,微绒毛由短变长,线粒体内嵴从无到有.(3)变态过程中羧酸酯酶和酸性磷酸酯酶的活性变化趋势基本相同,以六龄幼虫最强,预蛹期次之,蛹期最低.     

Developmental changes in Malpighian tubule cell structure.

Structural changes which occur in the Malpighian tubule yellow region primary cells during larval-pupal-adult development of the skipper butterfly Calpodes ethlius are described. The developmental changes in cell structure are correlated with functional changes in fluid transport (Ryerse, 1978a) in a way which supports osmotic gradient models of fluid secretion. Larval tubules are specialized for fluid secretion with deep basal infolds and elongate mitochondria-containing apical microvilli which provide channels in which osmotic gradients could be set up. The Malpighian tubule cells are extensively remodelled at pupation when fluid transport is switched off, but they persist intact through metamorphosis. At this time, the basement membrane doubles in thickness, the mitochondria are retracted from the microvilli and are isolated for degradation in autophagic vacuoles, and both apical and basal plasma membranes are internalized via coated vesicles for degradation in multivesicular bodies, which results in the shortening of the microville and the disappearance of the basal infolds. Mitochondria are re-inserted into the microvilli, and the basal infolds re-form in pharate adult stage Malpighian tubules when fluid secretion resumes. Adult tubules are similar in general structure to larval tubules and contain mitochondria in the microvilli and basal infolds. However, they differ from larval tubules in that they are capable of very rapid fluid transport, have a reduced tubule diameter and tubule wall thickness, a much thicker basement membrane and peripherally associated tracheoles. Mineral concretions of calcium phosphate accumulate in larval tubules, persist through metamorphosis and decline in number in adults, suggesting they serve some anabolic role.     

Mitochondrial Placement and Function in Insect Ion-transporting Cells

The ion-transporting epithelia of insects possess some unusualmorphological adaptations which promote close juxtapositionof mitochondria and the ion-transporting plasma membranes. Aparticularly striking example of this adaptation is providedby the movement of branches of mitochondria into and out ofthe apical microvilli in the Malpighian tubules. In the hemipteranRhodmus prohxus, the microvilli in the resorptive lower tubuleare small and contain no mitochondria during the non-transportingperiod. When ion transport is stimulated,either in vivo or invitro, there is a concomitant growth in microvillar volume andsurface area. In addition, branches of mitochondria enter thesemicrovilli. It has been shown that these mitochondrial movementsare driven by an actinassociated process involving the microvillarcore microfilaments. The stimulation for this movement in vivois the insect diuretic hormone. In the lepidopteran Calpodesethhus, the rates of fluid transport which the Malpighian tubulescan sustain vary during the insect's life stages. Larvae andadults show rapid transport, while pupal Malpighian tubulesshow none. In the larvae and adults, microvilli in the Malpighiantubules are large and contain mitochondria. In the pupae, reducedtransport is associated with mitochondrial retraction and microvillarshrinkage. These ultrastructural changes appear tobe regulatedby the insect's developmental hormones. In the Malpighian tubulesof adult female mosquitoes of the genus Aedes, intracellularinfection by microfiliarial nematodes has hen shown to causemitochondrial retraction and reduced rates of fluid transport.A model is presented which serves to summarize currently proposedmechanisms of membrane and mitochondrial function in the ion-transportingepithelia of insects.     

Early cellular responses in the Malpighian tubules of the mosquito Aedes taeniorhynchus to infection with Dirofilaria immitis (Nematoda)

Early ultrastructural changes in the Malpighian tubules of the mosquito, Aedes taeniorhynchus, were examined following infection with the nematode, Dirofilaria immitis. After ingestion by the mosquito, the microfilariae enter the cells of the Malpighian tubules, becoming intracellular. During early development, the filarial prelarvae reside in the cell cytoplasm surrounded by a clear zone without a delimiting membrane. Cells infected with prelarvae differed from uninfected cells and from cells in uninfected mosquitoes in that the volume of the apical microvilli was reduced and mitochondria were retracted from these microvilli. Morphometric analysis was used to quantify the ultrastructural consequences of infection. In infected cells, microvillar volume, the percent of microvillar volume occupied by mitochondria, and volume of mitochondria within the microvilli were significantly reduced.     

Fine structure of the Malpighian tubules of chironomus larva in relation to glycogen storage and fate of hemoglobin

The larval Malpighian tubules of Chironomus tentans were studied using light and electron microscopy. The tubules are composed of two cell types: primary and stellate cells. Both cell types lack muscles, tracheoles, and laminate crystals in the cytoplasm and mitochondria in the microvilli. The primary cells exhibit long, wide basal membrane infoldings associated with mitochondria. They have a number of canaliculi and long, closely packed microvilli. The stellate cells possess shorter interconnecting basal infoldings and shorter, well-spaced microvilli. Both cell types are linked by septate and gap junctions. They have cytoplasmic processes and pedicels which enclose narrow slits between them and that are apposed to a basal lamella. In the 'fed' larva, the cells are stuffed with glycogen which is depleted in the 'starved' larva. Both cell types are involved in the vesicular transport of biliverdin. The presence of coated vesicles, tubular elements and various forms of lysosomes in the primary cells suggests they transport and break down functional hemoglobin. Structural modification of basal infoldings, canaliculi and microvilli is strongly correlated with increased secretory activity of the Malpighian tubules in 'fed' versus 'starved' larva.     

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.     

The ultrastructure of Malpighian tubules and hindgut of Frankliniella occidentalis (Pergande) (Thysanoptera : Thripidae)

The ultrastructure of the western flower thrips, Frankliniella occidentalis (Pergande) (Order : Thysanoptera), has 4 Malpighian tubules that are free of the intestine as they leave their junction at the pyloric region. The tubules consist of an epithelium with a single type of microvillated cells; proximally, the cells are lined by a thin cuticle. Numerous mitochondria, basal infoldings of the plasma membrane and vesicles with varying densities suggest active transit of fluid in the cell for osmoregulation. Two of the Malpighian tubules are bent posteriorly and closely adhere to the hindgut in the region of the rectal pads where the 2 epithelia are separated only by a basal lamina. The ultrastructure of this region suggests possible fluid reabsorption from the gut lumen.     

Ultrastructure of the Malpighian Tubule Cells in the Mosquito Larvae, Anopheles sinesis

Ultrastructure of epithelial cells constituting the Malpighian tubule of Anopheles sinesis last instar larvae was observed with electron microscope. Malpighian tubule consists of four long and narrow tubule structures with principal cells in typical absorptive cells and regenerative cells forming the simple epithelium. Apical plasma membrane of the principal cell is differentiated into microvilli with one mitochondrion in each microvilli. Basal plasma membrane had extreme infolding to form a canaliculi and a well developed mitochondria was attached in the infoldings. And, rER, ribosomes, and vacuoles were well developed inside the cells. However, there were two main cell types depending on the differentiation of cell organelles. Type 1 cell was cubic, forming the distal portion of Malpighian tubule. The length of microvilli was approximately 4 μm and the basal infoldings were introjected to the depth of 2 μm inside the cell. On the other hand, Type II cell that formed the main proxinal portion was a low squamous type cells with shorter 2 μm of microvilli and the basal infoldings were introjected to the depths of 4 μm inside the cell. As for vacuoles scattered inside the cells, they were regularly observed in both Type I and II and the Type II cells had better developed cellular organelles. Although regenerative cells were extremely small, their cellular organelles were developed and their overall electron density was high that they appeared darker than the principal cells.     

The ultrastructure of the larval malpighian tubules of a saline-water mosquito

The larval Malpighian tubules of the saline-water mosquito Aedes taeniorhynchus were examined using light and electron microscopy. The tubules contain two cell types: primary cells and stellate cells. Primary cells are characterized by their size (70 μm × 70 μm × 10 μm) and an abundance of intracellular membranebound crystals. Two types of microvilli are found on the luminal surface of the primary cells: (1) small microvilli containing core microfilaments and extensions of endoplasmic reticulum, and (2) larger microvilli (≈3 μm in length) which in addition to the above components contain a mitochondrion along their entire length. Both microvillar types have abundant knobs lining the cytoplasmic surface of the microvillar membrane. These knobs, which are often found in insect ion transporting tissues, have been termed ‘portasomes’ by Harvey (1980). The possible role of these structures in ion transport and mitochondrial positioning is discussed. The stellate cells are much smaller than the primary cells, and lack intracellular crystals. Their microvilli are smaller as well (≈0.6 μm in length) and contain no endoplasmic reticulum. mitochondria or knobs. The cells types found in the saline-water mosquito larva, Aedes taeniorhynchus, are identical to those found in Aedes aegypti, indicating that the unique capacity of saline-water mosquito larvae to transport Mg²⁺ and SO₄|post|staggered|2− is not associated with the presence of an additional cell type.     

SR-BI is required for microvillar channel formation and the localization of HDL particles to the surface of adrenocortical cells in vivo

Scavenger receptor class B type I (SR-BI) mediates the selective uptake of HDL cholesteryl ester into liver and steroidogenic tissues. In steroidogenic cells, juxtaposed microvilli, or microvilli snuggled against the plasma membrane create microvillar channels that fill with HDL. Microvillar membranes contain SR-BI and are believed to be the site of HDL cholesteryl ester uptake. A recent study showed that SR-BI expression in insect cells elicits membrane structures that contain SR-BI, bind HDL, and closely resemble the ultrastructure of microvillar channels. In the present study we compared the ultrastructure of adrenal gland microvillar membranes in Srb1+/+ and Srb1-/- mice to test whether SR-BI is required for the formation of microvillar channels. The results show that SR-BI is absolutely required for microvillar channel formation and that the microvillar membranes of Srb1-/- mice are 17% thinner than in Srb1+/+ mice.We conclude that SR-BI has a major influence on plasma membrane ultrastructure and organization in vivo.     

Fine structure of larval malpighian tubules and rectal sac in the tick Ornithodoros (Pavlovskyella) erraticus (Ixodoidea: Argasidae)

The fine structure of the Malpighian tubules (Mts) and rectal sac (rs) is described in the larval tick Ornithodoros (Pavlovskyella) erraticus before and after feeding up to molting. Mts consist of structurally different pyramidal and cuboidal cells along the entire length of the tubule. In unfed ticks, the two types of cell are characterized by apical microvilli and a few basal membrane infoldings. The abundant pyramidal cells contain glycogen particles, lipid droplets, lysosomelike structures, and rickettsialike microorganisms. After feeding but before molting, pyramidal cells loose glycogen particles and become very dense and dramatically reduced in size. These cells are possibly involved in the formation of guanine crystalloids as an excretory product. In contrast, cuboidal cells, filled with glycogen particles, free ribosomes, and mitochondria in unfed larvae, grow steadily after feeding; their cytoplasm becomes rich in lipid droplets in addition to showing an increase in glycogen particles. Lipid and glycogen could be the source of energy required for water and ion reabsorption in which cuboidal cells are probably involved. The paired-lobe rs consists of one type of cuboidal cells with basal membrane infoldings and a brush-border microvilli covered by a fuzzy coat of glycocalyx. These cells grow rapidly after feeding; they have functional features indicating extensive, selective reabsorption of essential components from excretory products.     

中华蜜蜂工蜂蜡腺细胞的超微结构

本文描述了中华蜜蜂(Apis cerana)成体工蜂蜡腺细胞的超微结构.通过电镜观察发现蜡腺细胞具有许多质膜内陷形成的管腔,作为蜂蜡或其前体物的输送通道.细胞质中富含线粒体及粗面内质网,细胞核为不规则的形状,细胞质中还含有少量溶酶体,微管和微丝等结构.