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.     

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.     

Electron-microscopic study of the excretory system of hungry females of the tick Hyalomma asiaticum P. Sch. et E. Schl. 2]

In H. asiaticum the cells of the Malpighian tubules and these of the rectal cas have the uniform structure: the apical surface is covered with microvilli, the basal plasmatic membrane forms relatively small invaginations. As to ultrastructural characters, there is no distinct division of the Malpighian tubule into departments. The distal ends of the tubules are not only somewhat enlarged and form the so-called ampulla cells of which are noticeably flattened. The microvilli and basal folds of the plasmatic membrane in this area of the tubule are indistinct. The cells of the ampulla and the neighbouring area of the tubule are characterized by the presence of inclusions with mucopolysaccharide secretion confined by the membrane. The microvilli are most developed on cells of the proximal ends of the Malpighian tubules. Well developed microvilli of the rectal sac form a striated border each containing a microtube inside. The basal invaginations are developed here better than in the cells of the Malpighian tubules.     

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.     

Studies on water and ion transport in homopteran insects: ultrastructure and cytochemistry of the cicadoid and cercopoid Malpighian tubules and filter chamber

The filter chamber is a complex junction of anterior and posterior extremities of the midgut and Malpighian tubules. The sac-like anterior extremity, or filter chamber proper, comprises two cell types. These are large cuboidal cells which secrete a mucoprotein, and extremely thin cells which have regular tubular invaginations of the basal plasma membrane. The posterior extremity of the midgut and the internal Malpighian tubules coil round the filter chamber proper. They consist of thin epithelial cells identical in ultrastructure. The basal plasma membrane in these cells is formed into leaflets. A thin cellular sheath and thick muscle layers surround the filter chamber. The filter chamber proper is lined by the mucoprotein secretion of the cuboidal cells. This secretion appears to bind potassium ions. ATPase and alkaline phosphatase cannot be detected in the filter chamber epithelia. The structure and cytochemistry of the filter chamber suggests that water flows from filter chamber proper to midgut and Malpighian tubules by passive osmosis. This may be facilitated by ion binding in the filter chamber proper and by hydrostatic pressure engendered by contraction of the muscular coat. The Malpighian tubules appear to be structurally and chemically adapted for ion secretion by active transport and possibly for reabsorption in the Malpighian duct segment.     

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.     

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.     

Changes in cytoskeletal actin patterns in the Malpighian tubules of the fleshfly,Sarcophaga bullata (Parker) (Diptera : Calliphoridae), during metamorphosis

Using the rhodamine-labelled phalloidin staining method in combination with detergent extraction, metamorphic changes in actin filament patterns were investigated in the Malpighian tubules of the fleshfly, Sarcophaga bullata (Parker) (Diptera : Calliphoridae). Metamorphosis in this organ implies a process of dedifferentiation, followed by a process of redifferentiation. During dedifferentiation, the large basal actin bundles of the primary cells disappear and the microvillar membrane surface of these cells decreases. Concomitantly, several vesicles are pinched off from infoldings of the brush border. In older pupae, the Malpighian tubules redifferentiate to give rise to adult tubules with actin patterns similar to those of larvae. During redifferentiation of the tubules, the secondary cells display a marked increase in the number of actin filaments in their protrusions. The primary cells in the distal part of the anterior Malpighian tubules of late pupae display a well-developed basal pattern of thick parallel actin bundles. In most cases, major changes in actin filament patterns are found simultaneously with major changes in cell shape, indicating a close relationship between these actin filaments and the process of cellular remodelling.     

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.     

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.     

Ultrastructural evidence for paracellular fluid flow in the Malpighian tubules of a larval mayfly

The ultrastructure of the Malpighian tubules of larvae of the Mayfly Ecdyonurus dispar (Ephemeroptera) is described. There are about 60 tubules, which consist of four distinct regions. The most proximal section (region I) appears to be responsible for fluid secretion. A unique feature is the presence of channels leading off the main lumen, which end close to the basal border of the cells. Microvilli are confined to these channels in region I. Region II is a short spiral region, the cells of which possess long basal folds and associated mitochondria. Region III is a simple conducting tube leading to one of six collecting ducts (region IV) arranged radially around the gut. In each collecting duct there are two cell types present. Type 2 cells are relatively simple, but give rise to numerous, long, microvilli-like projections. Type 1 cells possess long basal folds, and curious membrane whorls in the apical zone. Evidence is presented which suggest that water movements into region I takes place via the paracellular route. Region II is probably a reabsorptive region, but the function of region IV, based on ultrastructural evidence is more difficult to elucidate.     

白蜡虫马氏管的超微结构

白蜡虫Ericerus Pela的马氏管由两条黄色膨泡串状的端管和一条公共管构成,通过公共管与消化道相连。端管和公共管细胞结构相似,都具有非胶原质的基膜,高度发达的基褶, 长而致密的微绒毛,微绒毛无线粒体插入,细胞质中线粒体少,且随机分布。细胞质的绝大部分为两种矿质-尿酸颗粒结晶所占据,一种为不规则结晶,另一种为轮纹状结晶。白蜡虫马氏管可能发生了合胞化,其排泄方式可能是一种以滞留排泄为主,离子梯度排泄方式为辅的特有的排泄方式。     

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.     

Ultrastructure of differentiated malpighian tubules from cockroach nymphs during the molting cycle

Differentiated Malpighian tubules of Periplaneta americana nymphs consist of four distinct regions. The distal, middle, and proximal regions are similar to the same regions in adult tubules. However, the transparent portion of the middle region was found to have ultrastructural characteristics different from those of the longer opaque segment of the middle region and the two other tubule regions. This newly distinguished region is called the lower middle region. Transitional zones, areas where cells show characteristics of two adjacent regions, are apparent between the distal and middle regions and between the middle and lower middle regions. The middle region of primary tubules undergoes an increase in autophagic activity and a modification of its basal infoldings and microvilli shortly before each molt. An increase in autophagic activity is also observed in the lower middle region near the time of molting.     

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.     

小地老虎马氏管细微结构的特点

本文通过光镜和电镜观察,研究了小地老虎grois ypsilon Rottemberg六龄幼虫和成虫马氏管及管壁细胞的形态特点和排泄方式.幼虫马氏管中不同细胞的分泌方式和亚细胞结构有很多差异,端段和中段的马氏管细胞基内褶发达,并发现在隐肾内的端段细胞中,有一类含有大量的线粒体.在幼虫中,胞吐排泄占有重要地位,并观察到有微绒毛顶部胞吐、微绒毛间胞吐和顶膜胞吐三类.成虫马氏管细胞主要有二种类型,即大型的基本细胞和小型的底细胞,前者为主,后者数量较少.基本细胞中存在复杂的液胞系,排泄以排放液胞为主.     

Studies on the morphology and ultrastructure of the Malpighian tubules of Halobiotus crispae Kristensen, 1982 (Eutardigrada)

The excretory and osmoregulatory system of Halobiotus crispae consists of two lateral and one smaller dorsal Malpighian tubules, which empty into the digestive tract in the transition zone of the midgut and rectum. The tubules are identical at the ultrastructural level, and consist of an initial segment with three large cells, a thin transitional distal part lacking a nucleus, and a proximal part with 9–12 nuclei. The initial segment possesses deep basal infoldings and interdigitating, finger-shaped processes of the plasma membrane, large mitochondria and giant nuclei. The distal part is a short section which supports the initial segment. Cellular offshoots from the succeeding proximal part constitute the distal part. The distal and proximal parts contain intercellular canals with concretions of variable size. The exit of the proximal part into the digestive tract is characterized by the presence of microvilli. Correlated with the different stages in the cyclomorphosis of H. crispae , we observed size variation of the Malpighian tubules; thus, pseudosimplex stages have the largest tubules. We present suggestions concerning the physiology of the tubules and compare the Malpighian tubules of Tardigrada with the Malpighian papillae of Protura.     

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.     

Growth and differentiation of secondary malpighian tubules in the cockroach,Periplaneta americana

Four differentiated Malpighian tubules (primary tubules) extend from the junction of the midgut and hindgut in newly hatched Periplaneta americana. Secondary tubules begin to develop near the base of the primary tubules before hatching and successive nymphal molts. The newly initiated tubules undergo cell division and extensive elongation through the middle of the following intermolt period. During this time, the cells of the distal, middle, and lower middle tubule regions are surrounded by a cellular sheath, have few cytoplasmic processes extending along their basal surfaces, have a small or nonexistent lumen, and contain extremely dilated cisternae of endoplasmic reticulum. The cellular sheath differentiates into the muscle which coils around the mature tubule. Tubules which begin development toward the end of one intermolt period begin to undergo cytodifferentiation toward the end of the next intermolt period. By the middle of an additional intermolt period, the basal infoldings and microvilli of cells in the distal, middle, and lower middle regions have the conformations typical for those regions in differentiated tubules; granular concretions and stellate cells are present within the middle region of the tubule.     

Actin redistribution in mosquito malpighian tubules after a blood meal and cyclic AMP stimulation

Fluid secretion by mosquito Malpighian tubules is critical to maintaining fluid and electrolyte balance after a blood meal. Endogenous cAMP levels increase in Malpighian tubules after a blood meal. Here, we determined if corresponding changes in intracellular actin distribution occur after a blood meal or dibutyryl-cAMP (db-cAMP) stimulation and whether altering actin turnover inhibits secretion. In untreated Malpighian tubules, beta-actin immunostaining was more intense in the apical region of adult Malpighian tubules than in the cytoplasm. Stimulation by a blood meal or db-cAMP significantly decreased beta-actin immunostaining in the non-apical region of the cell. Db-cAMP had similar effects in larvae and pupae Malpighian tubules. In contrast, no detectable shift in F-actin distribution was detected; however, F-actin bundles within the cytoplasm increased in size after treatment with db-cAMP. Pretreatment of Malpighian tubules with agents perturbing actin fiber assembly and disassembly decreased basal secretion rates and inhibited the stimulatory effects of db-cAMP. Our results show (1) beta-actin redistributes toward the apical membrane after a blood meal and this correlates temporally with increase urine flow rate and intracellular cAMP levels, (2) Malpighian tubules from all developmental stages exhibit this same response to db-cAMP-stimulation, and (3) dynamic assembly and disassembly of beta-actin is required for db-cAMP-stimulated secretion.