Ultrastructure of the internal medullary substance of the kidney in rodents of an arid zone

Peculiar ultrastructural features of the kidney internal medullary substance have been studied in some typical representatives of the Middle Asia desert and semi-desert fauna (Spermophilopsis leptodactylus and Meriones erythrourus). Papillary organization in the species studied has a specific high differentiation of the fine nephron loop (Henle's) parts; flattening (especially in Meriones erythrourus) of epithelium in the collecting tubes while its cytoplasm is rather poor in organelle; high contents of the interstitial cells and their tight junction with canaliculi, capillaries, floccular material of the interstitial tissue; thinning of the interstitial sheets, especially between the collecting tubes and vessels, presence of collagene fibres in the interstitium, that is especially, specific for all the species of the Spermophilopsis leptodactylus studied. It is possible to suppose that development of similar features in the structure of the kidney internal medullary substance, where the main water resorption takes place in the species investigated, is connected with their life in similar environmental conditions with low hydratation level and is aimed to increase efficiency of the concentrating apparatus work.     

黄胫小车蝗受精囊的亚显微结构

利用组织学方法,观察了黄胫小车蝗Oedaleus infernalis 受精囊的显微与亚显微结构。结果表明,黄胫小车蝗受精囊为单个,由高度卷曲的受精囊管和蚕豆状的端囊构成。受精囊壁主要由表皮层、上皮层、基膜和肌肉层构成;上皮层包含上皮细胞、导管细胞和腺细胞。上皮细胞在靠表皮层的边缘有大量的微绒毛,两相邻上皮细胞的细胞膜相互嵌入,并有细微的突起延伸在导管细胞及腺细胞之间,直到基膜,达基膜处的上皮细胞膜折叠,与腺细胞膜的折叠,一起形成迷宫样的指状突起,附着在基膜上。导管细胞有一个较大的核和分泌导管,连接于腺细胞的细胞腔和受精囊腔,将腺细胞中分泌物运输到受精囊腔中。腺细胞具有典型的分泌细胞特征： 含发达内质网、高尔基复合体及不同大小的囊泡。肌肉层位于受精囊最外层,附在基膜上。在受精囊不同部位的结构有差异。在交配前和交配后,受精囊腺细胞的亚显微结构也有差异。     

宽翅曲背蝗受精囊形态与超微结构观察

[目的]明确宽翅曲背蝗Pararcyptera microptera meridionalis雌虫受精囊的形态、组织结构与超微结构,为更好地认识昆虫受精囊的功能提供依据.[方法]本研究以宽翅曲背蝗已交配雌成虫为实验材料,利用光学显微镜和透射电子显微镜观察其受精囊的形态、组织结构和超微结构.[结果]宽翅曲背蝗受精囊由一个端囊和一条长的受精囊管组成,端囊用于储存精子.端囊和受精囊管有相似的组织学结构,由外到内依次为肌肉层、基膜、上皮层及表皮内膜.上皮层含上皮细胞、腺细胞和导管细胞3种细胞类型.腺细胞具有一个被有微绒毛的细胞外腔.腺细胞的分泌物经细胞外腔通过分泌导管进入到受精囊腔.分泌导管由导管细胞形成.[结论]在宽翅曲背蝗受精囊的端囊和受精囊管上,内膜和腺细胞的细胞外腔结构均存在差异,由此推测,端囊和受精囊管的功能存在一定差异.上皮细胞的超微结构特点显示上皮细胞具有支持、分泌和吸收的功能.     

Nephrotoxic action of platinum, chromium and cadmium compounds on marine bony fishes

Intra-abdominal injections of platinum, chromium and cadmium salts to Myoxocephalus scorpius produce nephrotoxic effect which includes the disturbances in magnesium secretion. Basic ultrastructural changes in the nephron cells of the fish after the injection of nephrotoxic substances are similar to those in mammals. Cis-platinum induces significant damage in the terminal part of the proximal tubules. One day after the injection of chromium compounds, total damage of the proximal tubule is observed, whereas cadmium salt affects cells within the whole nephron. After 5 days of administration of cadmium and chromium salts, partial recovery was found with respect to both functional and ultrastructural properties of nephron cells. Administration of nephrotoxic substances which selectively injure different parts of the nephron enabled to perform more exact differentiation of the nephron elements in marine teleosts.     

Bone morphogenic protein-7 induces mesenchymal to epithelial transition in adult renal fibroblasts and facilitates regeneration of injured kidney

In the kidney, a unique plasticity exists between epithelial and mesenchymal cells. During kidney development, the metanephric mesenchyme contributes to emerging epithelium of the nephron via mesenchymal to epithelial transition (MET). In the injured adult kidney, renal epithelia contribute to the generation of fibroblasts via epithelial-mesenchymal transition, facilitating renal fibrosis. Recombinant human bone morphogenic protein (BMP)-7, a morphogen that is essential for the conversion of epithelia from condensing mesenchyme during kidney development, enhances the repair of tubular structures in the kidney. In this setting, BMP-7 inhibits epithelial-mesenchymal transition involving adult renal epithelial tubular cells and decreases secretion of type I collagen by adult renal fibroblasts. In search of a mechanism behind the ability of BMP-7 to repair damaged renal tubules, we hypothesized that systemic treatment with BMP-7 might induce MET involving adult renal fibroblasts in the injured kidney, generating functional epithelial cells. Here we report that BMP-7 induces formation of epithelial cell aggregates in adult renal fibroblasts associated with reacquisition of E-cadherin expression and decreased motility, mimicking the effect of BMP-7 on embryonic metanephric mesenchyme to generate epithelium. In addition, we provide evidence that BMP-7-mediated repair of renal injury is associated with MET involving adult renal interstitial fibroblasts in mouse models for renal fibrosis. Collectively, these findings suggest that adult renal fibroblasts might retain parts of their original embryonic imprint and plasticity, which can be re-engaged by systemic administration of BMP-7 to mediate repair of tubular injury in a fibrotic kidney.     

Morphology and ultrastructure of the midgut in Piscicola geometra (Annelida, Hirudinea)

This paper presents information on the organization of the midgut and its epithelium ultrastructure in juvenile and adult specimens of Piscicola geometra (Annelida, Hirudinea), a species which is a widespread ectoparasite found on the body and gills and in the mouth of many types of fish. The analysis of juvenile nonfeeding specimens helped in the explanation of all alterations in the midgut epithelium which are connected with digestion. The endodermal portion (midgut) of the digestive system is composed of four regions: the esophagus, the crop, the posterior crop caecum, and the intestine. Their epithelia are formed by flat, cuboidal, or columnar digestive cells; however, single small cells which do not contact the midgut lumen were also observed. The ultrastructure of all of the regions of the midgut are described and discussed with a special emphasis on their functions in the digestion of blood. In P. geometra, the part of the midgut that is devoid of microvilli is responsible for the accumulation of blood, while the epithelium of the remaining part of the midgut, which has a distinct regionalization in the distribution of organelles, plays a role in its absorption and secretion. Glycogen granules in the intestinal epithelium indicate its role in the accumulation of sugar. The comparison of the ultrastructure of midgut epithelium in juvenile and adult specimens suggests that electron-dense granules observed in the apical cytoplasm of digestive cells take part in enzyme accumulation. Numerous microorganisms were observed in the mycetome, which is composed of two large oval diverticles that connect with the esophagus via thin ducts. Similar microorganisms also occurred in the cytoplasm of the epithelium in the esophagus, the crop, the intestine, and in their lumen. Microorganisms were observed both in fed adult and unfed juvenile specimens of P. geometra, which strongly suggests that vertical transmission occurs from parent to offspring.     

The rete testis of the goat, a morphological study

The rete testis of the goat can be divided into three parts, septal, mediastinal and extratesticular. The septal rete is short, relatively straight and connects the terminal part of the seminiferous tubules with the mediastinal rete. The mediastinal rete is a labyrinth of intercommunicating channels that occupies about two-thirds of the central axis of the testis. The extratesticular rete is located outside the testis at its extremitas capitata and forms sac-like dilations up to 2 mm in diameter. The rete testis, regardless of its location, is lined by simple cuboidal to simple squamous epithelium that invariably contains a few intra-epithelial lymphocytes and macrophages. The epithelial cells possess few microvilli and a centrally located flagellum at the luminal border. With the exception of a few small vesicles in the apical cytoplasm, morphological features associated with absorption such as coated vesicles, canaliculi, vacuoles and multivesicular bodies are absent. However, basolateral interdigitations between adjacent cells, another feature of absorptive epithelium, are frequently noticed. Most cytoplasmic organelles except mitochondria and free ribosomes are poorly developed, suggesting that caprine rete epithelial cells are not associated with protein/glycoprotein secretion. There is no evidence of sperm phagocytosis by the rete epithelium, but luminal macrophages containing sperm fragments are occasionally encountered. The structural-functional relationships of the rete epithelial cells are discussed.     

Comparative study of the olfactory epithelium of the three-spined stickleback (Gasterosteus aculeatus) and the nine-spined stickleback (Pungitius pungitius)

Summary The olfactory epithelium of the three-spined stickleback (Gasterosteus aculeatus) and the nine-spined stickleback (Pungitius pungitius) has been studied with a conventional histochemical and a novel immunological staining technique. In both species, the sensory epithelium is arranged in folds separated by non-sensory epithelial tissue. In the nine-spined stickleback, intrinsic folds consisting of non-sensory cells are found in the apical part of the sensory epithelium where they divide the surface of the sensory epithelium into small islets. These non-sensory cells are non-ciliated, flattened and piled on top of each other; they contain numerous electron-translucent vesicles. The intrinsic folds are absent from the sensory epithelium of the three-spined stickleback. In both species, axons of receptor cells form a layer of fibers in the sensory epithelium immediately above the basal cells. In the three-spined stickleback, thick branches of the olfactory nerve are frequently found in this layer. These branches are only occasionally observed in the sensory epithelium of the nine-spined stickleback. Thus, the three-spined stickleback and the nine-spined stickleback show considerable differences in the organization of the sensory regions of the olfactory epithelium.     

Fine structure of the pyloric region and hindgut of Tetrodontophora bielanensis (Waga) (Collembola)

The pyloric region in the alimentary tract of Tetrodontophora bielanensis consists of three parts, of which the first (P1) belongs to the midgut and the others (P2, P3) to the hindgut. Behind the pyloric region in the hindgut, sphincter (S), rectum (R1, R2) and rectal ampulla (AR) follow. Morphologically, the cells of part P1 differ in structure from the midgut epithelial cells described by Kazysztofowicz et al. [11], both by presence of microtubular bodies in an apical region and by the lack of the mitochondrial region. The cytoplasm of the cells of part P3 is filled with lysosome-like bodies with an unknown function. The authors suggest that they are connected with a secretion of the pheromons. The structure of rectum epithelial cells is typical of insects.     

The ultrastructure of the ejaculatory duct in the springtail Orchesella villosa (Geoffroy) (Hexapoda, Collembola) and the formation of the spermatophore

The initial part of the ejaculatory duct of Orchesella villosa contains a “valve” and a “sorter” avoiding respectively the reflow and allowing the separation of the secretion for the spermatophore stalk from the sperm fluid. For most of its length, the ejaculatory duct lumen is divided into two parts: in the dorsal part the sperm fluid flows while in the ventral district the secretion for the stalk occurs. Laterally, on both sides of the duct, longitudinal muscle fibers are present. The epithelium of the dorsal region consists of two types of long secretory cells; the most peculiar of them are those provided with extracellular cisterns flowing directly into the duct lumen as it occurs in 1st type of epidermal cells. These cells could be involved in the control of the viscosity of the sperm fluid. The second type of cells produce a secretion probably involved in the formation of the outer coat of the apical sperm droplet. The ventral epithelium consists of short cells contributing to the enrichment of the secretion for the spermatophore stalk and perhaps also to the viscosity of the secretion flowing in the lumen. In the distal part of the ejaculatory duct, the ventral district is provided with a thick layer of muscle fibers and with 3 + 3 cuticular laminae dividing the lumen into a series of slits through which the secretion of the stalk is squeezed out into filaments. This organization allows the twisting and hardening of these filaments. A drop of sperm fluid is laid on top of the long and rigid spermatophore stalk.     

Ultrastructure of the nephron of the one-humped camel, Camelus dromedarius

The nephron of the one-humped camel Camelus dromedarius was investigated by light and transmission electron microscopy. Besides the many features common to other mammalian kidneys, the nephron of the camel is unique in having an unusually thick basal lamina underlying the epithelial cells of the nephron, the thickest being found in part of the parietal layer of Bowman's capsule and the thin limb of the loop of Henle. In the latter, the membrane usually appears lamellated and contains numerous tiny vesicles. In other parts of the nephron, the basal lamina usually has a homogenous appearance. The possible significance of the thickening of the basal lamina is discussed in relation to the general high renal efficiency of the camel.     

The fine structure of the elasmobranch renal tubule: intermediate, distal, and collecting duct segments of the little skate.

Sharks, skates, and rays (Elasmobranchii) have evolved unique osmoregulatory strategies to survive in marine habitats. These adaptations include a complex renal countercurrent system for urea retention. The fine structure of the complete renal tubular epithelium has yet to be elucidated in any species of cartilagenous fish. The present study, which is a companion to our recent paper describing the ultrastructure of the neck and proximal segments of the elasmobranch nephron, uses thin sections and freeze-fracture replicas to elucidate the fine structural organization of the intermediate, distal, and collecting duct segments of the little skate, Raja erinacea, renal tubule. The epithelium of the intermediate, distal, and collecting duct segments consists of two major cell types: nonflagellar cells, the major epithelial cell type; and flagellar cells, described elsewhere. The intermediate segment consists of six subdivisions lined by cuboidal-columnar cells with variously elaborated microvilli and interdigitations of lateral and basal cell plasma membranes, as well as some subdivisions with distinctive vesicles and granules. The distal segment consists of two subdivisions, both of which are lined by a simple epithelium, and are distinguished from each other by their distinctive contents; dense bodies and granules. The collecting duct segment also has two subdividions, the first lined by a simple columnar epithelium and the second by a stratified columnar epithelium. Both subdivisions have apical secretory granules. The present findings show a more highly specialized and diverse epithelium lining the renal tubule of these cartilagenous fish than is found in either of the "adjacent" phylogenetic taxa, Agnatha or Ostheichthyes, suggesting significant differences among these groups in transepithelial transport mechanisms and renal function.     

The somatic envelopes around the germ-line cells of polytrophic insect follicles: Structural and functional aspects

The polytrophic ovarioles of three insect species, the fruit fly Drosophila melanogaster, the fungus gnat Bradysia tritici, and the honeybee Apis mellifera, were compared morphologically and with respect to the cytological organization of the peripheral somatic layers. Staining with rhodaminyl-phalloidin revealed differences in the organization of the muscle strands of the epithelial sheath and the microfilament pattern in the basal part of the follicular epithelium (mid-vitellogenic stages). Also, the size of the intercellular space between the follicle cells differed considerably in the three analyzed species. The basement membrane of Drosophila and Bradysia follicles was partially digested using purified collagenase. The observed morphological changes indicated that in both species the basement membrane of the follicular epithelium plays an important role in shaping the follicles. The possible functional significance of the species-specific structural differences is discussed.     

Mandibular glands of male European beewolves, Philanthus triangulum (Hymenoptera, Crabronidae)

Males of a solitary digger wasp, the European beewolf, Philanthus triangulum, possess large mandibular glands that have been reported to produce a scent marking pheromone. We analysed the morphology and ultrastructure of these glands using light microscopy as well as scanning and transmission electron microscopy. The paired glands are located laterally in the head and each side consists of a larger and a smaller part. Both parts possess a collecting duct each with distinct openings at the mandible base. However, the collecting duct of the larger part is additionally connected to the pharynx through a lateral extension. The collecting ducts are bordered by a monolayered epithelium lined with cuticle that exhibits conspicuous ramified protuberances. About 1400 acini consisting of class 3 gland cells surround the ducts and are connected to them through conducting canals. The main components in the cytoplasm of these gland cells are mitochondria, well-developed smooth endoplasmatic reticulum, and electron lucent vesicles suggesting a high secretory activity. The connection between the large gland parts and the pharynx suggests that the secretion of the mandibular glands might not only be delivered directly onto the mandibles but might also be transported to and stored in the postpharyngeal gland.     

Collective Cell Migration Drives Morphogenesis of the Kidney Nephron

Tissue organization in epithelial organs is achieved during development by the combined processes of cell differentiation and morphogenetic cell movements. In the kidney, the nephron is the functional organ unit. Each nephron is an epithelial tubule that is subdivided into discrete segments with specific transport functions. Little is known about how nephron segments are defined or how segments acquire their distinctive morphology and cell shape. Using live, in vivo cell imaging of the forming zebrafish pronephric nephron, we found that the migration of fully differentiated epithelial cells accounts for both the final position of nephron segment boundaries and the characteristic convolution of the proximal tubule. Pronephric cells maintain adherens junctions and polarized apical brush border membranes while they migrate collectively. Individual tubule cells exhibit basal membrane protrusions in the direction of movement and appear to establish transient, phosphorylated Focal Adhesion Kinase–positive adhesions to the basement membrane. Cell migration continued in the presence of camptothecin, indicating that cell division does not drive migration. Lengthening of the nephron was, however, accompanied by an increase in tubule cell number, specifically in the most distal, ret1-positive nephron segment. The initiation of cell migration coincided with the onset of fluid flow in the pronephros. Complete blockade of pronephric fluid flow prevented cell migration and proximal nephron convolution. Selective blockade of proximal, filtration-driven fluid flow shifted the position of tubule convolution distally and revealed a role for cilia-driven fluid flow in persistent migration of distal nephron cells. We conclude that nephron morphogenesis is driven by fluid flow–dependent, collective epithelial cell migration within the confines of the tubule basement membrane. Our results establish intimate links between nephron function, fluid flow, and morphogenesis.     

Ultrastructural changes in the oviductal mucosa throughout the sexual cycle in Bufo arenarum

In Bufo arenarum the oviduct exhibits conspicuous changes throughout the sexual cycle. In the present study, we analyzed the optical and ultrastructural characteristics of the oviductal pars convoluta mucosa, the portion responsible for jelly secretion, during both the preovulatory and postovulatory periods. Secretory epithelial cells, ciliated cells, basal cells, and glandular cells are described. Secretory epithelial cells are characterized by the presence of secretory granules, the size, shape and electron density of which vary markedly. Their contents are mainly released by exocytosis into the oviductal lumen. Moreover, in the preovulatory period, apocrine, and holocrine secretion processes frequently occur. During the postovulatory period, these cells exhibit a marked diminution of secretory granules. Ciliated cells show a typical ultrastructural organization. Basal cells are distinguished in the lower part of the epithelium by their heterochromatic nuclei and electron‐lucent cytoplasm. These cells, to the best of our knowledge, are reported for the first time in Amphibia. Glandular cells exhibit oval, round, or polyhedric granules, most of them with one or more cores. Our results indicate that the contents of epithelial and glandular secretory cells are partially secreted during the preovulatory period. Additional secretion occurs during the transit of the oocytes. J. Morphol. 239:61–73, 1999. © 1999 Wiley‐Liss, Inc.     

Mammary epithelial differentiation in vitro: minimum requirements for a functional response to hormonal stimulation.

Mammary epithelial differentiation is the culmination of responses to a complex sequence of hormonal stimuli. An in vitro model for this process should retain the basic features of in vivo epithelial differentiation. The IM-2 mouse mammary cell line responds to lactogenic hormone stimulation by synthesizing the milk protein beta-casein. Epithelial and fibroblastic clones derived from IM-2 lack this ability, but cocultures of these clones regain responsiveness to lactogenic hormone stimulation. Studies of the epithelial cell clone 31E under various culture conditions reveal that the role of fibroblastic cells in supporting synthesis and secretion of beta-casein can be supplanted by culture in filter chambers without addition of exogenous extracellular matrix components. Electron microscopic and immunofluorescence studies show that, under these conditions, 31E epithelial cells exhibit the morphology and intercellular organization characteristic of mammary epithelium. Transepithelial electrical resistance measurements indicate that the cells are well polarized. Analysis of glucose metabolism is consistent with this polarization; glucose is utilized from the basal chamber, and lactate is excreted into the basal chamber. Immunoblot analysis demonstrates the vectorial protein secretion expected of polarized mammary epithelium: laminin is secreted into the basal chamber, whereas beta-casein is secreted into the apical chamber in response to lactogenic hormone stimulation from the lower chamber. Thus, the maintenance of a polarized intercellular organization that permits access of the basolateral cell surface to nutrients is sufficient for a pure culture of an established mammary epithelial cell clone to retain differentiated epithelial function in vitro.     

The Ultrastructure of the Proboscis in Psammorhynchus tubulipenis Karling, 1964 and Cytocystis clitellatus Karling, 1953 (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in two species of free-living Platyhelminthes, Psammorhynchus tubulipenis and Cytocystis clitellatus is very alike but differs from previously described species. Both sheath and cone epithelium are composed of two circumferential belts. Only the basal cone epithelium is syncytial, while no nuclei were found in the distal belt of the sheath epithelium. The sheath epithelium is characterized by numerous infoldings of the basal plasma membrane. The nuclei present in the bulb belong to the proximal belt of the sheath epithelium and the apical cone epithelium. Nuclei of the basal cone epithelium are located insunk behind the proboscis bulb. The insunk cell parts pierce the septum of the bulb laterally near the proximal end. Different types of gland necks and sensory cells pierce the epithelia. Associated with the distal belt of the sheath epithelium, two sensory organs are found, containing multiciliary receptors with modified axonemata. Differences in organization of the proboscis musculature are described and compared with the organization in other species. The systematic position of both species is discussed in the light of the new findings.     

Epithelial structural changes in the urinary tubules of the kidney of the white rat in the early period of corrosive sublimate nephrosis

Examination of serial semithin (0.5 micron) methacrylate and paraffin (8 micron) sections of the rat kidney 6, 12, 24 and 48 hours after subcutaneous injection of sublimate in a dose of 0.6 mg/100 g bw has demonstrated that the damage to the different parts of the tubular component of nephron is heterogeneous in nature. Both complete and partial necrosis of nephrocyte cytoplasm can be seen in the proximal part of nephron. The distal parts of nephron and collective tubules are characterized by partial necrosis of the apical areas of the cytoplasm. During the period between 12 and 24 hours after sublimate injection, one can observe the onset of destructive processes together with intracellular recovery processes in partially damaged but still viable nephrocytes, which is confirmed by the enlargement of the nucleolar size. The regeneration of the tubular epithelium at the expense of cellular renewal was unmarked 24 hours after sublimate injection.