Development of the renal corpuscle during metamorphosis in the lamprey.

The renal corpuscle of the adult lamprey, Petromyzon marinus L., is formed during the programmed period of metamorphosis. Development is initiated early in this metamorphic period and is marked by the synchronous formation and growth of rudimentary nephron units (RNU) from longitudinal cord of nephrogenictissue extending from the posterior tip of the degenerating larval kidney to the cloaca and connected to the peritoneal epithelium. Detachment of the RNU from the peritoneum involves autolysis and cell death and is accompanied by their branching into five or six hexagonally-arranged nephrons which radiate from the original point of attachment. Differentiation of the epithelial cells at the proximal ends of the nephrons is preceded by the widening of lateral intercellular spaces, the formation of tubular lumina (primitive urinary spaces), the loss of apical cell junctions, and the development of a capillary network with its associated mesangium. With the extension of the capillaries and mesangium between the proximal ends of adjacent undifferentiated nephrons, visceral epithelial cells (podocytes), with long cell processes (trabeculae) and slit membranes, make their appearance. The urinary spaces resulting from this form of development are lined by the epithelium of the dilated ends of the nephrons (nephric capsules). The cells of these capsules differentiate mainly into podocytes, but a few parietal cells connect to the draining tubule. This method of development explains the unique form of the renal corpuscle in the adult lamprey. Despite the type of morphogenesis, this renal corpuscle possesses the fine-structural features seen in the renal corpuscles of other vertebrates.     

Ultrastructure of the pronephric kidney of embryos and prolarvae of the sea lamprey, Petromyzon marinus

Embryos of lampreys Petromyzon marinus were obtained through a technique of artificial fertilization. Samples of developmental intervals to the prolarval stage were prepared for transmission electron microscopy and the pronephros was examined. The pronephros was visible in the cardiac region of the coelom prior to the time of hatching of embryos and consisted of a renal corpuscle, nephrostomes, and proximal tubules connected to a pronephric duct. The renal corpuscle was comprised of poorly-defined vascular channels and a visceral epithelium of yolk-filled cells, the podocytes, with short major processes and pedicels resting on a basal lamina. The first proximal tubules possessed a delicate brush border of short microvilli but subsequent cellular differentiation yielded cells with all the components required for the process of endocytosis, a process which was demonstrated by uptake of the tracer, horseradish peroxidase. The distal tubules appeared later in development and were noted for abundant mitochondria and an extensive smooth tubular network. The timing of differentiation of various components of the nephron corresponds to that seen during morphogenesis of other vertebrate kidneys.     

Ultrastructural features of degeneration of the gallbladder during lamprey biliary atresia

Thin sections and freeze-fracture replicas were used to examine the fine structural features of degeneration of the gallbladder during lamprey biliary atresia. The cells of the epithelium undergo a progressive accumulation of dense bodies and vacuoles, loss of glycogen, condensation of the filamentous ectoplasm, fragmentation of microvilli, and dilation of cisternae of rough endoplasmic reticulum but eventually disappear by stage 4 of metamorphosis. Zonulae occludentes in the epithelium show a progressive increase in apical-basal depth as the junctional strands fragment. The possibility of an influence of transformed, subepithelial cells on degeneration of epithelial cells is suggested by close contact of the former with the thickened, highly pleated, epithelial basal lamina. The smooth muscle cells of the larval gallbladder are believed to transform during lamprey metamorphosis into these subepithelial cells which shed their external lamina, become intimately associated with collagen and other microfibrils, and which may be capable of phagocytosis. The events of gallbladder degeneration during lamprey metamorphosis show features of apoptosis.     

Ultrastructural changes in the intestinal connective tissue of Xenopus laevis during metamorphosis

Ultrastructural changes in the intestinal connective tissue of Xenopus laevis during metamorphosis have been studied. Throughout the larval period to stage 60, the connective tissue consists of a few immature fibroblasts surrounded by a sparse extracellular matrix: few collagen fibrils are visible except close to the thin basal lamina. At the beginning of the transition from larval to adult epithelial form around stage 60, extensive changes are observed in connective tissue. The cells become more numerous and different types appear as the collagen fibrils increase in number and density. Through gaps in the thickened and extensively folded basal lamina, frequent contacts between epithelial and connective tissue cells are established. Thereafter, with the progression of fold formation, the connective tissue cells become oriented according to their position relative to the fold structure. The basal lamina beneath the adult epithelium becomes thin after stage 62, while that beneath the larval epithelium remains thick. Upon the completion of metamorphosis, the connective tissue consists mainly of typical fibroblasts with definite orientation and numerous collagen fibrils. These observations indicate that developmental changes in the connective tissue, especially in the region close to the epithelium, are closely related spatiotemporarily to the transition from the larval to the adult epithelial form. This suggests that tissue interactions between the connective tissue and the epithelium play important roles in controlling the epithelial degeneration, proliferation, and differentiation during metamorphic climax.     

Use of dual section mRNA in situ hybridisation/immunohistochemistry to clarify gene expression patterns during the early stages of nephron development in the embryo and in the mature nephron of the adult mouse kidney

The kidney is the most complex organ within the urogenital system. The adult mouse kidney contains in excess of 8,000 mature nephrons, each of which can be subdivided into a renal corpuscle and 14 distinct tubular segments. The histological complexity of this organ can make the clarification of the site of gene expression by in situ hybridisation difficult. We have defined a panel of seven antibodies capable of identifying the six stages of early nephron development, the tubular nephron segments and the components of the renal corpuscle within the embryonic and adult mouse kidney. We have analysed in detail the protein expression of Wt1, Calb1 Aqp1, Aqp2 and Umod using these antibodies. We have then coupled immunohistochemistry with RNA in situ hybridisation in order to precisely identify the expression pattern of different genes, including Wnt4, Umod and Spp1. This technique will be invaluable for examining at high resolution, the structure of both the developing and mature nephron where standard in situ hybridisation and histological techniques are insufficient. The use of this technique will enhance the expression analyses of genes which may be involved in nephron formation and the function of the mature nephron in the mouse.     

Intercellular junctions during development of the definitive kidney in lampreys: freeze fracture and morphometric analyses

The changing morphology of intercellular junctions in renal morphogenesis during lamprey metamorphosis was followed using freeze-fracture replicas and morphometry. Gap junctions and particle aggregates among strands of occluding junctions are conspicuous in the differentiating podocytes of the renal corpuscle and in the early ciliated neck and proximal segments but not in the distal segment. The cells of the segmented nephron arise from alpha nephrogenic cells which have a focal aggregate (macula occludens) of 4.8 junctional strands. Upon the initiation of metamorphosis the number of strands increases to 8 in undifferentiated cells with either maculae or zonulae occludentes. Differentiation of both neck and proximal segments is accompanied by gradual transformation of a 7-strand zonula occludens to a 4-strand junction but it becomes more shallow in the latter segment. Two types of undifferentiated cell are recognized through five of the seven metamorphic stages. Cells of two types of distal segments begin differentiation at the midpoint of transformation and immediately show zonula occludens of different morphology. Distal segment I (pars recta) has 5 strands and a 0.250 mum depth whereas segment II has 8-9 strands with twice the apical-basal depth. The larval archinephric duct undergoes a moderate transformation in junctional morphology with the addition of 2 strands and no increase in apical-basal depth in zonulae occludentes during metamorphosis. Changes and development of types of intercellular junctions along the nephron in lampreys are discussed with reference to known regional functional specialization in this organism and with the morphology of renal tubular intercellular junctions in other vertebrates.     

Morphological changes in the liver of the sea lamprey, Petromyzon marinus L., during metamorphosis: I. Atresia of the bile ducts

The bile ducts in the liver of larval sea lamprey, Petromyzon marinus, undergo programmed degeneration during metamorphosis. The degenerative process is most dramatic in the middle metamorphic stages (3-5), and is asynchronous, occurring more rapidly in small peripheral biliary components than in larger, medial ducts. All classes of bile ducts within the biliary tree exhibit similar histological changes during regression. The initial evidence of degeneration in the epithelium is a folding of the basal lamina, and this is accompanied by cell shrinkage and disruption of cell order. "Shedding" of microvilli and cytoplasmic constituents then takes place at the apical surface resulting in the accumulation of periodic acid-Schiff positive membranous debris in the Lumen. The appearance of "hyalin bodies" in the lumen coincides with the depletion of intermediate-sized filaments from the cytoplasmic matrix. Numerous, large dense bodies, myelin figures, and autophagic vacuoles are consistently observed in necrotic cells. Following cytolysis, bile duct remnants become ensheathed within regions of fibrosis. Ultimately, these fibrous regions are replaced with cords of hepatocytes. By stage 7, all bile ducts have disappeared. The events of biliary atresia in lampreys are comparable to tissue regression which is associated with normal development and pathological conditions in other vertebrates but are particularly reminiscent of those in human biliary atresia. The unique ability of the adult lamprey to service without bile ducts enhances the value of this organism as an experimental model for studying human biliary atresia.     

Fine structure of the midgut of Sinopanorpa tincta (Navás) (Mecoptera: Panorpidae)

Fine structure of the midgut and degeneration of the midgut epithelium of the scorpionfly Sinopanorpa tincta (Navás) adults were investigated using light microscopy and scanning and transmission electron microscopy. The results show that the tubular midgut lacks gastric caeca and is composed of an outer longitudinal and an inner circular muscle layer, a basal lamina, an epithelium and a lumen from the outside to inside. A peritrophic membrane was not found in the lumen. A mass of nodules was observed on the surface of the basal lamina. Three types of cells were recognized in the epithelium: digestive, secretory, and regenerative cells. The digestive cells contain irregular-shaped infoldings in the basal membrane and two types of microvilli in the apical membrane. The secretory cells are characterized by irregular shape and large quantities of secretory granules in the basal cytoplasm. The regenerative cells are triangular in shape and distributed only in the nodules. The epithelial cells are degenerated through programmed cell-death mechanisms (apoptosis and necrosis). The type, function, and degeneration of the epithelial cells of the midgut are briefly discussed.     

金雕肾脏的组织学观察

利用生物显微技术观察了金雕Aquila chrysaetos肾脏的组织结构.结果表明,金雕肾实质由许多肾小叶构成,每个肾小叶可分为皮质和髓质两部分.肾单位由一个肾小体和一条与其相连的肾小管构成.肾小体由肾小囊和肾小球组成.肾小管分为近曲小管、髓袢、远曲小管和连接小管.集合管分为小叶周集合小管和髓质集合管两部分.具有发达的极周细胞.     

The pelvic kidney of male Ambystoma maculatum (Amphibia,urodela, ambystomatidae) with special reference to the sexual collecting ducts

This study details the gross and microscopic anatomy of the pelvic kidney in male Ambystoma maculatum. The nephron of male Ambystoma maculatum is divided into six distinct regions leading sequentially away from a renal corpuscle: (1) neck segment, which communicates with the coelomic cavity via a ventrally positioned pleuroperitoneal funnel, (2) proximal tubule, (3) intermediate segment, (4) distal tubule, (5) collecting tubule, and (6) collecting duct. The proximal tubule is divided into a vacuolated proximal region and a distal lysosomic region. The basal plasma membrane is modified into intertwining microvillus lamellae. The epithelium of the distal tubule varies little along its length and is demarcated by columns of mitochondria with their long axes oriented perpendicular to the basal lamina. The distal tubule possesses highly interdigitating microvillus lamellae from the lateral membranes and pronounced foot processes of the basal membrane that are not intertwined, but perpendicular to the basal lamina. The collecting tubule is lined by an epithelium with dark and light cells. Light cells are similar to those observed in the distal tuble except with less mitochondria and microvillus lamellae of the lateral and basal plasma membrane. Dark cells possess dark euchromatic nuclei and are filled with numerous small mitochondria. The epithelium of the neck segment, pleuroperitoneal funnel, and intermediate segment is composed entirely of ciliated cells with cilia protruding from only the central portion of the apical plasma membrane. The collecting duct is lined by a highly secretory epithelium that produces numerous membrane bound granules that stain positively for neutral carbohydrates and proteins. Apically positioned ciliated cells are intercalated between secretory cells. The collecting ducts anastomose caudally and unite with the Wolffian duct via a common collecting duct. The Wolffian duct is secretory, but not to the extent of the collecting duct, synthesizes neutral carbohydrates and proteins, and is also lined by apical ciliated cells intercalated between secretory cells. Although functional aspects associated with the morphological variation along the length of the proximal portions of the nephron have been investigated, the role of a highly secretory collecting duct has not. Historical data that implicated secretory activity concordant with mating activity, and similarity of structure and chemistry to sexual segments of the kidneys in other vertebrates, lead us to believe that the collecting duct functions as a secondary sexual organ in Ambystoma maculatum. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Ultrastructural changes in the connective tissue of the gastric region during the metamorphosis of Xenopus laevis

Development of the gastric connective tissue of Xenopus laevis during metamorphosis was investigated by electron microscopy. Throughout the larval period to stage 60, the layer of connective tissue underlying the gastric epithelium consists of immature fibroblasts surrounded by a sparse extracellular matrix. At the beginning of the transition from the larval to the adult epithelial form, at about stage 60, extensive changes occur in the connective tissue. The number of cells suddenly increses and different cell types appear. Numerous contacts between epithelial and connective tissue cells are established through random gaps in the thickened basal lamina. During stages 62–63, just after the beginning of the morphogenesis of adult-type glands, the basal lamina lining the glandular epithelium becomes thinner, and the number of contacts decreases rapidly except near the tips of the glands. After the glandular cells begin to produce zymogen granules at stage 64, contacts become rare. From stage 63, when the muscularis mucosae develops, until the completion of metamorphosis, the connective tissue consists mainly of typical fibroblasts. Outside the muscularis mucosae, the fibroblasts of the lamina propria are aligned in parallel with the curvature of the glands. These observations indicate that developmental changes in the connective tissue are closely related spatiotemporally to those of the epithelial transition from larval to adult form during metamorphic climax. Although some changes are similar to those in the intestine (Ishizuya-Oka and Shimozawa, '87b), others are specific to the gastric region, which suggests that connective tissue may have a role in organ-specific differentiation of the gastric epithelium.     

Transformation of the intestinal epithelium of the larval anadromous sea lamprey Petromyzon marinus L. during metamorphosis

The events in the transformation of the intestine of the larval lamprey into the adult intestine were followed through the seven (1–7) stages of metamorphosis in anadromous Petromyzon marinus L. Light and electron-microscope observations demonstrated that the processes of degeneration, differentiation, and proliferation are involved in the transformation. In the anterior intestine, degeneration of cells and the extrusion of others into the lumen results in the disappearance of secretory (zymogen) cells and the decline in numbers of endocrine and ciliated cells. Larval absorptive cells, with a prominent brush border, are believed to dedifferentiate into unspecialized columnar cells with few microvilli. Degeneration and removal of cells occurs by both autophagy and heterography and cells extruded into the lumen in the anterior intestine are phagocytosed by epithelial cells of the posterior intestine. The loss of epithelial cells during transformation results in the folding and degradation of parts of the basal lamina and in an extensive widening of the lateral intercellular spaces in all parts of the intestine. As metamorphosis is a nontrophic period of the lamprey life cycle, the possible morphological effects of starvation on the intestinal epithelium are discussed. The development of longitudinal folds is a consequence of the events of metamorphic transformation of the intestinal mucosa. Although an interaction between the epithelium and the underlying tissues is believed to be importent, the actual mechanism of fold development is unknown. The intestinal epithelium of adult lampreys develops from surviving cells of the larval (primary) epithelium. Unlike the situation in amphibians, there does not appear to be a group (nest) of undifferentiated larval cells which differentiate into the adult (secondary) epithelium. Instead, in lampreys, columnar cells that persist through the degradative processes seem to be the source of absorptive and ciliated cells and probably are responsible for mucous and secretory cells. Preliminary observations indicate that the intestinal epithelium of feeding adults is specialized into an anterior region which liberates a secretion, absorbs lipid, and possesses the machinery for ion transport. A posterior region absorbs lipid, secretes mucus, and likely is involved in some protein absorption.     

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.     

Alterations to the subepithelial layers of the larval alimentary tract during metamorphosis in the sea lamprey Petromyzon marinus,with emphasis on tissue interactions

Light-microscopic histochemistry and conventional electron microscopy were used to study the changes to the subepithelial layers in the larval esophagus of the sea lamprey Petromyzon marinus during metamorphosis. During early stages of metamorphosis, smooth muscle cells of the muscularis mucosae and tunica muscularis dedifferentiate into myofibroblast-like cells, which make contact with the basal lamina of the overlying mucosal epithelium. During later stages, these myofibroblast-like cells redifferentiate into smooth muscle cells, reforming the muscularis mucosae and tunica muscularis. Alterations to the extracellular matrix occur concomitantly.     

Evidence for particulate guanylate cyclase in rat kidney after stimulation by atrial natriuretic factor. An ultracytochemical study

Summary Cytochemical localization of particulate guanylate cyclase (GC) in rat kidney, after stimulation with atrial natriuretic factor (ANF), was studied by electron microscopy. In the renal corpuscle GC reaction product was localized on podocytes. Other segments of the nephron that showed ultracytochemical evidence of GC activity were the proximal convoluted tubule, the thick ascending limb of the loop of Henle and the collecting tubule. All GC positivity was associated with plasma membranes. Samples incubated in basal conditions (without ANF) did not reveal any GC reaction product. These results indicate that ANF is a strong activator of particulate GC. Our data also suggests that, through the enzyme, ANF acts directly on epithelial cells of tubules where Na⁺ reabsorption occurs. This is in agreement with the hypothesis that ANF has a direct tubular effect on natriuresis.     

Effect of intra-amniotic lipopolysaccharide on nephron number in preterm fetal sheep

Chorioamnionitis is an antecedent of preterm birth. We aimed to determine the effect of experimental chorioamnionitis in fetal sheep during late gestation on 1) nephron number, 2) renal corpuscle volume, and 3) renal inflammation. We hypothesized that exposure to chorioamnionitis would lead to inflammation in fetal kidneys and adversely impact on the development of nephrons, leading to a reduction in nephron number. At ～121 days of gestation (term ～147 days), pregnant ewes bearing twin or singleton fetuses received a single intra-amniotic injection of lipopolysaccharide (n = 6; 3 singletons, 3 twins); controls were either untreated or received an intra-amniotic injection of saline (n = 8; 4 singletons, 4 twins). One twin was used from each twin-bearing ewe. At ～128 days of gestation, fetuses were delivered via Caesarean section. Kidneys were collected and stereologically analyzed to determine nephron number and renal corpuscle volume. Renal inflammation was assessed using immunohistochemistry. Experimental chorioamnionitis did not affect body weight or relative kidney weight. There was a significant reduction in nephron number but no change in renal corpuscle volume in LPS-exposed fetuses relative to controls. On average, nephron number was significantly reduced by 23 and 18% in singleton and twin LPS-exposed fetuses, respectively. The degree of renal inflammation did not differ between groups. Importantly, this study demonstrates that exposure to experimental chorioamnionitis adversely impacts on nephron number in the developing fetus.     

Electron microscope studies of phosphatases in the small intestine of Rana temporaria during larval development and metamorphosis

Summary Changes in the ultrastructure, and distribution of phosphatases in the intestinal epithelium of Rana temporaria during development were consistent with other developmental changes. Alkaline phosphatase AMP-ase and ATP-ase were always associated with sites of absorption of foodstuffs into the cell. Initially, these were only the yolk platelets but at the onset of feeding the brush border lateral wall, membranes and associated absorption vesicles all became sites of activity. At metamorphosis when the larvae cease feeding, the enzyme activities decreased and became difficult to detect.In the early larval stages, acid phosphatase activity was confined principally to the lateral cell-wall membranes. This soon disappeared but was followed at metamorphosis by a dramatic increase in both the number of sites and their activity. In general, acid phosphatase appeared to be associated with areas of degeneration. The new epithelial cells which developed during metamorphosis appeared under the old epithelium. The cell debris from the larval epithelium was then expelled into the lumen of the intestine. The new epithelium contained sites of enzyme activity similar to those of the adult. Acid phosphatase was now present only in lysosome-like bodies and very sparsely on the brush border.These results are discussed in relation to dietary and structural changes. It is suggested that the presence of the enzymes at any site can be related to and anticipate these changes, possibly under hormonal control.     

Electron microscopy of extracellular materials during the development of a sea star,Patiria miniata (Echinodermata: Asteroidea)

The fine structure of conspicuous extracellular materials during the life history of a sea star (Patiria miniata) is described. The outer surface of the developing sea star is covered by two morphologically different cuticles that appear sequentially during ontogeny. The primary cuticle, which is about 120 nm thick and two-layered, is present from mid-blastula through the end of the larval stage. The secondary cuticle, which is about 1 micron thick and three-layered, first appears on the epidermis of the rudiment region of the larva and, after metamorphosis, covers the entire epidermis of the juvenile and adult stages. During ontogeny, there are only two conspicuous gut cuticles: the first lines the newly invaginated archenteron at the start of the gastrula stage, and the second lines the esophagus during the larval stage. A blastocoelic basal lamina first appears at mid-blastula and persists as subectodermal and subendodermal basal laminae. Ruthenium red-positive granules are detectable between the lateral surfaces of adjacent ectodermal cells during part of the gastrula stage; this transient intercellular material may possibly aid in lateral adhesion between cells.     

华鲮泌尿系统组织学的初步观察

2004年3月至9月采用常规组织学方法对华鲮泌尿系统作了研究,结果表明：华鲮泌尿系统包括中肾、输尿管、膀胱。中肾由肾小体和肾小管组成,无皮质、髓质之分,有肾小体聚集现象;肾小管可分为颈段、第一近曲小管、第二近曲小管、远曲小管、集合管。肾中散布有大量淋巴髓样组织,还有甲状腺滤泡和斯坦尼氏小体,显然华鲮的肾脏是一个具有多种生理功能的复合器官。输尿管位于两肾叶腹侧,其上皮为似复层,缺黏膜下层,无纵肌,外膜甚薄。左右输尿管在后端合并,稍微扩大,形成膀胱,膀胱内壁具有发达的绒毛,绒毛表面为变移上皮。     

Involution of seminiferous tubules in aged hamsters: an ultrastructural, immunohistochemical and quantitative morphological study

In this study, we examined the age-related changes on morphometric parameters and ultrastructure of seminiferous tubules, and on the expression of extracellular matrix proteins in lamina propria of Syrian hamsters. A significant decrease in the percentage of normal tubules and an increase in the percentage of hypospermatogenic and arrested maturation tubules was observed with aging. Aged animals showed a decrease in tubular diameter, tubular lumen, seminiferous epithelium volume and total tubular volume. However, the total length of seminiferous tubules was significantly increased with aging. The most important ultrastructural changes with aging were the thickening of the lamina propria, the presence of diverse abnormalities in the spermiogenesis process, degeneration of germ cells, and vacuolization and flattening of Sertoli cells showing abundant lipofucsin droplets and residual bodies. Laminin immunoreactivity was found along the lamina propria of seminiferous tubules both in young and aged animals. Fibronectin immunoreactivity was found along the lamina propria and blood vessels. Both laminin and fibronectin total volume of immunostaining per testis was increased in aged hamsters. In conclusion, the age-related changes in seminiferous tubules of hamster include: a decrease in tubular width and an increase in tubular length; widening of the lamina propria caused by a more extensive connective matrix between the peritubular cells and the basal membrane; and a strong disarrangement of the seminiferous epithelium, including germ cell degeneration and important alterations in both spermiogenesis and Sertoli cell structure.