Ultrastructure of the Protonephridia in the Dorvilleid Polychaete Apodotrocha progenerans (Annelida)

The achaetous dorvilleid polychaete Apodotrocha progenerans Westheide & Riser, 1983, possesses several pairs of segmentally arranged protonephridia. They consist of a blindly ending terminal cell and three tubule (emission) cells. The terminal cell is a flame bulb with unusual filtration area consisting of interdigitated pedicel-like projections. Each cell has its own tuft of flagella; and the emission channel is intracellular. The tube-shaped 'seamless' cells are slotted into each other like water-pipes.     

Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom-shaped structure in tubule cross-section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.     

Phylogenetic position of phylum Nemertini, inferred from 18S rRNA sequences: molecular data as a test of morphological character homology.

Partial 18S rRNA sequence of the nemertine Cerebratulus lacteus was obtained and compared with those of coelomate metazoans and acoelomate platyhelminths to test whether nemertines share a most recent common ancestor with the platyhelminths, as traditionally has been implied, or whether nemertines lie within a protostome coelomate clade, as suggested by more recent morphological analyses. Maximum-parsimony analysis supports the inclusion of the nemertine within a protostome-coelomate clade that falls within a more inclusive coelomate clade. Bootstrap analysis indicates strong support for a monophyletic Coelomata composed of a deuterostome and protostome-coelomate clade. Support for a monophyletic protostome Coelomata is weak. Inference by distance analysis is consistent with that of maximum parsimony. Analysis of down-weighted paired sites by maximum parsimony reveals variation in topology only within the protostome-coelomate clade. The relationships among the protostome coelomates cannot be reliably inferred from the partial sequences, suggesting that coelomate protostomes diversified rapidly. Results with evolutionary parsimony are consistent with the inclusion of the nemertine in a coelomate clade. The molecular inference corroborates recent morphological character analyses that reveal no synapomorphies of nemertines and flatworms but instead suggest that the circulatory system and rhynchocoel of nemertines are homologous to coelomic cavities of protostome coelomates, thus supporting the corresponding hypothesis that nemertines belong within a protostome-coelomate clade. The sequence data provide an independent test of morphological character homology.     

Protonephridial Excretory System in Vestimentifera (Siboglinidae,Annelida)

Ultrastructural study of the excretory tree of vestimentifera Ridgeia piscesae has shown that it consists of tubules that are blind at their distal ends. The tubules are lined with ciliated cells and have one or two multiciliated terminal cell(s) at the distal ends. In the tubule walls, there are putative ultrafiltration sites. The excretory tree tubules are interpreted as the secondary protonephridia.     

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.     

Epidermis and protonephridia of a free-living platyhelminth, Mesocastrada führmanni Voltz, 1898 (Rhabdocoela, Typhloplanoida): An ultrastructural study

The ultrastructure of the epidermis and the protonephridia of the free-living rhabdocoel Mesoscastrada führmanni is described. The epidermis consists of polarized cells, the nucleus located in the basal part of the cell and the mitochondria in the apical part. The surface is entirely covered by cilia anchored in the cytoplasm by horizontal and vertical striated rootlets. Cilia of the flame bulbs also have horizontal and vertical striated rootlets. The weir apparatus of the cyrtocyte is composed of a single row of ribs connected by a thin “membrane” of extracellular material. Bundles of microtubules, located in the ribs originate in the centrioles. Epidermal cells and flame bulbs of M. führmanni closely resemble those of the other Typhloplanoida examined so far.     

The evolution of protonephridia of the Platyhelminthes

Three types of flame bulbs are distinguished in the Platyhelminthes: type 1 has two cilia arising from a terminal cell and rootlets extending along the weir; type 2 has many cilia arising from a terminal cell and the proximal canal cell closely aligned with it; and type 3 has a non-terminal perikaryon forming many flame bulbs, each with many cilia and a single row of longitudinal ribs. Each type appears in various structural forms. Type 1 is found in the Catenulida; type 2 in the Macrostomida, Polycladida, Prolecithophora, Proseriata, Tricladida, Fecampiidae, and Neodermata; and type 3 in the Rhabdocoela and Lecithoepitheliata. The most likely evolutionary sequence is that type 3 is derived from type 2 and, perhaps, that type 2 is derived from type 1. Characters of the protonephridia show that the Rhabdocoela and the Neodermata form separate phylogenetic lineages; other similarities between these taxa are due to convergent evolution (or horizontal gene transfer?).     

扩张莫尼茨绦虫(绦虫纲:圆叶目)的原肾管及原肾管概念的评述

本研究应用透射电子显微镜研究了扩张莫尼茨绦虫原肾管的细胞学特征 ,莫尼茨绦虫原肾管的焰茎球为一个过滤器结构 ,类似于“挡河坝”样构造 ,此构造由端细胞和近管细胞外突形成的肋条 (或称杆 )相互交错排列而成。肋条之间由细胞外物质构成的“膜”结构连接 ,过滤作用通过该“膜”发生。焰细胞与近管细胞交界处有裂缝或孔与细胞外的结缔组织 (实质组织 )相通 ;原肾管的毛细排泄管细胞质索之间没有隔状联结 ;毛细排泄管及排泄管的管腔内有大量珠状微绒毛突起以增加表面积。从扩张莫尼茨绦虫及其它一些无脊椎动物原肾管的研究结果表明 ,原原肾管概念将焰细胞作为封闭的盲端已不再合适 ,需要进行修订 ,建议修订为 :原肾管是一种焰细胞系统 ,通常由焰细胞、管细胞和肾孔细胞组成 ,焰茎球作为过滤装置与周围的结缔组织 (实质组织 )有或没有裂缝 (孔 )相通     

CHLAMYDOMONAS FLAGELLA : I. Isolation and Electrophoretic Analysis of Microtubules, Matrix, Membranes, and Mastigonemes

Methods were developed for the isolation of Chlamydomonas flagella and for their fractionation into membrane, mastigoneme, "matrix," and axoneme components. Each component was studied by electron microscopy and acrylamide gel electrophoresis. Purified membranes retained their tripartite ultrastructure and were shown to contain one high molecular weight protein band on electrophoresis in sodium dodecyl sulfate (SDS)-urea gels. Isolated mastigonemes (hairlike structures which extend laterally from the flagellar membrane in situ) were of uniform size and were constructed of ellipsoidal subunits joined end to end. Electrophoretic analysis of mastigonemes indicated that they contained a single glycoprotein of ~ 170,000 daltons The matrix fraction contained a number of proteins (particularly those of the amorphous material surrounding the microtubules), which became solubilized during membrane removal. Isolated axonemes retained the intact "9 + 2" microtubular structure and could be subfractionated by treatment with heat or detergent. Increasing concentrations of detergent solubilized axonemal microtubules in the following order: one of the two central tubules; the remaining central tubule and the outer wall of the B tubule; the remaining portions of the B tubule; the outer wall of the A tubule; the remainder of the A tubule with the exception of a ribbon of three protofilaments. These three protofilaments appeared to be the "partition" between the lumen of the A and B tubule. Electrophoretic analysis of isolated outer doublets of 9 + 2 flagella of wild-type cells and of "9 + 0" flagella of paralyzed mutants indicated that the outer doublets and central tubules were composed of two microtubule proteins (tubulins 1 and 2) Tubulins 1 and 2 were shown to have apparent molecular weights of 56,000 and 53,000 respectively     

The nephridia of the interstitial polychaete Hesionides arenaria and their phylogenetic significance (Polychaeta,Hesionidae)

Summary The small hesionid polychaete Hesionides arenaria possesses paired segmental excretory organs that closely resemble solenocytic protonephridia. The nephridium consists of one terminal cell and four tubule cells which form the emission channel. From the terminal cell, up to six flagella arise each surrounded by a weir of ten regularly arranged cytoplasmic rods. The structure of the cytoplasm of three of the following cells suggests that they function in active transport and storage. Because all of the larger, more primitive species of this family are equipped with metanephridia, the possibility is discussed that these organs have been developed out of metanephridia. The Hesionides arenaria nephridium may be a morphological stage in the evolutionary pathway from metanephridia to solenocytes. This would mean that solenocytes can no longer be considered to be homologous in every case with other protonephridial organs in polychaetes and may well be derived several times independently out of metanephridia or true protonephridia.     

Ultrastructure of the protonephridial system of Dactylogyrus sp. and an unidentified ancyrocephaline (Monogenea: Dactylogyridae)

The ultrastructure of the flame bulbs and capillaries of the protonephridia of Dactylogyrus (probably anchoratus) from Carassius auratus in southeastern Australia, and of an unidentified ancyrocephaline from the marine teleost Priacanthus macracanthus in southern Queensland is described. The cilia of the flame are anchored in the terminal cell by means of basal bodies without distinct rootlets. The nucleus of the terminal cell is basal, and (in Dactylogyrus) partly lateral to the basal bodies. The weir consists of a row of internal and a row of external ribs (rods) connected by a ‘membrane’. The external ribs are continuations of the cytoplasm of a thick-walled ‘cytoplasmic cylinder’ (proximal canal cell) which tightly surrounds most of the flame and contains a septate junction; the internal ribs are continuous with the terminal cell. Internal leptotriches arise from the perikaryon of the terminal cell, and, in the ancyrocephaline, also from the internal ribs. The wall of the protonephridial capillaries contains a septate junction, a reticulum of interconnected spaces and, in the ancyrocephaline, also lamellae. Lateral flames are common in the capillaries of Dactylogyrus.     

Ultrastructure of the Flame Bulbs and Protonephridial Capillaries of Artioposthia sp. (Platyhelminthes,Tricladida, Geoplanidae)

The protonephridial terminal complex of Artioposthia is formed by one or two terminal cells, each with a nucleus located in the lateral wall of the flame bulb, and probably two proximal canal cells forming the wall of the protonephridial capillary. The weir is restricted to the proximal parts of the flame bulbs and consists of convoluted slits separated by thick cytoplasmic columns. Cross-striated ciliary rootlets running parallel with and obliquely or transversely to the longitudinal axis of the flame bulbs strengthen the walls of the flame bulbs and, to a lesser degree, that of the capillary. Numerous cristate mitochondria are present in the terminal and proximal canal cells. Cytoplasmic processes extend from the terminal cells into the adjacent tissue, and narrow internal leptotriches extend from the cytoplasm of the terminal cells into the lumen of the flame bulbs. The wall of the capillary contains many interconnected, liquid filled spaces that communicate with the lumen of the capillary, and two septate junctions. Phylogenetic implications of the findings are discussed.     

Schistosoma mansoni proteases Sm31 (cathepsin B) and Sm32 (legumain) are expressed in the cecum and protonephridia of cercariae.

Adult Schistosoma mansoni parasites live in the bloodstream of their vertebrate hosts where they consume red blood cells. Hemoglobin, released from the ingested red blood cells, is degraded by a variety of parasite proteases, including Sm31 (cathepsin B) and Sm32 (schistosome legumain). In this study the localization pattern of the Sm31 and Sm32 enzymes in cercariae (the infectious life cycle stage) was examined. Antibodies generated against recombinant Sm31 and Sm32 recognize their respective proteins in Western blots of soluble parasite extracts. Highest levels are seen in adult female extracts, whereas the level of both proteins is below detection in cercarial extracts. However, in fixed, whole cercariae, both proteins are seen in the cecum and protonephridia. In the cecum, the staining pattern has a granular appearance, suggesting that the proteins are packaged in vesicles. In the protonephridial system, Sm31 and Sm32 are detected in all 8 flame cells in the cercarial body and in both flame cells in the cercarial tail. The distribution of the 2 proteins differs in the flame cells. Examination of immunostained cercariae using laser scanning confocal microscopy shows that whereas Sm31 is located in the tubule cell, Sm32 is found in both the tubule cell and its adjoining cap cell. These findings suggest that the proteins are involved in the proposed excretory and osmoregulatory roles of flame cells.     

Intraluminal androgen binding protein alters 3H-androgen uptake by rat epididymal tubules in vitro

Previous experiments have shown that androgen binding protein (ABP) and androgens exist in high concentrations in the tissue and the lumen of the rat caput epididymis. The present experiments were performed to determine whether or not intraluminal APB affects tubule net uptake of androgens. Caput epididymal tubules were dissected into 2-cm segments, subjected to microperfusion into the tubule lumen, and incubated for 2.5 h in 35 degrees C minimum essential medium (MEM) containing 2.0 ng tritiated testosterone (3H-T) per ml. 14C-polytheylene glycol [PEG] was included as a contamination marker. In the first series of experiments, caput tubules were perfused with a control, artificial perfusion (MKB) containing no ABP or fresh rat rete testis fluid (RTF), which is known to contain ABP. Tubules incubated while containing RTF took up 138% of the tritiated androgens taken up by control tubules. In the second series of experiments, tubules were perfused with fresh caput epididymal lumen content, MKB alone, MKB containing either 5.0 ng purified rat ABP/microliters or 50 ng ABP/microliters. Tubules incubated while containing perfused MKB took up only 47% of the tritiated androgens taken up by tubules containing perfused native lumen content. Increasing intraluminal ABP concentrations in the MKB medium increased 3H-androgen uptake in a stepwise fashion. Intraluminal ABP at a concentration of 50 ng/microliters was associated with a 71% return of 3H-androgen uptake towards that amount of 3H-androgen taken up by tubules perfused with native lumen content. Intraluminal ABP enhances net androgen uptake by caput epididymal tubules from their surrounding medium in vitro.     

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.     

Ultrastructure of the protonephridia of larval Rugiloricus cf. cauliculus, male Armorloricus elegans, and female Nanaloricus mysticus (Loricifera)

The protonephridial system of several Loricifera was studied by transmission electron microscopy. A larval specimen of Rugiloricus cf. cauliculus possesses two protonephridia, which are "capped" frontally by a compact mass of still undifferentiated gonadal cells. Each protonephridium consists of four monociliary terminal cells and four canal cells with a diplosome but no cilia. Because of incomplete series of sections and unsatisfactory fixation, the outleading cell(s) could not be detected. In a male specimen of Armorloricus elegans, each gonad contains two protonephridia that open into the gonadal lumen. Each protonephridium consists of two monociliary terminal cells, each forming a filter, two nonciliated canal cells, and two nephroporus cells. The protonephridial lumina of the latter cells fuse to one common lumen, which unites with the gonadal lumen. Preliminary observations on the protonephridia of a female Nanaloricus mysticus reveal a more complicated arrangement of interdigitating terminal and canal cells. One or two terminal cells form their own individual filter or four cells form a common compound filter. The cilium of the terminal cells of all species investigated are surrounded by a palisade of nine microvilli that support the filter barrier made of an extracellular matrix. An additional filter diaphragm could be traced between the pores in the cell wall of each terminal cell of A. elegans. The urogenital system of the Loricifera differs from that of the Priapulida in that the protonephridia of the former are completely integrated into the gonad, whereas the excretory organs of the latter open into the urogenital duct caudally of the gonads.     

Morphology and function of Malpighian tubules and associated structures in the cockroach, Periplaneta americana.

This paper describes the different regions of the Malpighian tubules and the associated structures (ampulla, midgut, ileum) in the cockroach, Periplaneta americana. There are about 150 tubules in each insect. Each tubule consists of at least three parts. The short distal region is thinner than the other parts and is highly contractile. The middle region comprises most of the tubule length and is composed of primary and stellate cells. Primary cells contain numerous refractile mineral concretions, while stellate cells have smaller nuclei, fewer organelles, simpler brush border, and numerous multivesicular bodies. Symbiont protozoa are sometimes present within the lumen of the middle region near where it opens into the proximal region of the tubule. The latter is a short region that drains the tubular fluid into one of the six ampullae. These are contractile diverticula of the intestine located at the midgut-hindgut junction. The ampulla is highly contractile, and consists of a layer of epithelial cells surrounding a cavity that opens into the gut via a narrow slit lined by cells of unusual morphology. The proximal region of the tubule and the ampulla resemble the midgut in that they have similar micromal origin and reabsorptive function for the proximal region of the tubule and for the ampulla. A number of inclusions found within the tubule cells are described, including peroxisomes and modified mitochondria. Current theories of fluid transport are evaluated with regard to physiological and morphological characteristics of Malpighian tubules. The possible role of long narrow channels such as those between microvilli and within basal folds is considered, as is the mechanism by which these structures are formed and maintained. Also discussed is the role of peroxisomes and symbionts in the excretory process.     

Analysis of intracellular receptor/ligand sorting. Calculation of mean surface and bulk diffusion times within a sphere.

Cell surface receptors bind extracellular ligand molecules and transport those ligands into the cell by a process termed receptor-mediated endocytosis. Receptor and ligand molecules are sorted from one another after endocytosis, apparently within a structure consisting of intracellular vesicles and connected thin tubules. The experimental observation is that most free (unbound) ligand molecules are found in the lumen of the vesicles and receptors are located primarily within the tubules. Because equilibrium and geometric considerations do not explain this segregation, a kinetic scheme involving the passive diffusion of molecules from a vesicle into a tubule is investigated. Two possible sorting mechanisms are considered: first, that receptors are able to move into tubules more rapidly than ligand molecules due to an advantage in dimensionality and, second, that receptors diffusing into tubules are trapped there while ligands are not. Mean diffusion times for receptor and ligand movement into a tubule are calculated by solving Poisson's equation in two and three dimensions, respectively, on the surface of and within a sphere. Using estimated parameter values, we found that only the second scheme is able to account for the experimentally observed sorting. An estimate is obtained for the length of time a tubule and vesicle must be connected in order to remove a significant number of receptors into a tubule. The fraction of free ligand that is "mis-sorted" with the recycling receptor population and thus exocytosed is also determined.     

Postnatal development of the connexion between tubulus seminiferus and tubulus rectus in the bovine testis

Summary Histology and ultrastructure of the connexion of seminiferous and straight testicular tubules were studied in 58 bovine testes of 29 animals ranging from 4 to 52 weeks of postnatal development. In the 4th and 8th week seminiferous tubules are solid. Their non-germinal supporting cells possess spherical nuclei in a basal location and a great amount of granular endoplasmic reticulum. The straight tubules have a narrow lumen and a stratified epithelium rich in intercellular canaliculi. Between 20 and 25 weeks the seminiferous tubules acquire a lumen and develop a terminal segment, the tip of which (terminal plug) protrudes into the cup-shaped modification of the adjacent straight tubule. At 30 weeks the structural differentiation between seminiferous tubule proper and its terminal segment has proceeded: in the former spermatocytes and spermatids make their first appearance, and the supporting cells have transformed to Sertoli cells. In the latter the morphology of the supporting cell preserves a more primitive state. Starting from the 16th week and proceeding through the 30th week and further, the epithelium of the tubulus rectus close to the connexion with the seminiferous tubule becomes monolayered by rearrangement of its cells and advances along the basal lamina into the area of the seminiferous tubule. Those cells of the seminiferous tubule that are cut off from the basal lamina by invading rectus cells degenerate. Between 40 and 52 weeks the adult situation is principally achieved. The terminal segment of the seminiferous tubule is tripartite consisting of transitional region, intermediate portion, and terminal plug. The terminal segment is surrounded by a vascular plexus. The straight testicular tubule adjacent to the terminal segment is modified into a cup region encompassing the terminal plug, followed by a narrow stalk region, which is lined by simple columnar epithelium. Mononuclear free cells are a constant feature of the tubulus rectus epithelium in all stages of postnatal development.Supported by grant Wr 7/6-6 from the Deutsche Forschungsge-meinschaft