The ultrastructure of organelles appearing in spermatids and nutritive cells of Cipangopaludina malleata

Summary The ultrastructure of organelles appearing in the early typical and atypical spermatids, and the nutritive cells of Cipangopaludina malleata has been examined by a Siemens' electron microscope Elmiskop I.Mitochondria appearing in the early typical spermatid have doughnut-like profiles in which the internal ridges appear as triple-layered membranes arranged radially and extending into the interior of the organelle without reaching the other side. Each membrane 40–60 Å in width, separated by a clear interspace 60–90 Å wide, is characterized by a porous structure 20–30 Å in diameter which suggests a filtration apparatus for enzymes.Walls of the flattened saccules consisting the Golgi apparatus are calculated 35–60 Å thick, in which an electron-lucent, porous structure about 30 Å wide has been revealed.The smooth-surfaced endoplasmic reticulum is bordered by a triple-layered membrane consisting of two opaque layers with a less opaque interspace 20–30 Å wide. The outer membrane ca. 15 Å wide presents a more linear appearance than the dotted arrangement of the inner membrane 20–25 Å thick.The plasma membrane is composed of a triple-layered structure where two dense lines 15 Å wide are separated by a layer 20–30 Å thick of less density.The electron micrographs for the present studies were taken with the Siemens electron microscope, model Elmiskop I, at the Anatomical Institute of Kiel University, Germany. The one of the authors, G. Yasuzumi is deeply grateful to Prof. Dr. W. Bargmann and Dr. A. Knoop for the privilege of using this instrument and other equipments in the Laboratory.     

Golgi Tubule Traffic and the Effects of Brefeldin A Visualized in Living Cells

The Golgi complex is a dynamic organelle engaged in both secretory and retrograde membrane traffic. Here, we use green fluorescent protein–Golgi protein chimeras to study Golgi morphology in vivo. In untreated cells, membrane tubules were a ubiquitous, prominent feature of the Golgi complex, serving both to interconnect adjacent Golgi elements and to carry membrane outward along microtubules after detaching from stable Golgi structures. Brefeldin A treatment, which reversibly disassembles the Golgi complex, accentuated tubule formation without tubule detachment. A tubule network extending throughout the cytoplasm was quickly generated and persisted for 5–10 min until rapidly emptying Golgi contents into the ER within 15–30 s. Both lipid and protein emptied from the Golgi at similar rapid rates, leaving no Golgi structure behind, indicating that Golgi membranes do not simply mix but are absorbed into the ER in BFA-treated cells. The directionality of redistribution implied Golgi membranes are at a higher free energy state than ER membranes. Analysis of its kinetics suggested a mechanism that is analogous to wetting or adsorptive phenomena in which a tension-driven membrane flow supplements diffusive transfer of Golgi membrane into the ER. Such nonselective, flow-assisted transport of Golgi membranes into ER suggests that mechanisms that regulate retrograde tubule formation and detachment from the Golgi complex are integral to the existence and maintenance of this organelle.     

Developmental features of protophloem sieve elements in roots of wheat (Triticum aestivum L.)

Summary Protophloem sieve elements (PSEs) in roots of wheat (Triticum aestivum L.) are arranged in single vertical files. The number of PSEs within the files increases by symmetrical divisions, which take place after the completion of asymmetrical (formative) divisions and before the initiation of differentiation. The divisions are preceded by well defined pre-prophase bands (PPB) of microtubules, which surround the nucleus in an equatorial position. In the cytoplasmic region between the nuclear surface and the PPB, perinuclear and endoplasmic microtubules were observed. The perinuclear microtubules are considered as part of the developing spindle, while the endoplasmic ones interlink the perinuclear microtubules with the PPB. Dividing cells do not show any signs of incipient differentiation. The first and most reliable indication of a commencing differentiation is provided by the sieve-element plastids that begin to accumulate dense crystalloid inclusions in the very young PSEs. In mature PSEs plastids contain two kinds of crystalloid inclusions, dense and thin, in a translucent stroma. Depending on the plastid-inclusions criterion it was shown that: (a) the PSEs of a given root do not initiate differentiation at exactly the same stage, (b) the developmental sequence extends to a span of 7–9 actively differentiating PSEs arranged in a single vertical file, and (c) each PSE needs about 16–21 h to pass through the whole developmental sequence. In the last two differentiating PSEs of a file, mitochondria were found to be enveloped by single cisternae of ER. The association is temporary as it is lost in the first PSEs with an autolysed lumen. During differentiation, Golgi bodies were abundant and active in producing vesicles involved in cell wall development. Golgi vesicles were also found among the microtubules of the PPB, but no local thickening was observed. Golgi bodies disorganize in the last stages of autolysis and disappear in mature sieve elements.Abbreviations ER endoplasmic reticulum - MSE metaphloem sieve element - PPB pre-prophase band - PSE protophloem sieve element Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

The endomembrane system and mechanism of membrane flow in the green alga,Gloeomonas kupfferi (Volvocales,Chlorophyta) I. An ultrastructural analysis

Summary The endomembrane system of the chlamydomonad flagellate,Gloeomonas kupfferi (Chlorophyta), is complex. It consists of a proliferating ER network, a perinuclear complex of 14–18 dictyosomes and 8–12 vacuoles and an anterior contractile vacuole complex. The ER network extends from the nuclear envelope outwards, ensheafhs a dictyosome, extends out through a lobe of the chloroplast and terminates in the thin zone of peripheral cytoplasm between the chloroplast and plasmamembrane. The individual dictyosome is polar with distinct cis- and trans-faces. The cis-face is closely associated with transition vesicles emerging from the adjacent ER. Large vesicles emerge from peripheral swellings of terminal cisternae. The dictyosome-associated ER is connected to the peripheral vacuolar system. During cell division and cytokinesis, changes in the endomembrane system occur. Dictyosomes divide and quickly separate to form perinuclear complexes around the daughter nuclei. Each dictyosome undergoes morphological changes during this wall precursor-producing stage. ER lines the furrow zone and is closely associated with phycoplast microtubules. A discussion of the endomembrane system in membrane flow mechanics is provided.Abbreviations ER endoplasmic reticulum - OsFeCN Osmium ferricyanide     

über die Feinstruktur vonSynura petersenii unter besonderer Berücksichtigung der Morphogenese ihrer Kieselschuppen

Zusammenfassung Der Bau des FlagellatenSynura petersenii und die Substruktur der Mastigonemen werden beschrieben. Coated vesicles finden sich in Verbindung mit Golgi-Zisternen, Cytolysosomen, ER-Elementen, jungen Schuppenvesikeln und dem Plasmalemma. 17 nm dicke Tubuli kommen im Lumen von Elementen des ER und des Golgi-Apparates vor. Die Kieselschuppen entstehen in besonderen Schuppenvesikeln, die zunÄchst dicht an periplastidÄren ER-Zisternen liegen und die Form einer ovalen, flachen Zisterne haben und sich dann unter der Beteiligung der periplastidÄren ER-Zisterne und vielleicht der Mikrotubuli zu einer exakten Gu\form für die Kieselschuppen umbilden. Die Schuppenmorphogenese ist also auf eine Morphogenese des Schuppenvesikels zurückzuführen.

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The fine structure ofSynura petersenii with special reference to the morphogenesis of the silicified scales

Summary Cells of Synura petersenii were studied by electron microscopy. One flagellum is covered by little non-silicified scales and fitted with mastigonemes, whose middle piece mainly consists of two helically wound filaments with a diameter of 4.5 nm. They end in a longer and a smaller terminal fibril. The flagellar bases are fixed to the nucleus and the border of the flagellar pit by several elements of the flagellar root. From this root and from the border of the flagellar pit, microtubules extend along the plasmalemma and along the concave face of the plastids to the basal cell pole.The plastids are enveloped by a periplastidal cisterna of the ER which often is in continuity with the nuclear envelope. Within these compartments there are bundles of tubules with a diameter of 17 nm. Such tubules are also found within peripheral parts of Golgi cisternae of the distal face of the dictyosome.In the region of the dictyosome but also in other parts of the cell there are many coated vesicles. They seem to bud off the Golgi cisternae and fuse with cytolysosomes (which also may be derivatives of the Golgi apparatus), or with young scale forming vesicles, or with the ER, or with the plasmalemma.The silicified scales cover the cell body and are formed in special vesicles. At first these vesicles are ovoid, flattened cisternae attached to peripheral parts of the periplastidal cisterna. They undergo a complicated formation process. The margins fold over, the periplastidal cisterna locally mushrooms out and pushes outward on the central part of the scale forming vesicle. This complex protuberance then remodels into a hollow cylinder which is connected with the underlying parts by a short hollow stalk. In this way the scale forming vesicle represents a true mould for the scale. The morphogenesis of the scale therefore is a consequence of the morphogenesis of these membranes. Local growth of the membranes and perhaps microtubules play a role in this process.

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Wir danken Herrn Dr. W.Koch, Göttingen, für die überlassung einerSynura-Kultur und für wichtige Hinweise sowie der Deutschen Forschungsgemeinschaft für ihre Unterstützung.     

The Erv41–Erv46 complex serves as a retrograde receptor to retrieve escaped ER proteins

Signal-dependent sorting of proteins in the early secretory pathway is required for dynamic retention of endoplasmic reticulum (ER) and Golgi components. In this study, we identify the Erv41–Erv46 complex as a new retrograde receptor for retrieval of non–HDEL-bearing ER resident proteins. In cells lacking Erv41–Erv46 function, the ER enzyme glucosidase I (Gls1) was mislocalized and degraded in the vacuole. Biochemical experiments demonstrated that the luminal domain of Gls1 bound to the Erv41–Erv46 complex in a pH-dependent manner. Moreover, in vivo disturbance of the pH gradient across membranes by bafilomycin A1 treatment caused Gls1 mislocalization. Whole cell proteomic analyses of deletion strains using stable isotope labeling by amino acids in culture identified other ER resident proteins that depended on the Erv41–Erv46 complex for efficient localization. Our results support a model in which pH-dependent receptor binding of specific cargo by the Erv41–Erv46 complex in Golgi compartments identifies escaped ER resident proteins for retrieval to the ER in coat protein complex I–formed transport carriers.     

COPI-independent Anterograde Transport: Cargo-selective ER to Golgi Protein Transport in Yeast COPI Mutants

The coatomer (COPI) complex mediates Golgi to ER recycling of membrane proteins containing a dilysine retrieval motif. However, COPI was initially characterized as an anterograde-acting coat complex. To investigate the direct and primary role(s) of COPI in ER/Golgi transport and in the secretory pathway in general, we used PCR-based mutagenesis to generate new temperature-conditional mutant alleles of one COPI gene in Saccharomyces cerevisiae, SEC21 (γ-COP). Unexpectedly, all of the new sec21 ts mutants exhibited striking, cargo-selective ER to Golgi transport defects. In these mutants, several proteins (i.e., CPY and α-factor) were completely blocked in the ER at nonpermissive temperature; however, other proteins (i.e., invertase and HSP150) in these and other COPI mutants were secreted normally. Nearly identical cargo-specific ER to Golgi transport defects were also induced by Brefeldin A. In contrast, all proteins tested required COPII (ER to Golgi coat complex), Sec18p (NSF), and Sec22p (v-SNARE) for ER to Golgi transport. Together, these data suggest that COPI plays a critical but indirect role in anterograde transport, perhaps by directing retrieval of transport factors required for packaging of certain cargo into ER to Golgi COPII vesicles. Interestingly, CPY–invertase hybrid proteins, like invertase but unlike CPY, escaped the sec21 ts mutant ER block, suggesting that packaging into COPII vesicles may be mediated by cis-acting sorting determinants in the cargo proteins themselves. These hybrid proteins were efficiently targeted to the vacuole, indicating that COPI is also not directly required for regulated Golgi to vacuole transport. Additionally, the sec21 mutants exhibited early Golgi-specific glycosylation defects and structural aberrations in early but not late Golgi compartments at nonpermissive temperature. Together, these studies demonstrate that although COPI plays an important and most likely direct role both in Golgi–ER retrieval and in maintenance/function of the cis-Golgi, COPI does not appear to be directly required for anterograde transport through the secretory pathway.     

Movement and Remodeling of the Endoplasmic Reticulum in Nondividing Cells of Tobacco Leaves

Using a novel analytical tool, this study investigates the relative roles of actin, microtubules, myosin, and Golgi bodies on form and movement of the endoplasmic reticulum (ER) in tobacco (Nicotiana tabacum) leaf epidermal cells. Expression of a subset of truncated class XI myosins, which interfere with the activity of native class XI myosins, and drug-induced actin depolymerization produce a more persistent network of ER tubules and larger persistent cisternae. The treatments differentially affect two persistent size classes of cortical ER cisternae, those >0.3 μm² and those smaller, called punctae. The punctae are not Golgi, and ER remodeling occurs in the absence of Golgi bodies. The treatments diminish the mobile fraction of ER membrane proteins but not the diffusive flow of mobile membrane proteins. The results support a model whereby ER network remodeling is coupled to the directionality but not the magnitude of membrane surface flow, and the punctae are network nodes that act as foci of actin polymerization, regulating network remodeling through exploratory tubule growth and myosin-mediated shrinkage.     

FINE STRUCTURE OF CAPITULAR FILAMENTS IN THE COENOCYTIC GREEN ALGA PENICILLUS1,2,3

Capitular filaments of Penicillus capitatus contain a large central vacuole. The parietal cytoplasm is densely packed, devoid of chloroplasts in the growing tip, and becomes convoluted and sponge-like as extensions of the vacuole penetrate the cytoplasm in mature portions of the filament. Structure of organelles and their distribution in the filament are described. The vacuole contains a variety of inclusions, such as membranous configurations, spherical bodies, electron dense bodies, and calcium oxalate monohydrate crystals, each of the latter surrounded by a chamber associated with microtubules. Endophytic bacteria are present throughout the vacuole and occasionally in the tip cytoplasm. Some vacuolar components of P. pyriformis are described for comparison.     

THE FINE STRUCTURE OF MITOSIS AND CELL DIVISION IN THE CHRYSOPHYCEAN ALGA OCHROMONAS DANICA1

At the ultrastructural level, cell division in Ochromonas danica exhibits several unusual features. During interphase, the basal bodies of the 2 flagella replicate and the chloroplast divides by constriction between its 2 lobes. The rhizoplast, which is a fibrous striated root attached to the basal body of the long flagellum, extends under the Golgi body to the surface of the nucleus in interphase cells. During proprophase, the Golgi body replicates, apparently by division, and a daughter rhizoplast, appears. During prophase, the 2 pairs of flagellar basal bodies, each with their accompanying rhizoplast and Golgi body, begin to separate. Three or 4 flagella are already present at this stage. At the same time, there is a proliferation of microtubules outside the nuclear envelope. Gaps then appear in the nuclear envelope, admitting the microtubules into the nucleus, where they form a spindle. A unique feature of mitosis in O. danica is that the 2 rhizoplasts form the poles of the spindle, spindle microtubules inserting directly onto the rhizoplasts. Some of the spindle microtubules extend from pole to pole; others appear to attach to the chromosomes. Kinetochores, however, are not present. The nuclear envelope breaks down, except, in the regions adjacent, to the chloroplasts; chloroplast ER remains intact throughout mitosis. At late anaphase the chromosomes come to lie against part of the chloroplast ER. This segment of the chloroplast ER appears to be incorporated as part of the reforming nuclear envelope, thus reestablishing the characteristic nuclear envelope—chloroplast ER association of the interphase cell.     

Filaments and microtubules in the cytoplasm of the granulosa cells from the human follicle

Summary The cytoplasm of granulosa cells in human primordial follicles from normal women shows a system of filaments and microtubules. Filaments about 70–150 Å in diameter and several m in length can be seen as bundles or irregularly distributed. Microtubules about 200 Å in diameter are predominantly oriented in paranuclear regions. The relationships between cytoplasmic filaments and microtubules in granulosa cells and those of Sertoli cells are briefly discussed.     

Zum Feinbau des Periplasten und der Geißel von Trypanosoma brucei und Trypanosoma gambiense

Zusammenfassung Elektronenmikroskopische Untersuchungen an Geißelfibrillen und Mikrotubuli des Periplasten von Trypanosomen ergaben, daß beide Strukturen aus Protofilamenten aufgebaut sind. Die Protofilamente bestehen aus kettenförmig angeordneten globulären Untereinheiten von 45–50 Å Durchmesser. Die Mikrotubuli des Periplasten sind in ungefähr 150 Å-Abständen durch Querbrücken miteinander vernetzt. Es wird angenommen, daß diese Querbrücken durch abzweigende Protofilamente gebildet werden. Im Zusammenhang mit diesen Ergebnissen wird der Bau des Periplasten diskutiert.

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Ultrastructure of the periplast and the flagellum of Trypanosoma brucei and Trypanosoma gambiense

Summary Flagellar fibres and microtubules of the periplast of Trypanosomes are studied by electron microscopy. They both are shown to consist of protofilaments which are composed of globular subunits in beadlike array measuring 45–50 Å in diameter. The periplastic microtubules are connected by bridges which appear to be formed by protofilaments, branching off at intervals of approximately 150 Å from the microtubules. The structure of the periplast is discussed in detail.

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Durchgeführt mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Electron microscopy of the tracheal ciliated mucosa in rat

Summary The structure of the tracheal epithelial cells from rat has been studied by electron microscopy on approximately 200 Å thick sections with a resolution of better than 30 Å.The epithelium is found to be of a simple columnar type composed of ciliated cells, mucus producing (goblet) cells, basal cells and a fourth kind of cell, here called brush cell. A great number of non-ciliated cells has also been encountered. It has been proved that these represent goblet cells in different stages of intracellular synthesis of mucous granules. The ciliated cells have approximately 8–9 cilia per square micron and there are about 270 cilia on each cell, the calculated surface area being 33 square microns. They are covered by a 70 Å thick membrane. The ciliary filaments are arranged in a pattern of 2 separate ones in the center and a ring of 9 peripheral ones, each divided into 2 subfilaments by a wall with same thickness as the filamentous wall itself, this being 60 Å. The peripheral filaments are continuous with the basal corpuscles. The structure of the corpuscles as compared with earlier findings is discussed. A number of 0.05 micron thick and 1 micron long filiform projections emerge from the cell surface. No cuticle is present.The cell membrane facing adjacent cells is 90 Å and separated from their cell membrane by a 105 Å wide space, this space, being expanded towards a level corresponding to the proximal parts of the cell. A structure that represents terminal bar has been encountered. The cytoplasm is loose and composed of 160 Å thick granules. Spaces enclosed by 50 Å thick membranes with attached 160 Å thick granules (-cytomembranes) are rare. The Golgi zone is analyzed and its regular composition of -cytomembranes, granules and vacuoles is confirmed. The mitochondria with a mean width of 0.23 micron differ to their inner structure from the common type in that the triple layered membranes are highly interconnected. Large opaque granules are encountered in the cytoplasm. Ring-shaped, 850 Å wide, structures are present in the nuclear membrane. The goblet cells are not as abundant as the ciliated cells, the ratio being 14. Small filiform projections covered by a 95 Å thick membrane protrude from the cell surface. This membrane is continuous with the cell membrane, the latter with the same dimensions as in the ciliated cells. Terminal bars are present. The cytoplasm is very opaque due to a dense packing of the 165 Å opaque granules, many in clusters of 4–6. The -cytomembranes have the same dimensions as mentioned above for those present in the ciliated cells. The Golgi zone is of regular composition. There is a suggestion that the Golgi vacuoles and the -cytomembranes are involved in the formation of mucus. In the stage of cellular activity with but few mucous granules, there is a great number of large opaque granules, the size varying from 0.4–1 micron. The mitochondria with a mean width of 0.23 micron have an outer triple layered membrane with a total thickness of 180 Å. The central less opaque layer is 70 Å and the opaque layer on either side is 55 Å. The inner membranes are arranged parallel to each other and have a triple layered composition where the central less opaque layer is 65 Å and the opaque layers each 60 Å. The brush cells belong to the non-ciliated cells. They are encountered singly, surrounded by goblet cells. The surface structures are shaped like brushes or clumsy protrusions which emerge from the distal end of the cell, and are covered by a 95 Å thick membrane. There have been no suggestions of the brushes being cilia in a stage of growth, nor is it probable that they represent stereocilia. They most nearly resemble the intestinal brush border extensions and thus might serve as a resorbing structure.The cytoplasm of the brush cells appears of medium opacity between the ciliated cells and goblet cells and is composed of 155 Å opaque granules. The -cytomembranes are very rare. The Golgi zone is diminutive though of regular composition. The mitochondria are abundant and small with a mean width of 0.14 micron. The outer and inner membranes are triple layered with approximately the same dimensions as reported for the mitochondria of the ciliated and goblet cells. The inner membranes are very few, often only one or two are present. Some of the large opaque granules have inside a very regular arrangement of small 60 Å thick opaque granules arranged in a crystallinic pattern. In the cytoplasm 0.5–1 micron long bundles of 30–40 Å wide fibrils are encountered. The nucleolus shows a characteristic structure of concentrically arranged thin membranes. The basal cells are believed to represent lymphocytes or white blood cells. They sometimes rest on the basement membrane, sometimes are encountered in the distal part of the intercellular spaces. They are bordered by a 110 Å thick cell membrane and have a rather opaque cytoplasm characterized by 160 Å thick opaque granules. A very small Golgi zone is present. The mitochondria, the mean width being 0.14 micron, have triple layered outer and inner membranes, where the less opaque central layer is 65–70 Å and the opaque layers 45–50 Å each. The basement membrane has a thickness of 600 Å. No inner structure has been resolved. The basement membrane is separated from adjacent parts of the ciliated, goblet, brush, and basal cells by a 250 Å wide less opaque space. Below the basement membrane is the lamina propria of the trachea, which is composed of collagen and elastin fibers together with fibroblasts, white blood cells and lymphocytes. The relationship between different types of tracheal epithelial cells in rat has been analyzed. There has been found no indication of a transformation of any type of cells observed into a different type of cell. The development of basal cells via supporting cells or intermediate cells to goblet cells or ciliated cells has not been noticed. On the contrary, all cells that in light microscopy could have been considered to be supporting or intermediate cells, we have been able to recognize as brush cells or as goblet cells to a varying degree filled with mucous granules. If the cells did not seem to reach the cell surface it has been found to be due to a diagonal direction of the sectioning. In this connection it should be emphasized that this relationship is valid only in rat where it is known that the epithelium is of a simple columnar type as distinct from the conditions in man, that epithelium being of a pseudostratified columnar type.This paper is based on a report given at the meeting of Deutsche Gesellschaft für Elektronenmikroskopie in Münster, March 28–31, 1955 and at the Scandinavian Electron Microscope Society Meeting in Stockholm, May 13, 1955.     

Nervous system of the snailHelix aspersa

Summary The fine structure of neurosecretory nerves and endings associated with the sheath of the infraesophageal ganglion ofHelix aspersa is described. The sheath is a neurohemal organ whose vascularized stroma receives both monoaminergic and peptidergic endings. The latter occur along the surface of the nerves or scattered within the stroma. They include a complex population of vesicular profiles. The granular vesicles (1300–3000 Å in diameter) exhibit structural modifications that may be related to the intra-axonal release of their neurohormones. The agranular vesicles (500–2000 Å in diameter) occur in large numbers and lie mostly adjacent to the axon surface. Synaptoid specializations seem to represent active sites for the extracellular discharge of neurosecretory material. The monoaminergic endings so far studied lack synaptoid specializations and contain small granular (800–1300 Å in diameter) and agranular (700 Å in diameter) vesicles. Two kinds of non-neural cells are associated with the nerves: glial cells and melanocytes.Partly supported by Conicyt (Grant 105) and Comisión de Investigación Científica Universidad de Chile (Grant 48). The technical assistance of Mr. Arnold van Dun is gratefully acknowledged. We also thank the Department of Physics, Faculty of Physical Sciences and Mathematics, University of Chile, for the use of a Philips EM-300 electron microscope.     

Shuttle-like movements of Golgi vesicles in the tip of growingChara rhizoids

Summary In tip-growingChara rhizoids, the in-vivo saltatory movements of Golgi vesicles were recorded. The movements in radial direction back and forth between the ER aggregate and the plasma membrane occurred three times more often than movements passing the ER aggregate tangentially. The mean velocity of the class of Golgi vesicles observed (0.4–1 m in diameter) was approx. 0.3 m/s. Higher speed of 1–1.5 m/s occurred only in radial directions. Possibly, the ER aggregate is involved in guidance of the Golgi vesicles.Abbreviations DIC differential interference contrast - ER endoplasmic reticulum - OsFeCN osmium tetroxide-potassium ferricyanide Dedicated to the memory of Professor O. Kiermayer     

Filaments and rod-shaped tubulated bodies in the endothelia of anterior cerebral arteries in young rats

Summary Endothelia of the anterior cerebral arteries in rats aged 1 to 3 days were studied. Thin (about 50–90 Å) and thick (about 100–110 Å) filaments are present in the endothelia. Numerous spherical- or rod-shaped bodies, measuring approximately 0.07 to 0.3 m in diameter and up to 0.6 m in length occur in the endothelial cells. These bodies contain a tubular structure. The diameter of the individual tubules is about 200 Å. The present observations suggest that spherical- or rod-shaped inclusions are first synthesized in the rough endoplasmic reticulum and thereafter these materials are transported into the Golgi complex for maturation. A small number of the inclusions, however, may originate directly from the rough endoplasmic reticulum and not pass through the Golgi apparatus.A part of this study was demonstrated at the 70th Versammlung der Anatomischen Gesellschaft in Düsseldorf, April, 1–5, 1975The author thanks Mr. Tatsuro Fukushima for preparation of photographs     

Electron microscopic studies on the pars intermedia of the ferret

Summary The structure of the pars intermedia of the ferret has been studied with the electron microscope, with particular reference to the morphology of the glandular cells and their innervation. Two types of cell were found. The predominant cell is ovoid in shape and contains membrane-bound vesicles of varying size (1,000–5,000 Å) and density, the most electron-dense of which are associated with the Golgi region. The nucleus is indented and the cytoplasm contains rough endoplasmic reticulum. The second cell type is often associated with the colloid material and is elongated or stellate-shaped with long processes which extend between the predominant cells. It is devoid of cytoplasmic vesicles and has a poorly defined Golgi apparatus. Certain other structural features of this cell such as microvilli, cilia or cytoplasmic microfilaments are reminiscent of ependymal cells.Numerous nerve endings are observed throughout the pars intermedia, making synaptic contact with the predominant cell type. The majority contain vesicles with an electron-dense core measuring 750 Å; less frequently terminals contain dense granules measuring 1,000 A or more. Both also contain small electron-lucent vesicles (200–400 Å); occasionally terminals containing only the latter type are found. The pattern of innervation in the ferret is thus comparable to that previously observed in the cat, rather than that seen in rodents or monkeys, and the implications of this finding are discussed.We are indebted to Prof. Sir Solly Zuckerman, O. M., K. C. B., F. R. S., for his help and guidance and to Mr. J. Wallington for his unfailing technical assistance.     

A new interpretation of plasmodesmatal ultrastructure

Summary It is shown that simple, unbranched, plasmodesmata between young xylem ray cells of willow have no direct intercellular continuity apart from the plasmalemma which limits the cytoplasm and lines the plasmodesmatal canal. Each plasmodesma is traversed by a 200 Å diameter tubule (the desmotubule) which has a wall with probably 11 subunits arranged around a central cavity through which runs a 40 Å diameter rod. This rod is connected to the inside of the tubule wall, by fine filaments. At the ends of each plasmodesma the plasmalemma and cell wall are closely appressed to the tubule, thus precluding direct continuity between the cytoplasm of adjacent cells. Through the central part of the plasmodesmata the tubule is separated from the plasmalemma by a 90–100 Å wide gap. Cytoplasmic microtubules in the same tissue have a diameter of approximately 250 Å and a wall probably composed of 13 subunits: both desmotubules and cytoplasmic microtubules therefore have a centre-to-centre subunit spacing of about 47 Å. It is suggested that the desmotubules are not microtubules but may be nuclear spindle fibres which become trapped in the wall during cell plate formation. The endoplasmic reticulum, while closely approaching the plasmodesmata, is not continuous across them. It is thought most unlikely that the endoplasmic reticulum traverses plasmodesmata, as the dimensions of the central tubule — found here as well as by other workers — are smaller than those which would be expected to allow a stable molecular configuration in a unit membrane. The plasmalemma, where it lines the plasmodesmatal canal, appears to have particulate subunits in the outer opaque layers and the presence of these subunits may be attributable to the need for stability in membranes arranged about so small a radius.     

Mikrotubuli und Filamente in prospektiven Plättchenfeldern der Megakaryocyten

Zusammenfassung Megakaryocyten des Knochenmarkes des Menschen, der Ratte und der Maus wurden nach Fixierung mit Glutaraldehyd und nach Kontrastierung mit Uranylacetat und Bleihydroxyd elektronenmikroskopisch untersucht. Außer den bekannten submikroskopischen Strukturen lassen sich in den prospektiven Plättchenfeldern und in der marginalen Randzone der Megakaryocyten 200–250 Å breite Mikrotubuli und etwa 50 Å breite Filamente nachweisen. Diese gleichen in ihrer Struktur den Mikrotubuli und Filamenten der Thrombocyten des peripheren Blutes. Die Mikrotubuli entstehen im Cytoplasma der Megakaryocyten, ohne zunächst einem bestimmten Plättchenfeld zugeordnet zu sein. In frühen Stadien der Plättchenfelderbildung erkennt man meist nur einige Mikrotubuli innerhalb der Plättchenfelder, die sich zwischen Demarkationsbläschen hindurch in benachbarten Plättchenfeldern fortsetzen. Komplette marginale Bündel von Mikrotubuli sind in den Megakaryocyten nur selten zu beobachten. Die biochemischen und funktionellen Eigenschaften der Mikrotubuli und Filamente werden diskutiert.

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Microtubules and filaments in prospective platelet fields of megakaryocytes

Summary Megakaryocytes of bone marrow of man, rat and mouse were studied electronmicroscopically after fixation with glutaraldehyde and staining the ultrathin sections with uranyl acetate and lead hydroxide. Microtubules measuring 200–250 Å and filaments measuring 50 Å in thickness can be demonstrated in prospective platelet fields and marginal zones of megakaryocytes. These microtubules and filaments resemble those of the platelets of the peripheral blood. The microtubules are formed within the cytoplasm of the megakaryocytes without predilection of certain platelet fields. In early stages of the formation of platelet fields only a few microtubules can be detected within platelet fields which penetrate between demarcation vesicles into neighbouring platelet fields. In megakaryocytes complete marginal bundles of microtubules are rarely observed. Biochemical and functional properties of microtubules and filaments are discussed.

     

The neurohypophysis of the crested newt

Summary In the median eminence of the newt a medial region and two lateral regions are described.In cross section, the medial region appears to be made up of 1) an outer or glandular zone (Zone I) containing aldehyde-thionine-positive and negative nerve fibres and blood capillaries. Nerve fibres appear aligned in palisade array along the capillaries. 2) An inner zone (Zone II) made up of a) a layer of aldehyde-thionine-positive nerve fibres (fibrous layer) belonging to the preoptic hypophyseal tract and b) a layer of ependymal cells lining the infundibular lumen and reaching the blood vessels with their long processes.The lateral regions display a less pronounced stratification and aldehyde-thionine positive nerve fibres are nearly absent.A slender lamina (ependymal border) containing mainly aldehyde-thionine-positive nerve fibres and ependymal cells connects the median eminence to the pars nervosa.At the ultrastructural level, in the outer zone of the medial region at least 4 types of nerve fibres and nerve endings are identified:Type I nerve fibres containing granular vesicles of 700–1000 Å and clear vesicles (250–400 Å).Type II nerve fibres containing granular vesicles and polymorphous granules of 900–1300 Å and clear vesicles (250–400 Å).Type III nerve fibres containing dense granules of 1200–2000 Å and clear vesicles of 250–400 Å.Type IV nerve fibres containing only clear vesicles of 250–400 Å. In the inner zone too, all these nerve fiber types are found among ependymal cells, while the fibrous layer consists of nerve fibres containing granules of 1200–2000 Å in diameter.In the lateral regions Type I, Type II and Type IV nerve fibres and their respective perivascular terminals are found; axons containing dense granules (1200–2000 Å) are scanty. In these regions typical synapses between Type I nerve fibres and processes rich in microtubules are visible.The classification and functional significance of nerve fibres in the median eminence are still unsolved, but it may be assumed that nerve fibres of the medial region belong to both the preoptic hypophyseal and tubero hypophyseal tract, while the lateral regions are characterized by nerve fibres of the tubero hypophyseal tract. Peculiar specializations of the ependymal cells in the median eminence of the newt are also discussed.Work supported by a grant from the Consiglio Nazionale delle Ricerche.The authors are indebted to Mr. G. Gendusa and P. Balbi for technical assistance.