bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intranuclear membranous inclusions in oocytes of a viviparous teleost (Xiphophorus Helleri)
Authors: Azevedo Carlos 
Published: April 2021

ABSTRACT
Intranuclear inclusions were observed in oocytes of Xiphophorus helleri during prophase I. In osmium-fixed leptotene nuclei, the inclusions were made up of groups of membrane-limited vesicles or tubules with pale contents, situated near the inner nuclear membrane with which some of them exhibited apparent continuities. In zygotene nuclei, larger vesicles also appeared bounded by two or three membranes and containing tubules apparently invaginated from their walls. In pachytene-dictyate nuclei most vesicular bodies had a wall formed by stratified membranes, or were entirely made up of membranous whorls. In glutaraldehyde-osmium fixed material some of these myelin-like bodies showed a peculiar arrangement, consisting of concentric bands each containing thick inner dense lamellae 2·0–3·0 nm thick and a 5·0-nm outer lamella.
It is suggested that these inclusion bodies arise from the inner nuclear membrane of oocytes when cells start to grow intensely during prophase I. The bodies seem to become more complex at late prophase, probably by association of individual vesicles and the occurrence of multiple membrane invaginations, which may be related to active metabolic phenomena taking place at this stage in oocytes.
Regular structures in membranes: The lumenal plasma membrane of the cow urinary bladder
Authors: Knutton S. , Robertson J. D. 
Published: April 2021

ABSTRACT
The ultrastructure of the lumenal plasma membrane of the cow urinary bladder has been studied in thin sections of glutaraldehyde- and glutaraldehyde-H2O2-fixed specimens, by negative staining and freeze fracture. A regular hexagonal array of particles confined to polygonal plaques 0·1–0·4-μm in diameter and separated by 0·02-μm interplaque areas is revealed by all 3 techniques. Cross-sections through particulate areas fixed with glutaraldehyde-H2O2 display a tetralaminar structure consisting of the usual ∼ 8-nm-thick trilamellar unit membrane structure, on the external dense leaflet of which is located an additional ∼ 4-nm-thick stratum which is occasionally resolved into a row of regularly spaced ∼ 4-nm-diameter particles. Non-particulate areas feature only the ∼8-nm-thick trilamellar structure. Tangential sections reveal an hexagonal array of particles with a unit cell of ∼ 16 nm. Four membrane faces can be revealed by freeze fracture and etching of membranes of the cow urinary bladder; 2 complementary split inner membrane faces (A and B) revealed by the cleaving process and the lumenal and cytoplasmic membrane surfaces exposed by etching. Face B, which belongs to the external membrane leaflet and faces the cytoplasm, displays plaques of particles arranged in a hexagonal lattice with a unit cell of ∼ 16 nm. Face A, which belongs to the cytoplasmic membrane leaflet and faces the lumen, displays a complementary array of hexagonally packed pits. The hexagonally arranged particles also protrude into the lumenal membrane surface where they can occasionally be resolved into 6 ∼5-nm-diameter subunits; the cytoplasmic surface appears smooth. Six ∼ 5-nm-diameter subunits are also revealed in negatively stained preparations. The data are consistent with a model for the membrane in which the particles forming the hexagonal structure protrude above the lumenal membrane surface and also bridge most of the thickness of the membrane.
Contacts between pigmented retina epithelial cells in culture
Authors: Middleton C. A. , Pegrum S. M. 
Published: April 2021

ABSTRACT
The behaviour of primary cultures of dissociated embryonic chick pigmented retina epithelial (PRE) cells has been investigated. Isolated PRE cells have a mean speed of locomotion of 7·16 μm/h. Collisions between the cells normally result in the development of stable contacts between the cells involved. This leads to a gradual reduction in the number of isolated cells and an increase in the number of cells incorporated into islands. Ultrastructural observations of islands of cells after 24 h in culture show that junctional complexes are present between the cells. These complexes consist of 2 components: (a) an apically situated region of focal tight junctions and/or gap junctions, and (b) a more ventrally located zonula adhaerens with associated cytoplasmic filaments forming a band running completely around the periphery of each cell. The intermembrane gap in the region of the zonula is 6·0–12·0 nm. The junctional complexes become more differentiated with time and after 48 h in culture consist of an extensive region of tight junctions and/or gap junctions and a more specialized zonula adhaerens. It is suggested that the development of junctional complexes may be responsible for the stable contacts that the cells display in culture.
Evidence for a correlation between the number of marginal band microtubules and the size of vertebrate erythrocytes
Authors: Goniakowska-Witalińska Lucyna , Witaliński Wojciech 
Published: April 2021

ABSTRACT
In 23 species of vertebrates the dimensions of erythrocytes and the number of their marginal band microtubules were examined. A positive correlation was found between the size of erythrocytes and the number of microtubules. The absence of microtubules in diskoid erythrocytes of mammals – Camelidae – is discussed.
Freeze-fracture studies of frog atrial fibres
Authors: Mazet Françoise , Cartaud Jean 
Published: April 2021

ABSTRACT
The freeze-fracturing technique was used to characterize the junctional devices involved in the electrical coupling of frog atrial fibres. These fibres are connected by a type of junction which can be interpreted as a morphological variant of the ‘gap junction’ or ‘nexus The most characteristic features are rows of 9-nm junctional particles forming single or anastomosed circular profiles on the inner membrane face, and corresponding pits on the outer membrane face. Very seldom aggregates consisting of few geometrically disposed 9-nm particles are found. The significance of the junctional structures in the atrial fibres is discussed, with respect to present knowledge about junctional features of gap junctions in various tissues, including embryonic ones.
Motor proteins at the mitochondria–cytoskeleton interface
Authors: Kruppa Antonina J. , Buss Folma 
Published: April 2021

ABSTRACT
Mitochondria are multifunctional organelles that not only produce energy for the cell, but are also important for cell signalling, apoptosis and many biosynthetic pathways. In most cell types, they form highly dynamic networks that are constantly remodelled through fission and fusion events, repositioned by motor-dependent transport and degraded when they become dysfunctional. Motor proteins and their tracks are key regulators of mitochondrial homeostasis, and in this Review, we discuss the diverse functions of the three classes of motor proteins associated with mitochondria – the actin-based myosins, as well as the microtubule-based kinesins and dynein. In addition, Miro and TRAK proteins act as adaptors that link kinesin-1 and dynein, as well as myosin of class XIX (MYO19), to mitochondria and coordinate microtubule- and actin-based motor activities. Here, we highlight the roles of motor proteins and motor-linked track dynamics in the transporting and docking of mitochondria, and emphasize their adaptations in specialized cells. Finally, we discuss how motor–cargo complexes mediate changes in mitochondrial morphology through fission and fusion, and how they modulate the turnover of damaged organelles via quality control pathways, such as mitophagy. Understanding the importance of motor proteins for mitochondrial homeostasis will help to elucidate the molecular basis of a number of human diseases.
The eggshell of Drosophila melanogaster: I. fine structure of the layers and regions of the wild-type eggshell
Authors: Margaritis Lukas H. , Kafatos Fotis C. , Petri William H. 
Published: April 2021

ABSTRACT
The fine structure of the several layers and regional specializations in the Drosophila melano-gaster eggshell has been studied by a combination of shell isolation procedures and ultrastructural techniques (conventional TEM, whole-mount TEM, SEM, HVEM, freeze-fracture electron microscopy utilizing rotary replication, shadow casting, optical diffraction and stereo imaging).
The main shell consists of 5 layers: the vitelline membrane (300 nm thick), the wax layer, the innermost chorionic layer (40—50 nm), the endochorion (500-700 nm), and the exochorion (300-500 nm). The vitelline membrane consists of irregularly organized particles. The wax layer appears to contain multilayered hydrophobic plates which split tangentially upon freeze fracturing. The innermost chorionic layer is composed of a crystalline lattice. The endochorion is made of a thin (40 nm) fenestrated floor composed of 40-nm fibres and an outer solid (2oonm) roof covered with a network of 40-nm strands. Intermittently spaced pillar connect these 2 parts. Similarities in the substructure of the floor, pillars and roof suggest that they may be composed of similar or identical structural elements.
The specialized regions of the shell are the 2 respiratory appendages, the operculum area and the posterior pole. The appendages exhibit 2 sharply distinct surfaces, a dorsal side with isolated 1·5-µm plaques and a ventral side with strands of 40-50 nm connected in a network with openings of 70-80 nm. The operculum area, which includes the micropyle and the collar, is distinguished by 3 unique types of cell imprints. The posterior pole contains 2 distinctive populations of cell imprints: the central area has very thin intercellular ridges and a thin, perforated, endochorionic roof, while the peripheral area contains mixed, thick and thin, intercellular ridges and serves as a transition zone to the main shell pattern. The pillars in the central area of the posterior pole have a distinct arrangement, forming one peripheral circle within each cell imprint.
An analysis utilizing structural and developmental criteria indicates that as many as ten different populations of follicular epithelial cells may be involved in the construction of the various regions of the Drosophila eggshell.
Studies of membrane fusion vi. mechanism of the membrane fusion and cell swelling stages of sendai virus-mediated cell fusion
Authors: Knutton S. 
Published: April 2021

ABSTRACT
The membrane fusion and cell swelling stages of Sendai virus-mediated cell-cell fusion have been studied by thin-section and freeze-fracture electron microscopy. Sites of membrane fusion have been detected in human erythrocytes arrested at the membrane fusion stage of cell fusion and in virtually all cases a fused viral envelope or envelope components has been identified thus providing further direct evidence that cell-viral envelope-cell bridge formation is the membrane fusion event in Sendai virus-induced cell fusion. Radial expansion of a single virus bridge connecting 2 cells is sufficient to produce a fused cell. Membrane redistribution which occurs during this cell swelling stage of the fusion process is often accompanied by the formation of a system of membrane tubules in the plane of expansion of the virus bridge. The tubules originate from points of fusion between the bridging virus envelope and the erythrocyte membrane and also expand radially as cells swell. Ultimately membrane rupture occurs and the tubules appear to break down as small vesicles. When previously observed in cross-sectioned cells these membrane tubules were interpreted as sites of direct membrane fusion. The present study indicates that this interpretation is incorrect and shows that the tubules are generated subsequent to membrane fusion when 2 cells connected by a virus bridge are induced to swell. A mechanism to explain the formation of this system of membrane tubules is proposed.
Three-dimensional reconstruction of organelles inEuglena gracilisz.: I. qualitative and quantitative changes of chloroplasts and mitochondrial reticulum in synchronous photoautotrophic culture
Authors: Pellegrini Max 
Published: April 2021

ABSTRACTUltrastructural changes of chloroplasts and mitochondria have been observed in synchronously growing cells of Euglena gracilis Z, under photoautotrophic conditions. Application of the serial section technique allows estimation of the number and volume of these organelles. Several 3-dimensional reconstructions reveal their shape and distribution throughout the cell cycle.In young cells 10 separate diskoid or branched chloroplasts are found. They show the typical lamellar structure of euglenoid chloroplasts. During the growth phase (light period), they enlarge and their volume doubles. Some of them branch out, so that 20 lobes are formed. Thylakoids grow longer without change in number. The pyrenoid persists only during the first half of this period. During the cell division phase (dark period), branched chloroplasts divide along 2 planes which are perpendicular to each other and perpendicular to the thylakoid plane. All thylakoids are cut and their number does not change in the daughter chloroplasts. The plastidome volume constitutes 15–18% of the total cell volume over the entire life cycle.One of the most significant observations in this report is the presence of a single permanent mitochondrial reticulum during the whole cell cycle. This giant mitochondrion consists of an extremely branched network with delicate threads (0·4–0·6 μm thick) surrounding the chloro-plasts, nucleus and reservoir. It extends throughout the cell. During the growth phase, it becomes gradually longer and doubles in volume. The degree of branching increases but the thickness of the threads remains constant. During the division phase, the mitochondrial elements appear more restricted (0 ×4 μm thick) and the reticulum becomes progressively partitioned into 2 daughter networks. At any time of the cell cycle, the chondriome volume is about 6% of the total cell volume.These results are discussed in comparison with numerous relevant papers on fight and electron microscopy of animal and plant cells. They suggest that the descriptions of several authors on the plastidial cycle and the mitochondrial cycle in Euglena, both said to be characterized by alternate reticulate and fragmentary states, arise in part from questionable interpretation of random sections. It is evident that the form and distribution of organelles can be determined more precisely by serial sectioning.
Wall regeneration by plasmolysed cells from tissue suspension cultures of sphaerocarpos donnellii
Authors: Grusak Michael A. , Thomas Robert J. , Marsh Barry H. 
Published: April 2021

ABSTRACT
De novo synthesis of wall material by cells of Sphaerocarpos donnellii was followed using radioactive tracer techniques. Uniform uptake of [14C]glucose by plasmolysed suspension cultures was demonstrated autoradiographically. Liquid scintillation counts of acid- or alkali-soluble wall carbohydrates indicate that hemicellulose and cellulose make up the major wall fractions in control and plasmolysed tissues. The amount of label in walls of plasmolysed cells was significantly lower than in those of controls. Higher relative radioactivity in pectin and hemicellulose, and lower radioactivity in cellulose were found in plasmolysed tissue. These compositional changes may enhance wall stability by providing numerous sites for cross-linkage between cellulose microfibrils of regenerated walls.
Variations in the distribution and migration of centriole duplexes in mitotic ptk2 cells studied by immunofluorescence microscopy
Authors: Aubin Jane E. , Osborn Mary , Weber Klaus 
Published: April 2021

ABSTRACT
The localization and migration of centriole duplexes have been studied in PtK2 cells by indirect immunofluorescence microscopy using specific tubulin antibodies. The study demonstrated the usefulness of the immunofluorescence technique to quantitate studies of centriole migration and concomitant events such as cytoplasmic microtubule breakdown in large populations of cells. Centriole duplex locations in normal and Colcemid-treated interphase populations have been compared with duplex locations in prophase cells. A higher percentage of duplexes were found close to the nucleus in prophase than in interphase cells, but approximately 5% of the duplexes remained in the cytoplasm far removed from the nucleus in prophase and throughout the course of duplex separation. Duplex separation occurred along a wide variety of paths and duplexes did not have to be closely juxtaposed to the nuclear envelope for separation to occur. Some duplexes separated in the cytoplasm with no detectable nuclear attachment, with spindles forming far to the side of the condensing chromosomes. The timing of duplex separation did not always coincide either with chromosome condensation or with nuclear membrane breakdown, and in a small percentage of the cells separation occurred as late as prometaphase. These data suggest that normal spindle formation can occur despite the large variability in initial and final centriole duplex location, their migration patterns, and the timing of the different events. Breakdown of cytoplasmic microtubules began in prophase and progressed until prometaphase; the last cytoplasmic microtubules disappeared soon after the loss of the nuclear membrane.
The polypeptides of rat liver nuclear envelope: I. examination of nuclear pore complex polypeptides by solid-state lactoperoxidase labelling
Authors: Richardson Jonathan C. W. , Maddy Alun H. 
Published: April 2021

ABSTRACTPurified nuclei retaining a high degree of ultrastructural integrity were isolated by conventional centrifugation techniques. The cytoplasmic surface of these nuclei was iodinated using lactoperoxidase immobilized onto giant Sepharose beads; thus the outer nuclear membrane and the cytoplasmic surface of nuclear pore complexes were selectively labelled. Pore complexes in association with a fibrous lamina were isolated from these nuclei by removal of the nucleoplasm and extraction with Triton X-100. The chemical composition of the pore-lamina fraction was 93·6% protein, 6% RNA, 0.4% phospholipid. The labelling suggests that major polypeptides Ni (70000) and N2 (67000) and more than 10 other more minor polypeptides, ranging from 3 3 000 to 200 000 mol. wt, as being components of the nuclear pore complex. Polypeptide N3 (58000) is shown to be present only on the nucleoplasmic face of nuclear envelopes, probably in the fibrous lamina.
The polypeptides of rat liver nuclear envelope: II. comparison of rat liver nuclear membrane polypeptides with those of the rough endoplasmic reticulum
Authors: Richardson Jonathan C. W. , Maddy Alun H. 
Published: April 2021

ABSTRACT
Nuclear envelopes are separated into pore-lamina and membrane sub-fractions by extraction in 2.0% Triton X-100 followed by pelleting of the pore-laminae. The polypeptides of these subfractions are then compared with those from isolated rough endoplasmic reticulum. The dispositions of individual polypeptides in the cytoplasmic surface of nuclear envelopes and rought endoplasmic reticulum were studied by lactoperoxidase-catalysed iodination.
These studies show that although the nuclear membranes exhibit several homologies with the Triton-soluble polypeptides of the rough endoplasmic reticulum the relative proportion of individual polypeptides within the two systems are very largely different. The cytoplasmic surfaces of the 2 membrane systems show only 2 obvious homologies at 10 5 00 0 and 15 000 mol. wt and the overall impression is that, at least in rat liver, the outer nuclear membrane is very substantially differentiated from rough endoplasmic reticulum. It is concluded that the nuclear membranes may not be regarded as a mere continuum of the endoplasmic reticulum, but should be seen as a highly specialized membrane system in their own right.
P2: A behavioural mutant of Dictyostelium discoideum
Authors: Frantz Catherine E. 
Published: April 2021

ABSTRACT
Pa is a mutant strain isolated from the cellular slime mould, Dictyostelium discoideum strain NC-4. Pa differs from NC-4 in 3 major respects. Pa lacks the cyclic AMP chemotactic and signalling properties and the aggregative development of NC-4. P2 development consists of slow differentiation of resistant microcysts, which have not previously been reported in D. discoideum. Most important, Pa amoebae display a novel pattern of movement, quite distinct from that of NC-4 amoebae and any other related amoebae for which data are available.
Pa amoebae move on agar at a mean velocity of 13–3 μm/min, almost twice as fast as NC-4 amoebae. Pa amoebae have a persistence time, or directional memory ‘half-life’, of 13·3 min, over 3·5 times the NC-4 value. However, this measure is based on straight-line movement, and actual Pa persistence may be much greater because Pa amoebae move almost always in gradual left turns and left loops interspersed with occasional long, straight segments.
When Pa amoebae are plated in drops on agar, they migrate away in all directions, and the expanding drop edge can move at nearly the mean individual cell velocity. Spiral bands of amoebae can be seen in the expanding area of the drop; these invariably unwind from the original drop in a counterclockwise direction. The persistent left-turning behaviour of individual Pa amoebae is probably the major cause of this pattern of movement from drops. It also probably helps explain the similar coordinated banding behaviour observed in fields of cells. Amoebae move long distances in bands of contacting or separated cells, with no apparent organizing centre. Statistical analysis shows that Pa amoeb g have some tendency to cluster, and cell-cell contact interactions may be strong enough to promote band formation.