bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localization of freeze-fracture planes of yeast membranes
Authors: Hereward F. V. , Northcote D. H. 
Published: April 2021

ABSTRACT
In freeze-etch replicas the position of the plane of fracture along membranes is controversial; in an attempt to clarify the situation we have examined drops of yeast suspension frozen at − 160 °C, fractured and then freeze-substituted with a solution of osmium tetroxide in acetone. The drops were embedded in Araldite and sections were cut perpendicular to the plane of fracture to show where the cleavage had occurred.
At the tonoplast the membrane split and the plane of fracture ran between the 2 darkly staining lines. At the plasmalemma the cleavage plane was not clearly localized. The inner half of the membrane remained with the protoplast and darkly staining material could be seen on the wall. However, in some places the dark line at the surface of the protoplast could be resolved into 2 lines. The cleavage plane appeared to change at the invaginations of the plasmalemma, where on fracture the whole membrane sometimes remained attached to the wall.
Movement, fine structure, and fusion of pseudopods of an enclosed amoeba, Difflugiella sp
Authors: Griffin J. L. 
Published: April 2021

ABSTRACT
In Difflugiella sp., strain F-20, a small amoeba enclosed in a flexible mantle, pseudopods extended through a mouth or aperture and seemed to function only for movement and feeding. Pseudopods from different cells fused on contact and cell clumps shared common pseudopods and moved in a co-ordinated way. During locomotion, pseudopods or pseudopod complexes usually exhibited an activity cycle of 3 phases: anterior extension with the tip firmly adhering; stable hold as other pseudopods advanced; and flaccid posterior retraction. While distal adhesive tips advanced, proximal unattached parts of pseudopods simultaneously shortened as the cell body advanced.
Microtubules were numerous in pseudopods within the mouth but extended for only 1–2 μm into pseudopods up to 20–30 μm long. Microfilaments were present where pseudopods adhered to the substratum, to the mantle, or to bacteria and were also associated with pinocytotic invaginations. Pseudopod ground plasm was either reticulate or amorphous; no axial rods or aligned filaments related to pseudopod rigidity were seen.
Simultaneous pseudopod adhesion, extension, and proximal shortening apparently account for locomotion or cell body translation of Difflugiella. While some similarities to other amoeboid systems were noted, the need for detailed studies on different types of organisms or cells is emphasized.
The dogfish neuromuscular junction: dual innervation of vertebrate striated muscle fibres?
Authors: Bone Q. 
Published: April 2021

ABSTRACT
In the myotomal muscles of the dogfish, Scyliorhinus canicula, there are 2 major types of fibre. The red fibres at the periphery of the myotome receive a distributed en grappe pattern of innervation. There are subjunctional folds at these endings, and the nerve terminals contain vesicles around 50 nm in diameter. In contrast to this, the white twitch fibres of the myotome are innervated focally, by 2 nerve fibres passing to the same motor end-plate. These 2 fibres contain vesicles of different types. One type of nerve terminal contains vesicles around 50 nm in diameter; these terminals resemble those upon the red fibres. The other contains vesicles up to too nm in diameter, frequently possessing a dense core. It is suggested that the white twitch fibres of dogfish are innervated by 2 separate axons, possibly containing different transmitter substances.
Effects of denervation on the ultrastructure of insect muscle
Authors: Rees D. , Usherwood P. N. R. 
Published: April 2021

ABSTRACT
The structure of normal and denervated muscle fibres in the metathoracic retractor unguis muscle of the locust (Schistocerca gregaria) has been examined. Section of the 2 motor neurons which innervate this muscle results initially in muscle hypertrophy but this is followed about 4 days post neurotomy by progressive atrophy. Atrophy of the retractor unguis muscle is characterized by a decrease in muscle volume and degeneration of muscle organelles, e.g. mitochondria, sarcoplasmic reticulum, transverse tubular system, protein filaments, etc. During its later stages the degeneration of the denervated muscle is possibly assisted by the phagocytic action of haemocytes which invade the muscle.
Nematode-induced syncytium—a multinucleate transfer cell
Authors: Jones M. G. K. , Northcote D. H. 
Published: April 2021

ABSTRACTThe formation and structure of a syncytium induced by the potato cyst-nematode (Heterodera rostochiensis Woll.) in potato roots is described.At the permanent feeding site of the nematode larva, usually in the root cortex, the larva pierces a cell with its mouth stylet and injects saliva. Cell wall dissolution occurs to incorporate neighbouring cells into a syncytium. A column of cells is incorporated towards the vascular tissue. Centripetal advance is limited by the lignified xylem, then syncytial spread continues laterally along xylem parenchyma and pericycle cells.Wall protuberances form on syncytial walls adjacent to conducting elements. This indicates the syncytium is a multinucleate transfer cell, and by ingesting syncytial contents the larva is the nutrient sink. As syncytial expansion occurs, sieve elements are crushed and probably cease to function, hence protuberance development continues only against xylem elements.Cell alterations on incorporation into the syncytium involve expansion, loss of cell vacuole, nuclear hypertrophy and a proliferation of cytoplasmic organelles free to move through wall gaps into the communal cytoplasm.‘Boundary formations’ and microtubules are associated with the growing ends of protuberances, and appear to be involved in their synthesis. Fibrillar material, possibly cellulose microfibrils, occurs between the plasmalemma and the membrane of the ‘boundary formation’, and the forming protuberance.To induce the formation of the syncytium, the larva controls the differentiation of unspecialized cells to cells with a specific physiological function. The occurrence of wall protuberances suggests that transfer cells form as a response to solute flow.
A light-microscope study of the action of cytochalasin b on the cells and isolated cytoplasm of the characeae
Authors: Williamson R. E. 
Published: April 2021

ABSTRACT
The reversible inhibition of cytoplasmic streaming in cells of Nitella translucens by cytochalasin B was found to be accompanied by an increase in the number of mini-vacuoles in the endoplasm. Fibrils thought to drive the streaming were still present in inhibited cells. In droplets of cytoplasm obtained from cut cells of Chara corralina, the final number of fibrils formed was not sensitive to cytochalasin B, although the motility of these fibrils was highly so. The movement of organelles in the absence of visible fibrils and the rotation of chloroplasts were also inhibited. The evidence for the involvement of the microfilament system in cytoplasmic streaming is discussed. The way in which such microfilaments seem to be operating in characean cells differs from the most likely mechanism for their operation in other cytochalasinsensitive processes.
The effect of actinomycin d in vivo upon peripheral nucleoli and other nuclear organelles in oocytes of Triturus cristatus
Authors: Snow M. H. L. 
Published: April 2021

ABSTRACT
Exposure of the ovaries of Triturus cristatus to actinomycin D at a concentration of 100 /tg/ml causes characteristic changes in the peripheral nucleoli and other nuclear organelles in oocytes of o·6–1·1 mm diameter. Viewed with the light microscope untreated oocytes contain nucleoli that stain uniformly with a variety of dyes. They also appear homogeneous under phasecontrast optics. After 2 or 4 h of in vivo incubation with actinomycin D, oocyte sections stained with Haidenhain’s haematoxylin or viewed under phase-contrast optics show nucleoli composed of 2 regions. The more heavily stained or contrasted zone is crescent-shaped and directed away from the nuclear membrane. Neither sections stained with azure B bromide nor gallocyanin chrome alum show this feature. Ribonuclease digestion does not eliminate or alter it. Autoradiography with [3H]uridine indicates that all recently synthesized RNA is lost from the nucleolus during actinomycin D treatment. The zonation is not therefore a reflexion of RNA distribution. During recovery from actinomycin D poisoning there is a reduction in the degree of zonation shown by nucleoli which re-establish a normal appearance some 48 h after treatment.
Electron microscopy of peripheral nucleoli in oocytes sampled during this treatment indicates that the zonation is not associated with reorganization of ultrastructural components. During incubation with actinomycin D the coarse granules (20 nm diameter) are completely lost from the nucleolus. There is associated shrinkage of the nucleolus which after treatment is found to consist entirely of fibrils (5 nm thick) and small granules. The reappearance of the coarse granules during recovery is completed in about 48 h. It is thought that the loss of the granular component during treatment represents the movement of the 30-s precursor and the 18-s ribosomal unit from the nucleolus.
Some 20–30 μm inside the nucleus of untreated oocytes is a region containing many spheroidal bodies, less than 1·0 μm diameter. They have been termed micronucleoli and consist of granules 2·5–5 nm in diameter and fibrils of similar thickness. Actinomycin D treatment causes these components to segregate and eventually (within 24 h of treatment) the granular component is extruded. This component reappears during the second day after treatment. It is postulated that these micronucleoli represent the sites at which the 30-s ribosomal precursor undergoes its final maturation. The segregation of components induced by actinomycin D is probably the morphological manifestation of an abnormal metamorphosis of this precursor.
Treatment with actinomycin D also induces the immediate formation within the nucleus of crystalline bodies composed of lamellae 16 nm wide, 4 nm thick and with a centre-to-centre spacing of 8–10 nm. They are not present 24 h after treatment. They are thought to represent a protein fraction normally associated with periods of intense RNA synthesis.
Cytoplasmic localization during storage and translation of the mrnas of transition protein 1 and protamine 1, two translationally regulated transcripts of the mammalian testis
Authors: Morales Carlos R. , Kwon Yunhee K. , Hecht Norman B. 
Published: April 2021

ABSTRACT
During spermatogenesis in mammals, the transcripts of transition protein 1 (TP 1) and protamine 1 (Prm 1) are under translational regulation. Following their transcription in round spermatids, the mRNAs for TP 1 and Prm 1 are stored in the cytoplasm from 3–7 days before being translated towards the end of spermatogenesis. To test the hypothesis that the inactivation or activation of transcripts during spermiogenesis could be mediated by mRNA compartmentalization in the cytoplasm of spermatids, light and electron microscopy were used to localize, by in situ hybridization, the cellular and subcellular sites of stored and translated mRNAs for these two testisspecific transcripts. During early spermiogenesis (before step 7) nuclear transcripts of both TP 1 andPrm 1 were seen. After step 7 the TP 1 and Prm 1 mRNAs were only detected in the cytoplasm. Throughout spermiogenesis the cytoplasmic mRNAs were not localized to any membrane-bound organelles such as the endoplasmic reticulum or mitochondria or to non-membrane-bound structures such as the chromatoid body. These studies demonstrate that the translational arrest of the TP 1 and Prm 1 mRNAs is not primarily controlled by compartmentalized storage in the cytoplasm of spermatids. Moreover, when translation of these mRNAs occurs in elongated spermatids, the mRNAs are present throughout the cytoplasm.
High molecular weight tau: Preferential localization in the peripheral nervous system
Authors: Georgieff Irene S. , Liem Ronald K. H. , Mellado Wilfredo , Nunez Jacques , Shelanski Michael L. 
Published: April 2021

ABSTRACT
Using epitope mapping we have demonstrated that a high molecular weight protein (Mr ∼115× 103) present in brain and spinal cord is a member of the tau family of microtubule-associated proteins. Antibodies directed against the amino-terminal, middle and carboxyl-terminal portions of tau recognize this protein. A limited survey of neuronal tissues has shown that this high molecular weight tau protein is present in brain, spinal cord, dorsal root ganglia, dorsal and ventral roots and peripheral nerves. High molecular weight tau protein is expressed at higher levels in spinal cord than in brain and is the only form of tau detected in the adult peripheral nervous system.
Centrosome and microtubule dynamics during meiotic progression in the mouse oocyte
Authors: Messinger Susan M. , Albertini David F. 
Published: April 2021

ABSTRACT
The disposition, function and fate of centrosomes were analysed in mouse oocytes undergoing in vitro meiotic maturation, using multiple-label fluorescence microscopy. Oocytes fixed at various points during meiotic progression were double labeled with either human centrosome-specific antibody, 5051, and anti-tubulin antibodies or 5051 and MPM-2 antibodies in order to evaluate the microtubule nucleation capacity and phosphorylation status of centrosomes during this process. Double labeling with anti-tubulin antibodies revealed two populations of centrosomes that undergo stage-specific changes in number, location and microtubule nucleation capacity in relation to spindle assembly and cytoplasmic events. Specifically, one population was consistently associated with chromatin throughout meiotic maturation whereas a second population of cytoplasmic centrosomes exhibited maximal numbers and nucleation capacity at prometaphase and anaphase of meiosis-I. Quantitative evaluation of cytoplasmic centrosomes indicated increased numbers during the transition from diakinesis to prometaphase and metaphase to anaphase and total disappearance during telophase. Colocalization studies with MPM-2 revealed that centrosomes were always phosphorylated. However, at metaphase of meiosis I and II the microtubule nucleation capacity of centrosomes was diminished. These results suggest the existence of two discrete populations of centrosomes in the mouse oocyte that are coordinately regulated to subserve aspects of microtubule organization relative to both nuclear and cytoplasmic events.
The inner dynein arm complex: Compatible images from freeze-etch and thin section methods of microscopy
Authors: Burgess S. A. , Carter D. A. , Dover S. D. , Woolley D. M. 
Published: April 2021

ABSTRACT
A study has been made of the inner dynein arm complex in the sperm flagellum of Gallus domesticus. It has been found that images of the complex made from highly contrasted, approx. 20 nm, sections are very largely compatible with images made from replicas of rapidly cryofixed material. This suggests that neither technique seriously distorts the native state. From both types of image, we conclude that the most proximal group of inner dynein arm heads (IDA 1) is related to spoke SI and consists of 3 heads with fine connections to the B-tubule. IDA 2 consists of 2 such heads and is related to spoke S2. IDA 3 is apparently single headed and lies close to the A-attachment of spoke S3. This arrangement of ID As repeats every 96 nm. Between the IDAs and outer dynein arms (ODAs), lying close to IDAs 2 and 3, is a strap-like linkage to the next B-tubule; it is argued that this represents the circumferential link, nexin. In sections, but not consistently in replicas, IDA 2 lies closer to the plane of the nexin link than does IDA 1. In the presence of ATP and vanadate, little change is seen in the IDA complex except for an ill-defined alteration to IDA 1. It is speculated that the apparently smaller size of the inner arm heads (compared with the ODA major subunit) may have functional implications in relation to maximal sliding velocity.
Combined effects of extracellular matrix and growth factors on NBT-II rat bladder carcinoma cell dispersion
Authors: Tucker Gordon C. , Boyer Brigitte , Valles Ana Maria , Thiery Jean Paul 
Published: April 2021

ABSTRACT
Using the rat bladder carcinoma cell line NBT-II we showed that collagens but not laminin and fibronectin were able to induce cell scattering. Acidic fibroblast growth factor and transforming growth factor alpha also promoted NBT-II cell dispersion on glass or tissue culture plastic. We have now further analysed the scatter response to these two growth factors in the presence of extracellular matrix molecules. In the presence of growth factors, no peripheral single-cell dispersion occurred on fibronectin and laminin, although time-lapse video analyses revealed intense cell mingling and motility inside the monolayer forming around NBT-II aggregates. Patterns of strings or files of cells protruding from the monolayer were often observed. The presence of a scattering activity in the complex acellular extracellular matrix deposited by NBT-II cells themselves strongly suggested that substratum conditioning was responsible for this effect. On the other hand, the two growth factors accelerated collagen-mediated NBT-II individual cell dispersion and locomotion in a reversible way. As a marker of cell dissociation, we studied desmosome distribution in aggregate cultures: desmosomes were present in aggregates formed in suspension even in the presence of growth factors, whereas internalization occurred after cell-to-substratum contact. On laminin or fibronectin and in the presence of growth factors, peripheral cells inside the halo of NBT-II aggregates did not exhibit desmosome linkages. These observations suggest that scatter effects per se are dependent on the composition of the extracellular matrix. In particular, on a substratum nonpermissive for direct cell translocation, individual cell dispersion can be replaced by en bloc patterns of migration following substratum conditioning by the cells.
Enhanced expression of fibronectin by cmd/cmd chondrocytes and its modulation by exogenously added proteoglycan
Authors: Tsukahara Takashi , Okamura Miya , Suzuki Sakaru , Iwata Hisashi , Miura Takayuki , Kimata Koji 
Published: April 2021

ABSTRACT
Cartilage matrix deficiency (cmd/cmd) in mice is a genetic disorder associated with the failure of chondrocytes to synthesize the core protein of cartilage proteoglycan monomer (cartilage-PG). Immunohistochemical and biochemical analyses revealed enhanced accumulation of fibronectin in culture of cmd/cmd chondrocytes as well as in mutant cartilage tissue in vivo. Purified cartilage-PG, when added exogenously to a culture of cmd/cmd chondrocytes, caused a reduction in abnormal accumulation of fibronectin over several subsequent days of culturing. Using a fibronectin cDNA probe, we showed that, on the basis of total RNA, the fibronectin mRNA level was four or eight times higher in cmd/cmd chondrocytes than in the normal. The level of fibronectin mRNA in cmd/cmd cells was lowered by culturing the cells in the presence of added cartilage-PG. These findings suggest that the abnormal accumulation of fibronectin in the mutant cell culture is primarily due to elevation of fibronectin mRNA level, and that cartilage-PG in the extracellular matrix may affect the regulation of fibronectin biosynthesis at the steady-state level of mRNA.
Evidence for kinesin-related proteins in the mitotic apparatus using peptide antibodies
Authors: Sawin Kenneth E. , Mitchison Timothy J. , Wordeman Linda G. 
Published: April 2021

ABSTRACT
To identify kinesin-related proteins that may be important for mitotic function in embryonic and tissue culture cells we have generated polyclonal antibodies to two synthetic peptides corresponding to conserved regions of the kinesin motor domain. In Xenopus eggs we have identified a family of microtubule-binding proteins, recognized by one or both affinity-purified peptide antibodies but not by monoclonal antibodies that recognize conventional kinesin heavy chain. Like kinesin, most of these proteins bind to microtubules only upon addition of AMP-PNP or nucleotide depletion and are released upon subsequent addition of ATP. At least one protein, however, exhibits markedly distinct properties, binding readily to microtubules in the absence of AMP-PNP and/or nucleotide depletion. We also report that, unlike antibodies to conventional kinesin, the peptide antibodies to the kinesin motor domain immu-nofluorescently label spindles and kinetochores in mitotic tissue culture cells, suggesting that kinesin-like proteins may have important roles in chromosome movement and mitosis.
Down-regulation of scatter factor in MRC 5 fibroblasts by epithelial-derived cells: A model for scatter factor modulation
Authors: Kamalati Tahereh , Thirunavukarasu Birunthi , Wallace Andrew , Holder Nigel , Brooks Robert , Nakamura Toshikazu , Stoker Michael , Gherardi Ermanno , Buluwela Lakjaya 
Published: April 2021

ABSTRACT
Scatter factor/hepatocyte growth factor (SF/HGF) is a multifunctional cytokine produced by embryonic fibroblasts and other mesenchymal cells that affects the growth and/or the movement of certain epithelia. Here we report that expression of scatter factor activity by MRC 5 cells, a strain of normal human embryonic lung fibroblasts, is greatly reduced as a result of co-culture of these cells with SVK14, an SV40-transformed human kératinocyte cell line. Using a cDNA probe to the βchain of human HGF, we have found that the fall in SF activity in MRC 5/SVK14 co-cultures is accompanied by the loss of SF/HGF transcripts. As the inhibition of SF activity coincides with the disappearance of SF/HGF transcript, we conclude that inhibition of the SF activity expressed by MRC 5 cells by co-culture with SVK14 involves transcriptional regulation.
Transport of the cationic fluorochrome rhodamine 123 in an insect’s Malpighian tubule: indications of a reabsorptive function of the secondary cell type
Authors: Meulemans W. , Loof A. De 
Published: April 2021

ABSTRACT
The pathway of rhodamine 123 was examined after injection into Sarcophaga flies and after in vitro labeling of the Malpighian tubules. After in vitro labeling the primary cells only retained this potential-sensitive dye for a short period while all secondary cells accumulated the dye from the tubule lumen. In vivo the secondary cells also accumulated rhodamine 123 from the lumen, but the primary cells in the distal parts of all four tubules retained the dye for prolonged periods. This was most pronounced in the distal part of the anterior Malpighian tubules, where rhodamine 123 was eventually precipitated on the luminal concretions. Rhodamine 123 initially accumulated in the secondary cell mitochondria and eventually in intensely fluorescing vesicles, probably lysosomes. No evidence for endocytotic processes from the lumen was found using Lucifer Yellow CH, fluorescent dextrans and fluorescent albumin. Prior incubation with the ionophores valinomycin, nigericin, CCCP (all 1 μg/ml), dinitrophenol (1 mM) and NaN3 (10−2 M) inhibited the selective accumulation of rhodamine 123 to a large extent while monensin (1-5 μg/ml) showed little inhibitory effect. Furthermore, only cationic and no anionic or neutral dyes were accumulated by the secondary cells. In the fleshfly Calliphora and the fruitfly Drosophila, the dye rhodamine 123 also selectively accumulated in the secondary cells, as well in vitro as in vivo.