bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and differentiation of the Golgi apparatus and wall formation during carposporogenesis in the red alga, Gigartina teedii (Roth) Lamour
Authors: Tsekos Ioannes
Published: April 2021

The fine structure of the Golgi apparatus during development of carposporangia of Gigartina teedii has been studied. Dictyosomes in differentiating carposporangia undergo extraordinary changes in size and morphology.

Dictyosomes of gonimoblast cells and the auxiliary cell are composed of a stack of 5–7 straight cistemae and are approximately 0·18μm thick; from the structural and functional viewpoint, these are similar to dictyosomes in most other plants.

Hypertrophied Golgi cistemae with fibrillar contents occur in immature and nearly mature carposporangia. Secretory vesicles originate from the ends of cistemae and by complete vésiculation of terminal cistemae; vesicles with a diameter of 0·2–0·6 μm and fibrillar contents are abundant throughout the cytoplasm of immature and nearly mature carposporangia. Some vesicles secrete their contents into the carpospore wall. At this stage the dictyosomes are straight in profile and only some Golgi cistemae and Golgi vesicles show acid phosphatase activity.

Mucilage sacs appearing to be derived from either dilating endoplasmic reticulum or membraneous formations with a lysosomal character exist in both the mature gonimoblast cells and the immature carposporangia. These mucilage sacs constitute a considerable portion of the cytoplasmic volume and ultimately migrate to the outside of the cytoplasm. The mucilage sacs disappear completely in the mature carposporangia.

Throughout the development of the wall of immature and nearly mature carposporangia, multi-vesicular lomasome-like bodies, showing acid phosphatase activity, are released through the plasmalemma. Apart from any other possible activities, these bodies seem to contribute to the plasticity of the expanding cell wall.

The older carposporangia are recognized by having very active dictyosomes with a semicircular profile, producing vesicles with an electron-opaque centre (cored vesicles). These vesicles are likely to contain glycoproteins and to contribute to the formation of vacuoles with fibrous contents, as they are dominant in the carpospores before their liberation.

The dictyosomes of older carposporangia are composed of a polarized stack usually composed of 7 to 11 cistemae. They exhibit anomalous, densely staining, laminated mid-regions, which are formed due to close apposition of 6—7 adjacent cistemae from the forming face. The mid-regions of the rest of the cistemae towards the maturing face have large intercistemal spaces, which usually contain darkly staining small vesicles probably originating from the endoplasmic reticulum. The cistemae towards the maturing face contain dense granules.

Observations suggest that materials polymerize into fibrils within the Golgi system and the inflated Golgi-derived vesicles participate directly in the formation of the fibrillar network of the carpospore wall in the Gigartina teedii.
Immunological delineation in normal and malignant cells of a membrane protein involved in glucose transport: I. Preparation and properties of the antibody
Authors: Gingrich R. D. , Wouters M. , Bramwell M. E. , Harris H.
Published: April 2021

Partially purified preparations of the 200000 Mt membrane glycoprotein described by Bramwell & Harris were used as antigens to generate monoclonal antibodies. Whether the protein was prepared from human or mouse tumours, the mice immunized with it yielded monoclonal antibodies of broadly similar specificities. All the antibodies obtained were of the immunoglobulin M class, despite a prolonged immunization schedule, and recognized an antigen that was present on the surface of mouse, rat and human cells. One such antibody, M/27, was studied in detail. With the exception of 2 rat kidney cell lines, the antigen detected by M/27 was found on the surface of all cells grown in culture, whether malignant or not. However, in the mouse, the species in which the antibody was generated, M/27 discriminated sharply between malignant tumours and normal tissues excised directly from the animal. In normal adult or embryonic mouse tissues, whether they were composed of multiplying cells or not, the antigen detected by M/27 was present on the cell surface only at the lower limit of detection, if at all. Malignant mouse tumours grown in the animal produced large amounts of the antigen. Explantation of embryonic mouse fibroblasts induced the expression of the antigen, which was not detected on these same cells in their normal habitat in the growing embryo. Conversely, non-malignant cells that express the antigen in vitro cease to do so when they are re-introduced into the animal. The antigenic determinant appeared to be polypeptide in nature rather than polysaccharide.
A critical evaluation of Bernhard’s EDTA regressive staining technique for RNA
Authors: Pearson E. C. , Davies H. G.
Published: April 2021

The EDTA regressive staining procedure to detect RNA (Bernhard’s technique) is based on the proposition that after staining ultrathin sections with uranyl the stain is preferentially removed from DNA rather than RNA by the action of the chelating agent EDTA. Whilst attempting to use the EDTA regressive staining procedure to detect the presence of RNA in the large granule complexes of chicken erythrocyte nuclei, certain anomalous staining patterns were observed in the chromatin of these nuclei. Essentially, these were that the edges of condensed chromatin bodies stained positively for RNA even though this molecule is known not to be present there in significant quantities. The staining patterns suggested that chromatin was retaining its stain in a manner expected of RNA but not DNA as a consequence of EDTA-containing species failing to pass freely through the section. This hypothesis was tested by carrying out the EDTA procedure on embedded specimens of a DNA-containing virus, simian virus 40 (SV40), small enough not to be exposed at the surface of the section. In this way it has been shown that virus particles completely surrounded by resin destain so much more slowly than chromatin, which is accessible at the surface of the section, that without any other information it would be concluded that the viruses contained RNA, not DNA. This apparently anomalous result arises because the difficulties encountered by stain or EDTA molecules in passing through a plastic section were not appreciated at the time of the initial pubheation of the technique. The observations are discussed in the light of recent knowledge that has been gained on the kinetics of staining by measuring the electron-scattering densities of stained sections, similar measurements having been made on sections stained by Bernhard’s technique. A model for the mechanism of the EDTA regressive staining technique consistent with the experimental observations is proposed and the conditions under which Bernhard’s staining procedure retains its specificity are defined. Briefly, these conditions are that: the sections be stained for only a short period with uranyl before treating them with EDTA even though such brief staining is undesirable for quantitative measurements of stain uptake into biological material; andthat sections stained in lead only be compared as controls with sections stained by Bernhard’s technique so that any specificity of lead for sub-cellular components is not confused with a positive indication of the presence of RNA.

Unless these conditions are fulfilled, results obtained by the use of the regressive staining technique may be highly misleading.
Qualitative and quantitative differences in spreading of human fibroblasts on various protein coats. modulation by treatment of the cells with amines
Authors: Cassiman J. J. , Van Der Schueren B. , Van Leuven F. , Van Den Berghe H.
Published: April 2021

In contrast to established cell lines, normal human skin fibroblasts spread on their own fibronectin. The present investigation has examined whether human fibroblasts, like established cell lines, would be capable of spreading on substrata coated with proteins with different reactivity towards the cell surface. Coverslips were coated with human serum, fibronectin, α2macroglobulin–trypsin, a polyspecific anti-fibroblast antibody and a polyspecific anti-calfserum antibody. The attachment of the cells to these substrata was of the same extent. Spreading was examined qualitatively using phase, interference contrast and reflection contrast optics on live cells, as well as scanning electron microscopy on fixed cells. To quantitate the maximum degree of cell spreading a semi-automated system was used, which measured the cell perimeter on a large number of cells. The distributions of the degree of cell spreading on the five substrata were compared statistically. The qualitative and quantitative differences observed on the various substrata could be further differentiated by adding various amines to the cells during 60 min spreading or during a 30 min preincubation before spreading. No strict correlation could be found between the effect of the amines on attachment or on spreading and their presumed effects on cellular transglutaminases. The results clearly indicate that the spreading of human fibroblasts can be modulated by the nature of the substratum and that, by using quantitative methods, these differences in behaviour can be measured accurately.
Alveolar sacs of Tetrahymena: ultrastructural characteristics and similarities to subsurface cisterns of muscle and nerve
Authors: Satir Birgit H. , Wissig S. L.
Published: April 2021

The ultrastructure of the layer of alveolar sacs of Tetrahymena thermophila and its relationship with the plasma membrane were examined in thin sections and freeze-fracture replicas.

In thin sections, the plasma membrane and outer alveolar membrane are seen to parallel each other closely and are linked by struts 9 nm wide spaced at 9 nm intervals. The plasma and alveolar membranes have different ultrastructural characteristics. The unit-membrane structure of the plasma membrane is asymmetric and thicker than that of the alveolar membrane. The unit-membrane structure of the alveolar membrane is symmetric. The lateral borders of adjacent alveolar sacs are closely apposed and flattened against one another, forming alveolar sutures. The pellicle at the cell surface, consisting of the plasma membrane, the alveolar sacs and the underlying epiplasm, overlies a single layer of mitochondria and a single layer of flattened cisterns of rough-surfaced endoplasmic reticulum (RER).

Examination of freeze-fracture replicas reveals that the plasma membrane and the inner and outer alveolar membranes each have a unique population of unit-membrane particles. This suggests that they are separate membrane domains. The appearance of alveolar sutures, i.e. the apposed lateral borders of adjacent alveolar sacs, suggests that the alveolar membranes in this region are more rigid than elsewhere and may be sealed together by an adhesive substance. Interruptions in the sutures are interpreted as indicating that adjacent alveolar sacs are connected by small isthmuses or channels, confirming earlier reports that alveolar sacs are large chambers within a continuous, interconnected system.

Alveolar sacs, in their relationship with the plasma membrane, closely resemble the subsurface cisterns of nerve and muscle cells. In muscle cells, the cisterns participate in the regulation of the cytoplasmic calcium ion concentration that controls contraction of myofilaments. Several functions of the surface of Tetrahymena, e.g. secretion of mucocysts and ciliary motility, are believed to be calcium-dependent, and the alveolar sacs may play a role in mechanisms that control the concentration of this divalent cation in localized regions along the cell surface.

The alveolar sacs contain laminated inclusion bodies that appear to be rich in phospholipid. The inclusion bodies may represent reserves of phospholipid material stored in preparation for membrane formation.
Effect of tubulin-binding agents on the infiltration of tumour cells into primary hepatocyte cultures
Authors: Roos Ed , Van de Pavert Ilja V.
Published: April 2021

The influence of tubulin-binding agents on the infiltration of murine MB6A lymphosarcoma and TA3 mammary carcinoma cells into primary rat hepatocyte cultures was studied. Colchicin, nocodazole and vinblastin reduced the number of infiltrating lymphosarcoma cells, probably by interfering with the adhesion of these cells to the exposed hepatocyte surface. However, the subsequent infiltration of cells that did adhere was not affected or even slightly stimulated. The reduced adhesion appears to be due to an effect on both the MB6A cells and the hepatocytes.

In contrast, adhesion of TA3 cells was not reduced and infiltration was markedly enhanced by these agents, due to an effect on the TA3 cells but probably not on the hepatocytes.

These observations support previously described morphological evidence for differences between the infiltration mechanisms of the two tumour cell types. It is concluded that the system within the hepatocytes involved in adhesiveness of the exposed surface to MB6A cells is distinct from that mediating other types of adhesion. The tendency of TA3 cells to invaginate hepatocytes may be due to disturbances in tubulin-dependent processes.
A re-evaluation of the relationships between the fibrillar centres and the nucleolus-organizing regions in reticulated nucleoli: ultrastructural organization, number and distribution of the fibrillar centres in the nucleolus of the mouse sertoli cell
Authors: Mirre C. , Knibiehler B.
Published: April 2021

In mouse testis, the diploid Sertoli cell displays one large nucleolus flanked symmetrically by two heterochromatic masses. The hybridization in situ with [3H]rRNA confirmed that the ribosomal cistrons are localized within the central nucleolar mass. At the ultrastructural level this nucleolar mass appears to be reticulated and contains numerous fibrillar centres. These fibrillar centres are surrounded and interconnected by an electron-opaque fibrillar network, which constitutes the reticulated nucleolonema of the nucleolus. Ag-NOR staining reveals the presence of the argyrophilic proteins associated with active nucleolus-organizing regions (NORs) within both the fibrillar centres and the electron-opaque fibrillar component. Autoradiographic studies after [‘H]uridine incorporation show that ribosomal DNA transcription only takes place in this dense fibrillar component. Three-dimensional reconstruction of four Sertoli cell nucleoli after serial sectioning reveals that the size and number of the fibrillar centres are very variable from one cell to another (26, 35, 38 and 41 fibrillar centres). The analysis of the volume occupied by the fibrillar centres as compared to the whole nucleolar volume demonstrates that the larger the nucleolus, the more fibrillar centres it contains, but also the more numerous the fibrillar centres, the larger their total volume. While in each case the number of the NORs is virtually the same, i.e. ten.

In the light of these results we concluded that, at least in reticulated nucleoli, there is no numerical relationship between the number of fibrillar centres and the number of NORs, and that the fibrillar centres cannot be considered only as the nucleolar counterparts of the NORs. Moreover, the increasing number of fibrillar centres from the smallest nucleolus to the largest one is difficult to explain by the previously postulated hypothesis of a reserve of inactive rDNA packaged in the fibrillar centres. These data led us to reconsider the role of the fibrillar centres in the transcriptional activity of reticulated nucleoli.
Structural changes in dividing sea-urchin eggs induced by the volatile anaesthetic halothane
Authors: Hinkley Robert E. , Chambers Edward L.
Published: April 2021

Fertilized Lytechinus eggs exposed to the volatile anaesthetic halothane before metaphase do not undergo cytoplasmic cleavage. This effect has been correlated with the failure of the contractile ring to assemble. Comparative studies on mitotic apparatuses isolated from control and halothane-treated cells show that halothane significantly impairs both spindle and aster growth as early as metaphase. When transferred to control solutions, halothane-treated cells initiate furrowing activity in association with either the first or second mitotic division, depending on the duration of the exposure to anaesthetic and the concentration employed. In contrast to these effects, halothane has no effect on any aspect of the cleavage process if applied later than metaphase. In this case, furrows develop even in the presence of halothane, deepen progressively, and complete cell division. These observations confirm and extend previous studies on echinoderm eggs exposed to volatile anaesthetics, and support the view that anaesthetic agents indirectly prevent cell cleavage by inhibiting the growth of the mitotic apparatus.
Electron microscopy and x-ray microanalysis of calcium-binding sites on the plasma membrane of Beroe giant smooth muscle fibre
Authors: Nicaise G. , Hernandez-Nicaise M. L. , Malaval L.
Published: April 2021

When they are fixed with glutaraldehyde in the presence of calcium ions, the plasma membranes of Beroe giant smooth muscle fibres display micropapillae filled with an electron-dense deposit. After freeze-fracturing of fixed tissue, the micropapillae are still present, therefore their shape and size are determined during or before glutaraldehyde fixation, and are not due to rearrangement during subsequent steps of tissue processing; intramembranous particles are seen at the periphery rather than at the top of micropapillae. In conventional stained sections, the surface of most micropapillae is surrounded by fine fibrils; when the fuzzy coat is separated from the muscle cell by a clear space, this fibrillar material becomes conspicuous and links the micropapillae to the coat. After calcium-free (EGTA) fixation, the plasma membrane is completely free of electron-dense sites but ‘empty’ micropapillae can be seen. X-ray microanalysis of single electron-dense deposits by wavelength-dispersive spectrometry reveals a high calcium content. A weak osmiophily is suspected, but does not seem to interfere with this analysis of calcium. The highest peak-to-background ratios for calcium were obtained using the smallest aperture of the Wehnelt of the analytical microscope.

In the Discussion, the micropapillae are compared to similar structures described by other authors in a variety of cell types.
The accessibility of certain proteins on embryonic chick neural retina cells to iodination and tryptic removal is altered by calcium
Authors: Cook James H. , Lilien Jack
Published: April 2021

We have used cell-surface-specific labelling techniques and two-dimensional gel electrophoresis to identify proteins on embryonic chick neural retina cells and to determine the effects of Ca2+ on their accessibility to labelling and tryptic removal. A number of proteins on these cells are, in the presence of Ca2+, relatively inaccessible to iodination and/or tryptic removal. Of these, a glycoprotein of M, approx. 130 × 103, with a pl of approx. 4·8, is the major cellsurface-iodinatable species that is retained during trypsinization in the presence of Ca2+. The removal of Ca2+ renders this glycoprotein much more accessible to both procedures. Its accessibility to these probes decreases on re-addition of Ca2+. The accessibility of its oligosaccharide moiety to galactose oxidase is, however, unaltered by the removal of Ca2+. These characteristics, together with immunological data presented elsewhere suggest that this glycoprotein may be a component of the Ca2+-dependent adhesive system that can be demonstrated on these cells.
Proplastid dna synthesis at pachytene in pollen mother cells of Lilium henryi
Authors: Smyth D. R.
Published: April 2021

About three-quarters of the DNA synthesis occurring in pachytene pollen mother cells of Lilium henryi takes place in proplastids. Only around 15 % can be attributed to mitochondrial labelling and 10% to nuclear DNA synthesis. Label was identified in the proplastid genome by its location in electron microscopic autoradiographs, by its buoyant density (1·698 g/ml), and by its specific hybridization to chloroplast DNA sequences from spinach. Proplastids, while apparently not dividing at pachytene, may be replicating their DNA in readiness for subsequent proliferation in developing microspores. The annealing properties of plastid DNA closely parallel those of labelled pachytene DNA sequences implicated in meiotic exchange events.
A survey of dna repair incision activities after ultraviolet irradiation of a range of human, hamster, and hamster-human hybrid cell lines
Authors: Collins Andrew , Jones Carol , Waldren Charles
Published: April 2021

We describe a rapid and simple assay for DNA damage and repair in mammalian cells, based on the partial unwinding of nicked DNA in alkali, and involving transfer of this DNA to nitrocellulose and the digestion of single-stranded DNA with S, nuclease, all steps taking place on tissue-culture chamber slides. Direct breakage of DNA by ionizing radiation has been examined, and we have developed a standard procedure for measuring enzymic breakage of DNA as an index of excision-repair capacity following ultraviolet irradiation.

We report a wide range of repair capacities among various hamster and human cell lines, with considerable overlap between the two species. Hybrids between hamster and human cells tend to display repair activity characteristic of the hamster parent.
Nuclear transplant studies on the reduction in numbers of presumptive germ nuclei in excon jugants of Paramecium caudatum
Authors: Mikami Kazuyuki
Published: April 2021

Nuclear differentiation in exconjugants of Paramecium caudatum is closely associated with a brief localization of the postzygotic nuclei near the opposite ends of the cell, with the germinal nucleus (micronucleus) in the anterior region and the somatic nuclei (macronuclei) in the posterior region. The posterior nuclei cannot regenerate to produce micronuclei when all four anterior nuclei are removed. There is no difference among the anterior four presumptive micronuclei, because, when any three of them were removed, the remaining nucleus was able to divide at each postconjugational fission and to persist as a micronucleus during the vegetative phase. This conclusion agrees with the results of transplanting a presumptive micronucleus into a vegetative cell. Cells during the vegetative phase, however, normally have only one micronucleus. Micronuclear number must be reduced to arrive at the uni-micronucleate condition after the stage of macro- and micronuclear differentiation. Elimination of supernumerary presumptive micronuclei, which had been indicated by morphological observations, was confirmed by the results of nuclear transplantation studies.
Infiltration of lymphosarcoma cells into hepatocyte cultures: inhibition by univalent antibodies against liver plasma membranes and lymphosarcoma cells
Authors: Middelkoop Otto P. , Roos Ed , Pavert Ilja V. Van De
Published: April 2021

The number of murine MB6A lymphosarcoma cells that infiltrated rat hepatocyte cultures was found to be diminished after treatment of the lymphosarcoma cells with univalent antibodies raised against these tumour cells (anti-MB6A Fab), and also after treatment of the hepatocyte cultures with univalent antibodies directed against rat liver plasma membranes (anti-LPM Fab).

The inhibition of infiltration by anti-MB6A Fab and an anti-LPM Fab raised against sinusoidal face-enriched membranes could be entirely attributed to their interference with adhesion of MB6A cells to the exposed surface of the hepatocytes, because infiltration of the adherent cells was not inhibited. Anti-LPM Fab raised against contiguous face-containing LPM, on the other hand, inhibited the adhesion to the exposed surface and the subsequent infiltration of adherent cells. These observations suggest that specific membrane constituents of both MB6A cells and hepatocytes take part in liver infiltration, and that there may be two different hepatocyte components involved, one mediating adhesion to the exposed surface and the other taking part in the infiltration process proper.
Unrelated surface control of commitment to growth and attachment in isolated adult rat hepatocytes
Authors: Blanquet P. R.
Published: April 2021

The relation between surface glycoconjugate molecules involved in the control of commitment to growth and attachment was investigated in adult Wistar rat hepatocytes in primary culture. On the one hand, the approach has been to analyse the binding of 3H-labelled con-canavalin A ([3H]Con A) to cell surfaces when these two cellular phemona were in turn modulated. The replacement of calf serum (CS) by foetal calf serum (FCS) in culture medium greatly enhanced cell attachment, its effect being about the same as that of FCS adsorbed to glass culture plates, but this change did not significantly affect the growth-stimulatory process. In contrast 2 or 3 μM-cytochalasin D (CD), which is known to act specifically on the inner face of the cell membrane, reversibly decreased the [*H]thymidine (dThd) incorporation in both CS-containing and FCS-containing media, but had only a very moderate effect on cell attachment. The reversible effect of the drug, 100, was followed by PH]leucine incorporation, as well as by measuring the [‘H]dThd incorporation in media with CD plus insulin and glucagon. Hepatocytes were assayed for binding either in buffered solution (at 4 or 37 °C) or in serum-containing media (at 37 °C). The Hill coefficients were calculated to be near 2·2 and 1·9, respectively for CS-stimulated and FCS-stimulated cells, and around 1·6 for CD-treated and glutaraldehyde-fixed cells. We interpret these results as showing that two different types of surface components might be involved in the control of commitment to growth and attachment. On the other hand, evidence was presented to indicate that these components really bind Con A. First, Con A treatment in buffered solution of cells previously attached in the presence of CS or FCS resulted in a progressive inhibition of EGTA-mediated cell detachment from substrata. Secondly, Con A reversibly decreased [3H]dThd incorporation in both CS-containing and FCS-containing media through a specific interaction with the cell surface. We conclude that entrance into S phase and attachment to serum protein substrata are unrelated phenomena in isolated adult rat hepatocytes and seem to be regulated by two species of surface glycoconjugateβ.
Cell-substrate contacts in cultured chick embryonic cells: an interference reflection study
Authors: Ireland Grenham W. , Stern Claudio D.
Published: April 2021

Cell-substrate contacts in explants of different regions of early chick tissues were investigated using the technique of interference reflection microscopy. All the explants spread as epithelial sheets. During initial spreading a peripheral zone of 2–3 cells formed broad contacts with the substrate. In spread explants some cells in the centre made broad substrate contacts. A mat of extracellular material containing fibronectin was found under the explants. Focal contacts and focal adhesions increased in number during culture, and stress fibres were associated with them. These changes in cell contacts appeared more quickly in some tissues than in others. After 24 h, explants of hypoblast and definitive endoblast could easily be distinguished but by 7 days they were very similar. In the absence of serum, specialized cell contacts developed more quickly; in higher concentrations of serum, more slowly. Confrontations between explants were also examined. The most conspicuous feature was that cells in invading explants normally underlapped invaded cells. Invasion from above by an unspread explant could occur even if the invaded explant had formed many focal adhesions.
Attachment of Paramecium to polystyrene surfaces: A model system for the analysis of sexual cell recognition and nuclear activation
Authors: Kitamura Akio
Published: April 2021

In the ciliate Paramecium caudatum, only mating-reactive cells can attach to the polystyrene surface of Petri dishes. The attachment of mating-reactive cells occurs exclusively at the tips of ventrally located cilia (mating-reactive cilia) and appears to involve a hydrophobic interaction. An increase in the hydrophilic nature of the polystyrene surface following treatment with sulphuric acid results in the loss of attachment of reactive cells. The presence or absence of Ca ions and varying the ionic strength of the medium have no effect upon attachment. Although attachment reactivity is closely correlated with mating reactivity, the attachment sites appear distinct from the mating recognition sites, as suggested by the following experimental results: (1) cells that lose mating reactivity following treatment with trypsin are still able to attach to the polystyrene surface; (2) the attachment of cells appears temperaturedependent over a range where mating reactivity remains uneffected; (3) mating reactivity is quickly lost as a result of attachment to the surface of the dish. While the mechanism of attachment is not the same as sexual recognition, the attachment to the polystyrene surface initiates the early stages of the conjugation process. Cells that attach show micronuclear migration while unattached cells do not. The maximum rate of micronuclear migration occurs approximately 30 min after attachment. Meiosis does not occur following migration in the attached cells as in cells that are sexually mating. The relationship between the mating substance and the attachment substance is discussed, while the utilization of the attachment phenomenon for other experimental procedures is proposed.
A cell spreading factor, abundant in human placenta, contains fibronectin and fibrinogen
Authors: Aplin J. D. , Foden L. J.
Published: April 2021

A salt extract from human normal-term placental extracellular matrix contains material that rapidly adsorbs to glass or tissue-culture plastic and promotes the spreading of fibroblastic and epithelioid cell lines. The cellular response to placental spreading factor (PSF) is characterized and compared with the response to fibronectin. The active component is shown to contain antigenic determinants that cross-react with antibodies to fibronectin and fibrinogen. The activity is not retained on gelatin-Sepharose but another component of the extract (∼ 185000 molecular weight) is retained. Partial purification is reported, and the possible involvement of PSF in trophoblastic invasion of the uterine wall is discussed.
Nucleolar fibrillar centres in plant meristematic cells: Ultrastructure, cytochemistry and autoradiography*
Authors: Risueño M. C. , Medina F. J. , Díaz De La Espina S. Moreno
Published: April 2021

In plant cells nucleolar fibrillar centres (FCs) undergo ultrastructural changes, depending on the nucleolar activity. We have found two types of FC structure in nucleoli with either high or low activity, to which we have given the conventional names of homogeneous and heterogeneous, respectively. The first type is characterized by the presence of fibres that we describe structurally and cytochemically as decondensed chromatin; the second type, in addition to these fibres, contains a variable number of dense cores made up of condensed chromatin. Moreover, RNA does not appear to be present in FCs, while proteins are a major component.

Autoradiography after tritiated uridine incorporation shows that FCs are not the site of transcription, but that this takes place in the fibrillar component; the same result is obtained using the lead acetate fixation technique for detecting orthophosphate ions. This fact leads us to think that FCs are not the whole interphasic counterpart of the mitotic nucleolar organizing region (NOR), as stated by other authors, but only the portion of the NOR that is temporarily inactive in transcription; the transcriptionally active part of the NOR is in the fibrillar component, bound to its earliest product of transcription. Thus, FCs and the fibrillar component constitute a functional unit.
Ultrastructural studies in the rhodophyta: I. Development of mitotic spindle poles inApoglossum ruscifolium, kylin
Authors: Dave A. J. , Godward M. B. E.
Published: April 2021

The ultrastructure of somatic mitosis in the germlings of Apoglosrum ruscifolium, Kylin, fixed from its natural habitat, was examined to investigate spindle-pole development and the role of the ‘polar ring’. It was found that the polar ring originates from a special nuclear pore raised above a small projection of the nuclear envelope. The initiation of mitotic polarity takes the form of changes in the nuclear envelope. These are: close crowding of pores, heavy deposition of electron-opaque material and attachment of microtubules. No such phenomena are to be observed in the equatorial regions of the nuclear envelope, which persists throughout mitosis. The next stage is the development of ‘clear zones’, which become filled with microtubules excluding all other structures, notably ribosomes, at both poles. At pre-metaphase, microtubules begin to be extended from the clear zones through polar fenestrae in the nuclear envelope into the nucleus itself. With subsequent development of the intranuclear spindle, the microtubules in the clear zones show signs of degeneration. At metaphase, the polar regions of the nuclear envelope begin to return to their normal conditon. After metaphase, the polar rings degenerate. Thus it is primarily the nuclear envelope, via its polar modifications, which begins the organization of the mitotic spindle.

The capabilities of nuclear pores are summarized. In the Discussion, the polar rings are compared with procentrioles; since they appear to have a passive role in spindle-pole organization, it is suggested that they may represent an evolutionary stage prior to the procentriole. The origin of the centriole ultimately from a nuclear pore is presented as an hypothesis. It is concluded to be unlikely that the polar ring is a degenerate centriole, and therefore it is proposed that the red algae never had centrioles in the course of their evolution. Thus the view of the non-flagellate ancestry of the red algae is supported.
Neutrophil granulocytes: adhesion and locomotion on collagen substrata and in collagen matrices
Authors: Brown A. F.
Published: April 2021

Neutrophil granulocytes (PMNs) adhere poorly to and are unable to locomote on collagen-coated glass; they are able to attach to and invade three-dimensional matrices of collagen fibres. Invasion is largely independent of adhesion to the fibres, does not occur by proteolysis of the gel, and is not affected by the presence of fibronectin or chondroitin sulphate. Invasion is reduced by increasing the concentration of collagen in the gel or by the presence of hyaluronic acid. It is proposed that in both these situations there is physical obstruction of PMN movement. The ability to locomote through tissues of very variable properties in vivo is important in the role of the PMN in inflammation.
Cytoskeleton and pericellular matrix organization of pure adult human keratinocytes cultured from suction-blister roof epidermis
Authors: Kariniemi A.-L. , Lehto V.-P. , Vartio T. , Virtanen I.
Published: April 2021

Pure adult human kératinocyte cultures were raised from suction-blister roof epidermis and cultured in MCDB-151 medium. In primary culture the epidermal cells rapidly adhered, spread and began to proliferate on collagen-coated growth substrata but not on uncoated plastic or glass substrata. A fibrillar keratin-specific fluorescence, showing a typical cell-cell arrangement, was seen in all cells in indirect immunofluorescence microscopy, whereas only some cells also showed vimentin-specific staining. A fine fibrillar fibronectin-specific surface staining was seen at the margin of attaching cells and in marginal cells of spreading cell islands, whereas no fluorescence could be seen in epidermal cells, with antibodies against type IV collagen or laminin. Interestingly, the marginal cells also showed intracellular fibronectin. The synthesis of fibronectin in epidermal cell cultures could also be revealed by metabolic labelling experiments with [35S]methionine.

In contrast to primary cultures, subcultivated kératinocytes also adhered to uncoated plastic and glass substrata. After subcultivation, keratin and surface fibronectin distribution remained unaltered but after some subcultivations, most of the cells also showed fibrillar vimentin and expressed fibronectin intracellularly.

The results show that the suction-blister method provides an easy way to obtain pure epidermal cell cultures without contaminating mesenchymal cells. Our results also suggest a direct role for fibronectin but not for collagen type IV or laminin in adhesion and spreading of epidermal cells in vitro.
Isolation and electrophoretic characterization of the plasma membrane of sea-urchin sperm
Authors: Cross Nicholas L.
Published: April 2021

A subcellular fraction containing plasma membranes was isolated from flagella of the sperm of Strongylocentrotus purpuratus by differential centrifugation, and analysed by sodium dodecyl sulphate/polyacrylamide gel electrophoresis. Coomassie Blue staining revealed nine major bands and 14 minor species. Five bands of apparent molecular weights ∼200 × 103, 149 × 103, 120 × 103, 75 × 103 and 59× 103 also stained with periodic acid-Schiffs reagent and so are probably glycoproteins. These five components are externally exposed, as determined by lactoperoxidase-catalysed radio-iodination. Isolation of membranes from radio-iodinated sperm results in an enrichment of about tenfold in the specific activity of 125I. Comparison of the electrophoretic patterns of labelled sperm and of the membranes isolated from 125I-labelled sperm suggests that no major labelled proteins are lost during the isolation procedure, and so to this extent the membrane fraction is representative of the entire sperm plasma membrane.
Plasma membranes, cell junctions and cuticle of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea
Authors: Kukulies J. , Komnick H.
Published: April 2021

The cell membranes and cell junctions of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea were examined in thin sections and by freeze-fracture. These epithelia function in active ion absorption and maintain a high concentration gradient between the haemolymph and the fresh-water environment. Freeze-fracturing reveals fine-structural differences in the intramembraneous particles of the luminal and contraluminal plasma membranes of these epithelia, reflecting the functional diversity of the two membranes, which are separated by the junctional complex. The particle frequency of the basolateral plasma membranes is reduced after transfer of the larvae into high concentrations of environmental salinity.

The junctional complex is located in the apical region and composed of three types of cell junctions: the zonula adhaerens, seen in freeze-fracture as a nearly particle-free zone; the extended and highly convoluted pleated septate junction and randomly interspersed gap junctions of the inverted type. Gap junctions also occur between the basolateral plasma membranes. They provide short-cuts in the diffusion pathway for direct and rapid co-ordination of the interconnected cell processes.

Colloidal and ionic lanthanum tracer solutions applied in vivo from the luminal side penetrate through the cuticle via epicuticular depressions, but invade only the apical portion of the junctional complex. This indicates that the pleated septate junction constitutes a structural control of the paracellular pathway across the chloride epithelia, which are devoid of tight junctions. The structure of the pleated septate junctions is interpreted as a device for the extension of the diffusion distance, which is inversely related to the net diffusion. A conservative estimate of the total length of the junction, and the number and extension of septa reveals that the paracellular route exceeds the transcellular route by a factor of 50.
Rate of cell cycle initiation of yeast cells when cell size is not a rate-determining factor
Authors: Lord P. G. , Wheals A. E.
Published: April 2021

The control of cell proliferation under steady-state conditions in the budding yeast, Saccharomyces cerevisiae, is well described by either the tandem or sloppy size control models, both of which suggest that differences in cycle time between individual cells or between parents and daughters is largely due to differences in birth size. These models have been investigated further under conditions in which cell size has not been a rate-determining factor for cell cycle initiation. Two approaches have been used. The first involves the growth of cells in low concentrations of hydroxyurea (HU), which has the effect of prolonging the duration of DNA synthesis. This leads to a lengthening of the budded period, which in turn leads to daughter cells being larger at division than the normal cell cycle initiation size of daughters in steady-state populations. The second approach involves the accumulation of cells at the key control point of the cycle, called start, using the pheromone α-factor. Since growth is unaffected, all cells eventually become larger than the volume at which they would normally initiate the cell cycle. The kinetics of proliferation were followed after release from α-factor arrest. The results from both approaches were broadly consistent with the predictions of both models. However, abolition of birth-size differences between parents and daughters in the presence of HU did not lead to a complete disappearance of differences in either cycle time or proliferation kinetics. Furthermore, following release from α-factor arrest, the rate of cell cycle initiation of parent cells was slower than in steady-state culture and the daughters’ cells behaved as if comprising two separate populations. These discrepancies suggest that besides a size difference, there are additional physiological differences between parent and daughter cells.
Organization and development of the macronuclear anlage in Stylonychia Notophora stokes
Authors: Sapra G. R. , Dass C. M. S.
Published: April 2021

The development of the macronuclear Anlage of Stylonychia notophora was studied by means of cytochemical and autoradiographic techniques. In early stages of its differentiation, the Anlage has its chromatin distributed homogeneously. Nine to ten hours later chromosomes are noticed; the nucleus is possibly diploid. Following this, the number of chromosomes increases progressively resulting in polyploidy. Later, chromosomes uncoil and polytenization follows. After consolidation and shrinkage of these chromosomes, the Anlage splits into two bodies. Five series of replication bands quickly pass through each and the vegetative macronucleus results.

Synthesis of RNA by the new macronucleus starts soon after the shrinkage stage. The old macronuclei break up into small spherical bodies which are gradually resorbed in the cytoplasm.

When [3H]thymidine is provided continuously to the exconjugants, there is little uptake into the Anlage until the old macronucleus is completely resorbed. Only after this, heavy labelling is noticed. Fate of the previously labelled macronuclei during conjugation shows that their breakdown products are re-utilized for the development of the new macronucleus.
Morphogenesis of a large micro tubular organelle and its association with basal bodies in the ciliate Nassula
Authors: Tucker J. B.
Published: April 2021

The cytopharyngeal basket in Nassula consists largely of microtubules. During binary fission the old basket is resorbed and simultaneously two new baskets develop. Changes in basket structure occurring dunng basket development and resorption, and variations in the lengths of baskets during the interfission period have been examined using phase-contrast and electron microscopy. These examinations indicate the manner in which several different processes influence the shapes, sizes, positions, and numbers of the various basket components.

Early in development some of the microtubular basket components contact certain basal bodies from which they subsequently detach, and then, while most of them assemble into the positions they occupy in the mature organelle, they are temporarily associated with a reticulum of microtubules. Several of these components are not included in a new basket and some of them are resorbed; development of the others continues and they establish microtubular connexions to basal bodies different from those to which they were previously attached. Other basket components commence development after assembly of the microtubular components and form in contact with them, even if they have not been included in a new basket. The majority of microtubules apparently lengthen by accumulating material exclusively at one of their extremities Baskets of starving organisms gradually shorten by loss of material from their bottoms but lengthen again when the organisms feed The bulk of an old basket is not enclosed in a vacuole when it is resorbed; breakdown of tubules progresses from their extremities after loss of intertubular cross-connexions
Freeze-etch studies on fish skeletal muscle
Authors: Bertaud W. S. , Rayns D. G. , Simpson F. O.
Published: April 2021

The results of a freeze-etch study of skeletal muscle cells of a fish, the Black Molhe (Mol lienesta sp), correlated well with published descriptions of sectioned material. The arrays of apertures of the T-tubules at the cell surface were clearly demonstrated. Numerous vesicles, communicating with the extracellular space, were also seen at the cell surface. The relation ship of the T-tubules with the adjoining sarcotubular cisternae was studied; in transverse fractures at Z-levels there was a tendency for pieces of T-tubule to adhere to the cisternae No scalloping of the sarcotubular membrane was noted where it apposed the T-tubule, but some ridges on its luminal surface were demonstrated at these regions; elsewhere the luminal surface of the sarcotubular membrane was densely covered with particles. In the myofibrils, a reversal of polarity of the structure of the thick filaments was suggested at the M-line.
Calcium and microtubule sliding in ciliary axonemes isolated from Paramecium caudatum
Authors: Mogami Yoshihiro , Takahashi Keiichi
Published: April 2021

Microtubule sliding was induced in axonemes obtained from isolated cilia of Paramecium caudatum when they were exposed to a reactivating solution containing ATP after mild treatment with trypsin. Over a very wide range of concentrations (lnM-4mM), Ca2+ in the reactivating solution had no effect on the proportion of axonemes that disintegrated as the result of microtubule sliding. Also, the velocity of sliding, determined by cinematography, and the polarity of the direction of sliding-force generation, determined by electron microscopy with regards to the base-to-tip axis of the cilium, were not affected by Ca2+. The results indicate that the Ca sensitivity, which is responsible for the ciliary reversal response, was removed from the axoneme, possibly as the result of trypsin treatment. It is thus unlikely that Ca sensitivity is attributable to the basic sliding machinery that powers ciliary movement.
Aequorin measurements of free calcium in single mammalian cells
Authors: Cobbold Peter H. , Cuthbertson K. S. Roy , Goyns Malcolm H. , Rice Veronica
Published: April 2021

The calcium-triggered photoprotein aequorin has been used as a sensitive indicator of cytoplasmic free calcium in cells of relatively large size. We describe here several novel modifications to the technique that make it possible to detect resting levels of free calcium in single mammalian oocytes, fibroblasts and granulosa cells. Concentrations of free calcium as low as 1 × 10−7M have been measured in single fibroblasts, corresponding to a detection limit of 10−18mol.