bluuebunny/crossref_metadata_2025 huggingface dataset:
Monoclonal antibodies against a nucleolar protein from differentiating chick muscle cells
Authors: Morris G. E. , Man Nguyen Thi , Head L. P.
Published: April 2021

Two monoclonal antibodies, NORM and NORA, bind specifically to a 37 000 molecular weight protein in total protein extracts of chick skeletal muscle cell cultures. They have been used to follow changes in the amount and distribution of this protein during terminal differentiation and the associated cessation of cell division.

Immunofluorescence microscopy shows that the antigen is found almost exclusively in the nucleolus in interphase cells and is dispersed in the cytoplasm during mitosis. Low doses of actinomycin D cause segregation of nucleoli into DNA fibrils and ribonucleoprotein granules, and the antigen is clearly associated with the latter. High doses of actinomycin D cause shrinkage of the nucleolus and the antigen is dispersed within the nucleoplasm, but not released into the cytoplasm. The amount and distribution of antigen is similar in all cell types (myoblasts, myotubes and fibroblasts) and there are no major changes during muscle differentiation.

From known changes in ribosomal RNA metabolism during myogenesis and after actinomycin D treatment, we suggest that the 37 000 Mr protein is involved in some post-transcriptional aspect of ribosome production and that its concentration and distribution may be related to the concentration of ribosomal RNA in the nucleolus.
Isolation and characterization of alkaline phosphatase-containing granules (phosphasomes) from human polymorphonuclear leucocytes
Authors: Smith Gillian P. , Sharp Gaynor , Peters Timothy J.
Published: April 2021

Human polymorphonuclear leucocytes were homogenized in isotonic sucrose and subjected to analytical subcellular fractionation by centrifugation on a discontinuous sucrose density gradient to produce a phosphasome-enriched fraction, contaminated primarily by plasma membrane. Experiments to separate these membrane fractions by centrifugation on gradients of Nycodenz or Percoll, or by toroidal coil counter current chromatography, were unsuccessful.

Fractionation carried out on neutrophils previously suspended in isotonic sucrose containing a low concentration of digitonin resulted in the preparation of a highly purified phosphasome fraction, free of plasma membrane components. Electron-microscope cytochemistry of the purified fraction identified the phosphasomes as regular and irregular-shaped spheres and rods, the alkaline phosphatase being associated with the inner aspect of the vesicle membrane. These granule structures were very similar to phosphasomes observed in intact neutrophils. A proportion of the endoplasmic reticulum and Golgi membrane marker enzymes remained associated with the phosphasomes throughout the separation procedures.
Shape-dependent regulation of cytoskeletal protein synthesis in anchorage-dependent and anchorage-independent cells
Authors: Reiter Theresa , Penman Sheldon , Capco David G.
Published: April 2021

We examine changes in protein synthesis that accompany suspension (i.e, shape alteration) of anchorage-dependent and anchorage-independent cells using a newly developed cell fractionation procedure based on detergent extraction. Using this procedure, a cell can be divided into four distinct and independent fractions: soluble, cytoskeleton, chromatin and nuclear matrix– intermediate filament. This fractionation procedure is used to investigate protein synthetic events associated with the release from anchorage-dependent growth, characteristic of transformed cells. Suspension results in several unexpected events in both anchorage-dependent (3T3) cells and anchorage-independent (SVPy 3T3) cells. Suspension of 3T3 cells results in a reduction of total protein synthesis; however, two proteins are enhanced in their amount of synthesis. Suspension of SVPy 3T3 results in about 20 proteins proceeding through short and long-term alterations in the rate of synthesis. The synthesis of some of these proteins is inhibited, others undergo a transient decrease in synthesis upon suspension and then increase above their rate in the anchored state, while the synthesis of others steadily increases after suspension. Suspension of anchorage-dependent cells results in a fraction specific shift in the rates of protein synthesis. Possible roles for these fraction-specific proteins are considered.
Immunocytochemical identification of cytotrophoblast from other mononuclear cell populations isolated from first-trimester human chorionic villi
Authors: Butterworth Bridget H. , Loke Y. W.
Published: April 2021

Trophoblast biologists are often uncertain as to what cell types they are investigating because the mononuclear cell populations prepared from trypsinization of human first-trimester chorionic villi are morphologically very similar. In the present study, immunocytochemical and phagocytic markers have been used to distinguish cytotrophoblast populations from cell types derived from the mesenchyme of the chorionic villus.

Two anti-trophoblast monoclonal antibodies generated in our own laboratory (18B/A5 and 18A/C4) were found to be very efficient in identifying cytotrophoblast, which made up 35–40% of the cells in a smear. Most cytotrophoblast cells did not stain with a monoclonal anti-HLA-A,B,C antibody but a few cells (5 %) were found to express both trophoblast and HLA-A,B,C antigens by a double-labelling technique.

Endothelial cells from villous capillaries could be identified by a rabbit anti-factor VIII antibody. These cells formed 28 % of the population in a cytospin smear.

Macrophages from the villous mesenchyme were less readily separable as neither specific monoclonal antibodies nor localization of enzymes were found to be effective. However, these cells could be identified by their ability to phagocytose carmine. About 15% of the cells in a smear consisted of macrophages.

The procedure described should prove useful in judging the efficiency of isolation methods from human placental cells.
Unusual structural features and assembly of gap and pleated septate junctions in embryonic cockroach CNS
Authors: Swales Lesley S. , Lane Nancy J.
Published: April 2021

Junctional assembly in the developing CNS in cockroach embryos has been studied during the last half of neurogenesis. Atypical linear tracts of gap junctions are found to develop between attenuated cytoplasmic glial cell processes and their overlying perineurial cells during the last third of development. During both perineurial and glial gap-junctional formation, 13 nm E face (EF) intramembrane particles (IMPs), such as are characteristic of arthropod gap junctions, are seen initially as free IMPs; these then become arranged in 100se irregular clusters or alignments and finally are aggregated in plaques. P face ridges (or EF grooves), typical of tight junctions, are found on the same perineurial membrane face as assembling gap-junctional PF pits (or EF particles). Pleated sepate junctions also develop between adjacent perineurial processes during the last third of embryogenesis; these form by the apparent migration of individual 8 nm PF IMPs into meandering rows, which then become aligned in numerous orderly parallel stacks. Although all these junctions occur on the same perineurial membrane face, the IMPs that form the different junctional types never appear to be confused during junctional assembly. The cues to signal the advent of these precise patterns, however, are unknown.
Pollen–stigma interaction in Brassica. III. hydration of the pollen grains
Authors: Zuberi M. I. , Dickinson H. G.
Published: April 2021

A method is described by which the changes in shape that accompany hydration of Brassica pollen grains may be rapidly measured. Using this technique it has proved possible to chart the small amount of hydration that takes place on anthesis, in addition to the response of pollen to a range of relative humidities in vitro and in vivo. Such measurements, together with pollen transfer experiments, indicate that under normal field conditions self-pollen undergoes a brief period of hydration followed by some loss of water and that, in the course of this hydration, many pollen grains are inhibited from further growth. Raised levels of atmospheric water cause a variety of responses in self-pollen, ranging from tube growth through the pistil to the ovary, to tubes inhibited at the stigmatic surface, accompanied by the formation of callose. Surprisingly, compatible cross-pollen is also affected by high humidity, often developing extended tubes that are incapable of penetrating the stigmatic cuticle. The development of stigmatic callose is also stimulated by these tubes, as also occurs when other members of the Cruciferae are induced to germinate on Brassica stigmas by high levels of atmospheric water. This formation of callose in response to challenge by all types of pollen tube suggests models for the self-incompatibility response in Brassica that involve a direct linkage between S (incompatibility) gene products and the formation of callose may require some re-examination. Close study of the operation of the self-incompatibility system in a number of individuals has revealed all aspects of the response to be heavily dependent on the particular S genes possessed by the plant.
Experimental analysis of the reproduction of spindle poles
Authors: Sluder Greenfield , Begg David A.
Published: April 2021

We have investigated the functional properties of the mechanisms that control the reproduction of spindle poles in fertilized sea-urchin eggs. By prolonging mitosis by three independent means, we show that a spindle pole can split during mitosis into two functional poles of normal appearance. However, these poles have only half the normal reproductive capacity; each daughter cell that receives a split pole, always forms a monopolar spindle at the next division. Each monopolar spindle appears to be exactly half of a spindle because two of them can come together to form a functional bipolar spindle of normal appearance. The poles of such spindles show normal reproduction in subsequent divisions.

By following the development of individual cells with monopolar spindles, we show that such a cell can stay in mitosis longer than normal, and the single pole splits into two asters, which move apart to give a functional bipolar spindle. The poles of such a spindle have only half the normal reproductive capacity, because the two daughters of the cell always form monopolar spindles at the next mitosis. This novel cycle of development is often repeated. The occurrence of such phenomena does not depend upon the method used to induce monopolar spindles. These results show that each normal pole has two polar determinants. The results also demonstrate that the reproduction of spindle poles consists of three distinct events: splitting of the polar determinants, physical separation of the two determinants, and duplication of the determinants to return the pole to a duplex state. Splitting and duplication are distinct events because they can be experimentally put out of phase with each other for several cell cycles.
Intracellular antigens associated with the cytoplasmic surface of phagolysosomes
Authors: Vaux David J. T. , Gordon Siamon
Published: April 2021

Monoclonal antibodies were prepared to study the cytoplasmic face of latex phagolysosomes isolated from thioglycollate-elicited mouse peritoneal macrophages. Phagolysosomes obtained by sucrose flotation contained latent β-glucuronidase activity and tightly associated cellular proteins and glycoproteins. Fluorescence-activated cell sorter analysis, scanning and transmission electron microscopy showed that the particle preparation contained > 98% monomers and dimers, invested with a smooth layer of membrane and minimally contaminated with cytoplasmic adhesions. Sera from immunized rats bound preferentially to isolated phagolysosomes rather than intact cells and monoclonal antibodies PL-1 and PL-4 were isolated on this basis. Indirect fluorescent, radio- and peroxidase immunobinding assays with intact and methanol-permeabilized cells confirmed that antigens PL-1 and PL-4 were exclusively intracellular and that well-washed phagolysosomes bound both antibodies. These antigens were found in a variety of cells from several species and in macrophages not fed latex. Although the PL-1 antigen could not be immunoprecipitated, intracellular staining was characteristic of intermediate filament distribution, that is, it was in the form of a fine intersecting network, which collapsed, reversibly, in a rim round the nucleus upon treatment with colcemid. The staining pattern was undetectable in cells 1 h after adherence to a substratum, but gradually appeared after 6–12 h. The PL-4 antibody has been shown elsewhere to define a Ca2+-binding protein of approximately 20000 molecular weight, which is phosphorylated during phagocytosis. This antibody stained stress fibres and revealed a widespread punctate distribution of antigen within cells at all stages after adhesion. The nature of the association between these intracellular antigens and phagolysosomes and their possible role in phagocytosis are not known.
Microtubules in immature oocytes of Xenopus laevis
Authors: Heidemann Steven R. , Hamborg Marlyn A. , Balasz Jay E. , Lindley Steven
Published: April 2021

Previous work indicated that immature oocytes of Xenopus were incapable of assembling microtubules but that competence was achieved during maturation. We report here that small numbers of microtubules do exist in immature oocytes. Consistent with this finding, ultrastructural observations indicate that brain microtubules injected into immature oocytes persist in large numbers for at least 30 min. We report that the tubulin dimers of mature and immature oocytes are equally capable of assembling with brain tubulin in vitro. We confirmed previous results that injection of taxol into immature oocytes has no effect when assayed by light microscopy. However, ultrastructural observations suggest that some microtubule assembly is stimulated by taxol. We tested for the ability of immature oocytes to elongate microtubules from ‘seeds’ by injecting deciliated pellicles of Telrahymena. No elongation was observed either by light or electron microscopic observation. We conclude that the immature oocyte is capable of very limited microtubule assembly and that a marked increase in assembly competence occurs during maturation. Our data suggest that the change in assembly competence during maturation is due to the release, activation or synthesis of a stimulatory co-factor.
Regulation of ciliary reversal in triton-extracted Paramecium by calcium and cyclic adenosine monophosphate
Authors: Nakaoka Yasuo , Ooi Hideyuki
Published: April 2021

A Triton-extracted model of Paramecium swims forwards when the Ca2+ concentration in the reactivation medium containing ATP is below 10−6M and swims backwards when Ca2+ concentration is above 10−6M. We found that cAMP (adenosine 3’ :5’-cyclic monophosphoric acid) inhibited Ca-induced backward swimming of the model and caused forward swimming even when the [Ca2+] was above 10−6M. This effect of cAMP was abolished by an inhibitor of cAMP-dependent protein kinase. In order to study the possible role of phosphorylation in the regulation of ciliary orientation, ATP in the reactivation medium was replaced by an ATP analogue, ARPγS (adenosine 5’-O-3-thiotriphosphate), which irreversibly thiophosphorylates proteins. In ATPγS medium, the model ceased both swimming and ciliary beating, but the orientation of cilia was dependent on [Ca2+]. At low [Ca2+], cilia were perpendicular to the cell surface and, with increase in [Ca2+], their orientation gradually changed towards the cell anterior. Such a change in ciliary orientation corresponds roughly to the change in the swimming direction observed in ATP medium. The ciliary orientation towards the anterior of the cell in ATPγS medium at high [Ca2+] was maintained when [Ca2+] was decreased. In contrast, in ATP medium, the swimming direction was reversibly changed with changes in [Ca2+]. These results suggest that the ciliary orientation is regulated not only by Ca2+ but also by cAMP, probably via protein phosphorylation.
An epithelial scatter factor released by embryo fibroblasts
Authors: Stoker Michael , Perryman Marion
Published: April 2021

Medium conditioned by human embryo fibroblasts breaks structural junctions between several types of epithelial cells, leading to separation and scattering of the cells. An assay developed in MDCK cells shows activity up to a dilution of at least 1 in 64, equivalent to less than 100 ng of total protein. The activity is non-dialysable, heat-labile, and sensitive to trypsin, and it is assumed to be due to one or more proteins. After addition of the factor, separation of MDCK cells begins in about 15 min and is complete in 10 h. It increases migration of MDCK cells into wounds, and causes collapse of domes. Locomotion of isolated cells is not enhanced, but cell shape is affected by local membrane movement. Under the culture conditions used the factor, or an associated protein, causes a weak inhibition of cell growth without cytotoxic activity. The scattering factor has not been purified, nor has a physiological role been identified, but it might be concerned in the mobilization of epithelial cells.
The cell cycle of symbiotic Chlorella II. the effect of continuous darkness
Authors: Mcauley P. J.
Published: April 2021

When green hydra were grown in continuous darkness the mean cell size of their symbiotic algae was smaller than when grown in light and numbers of algae per digestive cell were reduced. The former was due to a reduction in size at which the algae divided, and the latter to a loss of synchrony of algal mitosis with that of digestive cells after transfer to darkness. Eventually, algal mitosis regained synchrony with that of digestive cells. Division synchrony was not lost in reinfected hydra (with lower than normal numbers of algae per cell) transferred to darkness; this, and the observation that synchrony in normal animals transferred to darkness was regained when algal numbers per cell had fallen to a new, lower level, suggested that the initial inhibition of algal mitosis was due to competition for a limited supply of heterotrophically required metabolites.

When dark-grown hydra were returned to light there was no delay in algal division and a steady increase in the size of dividing cells, suggesting that the smaller division size in darkness was not due simply to the critical size for division being set at a lower value. In light, algal division size varied with frequency of host feeding, but this had less effect on algal division size in darkness.

It is suggested that the critical cell size that algae must attain before being able to complete the cell cycle is the same in light and darkness, but in light mitosis is restricted by some exogenous factor so that algae grow beyond the critical size without dividing. In darkness both algal cell growth and division are dependent on exogenously supplied metabolites, and cell growth rather than the division factor is limiting. The precise nature of the restriction on algal division remains unknown.
The origin of prespore vacuoles in Dictyostelium discoideum cells as analysed by electron-microscopic immunocytochemistry and radioautography
Authors: Takemoto Keiko , Yamamoto Akitsugu , Takeuchi Ikuo
Published: April 2021

Prespore vacuoles (PSVs) are specifically formed in prespore cells of the cellular slime moulds and contain spore-specific antigens. We have examined the processes of PSV formation in Dictyostelium discoideum, using both the methods of immunoelectron microscopy with antispore serum and electron-microscopic radioautography with [3H]fucose, which is specifically incorporated into prespore cells. When prespore cells begin to differentiate at the late aggregation stages the Golgi apparatus, consisting of stacked cisternae and numerous vesicles, becomes conspicuous. Vesicles and flat sacs containing fibrous and membranous materials, respectively, are derived from Golgi cisternae. Spore antigens are found in these structures as well as in immature and mature PSVs. Fucose is incorporated into the same structures. When prespore differentiation is completed, the Golgi cisternae almost disappear and both antigens and fucose are localized in mature PSVs. The Golgi apparatus is scarcely observable in prestalk cells. Moreover, a similar pattern of changes in the Golgi apparatus and related structures occurs during the re-differentiation of prespore cells within prestalk isolates. It is concluded from these findings that PSVs are derived from the Golgi apparatus, the development of which is closely related to the differentiation of prespore cells.
Morphology and locomotion of individual epithelial cells in culture
Authors: Brown R. M. , Middleton C. A.
Published: April 2021

The behaviour in culture of epithelial cells derived from chick embryo pigmented retina epithelium (PRE), corneal epithelium (CE) and epidermis has been studied using time-lapse cinemicrography. The analysis concentrated on the morphology and movement of individual isolated cells, lacking contacts with other cells, during a 24 h period starting 1–3 h after the cells were plated out in primary cultures.

Isolated cells from all three sources could change morphology and reversibly exhibited either a poorly spread or a well-spread morphology. While poorly spread, the different cell types all appeared similar and all blebbed vigorously. In contrast, while well spread, the cells did not bleb significantly but there were other differences between them. Well-spread CE cells were always polarized by the presence of a dominant leading lamella but well-spread PRE cells were always unpolarized. Well-spread epidermal cells exhibited both a polarized and an unpolarized morphology.

The tendency of individual isolated cells to change morphology varied with cell type. PRE cells were the most stable. Nearly 80% of them retained the same morphology throughout the period of analysis and only 1% of them showed three or more changes in morphology during this period. In contrast, 22% of CE cells and 37% of epidermal cells showed three or more changes in morphology during the period of observation. Isolated cells of all three types spent a greater proportion of the time exhibiting a poorly spread morphology than they spent exhibiting any alternative well-spread morphology.

The analysis revealed a relationship between the morphology of isolated cells and the speed of their locomotion. Only cells with a well-spread polarized morphology showed significant movement. CE and epidermal cells with this morphology moved three to four times faster than their counterparts with a poorly spread morphology or, in the case of epidermal cells, with a well-spread but unpolarized morphology. Actively moving PRE cells were not seen and this correlates with the absence of cells with a well-spread polarized morphology from cultures of this type.

These findings are discussed in the light of similar investigations of cell behaviour in other epithelial cell types and fibroblasts.
Effects of hyaluronate and hyaluronate binding proteins on cell motile and contact behaviour
Authors: Turley E. A. , Bowman P. , Kytryk M. A.
Published: April 2021

The effects of hyaluronate on the morphology, motile and social behaviour of embryonic chick heart fibroblasts were examined in the presence or absence of hyaluronate binding proteins (HABP). HABP were inserted onto fibroblasts after treating cells with 0·2M-urea. Such treatment increased the binding of [125I]HABP to cell monolayers: at saturation, binding was increased threefold compared to untreated monolayers. Generally, the distribution of added HABP was similar to that of endogenous HABP as detected by immunochemistry. [3H] hyaluronate bound to HABP-treated monolayers in amounts that were proportional to the amount of HABP added. HABP alone reduced cell motility, decreased cell underlapping (measured as a nuclear overlap ratio) and promoted cell spreading. Hyaluronate added by itself had no significant effect on cell behaviour. However, in the presence of HABP, hyaluronate increased cell motility, reduced cell spreading, promoted the appearance of surface blebbing and ruffles, and significantly increased the nuclear overlap ratio. These biological effects were proportional to the amounts of hyaluronate and HABP that bound to heart fibroblasts. Fibronectin, bovine serum albumin or sulphated glycosaminoglycans added together with HABP did not mimic the effects of hyaluronate and had little effect additional to HABP alone. The role of HABP as a putative cell binding molecule for hyaluronate and the relationship of hyaluronate to cell social and motile behaviour are discussed in the light of these findings.
An investigation of the centriole cycle using 3t3 and cho cells
Authors: Alvey P. L.
Published: April 2021

An investigation of the centriole cycle was based on serial-section electron microscopy of the centrioles of 790 3T3 cells and 40 CHO cells (incomplete sets of sections were excluded from the analysis). Time-course studies indicated that procentrioles first appear 4 h after the start of S-phase; evidence was obtained to suggest that they elongate progressively during the subsequent stages of the cell cycle, and that they start to separate from their parents during mitosis. An association of the structural features of the centriole cycle with the Two-transition Model of the Cell Cycle was ruled out by the finding of two centrioles in most quiescent cells, and the appearance of procentrioles in S-phase in transiently stimulated cells.
Effect of Cerophylr growth medium on exocytosis in Tetrahymena thermophila
Authors: Pesciotta Donna M. , Satir Birgit H.
Published: April 2021

Culturing the ciliate Tetrahymena thermophila in CerophylR has provided an opportunity for studying the assembly and/or synthesis of the intramembrane particle array, the rosette, which marks the site of exocytosis in these cells. Cultures grown in this medium cease cell division after only 12 h and enter ‘stationary phase’ earlier (12 h of growth) relative to growth in standard medium (proteose peptone). In addition, the cell changes from the normally observed pear-shaped body to a thinner more ellipsoid form. Despite the initial similarities to starving cells, several differences are observed in the CerophylR-grown cells. One is that cell size remains constant for at least 72 h in contrast to starved cells. Secondly, in spite of this block in cell division, results from freeze-fracture replicas of the cell membrane of these cells show that they continue to assemble rosettes, the number of which increases approximately six times, from 0·34 rosette/^m2 to 2-1 rosettes/μm2. Addition of the protein synthesis inhibitor, cycloheximide (6 h exposure), during growth in CerophylR shows that 70% of rosettes can be assembled, despite the blockage of translation, by using pre-existing component(s) from a pool. The remaining 30% must involve de novo synthesis of one or more components; this percentage can be increased with longer exposure to the drug. Thirdly, an apparent increase in the number of mucocysts is observed by thin-section electron microscopy. At first (12–24 h) only docked mucocysts seem to accumulate in the cell. However, by 36 h a considerable increase seems to have taken place, particularly in the number of mucocysts located in the cytoplasm. In the cycloheximide-treated cells this increase in mucocysts begins to be blocked after 6 h of exposure to the drug. These observations are in agreement with the results obtained from the freeze-fracture data on the concomitant increase in number of rosettes. This system therefore offers the first possibility of exploring the biosynthesis of these components.
Cell hybridization and cell agglutination: I. enhancement of cell hybridization by lectins
Authors: Matsuya Yutaka , Yamane Isao
Published: April 2021

A great increase in hybridization frequency of cultured rodent cells was obtained when conventional cell fusion using 50% polyethylene glycol (PEG) was combined with a cell agglutination produced by plant lectins. The rate of appearance of hybrid colonies was found to be correlated with the extent of cell agglutination by lectin, as well as with cell fusion induced by subsequent PEG treatment. Phytohemagglutinin (PHA), wheat germ agglutinin, Wistaria floribunda agglutinin and concanavalin A were all active ; the most effective was PHA. When parental cells in a monolayer were treated with PHA followed by PEG, the resuting hybridization frequency was very low because of markedly decreased viability, whereas the same cells in suspension yielded hybrid colonies at a higher rate.

These results suggest that the enhancement of hybridization by PHA/PEG treatment was brought about by the ability óf lectin to agglutinate cells.
Genesis of cilia and microvilli of rat nasal epithelia during pre-natal development: II. olfactory epithelium, a morphometric analysis
Authors: Menco Bert Ph. M. , Farbman Albert I.
Published: April 2021

Rat foetuses from intra-uterine days E14 through E22 (day before parturition) and adults were used for a quantitative scanning electron-microscopic examination of ciliogenesis in olfactory receptor cells and microvillogenesis in olfactory supporting cells. Four developmental stages in olfactory ciliogenesis can be discerned. Two of these are characterized by the presence of primary cilia only, the other two concern outgrowth in number and length of secondary cilia. (1) Primary cilia on undifferentiated cells; this stage occurs up to E14. (2) Primary cilia on differentiating olfactory receptor and also olfactory supporting cells. This stage begins at E14 and lasts, for the olfactory receptor cells, at least up to E22. On the supporting cells primary cilia are rarely observed after E18. Virtually all primary cilia are about 1 gm long. Up to E21 dendritic endings with primary cilia occur more frequently than those with any other number of cilia; all endings have a transitional stage in which they bear primary cilia only. (3) Secondary olfactory cilia increase in number. From E16 onwards the cells become multiciliated. Beginning at this stage and continuing up to E22 an average of one cilium per day is added to the endings. At E22 the average number of cilia observed per ending is about 70% of that in adults; more than 90% of the endings are multiciliated. From E15 to E22 the exchange rate between receptor cells with only primary cilia and multiciliated cells is about 0·5 × 106 cells/cm2 per day. When considered in the light of electrophysiological data on developing rats, our data suggest that when the cells have just primary cilia, they may respond indiscriminately to all odorants, whereas multiciliated cells display odorant specificity. (4) Secondary olfactory cilia increase in length. From E14 to E19 and over the whole population of receptor cells the cilia grow at an average rate of about 0·5 μm/day. Proximal parts of olfactory cilia are longer than primary cilia; olfactory cilia begin to taper in increasing numbers around E18. At E19 the receptive membrane surface, i.e. regions of the cells facing the nasal lumen, of individual cells is about 8%, and the increase in epithelial surface due to sprouting of cilia is 5% of such values in adult animals. Concomitant with the onset of tapering of olfactory cilia, i.e. around E18, microvilli of supporting cells show a spurt in growth from about 0·4 μm to about 1·3 μm. Unlike olfactory cilia they show no growth, on average, after E19. We make a case for the involvement of modified primary cilia (insects) and secondary cilia (vertebrates) in chemosensory reception.
Direct transfer of β-glucuronidase from mouse macrophages to other types of cell
Authors: Dean M. F. , Mcnamara A. , Jenne B. M.
Published: April 2021

Rabbit polyclonal antibodies were raised against β-glucuronidase purified from mouse liver. This antiserum immunoprecipitated the β-glucuronidase secreted by mouse fibroblasts but did not cross-react with the same enzyme isolated from human tissue. The β-glucuronidase present in mouse 3T3 fibroblasts and mouse peritoneal macrophages was clearly identified by indirect immunofluorescence, using the antiserum and an FITC-conjugated second antibody, while human fibroblasts with normal levels of β-glucuronidase activity did not fluoresce when tested with the same reagents. A range of human fibroblasts, human neuroblastoma and rat glioma cells did not fluoresce when incubated with the antibody but did fluoresce after they had been co-cultured for 24 h with mouse macrophages, showing that mouse β-glucuronidase had been transferred from adherent macrophages into adjacent recipient cells. Transfer took place even when receptor-mediated endocytosis was blocked with a suitable competitive ligand, the transferred enzyme being visible mainly as a bright punctate fluorescence with a lysosome-like distribution. Macrophages thus have the potential to act as donors of lysosomal enzymes to a wide range of recipient cells and to transfer enzymes to them during direct cell-to-cell contact.
Subplasmalemmal calcium-binding microregions in Acanthamoeba
Authors: Sobota A.
Published: April 2021

Acanthamoeba cells, fixed with glutaraldehyde supplemented with calcium ions, show Ca-dependent, electron-dense deposits (CaDD) at the cytoplasmic surface of the plasma membrane. The formation of CaDD is stimulated by pre-incubation and fixation of the cells in the presence of ATP. Chemical analysis of the trichloroacetic acid extracts of CaDD-containing cells demonstrates that adenosine monophosphate, pyrophosphate and inorganic phosphate are probably the compounds involved in the formation of CaDD. Treatment of CaDD-containing cells with exogenous phosphatase evokes the disappearance of electron-dense material and a fine fibrillar network can be observed inside the ‘empty’ CaDD. The ability to restore CaDD in the presence of calcium ions with either pyrophosphate or orthophosphate confirms the suggestion that calcium/phosphate salts may be deposited in special subplasmalemmal calcium-binding microregions.
Attachment of sponge cells to collagen substrata: Effect of a collagen assembly factor
Authors: Diehl-Seifert Bärbel , Kurelec Branko , Zahn Rudolf K. , Dorn August , JeriČevic Biserka , Uhlenbruck Gerhard , Müller Werner E. G.
Published: April 2021

Collagen, isolated from the sponge Geodia cydonium in the absence of denaturing agents, had the typical amino acid composition and was associated with the carbohydrates galactose and glucose. The resulting individual fibrils with a diameter of 23 nm, displayed a 19-5 nm periodicity with one intraperiod band. A collagen assembly factor (CAF) was identified in and partially purified from the extracellular space. The CAF reacted with antibodies against intact Geodia cells but not with antibodies against Geodia lectin and Geodia aggregation factor. In the presence of the CAF, the collagen fibrils reconstituted collagen bundles in an ordered sequence of events, which were followed by electron-microscopical and biochemical methods. Bundle formation was not dependent on the presence of the homologous lectin, glycoconjugates or aggregation factor. Homologous cells (Geodia archaeocytes) were determined to attach only to those Geodia collagen substrates that contained CAF. The attachment of these cells did not require fibronectin or Geodia lectin. Homologous glycoconjugates or NaOH-treated collagen inhibited cell attachment. Collagen from the sponge Chondrosia reniformis, even in the presence of Geodia CAF, was no appropriate substrate for Geodia cell attachment. Whether collagen is a component of cell-matrix interactions in sponge systems also in vivo is discussed.
Role of particle electrostatic charge in adhesion and ingestion in Dictyostelium discoideum amoeboid cells
Authors: Hellio Raymond , Ryter Antoinette
Published: April 2021

The use of colloid iron hydroxide, Alcian Blue and enzymic treatments confirmed that the negative charges of Dictyostelium discoideum cell surface are mostly due to carboxylic groups. The role of electrostatic charges in adhesion and ingestion was determined by exposing cells to untreated latex beads, polylysine or polyglutamic-acid-coated beads, or carboxylated beads. This study showed that negatively charged beads presented a weaker adhesion strength than positively charged ones and that adhesion was strongest with untreated beads. This shows that hydrophobic forces are stronger than those induced by opposite electric charges between particle and cell surface. The ingestion rate was not directly related to adhesion because negatively charged beads presented the highest phagocytic rate, polylysine-coated beads had the lowest and neutral beads an intermediate one.

The treatment of cells with polylysine or polyglutamic acid before neutral bead addition generally enhanced the ingestion rate. Electron microscopic observations made on polylysine-treated cells showed, however, that this stimulating effect was not due to the presence of the polymer on the cell surface but to a membrane clearance phenomenon occurring during polymer elimination.

All these observations have led to the conclusion that the electric charges of the particle do not play a major role in D. discoideum phagocytic ability. Hydrophobic forces and probably other unknown parameters related to the cell surface properties are more important.
Studies on the mechanism of hydrated collagen gel reorganization by human skin fibroblasts
Authors: Guidry Clyde , Grinnell Frederick
Published: April 2021

During reorganization of collagen gels by human skin fibroblasts the total protein content of the gels remained approximately constant. Only 5% of the collagen was degraded, although the volume of the gels decreased by 85% or more. It could be concluded, therefore, that gel reorganization required physical rearrangement of pre-existing collagen fibrils rather than degradation of the original collagen and resynthesis of a new matrix. Collagen molecules in the gels were not covalently crosslinked or otherwise modified enzymically during gel reorganization, as determined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and collagen re-polymerization studies. Serum was required for gel reorganization and, in the absence of serum, cell spreading was predominantly filipodial, i.e. there was little cytoplasmic reorganization. At the electron-microscopic level it was found that many more collagen fibrils became associated with the cells in the presence of serum than in its absence. Serum was also found to promote the synthesis and secretion of proteins by the cells, and conditioned medium could take the place of serum in promoting gel reorganization. The involvement of cell-secreted factors was also demonstrated by the ability of cycloheximide to inhibit gel reorganization. Finally, when gel reorganization was stopped by adding cytochalasin D to the incubations or removing cells by detergent treatment, a small but significant re-expansion of the collagen fibrils was observed. Consequently, a portion of the collagen that had been physically reorganized by the gels was unstable and could not hold its position without continued force exerted by the cells.
Suppression of malignancy in hybrid cells: The mechanism
Authors: Harris Henry
Published: April 2021

When malignant cells, defined by their ability to grow progressively in genetically compatible hosts, are fused with diploid fibroblasts of the same species, the resulting hybrid cells, so long as they retain certain specific chromosomes donated by the diploid parent cell, are non-malignant. When these particular chromosomes are eliminated from the hybrid, the malignant phenotype reappears, and the segregant cell is again able to grow progressively in vivo. In the present experiments the histological character of the lesions produced by the inoculation of crosses between malignant and non-malignant cells was examined. It was found, in a wide range of material, and without exception, that where one or other of the parent cells in the cross was of fibroblastic lineage, malignancy was suppressed when the hybrid cells produced a’collagenous extracellular matrix in vivo; and it reappeared when genetic segregants were produced that had lost the ability to produce this matrix. These results are interpreted in terms of a general model in which it is proposed that the progressive multiplication of malignant cells in vivo is a secondary consequence of a genetically stable impairment of terminal differentiation.
Influence of vinblastine sulphate on the deployment of microtubules and ribosomes in telotrophic ovarioles
Authors: Stebbings H.
Published: April 2021

Ovarioles of Notonecta glauca glattca have been treated with vinblastine sulphate (VBL),primarily to examine the effects of the drug on the microtubules which pack the trophic core and nutritive tubes, 10–4 M VBL had little effect on the microtubules. VBL at 10–3 M reduced the number of microtubules in nutritive tubes, while after 2 ×10–3 M VBL microtubules were rare. All 3 concentrations of VBL induced the formation of crystalline structures in the trophic coreand nutritive tubes, and to a lesser extent in the nutritive cells and follicle cells. In transverse sections crystals appeared to be composed of distinct hexagonal units and in longitudinal sections crystals showed as dark parallel lines with darker dots at regular intervals along their length. With 10–4 M VBL, the crystals were compact and close to the walls of nutritive tubes, but after treatment with stronger concentrations of VBL the crystals were web-like and scattered over cross-sections of tubes.

In addition to VBL having a destructive effect on the microtubules in the trophic core and nutritive tubes, there was also a reduction in the number of ribosomes. This overall reduction in ribosome quantity could not be attributed to the inhibition of RNA synthesis by VBL.

In regions of ovarioles where microtubules were arranged in parallel masses, as in the nutritive tubes and trophic core, the long axes of crystals were always similarly aligned. Other wise crystals were randomly oriented. The possible mode of formation, and composition, of crystals is discussed.
Microtubules in the heliozoan axopodium: iii. degradation and reformation after dilute urea treatment
Authors: Shigenaka Y. , Roth L. E. , Pihlaja D. J.
Published: April 2021

The precise microtubule array present in the heliozoan axopodium has been studied by experimental degradation by using the protein denaturing agent urea. Since concentrations used in typical applications were found to destroy the whole organism immediately, very dilute solutions, usually 0·15 M, were used to study axopodial retraction, which was shown to occur in 2 stages: the distal half reacts immediately and is lost in very few minutes, largely by release of segments, while retraction of the proximal half may extend over an hour. Recovery of axopodial length by removal of organisms to distilled water is possible if treatment is not carried to full axopodium loss, though organisms must be treated with solutions more dilute than 0·1 M to avoid lysis. Electron-microscopic study of retracting axopodia showed degradation of micro tubules at innumerable points even in the proximal regions. Similar studies of untreated organisms showed that the typical microtubule array is found throughout the proximal portion but is progressively imprecise in the distal portion as the tip is approached. High lability to urea is therefore correlated with reduced order and reduced numbers of long linkage elements in the microtubule array. An intra-microtubule metastability is proposed and is discussed with regard to the formation of axonemes, the use of dilute urea to test microtubule stability differences, and the gradion hypothesis presented in previous work.
Studies on the structure and cellular location of various ribosome and ribosomal rna species in the green alga Chlamydomonas reinhardi
Authors: Bourque D. P. , Boynton J. E. , Gillham N. W.
Published: April 2021

Under ionic conditions effecting little or no subunit dissociation, Chlamydomonas reinhardi contains 2 major classes of ribosomes with generic sedimentation velocities of 83 and 70s and 3 minor classes with sedimentation velocities of 66, 54, and 41 s. Ribosomal RNAs with sedimentation velocities of 25, 23, 18, 16 and 5 s have been identified. The 70-sribosomes are in the chloroplast and contain 23-, 16- and 5-s ribosomal RNA whereas the 83-s ribosomes are in the cytoplasm and contain 25-, 18- and 5-s ribosomal RNA. Numbers of chloroplast ribosome particles counted in electron micrographs of wild type C. reinhardi and the ac-20 and y mutants have been compared with relative amounts of 70-s ribosomes determined by sucrose gradient sedimentation and amounts of 23-, 16-and 5-s ribosomal RNA determined by gel electrophoresis. In response to reduced concentrations of magnesium the 70-s ribosomes of wild type are susceptible to a progressive reduction in sedimentation velocity whereas the 66-s ribosomes of the mutant ac-20 are not. Chlorophyll synthesis and the formation of the chloroplast lamellar system do not appear to be correlated with the relative amounts of chloroplast ribosomes.
Red-light stimulation of prolamellar body recrystallization and thylakoid formation in barley etioplasts
Authors: Berry D. R. , Smith H.
Published: April 2021

The etioplasts of fully dark-grown barley leaves exhibit a relatively low frequency of crystalline prolamellar bodies (ca. 16–20%). Brief red-light treatment leads to rapid disruption of all prolamellar bodies followed by a slow reformation in the subsequent dark period. When several red-light treatments are given with intervening 3-h dark periods, a marked increase in the proportion of crystalline prolamellar bodies is seen. It is suggested that this phenomenon may be associated with the regeneration of protochlorophyll.

Red-light pretreatment stimulates the formation of granal thylakoids upon subsequent transfer to continuous white light. This response is correlated with the phytochrome-mediated shortening of the lag phase in chlorophyll-synthesis under identical conditions.

Regular arrays of hexagonal tubules 16–19 nm in diameter have been observed often in close juxtaposition to the newly forming thylakoid membranes. These may be aggregations of Fraction I protein, although their exact nature and function is at present Unknown.
Fine structure study of pollen development in Haemanthus katherinae baker: I. formation of vegetative and generative cells
Authors: Sanger Jean M. , Jackson W.T.
Published: April 2021

When microspores of the African blood lily divide, they form pollen grains which consist of 2 cells of unequal size. This is accomplished when the microspore nucleus is displaced from the centre of the grain prior to division. The displacement is always towards the side of the grain opposite the furrow, and large vacuoles form in the cytoplasm between the furrow and the nucleus. During cell division the cell plate curves around one daughter nucleus and fuses with the pollen wall to enclose the generative cell. The cell-plate attachment always occurs with the wall that is opposite the furrow of the grain. Most of the microspore’s organelles become incorporated in the larger vegetative cell, whereas the generative cell has few, if any, plastids and only a small number of other organelles. The wall around the generative cell is composed of finely fibrillar material enclosed within 2 unit membranes. The generative cell eventually becomes detached from the pollen wall, becomes spheroidal, and moves to a position near the centre of the pollen grain. At the same time, the large vacuoles disappear from the vegetative cell and the number of organelles increases substantially.