bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution and dynamics of nematocyte populations in Hydra Attenuata
Authors: Bode H. R. , Flick Kristine M.
Published: April 2021

The distribution and dynamics of the 4 nematocyte populations of Hydra attenuata were investigated. Ninety-seven per cent of all nematocytes, including all 4 types, are mounted in the battery cells of the tentacles. The remaining 3%, including 2 types (stenoteles and holotrichous isorhizas) are mounted in the ectoderm of the body column. Eighty-two per cent of all nematocytes are desmonemes; 11%, atrichous isorhizas; 5%, stenoteles; and 2%, holotrichous isorhizas. The density of each nematocyte population increases along the length of the tentacle towards the tip. The percentages of the total nematocytes per quarter of tentacle for each of the 4 quarters starting at the base is 15, 18, 25 and 42% respectively.

The turnover time of the nematocyte populations in the tentacles was measured with 2 methods. First, the transit time for a carbon-marked battery cell from the base to the tip of the tentacle was measured. Secondly, the time required to replace the unlabelled nematocytes in the tentacles with [3H]proline-labelled nematocytes was measured. In both cases the time was 7–9 days.

Based on these data (distribution and turnover time) a model was constructed for the dynamics of the nematocyte populations in the tentacles. The numbers of nematocytes produced daily in the body column as predicted by the model are in reasonable agreement with the measured values.
Bhk21 fibroblast aggregation inhibited by glycopeptides from the cell surface
Authors: Vicker M. G.
Published: April 2021

Glycopeptides were removed by trypsinization from the surface of baby hamster kidney cells (line BHKzi-C13), digested by pronase and separated into 2 fractions by exclusion chromatography. The addition of small amounts of either glycopeptide fraction to shaken suspensions of lightly trypsinized cells inhibited their rapid aggregation, but one fraction was more active than the other and in higher concentrations it was able to inhibit aggregation completely. After this fraction was purified by high-voltage electrophoresis one subfraction also inhibited aggregation. The effect of the glycopeptides increased following their pretreatment with neuraminidase, but preincubation with periodiate or galactose oxidase destroyed all activity. Galactose oxidase also inhibited cell aggregation directly. Similar glycopeptides from virus-transformed BHK21 cells, oligosaccharides and intact and desialysed human urinary glycoproteins had comparatively little or no effect on BHK21 cell aggregation. The results suggest terminal β-galactosides and possibly α-galactosides, and to some extent a particular substructure of cell surface heteroglycans are necessary for their inhibitory activity. The parent, plasma membrane glycoproteins might serve as adhesive binding sites in cell cohesion, but some evidence indicates cell surface sialyl- and galactosyltransferases may not ordinarily act as their complementary binding receptors.
A highly infectious ‘mycoplasma’ that inhibits meiosis in the fungusCoprinus
Authors: Ross I. K. , Pommerville J. C. , Damm Deborah L.
Published: April 2021

We have discovered a cytoplasmically inherited infectious agent that inhibits meiosis in a species of Coprinus, a basidiomycetous fungus. From infectivity, filtration, centrifugation and ultrastructural studies we believe the agent to be a mycoplasma. The agent is highly infectious to several strains of the host species and is capable of spreading rapidly through infected hosts. No pathological effect has been seen on any aspect of growth or differentiation of the fungus except for the inability of infected strains to undergo meiosis. The failure of meiosis results in mushrooms that do not produce the normal black spores and are therefore pale in colour. The paleness represents a simple assay for the presence and activity of the infectious agent. Infected hosts do not display any ultrastructural abnormalities in the vegetative stages, only in the cells in which meiosis should occur. In the meiotic cells, at the time when normal cells are undergoing synapsis and synaptinemal complexes are forming, the vacuoles of the infected cells become occupied with vesicular, membrane-bound bodies resembling in shape and form mycoplasmas. Extracts from infected clones may be filtered through 0·2-μm filters and retain full infectivity. The infectious material may be pelleted from such extracts at only 10000g. Migration experiments, as well as the filtration studies, rule out involvement directly of nuclei. The high rate of infection and spread of the mycoplasma through the host, combined with the anatomical simplicity of the host, make this an ideal system in which to study the basis of infection. The singularity of the pathological effect make this host-parasite association useful in studying both the underlying mechanisms of mycoplasma pathogenicity and to investigate the regulation of meiosis. This is only the second report of mycoplasmas in fungi.
Relations between the nuclear activity and the variable 3H-amino acid incorporation pattern in Amoeba Proteus
Authors: Chatterjee S. , Bell L. G. E.
Published: April 2021

Tracer kinetic studies have revealed the existence of a variable pattern of ‘H-amino acid incorporation into amoeba proteins during the early G2 phase of the cell cycle. Two peaks of incorporation of [3H]leucine were found to occur at 19 and 22 h, whereas a single peak at 17 h was noticed in the amoebae labelled with [3H]lysine. An almost 2-fold increase of the labelled amino acid incorporation occurred during the peak periods, while the other periods showed a more or less steady state of incorporation, suggesting a basal rate of synthesis at these times.

In a detailed study involving the peaks and the basal incorporation periods of [3H]leucine, it was shown that the removal of the nucleus or Actinomycin D treatment eliminated the peaks but the base line protein synthesis was not affected. This suggests that for the peak synthetic periods, mRNA is probably transcribed concurrently, followed by immediate translation, whereas long-life mRNA accounts for the basal synthetic activity.
Organization of intramembrane particles in freeze-cleaved gap junctions of rat graafian follicles: optical-diffraction analysis
Authors: Amsterdam A. , Josephs R. , Lieberman Mara E. , Lindner H. R.
Published: April 2021

Gap junctions were identified in the membrana granulosa and cumulus oophorus, and between cells of the internal theca, of the preovulatory rat follicle. In replicas of freeze fractured follicles, the A face presented clusters of closely packed intramembrane particles, 7—9 nm in diameter, forming a mosaic pattern, while the B face showed a similar pattern of small pits. Optical diffraction analysis of these electron micrographs revealed that both the intramembrane particles and the corresponding pits were organized in hexagonal lattices with centre-to-centre spacing of 9—10 nm. In small junctions (up to 0·4 μm in diameter), both A and B faces generally consisted of a single lattice, while large junctions (0·5–2 μm) contained multiple lattices differing in orientation. Occasionally intramembrane particles and pits were more loosely arranged throughout the junctional area and failed to show a hexagonal pattern.

Both granulosa and thecal cells often contained intracellular vesicles resembling annular junctions. These contained intramembrane particles whose assembly resembled that of the gap junctions with regard to periodicity and lattice organization. Examination of thin sections suggested that small gap junctions occur also between cytoplasmic processes of coronal cells and the oolemma. No tight junctions were detected between granulosa cells and between thecal cells.
Differentiation for aggregation in the cellular slime moulds: the emergence of autonomously signalling cells in Dictyostelium Discoideum
Authors: Raman R. K. , Hashimoto Yohichi , Cohen M. H. , Robertson A.
Published: April 2021

The results of experiments on small populations of Dictyostelium discoideum, directed towards the measurement of the development in time of the competence of the cells to signal autonomously, are reported. This competence is quantified by Xs, the intrinsic probability that a given cell may turn autonomous. The data show an early exponential growth in time of X3, followed by saturation. The saturation value depends on the population size suggesting that the differentiation is a co-operative phenomenon. The differentiation of autonomous cells starts roughly 7 h after the removal of food and saturates within 21h.
Metabolic requirements for interactions between nuclear and cytoplasmic membranes in the repair of damaged amoeba nuclei
Authors: Flickinger Charles J.
Published: April 2021

Amoeba nuclear envelopes were damaged using microsurgery, and metabolic requirements for the steps in their repair were studied, by placing the cells in a solution containing one of several metabolic inhibitors. The first step in repair, the association of pieces of endoplasmic reticulum with holes in the nuclear membranes, appears to be a passive process since it was not affected by inhibitors of energy production, RNA synthesis, or protein synthesis. In contrast, fusion of pieces of endoplasmic reticulum with the nuclear membranes at the margins of the holes was blocked by KCN and dinitrophenol, indicating that membrane fusion requires energy derived from respiration, but RNA and protein synthesis inhibitors did not prevent fusion of pieces of endoplasmic reticulum with the nuclear membranes. The subsequent completion of repair and restoration of intact nuclear membranes was almost completely blocked by inhibitors of respiration, and it was reduced in the presence of actinomycin and emetine, suggesting that in addition to a requirement for energy, some later steps in the repair of the nuclear membranes require RNA and protein synthesis.
Electron-microscope observations on cell nuclei in various tissues of a teleost fish: the nucleolus-associated monolayer of chromatin structural units
Authors: Davies H. G. , Haynes M. E.
Published: April 2021

Observations on stain uptake by thin sections through condensed interphase chromosomes in cells from epithelial and muscle tissue in kidney and intestine, and also in fibroblasts, show a distribution into DNA-rich and DNA-poor phases similar to that already described in cells from the connective tissue blood. In all the nuclei the nucleolus, when adjacent to the nuclear envelope, is separated from the inner membrane by a monolayer of chromatin structural units, similar to the monolayer enclosed on both sides by nuclear envelope, previously described in a wide variety of organisms. The data provide further support for the hypothesis that the condensed interphase chromosomes in eukaryotes are characterized by essentially similar structural units folded to form similar patterns. This hypothesis, regarding the higher order units, is consistent with data of others which show that histones and DNA fold to form similar repeating subunits in chromatin, irrespective of the base sequence in the DNA and the origin of the histones.
Ultrastructural site variations in mouse epidermal organization
Authors: Allen T. D. , Potten C. S.
Published: April 2021

Mouse dorsal, ear, tail and foot epidermis are compared according to their tissue architecture and cell kinetics. Cell proliferation is expressed in terms of the daily volume of keratin replaced. The stratum corneum may be organized into vertical columns of squames, which may have minimal overlap as in dorsum and ear, or maximal overlap as in tail. Individual areas are adapted to their function both in squame fine structure and rate of cell replacement. The surface keratin loss/replacement rate is at its highest in foot and tail, and lowest in ear and dorsum. Observations on hairless mouse dorsum are also included.
The blepharoplast of Marsilea: its De Novo formation and spindle association
Authors: Hepler P. K.
Published: April 2021

Blepharoplast formation and function has been investigated by light and electron microscopy in developing microspores of the water fern Marsilea vestita. When single-celled microspores are hydrated they undergo a series of 9 cell divisions producing 7 sterile cells plus 32 spermatids. The blepharoplast, a densely staining, spherical inclusion (0·5–1·0 μm in diameter) interpenetrated by numerous lightly stained channels, is a precursor organelle for the production of the 100—150 basal bodies of the motile sperm. During development it arises twice in the dividing spermatogenous cells; first in telophase of the second to last or 7th division, and again in telophase of the next to last or 8th division. The blepharoplast first forms on the distal side of the nucleus during telophase of the 7th division but soon degenerates as the cell enters prophase and metaphase of the 8th division. During telophase of the 8th division the blepharoplast again arises in the cytoplasm near a small indentation of the nuclear envelope. The forming blepharoplast consists of a sphere of lightly stained flocculent material within which 2 plaques separated by 40–50 nm arise. Each plaque possesses 2 dense layers (20 nm) separated by a light layer (10 nm). During subsequent development the distal layer of each plaque becomes progressively more densely stained. Light-staining channels appear within the accumulating dense material and 2 hemispherical blepharoplasts emerge. The blepharoplasts become spherical through continued growth and finally separate from each other as they move to the spindle poles during prophase of the last or 9th division.

The blepharoplast appears to act as a microtubule organizing centre during formation of the spindle apparatus in prophase of the 9th division. While it remains at the pole throughout mitosis it does not continue to serve as the focal point for the spindle tubules. During metaphase-anaphase of the 9th division the blepharoplast swells, and the channels at its surface begin transforming into procentrioles and finally basal bodies.

The results support the contention that basal bodies in Marsilea arise de novo, since no preexisting template such as a centriolar pinwheel is observed and since the intermediates which initially occur are structurally dissimilar from a procentriole.
Ultrastructural and enzymic modulation of hela cells induced by sodium butyrate and the effects of cytochalasin b and colcemid
Authors: Deutsch S. I. , Silvers D. N. , Cox R. P. , Griffin M. J. , Ghosh N. K.
Published: April 2021

Sodium, butyrate causes HeLa cells to assume an elongated and jagged shape. Ultrastructurally this change is associated with the formation of bundles of microfilaments. Desmosomes were present between adjacent cells. No increase in microtubules was observed in the butyrate-treated cells.

Butyrate induces an increase in the activity of 2 membrane-bound enzymes, alkaline phosphatase and 5’-nucleotidase; however, the activity of a third membrane enzyme, acetylcholine esterase, is reduced. The activities of the several other enzymes with different subcellular localizations are not significantly increased. Colcemid and cytochalasin B prevent or reverse the butyrate-mediated change in HeLa cell morphology and also partially inhibit the induction of alkaline phosphatase activity in these cells. The effect of cytochalasin B on alkaline phosphatase induction may be caused by a reduction in protein synthesis produced by this fungal metabolite.
Neutral protease activity of rous sarcoma (RSV) transformed chick embryo fibroblasts
Authors: Spataro Ann C. , Morgan H. R. , Bosmann H. B.
Published: April 2021

The proteolytic activities of normal, Schmidt Ruppin Rous sarcoma virus (SR-RSV transformed, and infected (RAV) chick embryo fibroblasts (CEF) have been measured by a highly sensitive technique using 3H-acetylated haemoglobin as a substrate. When all 3 types of CEF cells were maintained in serumless media, no differences were detected in the amount of pH 3·4 protease activity released into the media over a 24–h period, and only negligible amounts of pH 7·6 proteolytic activity were found. When normal, transformed, and infected cells were maintained in serumless media and later incubated with 3H-acetylated haemoglobin, a significant proteolysis of the haemoglobin, a 6-fold increase compared to the normal CEF cells, was associated only with plates containing SR–RSV–CEF cells. A fluorescent assay for peptides confirmed that SR–RSV–CEF cells have increased cell-associated proteolytic activity. The net surface charge of the transformed CEF cells was unchanged by maintenance in serumless media but the net surface negativity of the normal and RAV-CEF cells was significantly increased by incubation in media minus serum for 24 h. This suggests that normal CEF cells, maintained in media plus serum, have a substance masking their surface charge which is absent from the surface of transformed cells, possibly because of proteolytic degradation.
Aggregation in Polysphondylium
Authors: Jones Michael E.
Published: April 2021

Dense aggregating fields of P. violaceum and P. pallidum exhibit propagated waves which may be analogous to those seen in Dictyostelhim discoideum. As in D. discoideum the wave velocity is determined by an intracellular delay between stimulation and response, rather than by the diffusion coefficient of the acrasin.

The frequency of the propagated wave overlaps that of aggregating D. discoideum, so that absence of coaggregation reported by Raper & Thom is unlikely to be based on specificity of the propagated wave parameters, but rather on a difference in the chemical acrasin itself, as argued on independent evidence by Bonner. Despite this difference in the chemical nature of the acrasin, the presence of propagated waves in Polysphondylium with frequencies similar to those in D. discoideum, taken together with evidence for a diffusible acrasin, suggests that the mechanism of aggregation is substantially the same in both genera.
Electron-microscopic study of the spindle and chromosome movement in the yeast Saccharomyces Cerevisiae
Authors: Peterson Joan B. , Ris Hans
Published: April 2021

Mitosis in the yeast Saccharomyces cerevisiae was investigated in thick (0·25–1 μm) serial sections with a high voltage electron microscope and in preparations of spheroplasts spread on a water surface. Spindle microtubules originate from a plaque-like structure called the spindle pole body (SPB) which is inserted within the persisting nuclear envelope. Early in mitosis the SPB duplicates and a set of long and short microtubules develops on each SPB. The spindle arises as the SPBs separate on the nuclear membrane and reorient so that the microtubules fall into line. Chromosomes do not condense and are not individually visible. Genetic studies, however, have indicated that there are 17 linkage groups. The number of microtubules was determined in diploid and haploid spindles on serial stereo micrographs. In diploid mitosis about 40 microtubules issue from a SPB. Most are non-continuous and often they are visibly associated with a chromatin fibre. The spindle in haploid cells is similar except that the number of microtubules is about half that in diploid cells and the SPB is smaller. The pole-to-pole microtubules vary in number from spindle to spindle, but in each case enough microtubules are present to account for each linkage group being associated with a single non-continuous microtubule. We conclude that mitosis in yeast is comparable in its general aspect to that observed in typical eukaryotes.
Lectin receptor sites on rat liver cell nuclear membranes
Authors: Virtanen Ismo , Wartiovaara Jorma
Published: April 2021

The presence and localization of lectin receptor sites on rat liver cell nuclear and other endomembranes was studied by light and electron microscopy using fluorescein and ferritin-coupled lectin conjugates.

Isolated nuclei labelled with fluorescein-conjugated Concanavalin A (Con A) or wheat germ agglutinin (WGA) often showed membrane staining, which sometimes was especially bright on small stretches of the nuclear surface. Unlabelled nuclei and nuclei with a complete ring fluorescence were also seen. The nuclear fluorescence corresponded in intensity to that seen on the surface of isolated rat liver cells.

Con A-ferritin particles were seldom detected on the cytoplasmic surface of the intact nuclear envelope. However, at places where the 2 leaflets of the envelope were widely separated or where the outer nuclear membrane was partly torn away, heavy labelling was seen on the cisternal surface of both the inner and outer nuclear membranes. Labelling with Con A-ferritin was also found on the cisternal side of rough endoplasmic reticulum present in the specimens. No labelling was seen on the cytoplasmic surface of mitochondrial outer membrane.

The results demonstrate the presence of binding sites for Con A and WGA in nuclei and an asymmetric localization of these sites on the cisternal side of ribosome-carrying endomembranes in rat liver cells.
Ultrastructural studies on the surface membrane of the mouse egg
Authors: Eager Deborah D. , Johnson M. H. , Thurley K. W.
Published: April 2021

Fertilized and unfertilized mouse eggs were examined by scanning and transmission electron microscopy for evidence of mosaicism in the organization and concanavalin A-binding properties of their surface membranes. No obvious quantitative mosaicism in concanavalin A binding was noted. The egg membrane was microvillous over most of its surface, but was smooth in the region overlying the 2nd metaphase spindle of the unfertilized egg and on the polar body of the fertilized egg.
Morphological changes in frog pronephric cell surfaces after transformation by herpes virus
Authors: Tweedell Kenyon S. , Williams Daniel C.
Published: April 2021

A scanning electron-microscope study has established that there are major modifications in the surface membranes of malignant cells transformed from the pronephric kidney of the frog. Tumours were induced in vivo after exposure of embryos to Lucké Herpes virus. A pronephric cell line from normal embryos and 3 tumour cell lines derived from experimentally induced adenocarcinomas of the pronephros were observed. The normal embryonic kidney cells have their surfaces covered with long fingerlike microvilli throughout the cell cycle. In contrast, the surface of the pronephric tumour cells are mainly covered by multiple, ruffled or parallel straight microridges and short, stubby microvilli. These comparisons were made on cells subject to similar culture conditions. The topographic changes in the tumour cells are considered significant since the characteristic microridges and stubby villi were consistently found in all 3 pronephric tumour lines.
The preprophase band: Possible involvement in the formation of the cell wall
Authors: Packard Mary J. , Stack Stephen M.
Published: April 2021

Numerous vesicles were observed among the microtubules of the ‘preprophase’ band in prophase cells from root tips of Allium cepa. The content of these vesicles looks similar to the matrix of adjacent cell walls, and these vesicles often appear to be involved in exocytosis. In addition, the cell walls perpendicular to the plane of (beneath) the preprophase band are often differentially thickened compared to the walls lying parallel to the plane of the band. Our interpretation of these observations is that the preprophase band may direct or channel vesicles containing precursors of the cell wall to localized regions of wall synthesis. The incorporation of constituents of the cell wall into a narrow region defined by the position of the preprophase band may be a mechanism that ensures unidirectional growth of meristematic cells.
Interrelationships between golgi, gerl and synaptic vesicles in the nerve cells of insect and gastropod ganglia
Authors: Lane Nancy J. , Swales Lesley S.
Published: April 2021

In addition to demonstrating synaptic vesicles, staining with the zinc-iodide-osmium tetroxide (ZIO) method reveals the presence of positively reacting GERL membranes in association with the Golgi complex and lysosomes in the nerve cell bodies within ganglia from the locust Schistocerca gregaria and the gastropod molluscs, Limnaea stagnalis and Helix aspersa. A positive response to ZIO occurs in certain Golgi vesicles and saccules, in GERL (Golgi-endoplasmic-reticulum-lysosomes), in multivesicular bodies as well as residual bodies and in small vesicles and cisternae of axonal smooth endoplasmic reticulum (ER). The interrelationships between these organelles are considered in view of the similarity of the ZIO localization to phosphatase-rich sites in the neuronal perikarya and with respect to the possibility that components of the synaptic vesicles are formed in the Golgi region of the cell and migrate via the axonal smooth ER to the synaptic regions.
The effects of spectinomycin and ethidium bromide on the synthesis of organelle rrna and on ultrastructure in Ochromonas danica
Authors: Smith-Johannsen Heidi , Fromson David , Gibbs Sarah P.
Published: April 2021

The effects of 24-h exposure to spectinomycin (100 μg/ml) and ethidium bromide (1 μg/ml) on the accumulation of chloroplast and mitochondrial rRNAs and on organelle ultra-structure were studied in greening cells of Ochromonas danica. Cells treated with ethidium bromide for 24 h divide at the same rate as controls but contain less than one third the normal amount of mitochondrial rRNA. Ultrastructural observations showed that these cells contain only 10% the number of mitochondrial ribosomes found in controls as well as fewer mitochondrial cristae. Ethidium bromide has no effect on chloroplast ultrastructure in Ochromonas.

Greening cells treated with spectinomycin grow at close to control rates but contain 30–40% less chloroplast rRNA than do controls. Electron microscopy showed that spectino-mycin disrupts the organization of chloroplast membranes and reduces the number of chloroplast ribosomes by 30%. Under these conditions, spectinomycin has no effect on mitochondrial rRNA or ultrastructure. Since spectinomycin is a specific inhibitor of translation on 70s ribosomes, these results are consistent with the possibility that at least some chloroplast ribosomal proteins are synthesized in the chloroplast of Ochromonas.
Fertilization in brown algae: III. preliminary characterization of putative gamete receptors from eggs and sperm of Fucus serratus
Authors: Bolwell G. P. , Callow J. A. , Evans L. V.
Published: April 2021

Membrane fractions have been isolated from eggs of Fucus serratus which inhibit fertilization in a species-specific manner. This activity is destroyed by α-fucosidase and a-mannosidase. Some 6% of the protein of this membrane fraction binds to Con A-agarose, following SDS solubilization, and when eluted with α-methyl mannoside inhibits fertilization when preincubated with sperm, but not eggs. This inhibitory activity is species-specific and destroyed by α-fucosidase but not by trypsin. SDS-gel electrophoresis reveals 1 band staining strongly with Coomassie Brilliant Blue G and weakly with the PAS reagent. This major band represents a glycoprotein with an approximate molecular weight of 30000 Daltons.

Membrane fractions from sperm of Fucus serratus solubilized in KC1 yielded a proteincontaining fraction, after affinity chromatography on desulphated fucoidan-Sepharose. This fraction is 100-fold more effective in inhibiting fertilization after preincubation with eggs than either Con A or fucose-binding protein. It is species-specific and inhibition is reversed when pretreated eggs are washed with fucoidan. Activity is destroyed by heat and trypsin and only one diffuse band is apparent on SDS gels. This stains positively with Coomassie Brilliant Blue G but not with PAS and has a molecular weight of approximately 60000 Daltons.

Tentative calculation of the numbers of putative receptor molecules gives a figure of 2·5 × 106 receptors per egg and 1·8 × 105 receptors per sperm.
Isolation of plasma membranes from purified mouse spermatogenic cells
Authors: Millette Clarke F. , O’Brien Deborah A. , Moulding Christopher T.
Published: April 2021

Plasma membranes have been prepared from purified pachytene spermatocytes, round spermatids and residual bodies of the adult mouse testis using procedures modified from other authors’. Isolated membranes have been examined using electron microscopy, lectin binding and enzymic assays. Ultrastructural observation reveals smooth unit-membrane vesicles from 0 · 4 – 1 · 7 μ m diameter. No contamination by nuclei, mitochondria or lysosomes is detected microscopically. Radiolabelled lectin-binding experiments [125I-RCA1, 125]-green pea lectin] indicate that cell surface label cofractionates with material identified morphologically as plasma membrane. Estimates of total recovery of membrane, based upon the lectin data, average 33%. Biochemical analysis of subcellular markers reveal that no detectable DNA and only 1.2% of the total cellular RNA cofractionate with membranes. A variety of enzyme assays suggests little contamination by cytosol enzymes, Golgi material or mitochondria. Assays of 5 ‘-nucleotidase (E.C. 3.1.3.5) indicate that this enzyme is not a major component of developing mouse spermatogenic cell membranes. Instead, Sertoli cells represent the most important source of this enzyme in the adult seminiferous tubule. Polyacrylamide gel analysis of membranes isolated from purified germ cells reveals significant differences in the protein compositions of pachytene spermatocyte and round spermatid membranes. The preparation of highly purified plasma membranes from homogeneous populations of spermatogenic cells should facilitate the biochemical characterization of cell surface antigens specific to developing male germ cells.
The myocardial plasma membrane during development: influence of glutaraldehyde fixation on the density and size of intramembranous particles
Authors: Gros Daniel , Potreau Daniel , Mocquard Jean-Pierre
Published: April 2021

The ultrastructure of the plasma membrane of mouse myocardial cells has been studied during development (from 10 days post-coïtum to the adult stage) using the freeze-cleave method, and the effect of glutaraldehyde-fixat10n on this structure has also been evaluated. Blebs, free of intramembranous particles (IMP), were found to be dependent upon the developmental stage and upon fixation with glutaraldehyde. On P and E fracture faces, the presence of IMP-free areas was age-dependent and fixation-independent. No difference was demonstrated in the IMP density during heart development. Fixation with glutaraldehyde retains in the plasma membrane approximately 40% of IMP, probably by preventing an alteration induced by glycerol. Whatever the developmental stage, E face-associated particles are significantly larger than P face-associated particles. The diameter of both types of particle increases slightly but irregularly as myocardial cells mature. Fixation reduces the particle size on both fracture faces in such a way that no significant difference between them can be demonstrated.
Evidence of low molecular weight rnas involved in permanent character changes in amoebae
Authors: Hawkins Shirley E.
Published: April 2021

Previous studies have established that ‘informational molecules’ present in cytoplasmic fractions of A. discoides may be transferred by microinjection into A. proteus. Clones derived from injected cells showed various changes, including lowered sensitivity to growth in streptomycin and neomycin, in which respects they resembled A. discoides. These changes in response to antibiotics were transferred independently and were permanent, the information being replicated over many generations. The most ‘active’ material in terms of the number of clones showing character changes was found following injection of 16s ribonucleoprotein obtained after sucrose density gradient centrifugation of the microsomal fraction. Polyacrylamide gel electrophoresis of the 16s material showed 3 small peaks of RNA. In order to obtain adequate amounts of material, these peaks of RNA were identified in electrophoresis profiles of RNA extracted from the whole microsomal fraction, and RNA eluted from these latter gels was injected into A. proteus. Although the number of surviving clones was low, all were examined for their response to growth in either streptomycin, neomycin, erythromycin or chloroquine. After injection of RNA eluted from the 3 small peaks of RNA (slices 26-33), 8 out of 10 and 9 out of 10 clones showed lowered sensitivity to growth in streptomycin and neomycin respectively, and resembled the donor A. discoides. No changes in response to antibiotics were obtained from clones derived from cells injected with RNA eluted from another region of the gel, or after ribonuclease treatment of the RNA from slices 26-33. The relative molecular weights of these ‘informational’ RNA molecules were found to be between 9 and 13 × 104 Daltons.
Spontaneous spatio-temporal organization in yeast cell suspension
Authors: Jacobsen H. , Busse H. G. , Havsteen B.
Published: April 2021

Under suitable conditions of substrate supply, cell suspensions of yeast Saccharomyces uvarum may display synchronized oscillations of glycolytic metabolism.

Also in an unstirred suspension, spatial patterns can be induced by continuously feeding enzymically liberated glucose into the system. The absorption of NADH in the suspension was measured in an annular cuvette. The observed structures display moving waves, which travel over a distance of some centimetres in the cell suspension and seem to originate from a volume element in which the phase is ahead of those of its neighbours. The wavelength is estimated to be about 10 cm and the velocity of spreading of the wave is about 5 cm/min. Waves are only observed in the beginning of glycolytic oscillations. Subsequently the spatial synchrony usually increases and destroys the previous organization.

Similar spatio-temporal structures are observed during aggregation of the slime mould Dictyostelium discoideum and in the chemical reaction system of Belousov and Zhabotinsky.
Cytoskeleton changes in fibroblast adhesion and detachment
Authors: Badley R. Andrew , Woods Anne , Carruthers Linda , Rees David A.
Published: April 2021

The organization of the cytoskeleton in several anchorage-dependent fibroblast types has been compared with the pattern of adhesions to a glass substratum which will support either their growth or just their spreading. Components were stained separately for immunofluorescence microscopy using specific antisera against actin, tubulin, and gizzard 10-nm filament protein, and the adhesions were visualized by interference-reflexion microscopy.

Of the cytoskeleton features, only stress fibres could be related to the pattern of focal adhesions; as shown before, each focal adhesion lies directly beneath a stress fibre, often near the terminus. Cells spread on fibronectin-treated glass in serum-free medium to arrest the development of focal adhesions, show correspondingly underdeveloped stress fibres. Actin geodesic domes, microtubules, and 10-nm filaments showed no relations with the adhesion pattern. During cell rounding leading to detachment with either EGTA or trypsin, stress fibres begin to disperse in advance of shape change whereas microtubules and 10-nm filaments seem to alter their distribution as a consequence of shape change. We therefore confirm that stress fibres are the cytoskeleton features most directly related to focal adhesions and are cytoskeleton targets for 2 agents which cause rounding and hence detachment.

The sequences of events in dispersal of stress fibres by EGTA and by trypsin showed significant differences in detail. With trypsin, fibres higher in the cell and terminating at the cell edge were more sensitive than most basal fibres and, during disintegration, all types of fibre went through an intermediate ‘beaded’ structure. With EGTA, all stress fibres seemed to be similarly susceptible and the beaded stage was not seen. The implications of these differences for our understanding of the mechanisms of dispersal of stress fibres are discussed.
Analysis of the cell adhesion mechanism using somatic cell hybrids: I. aggregation of hybrid cells between adhesive v79 and non-adhesive ehrlich’s ascites tumour cells
Authors: Aoyama Hirohiko , Okada T. S. , Takeichi Masatoshi
Published: April 2021

V79 Chinese hamster cells dissociated with 1 mM EDTA retain 2 kinds of cell adhesion mechanisms, one dependent on Ca2+ and the other independent of Ca2+. Ehrlich’s ascites tumour (EAT) cells are provided with neither Caa+-dependent nor Ca2+-independent mechanisms. Studies on the aggregation of cells of 25 different hybrid clones obtained by fusing these 2 lined cells revealed the following points with regard to adhesive properties of hybrid cells. (1) The activity of the Ca2+-independent mechanism was lower in most hybrid clones than in parental V79 cells. (2) There were a few hybrid clones whose Ca2+-dependent mechanism activity was lower than in V79 cells. In these clones, the Ca2+-independent mechanism was also less active than the parental cells. (3) A hybrid clone with reduced Ca2+-dependent mechanism activity only was not found. (4) All the hybrid clones have at least one set of chromosomes derived from V79. (5) The number of chromosomes derived from EAT cells tended to be less in hybrid clones with lower aggregative ability.

These results can be explained by assuming that the activity of the Ca2+-independent and Ca2+-dependent mechanisms of V79 cells may be differently inhibited by genes contained in EAT cells.
Fusion of human erythrocytes induced by sendai virus: Freezefracture aspects
Authors: Silva Pedro Pinto Da , Shimizu Kazufumi , Parkison Clifford
Published: April 2021

Analysis of the freeze-fracture morphology of human erythrocytes during Sendai virus-induced fusion indicates that it occurs in several spots, with the formation of membranebound cytoplasmic connexions. Radial expansion of these connexions causes the formation of a polymorphic network of membrane tubules with a lumen continuous with the external space. Our results are best explained assuming that the viral envelopes do not necessarily participate directly in inter-membrane fusion but, instead, indirectly through conditioning and modification of the erythrocyte membranes by viral membrane components.
Temperature-sensitive periods of mutations affecting cell division in Tetrahymena thermophila
Authors: Frankel Joseph , Mohler Jym , Frankel Anne Koopmans
Published: April 2021

Temperature-sensitive periods were determined by application of temperature shifts and shocks to 3 temperature-sensitive cell division arrest (cda) mutants of Tetrahymena thermophila. A restrictive temperature, 36 °C, was found at which all 3 mutants are fully penetrant, yet other physiological effects are minimal. At this temperature, the temperature-sensitive period of cdaC2, is a unique 5-min period in mid-division, that of cdaAi is a similarly brief period situated about 0.5 h prior to cell division, while the temperature-sensitive period of cdaHI is 20 to 30 min long and immediately precedes cell division. These periods either coincide with (cdaC2, cdaHI) or immediately precede (cdaAt) the onset of phenotypic abnormality at the restrictive temperature. Brief exposure to 36 °C during the temperature-sensitive period in any of these mutants brings about irreversible arrest of division furrows in progress or preparation. Mutant cells suffering such arrest can, however, divide again at a permissive temperature by forming new furrows at different sites.
Vitellogenesis in the stick insect Carausius morosus I. Specific protein synthesis during ovarian development
Authors: Giorgi Franco , Macchi Fausto
Published: April 2021

Vitellogenesis in the stick insect Carausius morosus (Br.) has been studied with the goal of identifying vitellogenin in various tissues. Following exposure in vivo to radioactive amino acids, oocytes in the medium size range are labelled with a minimum delay of 6 h after the time of injection. Incorporation of radioactivity under these conditions is shown to depend upon accumulation of proteins rather than on a differential rate of protein synthesis in succeeding stages of oogenesis.

By immunochemical analyses, it is shown that at least two antigens are common to both haemolymph and ovary and that one of these is also present in the fat body. Both antigens are labelled during exposure to radioactive amino acids. When analysed by SDS polyacrylamide gel electrophoresis, extracts from both haemolymph and ovary appear to share a number of protein fractions which range in molecular weight from 40000 to 200000 Daltons. The labelling pattern exhibited by these fractions is clearly indicative of a protein transfer from the fat body to the oocyte. Fat body cultured in vitro for up to 4 h releases a major macromolecular complex in the external medium. The latter has been identified as vitellogenin by both immunoprecipitation assay and SDS polyacrylamide gel electrophoresis. The protein which is synthesized and secreted under these conditions results from the processing of a protein complex of higher molecular weight.
Relationships between mitochondrial outer membranes and agranular reticulum in nervous tissue: ultrastructural observations and a new interpretation
Authors: Špaček J. , Lieberman A. R.
Published: April 2021

This study is concerned with extensions of the outer membrane of mitochondria in cells of nenous tissue, and with possible relationships between the extensions and the agranular reticulum. A variety of preparative techniques was applied to a large number of different central nervous tissues (CNS) and peripheral nervous tissues (PNS), using conventional thin sections, thicker sections (100 nm or more) and 3-dimensional reconstructions of serial thin sections. Extensions were commonly observed, particularly from the ends of longitudinally oriented mitochondria in axons and dendrites. Often these had the appearance of, and could be traced into apparent continuity with, adjacent elements of the agranular reticulum. In addition to these apical tubular extensions, we also observed and reconstructed short lateral tubular or sac-like extensions and vesicular protrusions of the outer mitochondrial membrane. We discuss and discount the possibility that the extensions are artefacts, consider the structural and biochemical similarities between the outer mitochondrial membrane and the agranular reticulum and propose that the outer mitochondrial membrane is part of the agranular reticulum (or a specialized portion of the agranular reticulum). We suggest that the translocation of mitochondria in nerve cells, and probably in other cells as well, involves movement of the inner mitochondrial membrane and the enclosed matrix (mitoplast) within channels of agranular reticulum in continuity, or in transient continuity, with the outer mitochondrial membrane.
Flagellar roots, mating structure and gametic fusion in the green alga Ulva lactuca (Ulvales)
Authors: Melkonian M.
Published: April 2021

The slightly anisogamous gametes of Ulva lactuca exhibit a cruciate flagellar root system consisting of 4 microtubular roots (4-2-4-2-system) and an elaborate system of fibrous roots associated with the 2-stranded microtubular roots. Two fibres (32-nm striation periodicity; system I fibres) closely underlie each of the 2-stranded roots, while different fibres (150-nm striation periodicity; system II fibres) run parallel to the root microtubules, and are 150-200 nm more internally located. Female gametes have 4 system II fibres, 3 of which are combined into a compound fibre associated with one microtubular root, while the fourth fibre is associated with the opposite root. In male gametes only 2 system II fibres are present, each underlying one of the two 2-stranded roots.

A special region of the plasmalemma of both gamete types about 0·5 µ m away from the basal bodies and located between 2 adjacent microtubular roots is structurally specialized and acts as a mating structure in gametic fusion. The region is oval-shaped and up to I·I µ m long with a maximum diameter of 0·7 µm. A continuous electron-d ense boundary layer underlies the plasmalemma at the edges of the mating structure. In both gamete types the mating structure consists of a fuzzy layer of material underlying the plasmalemma and special granules (60 nm diameter) are associated with this layer on its cytoplasmic side. In addition diffuse material overlies the mating structure, especially in male gametes. The mating structure is connected to 3 different kinds of flagellar roots: the boundary layer is linked to a 2-stranded microtubular root and its associated system I fibre; the fuzzy layer of the mating structure is connected with a system II fibre; and in female gametes this is the compound system II fibre.

The ultrastructural changes which occur after mixing the 2 gamete types have been followed. Mating structure activation involves contraction of system II fibres (change of striation periodicity to 100 nm), detachment of special granules from the fuzzy layer of the mating structure and their replacement by electron-transparent vesicles at the prospective cell fusion site. Furthermore, release of electron-dense contents from Golgi-derived vesicles in the anterior part of both gamete types precedes cell fusion. Cell fusion is exclusively initiated in a region delimited by the 2 mating structures. After partial dissolution the 2 plasma membranes unite within the mating structure regions.

The ultrastructure of gametic fusion in Ulva lactuca is compared to that of other green algae and the significance of flagellar roots in the mating process of green algae is discussed.
The effects of Con A on cell surface shedding in cell cultures
Authors: Doetschman Thomas C.
Published: April 2021

A cell surface immobilizing concentration of Con A inhibits the shedding of [sH]fucose-containing glycoproteins from the surface of chick embryonic leg and breast muscle cell cultures and cultures of the rat skeletal muscle cell line L6. The Con A-induced inhibition of shedding is much less in the mouse fibroblast cell line 3T3. In all 4 cell types the lectin inhibits the shedding of some fucosyl-glycoproteins more than others, especially those of a lipid-containing fraction which is excluded in Biogel A-5m chromatography. This differential nature of the Con A effect is not changed by the cytoskeletal disruptors cytochalasin B or colchicine. Con A causes an increase in the amount of trypsin-sensitive surface fucosyl-glycoprotein in the cell surface and appears to decrease the overall amount of cell surface degradation suggesting that the inhibition of shedding caused by Con A is not due to an increase in internalization and degradation. The data suggest that some shedding may occur at specific cell surface sites to which surface materials must laterally migrate.
Observations on the mitochondrial reticulum in the yeast Candida utilis as revealed by freeze-fracture electron microscopy
Authors: Keyhani Ezzatollah
Published: April 2021

Freeze-fracture of Candida utilis yeast cells grown to early logarithmic phase (5 h) and stationary phase (24 h) revealed a branched mitochondrial reticulum both in longitudinal and transverse cross-fracture studies. In contrast, longitudinal and transverse sections of permanganate-fixed cells showed that the small ovoid or spherical mitochondria were located at the periphery of the cell, without formation of a reticulum. Data indicate that the separate mitochondrial profiles seen in thin sections of permanganate-fixed yeast cells are not separate round or ovoid mitochondria, but rather are cross-sections of the mitochondrial reticulum.