bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assay of intercellular adhesiveness using cell-coated sephadex beads as collecting particles*
Authors: Vosbeck Klaus , Roth Stephen 
Published: April 2021

ABSTRACT
A simple, rapid and precise method, based on a previous method, for measuring relative rates of intercellular adhesion is described. DEAE-Sephadex beads were treated with nitrocellulose in order to allow cells to grow on their surfaces. Balb/c 3T3 and Balb/c 3T12 cells were used to characterize the assay. They formed confluent cell layers on nitrocellulose-treated DEAE-Sephadex. These cell-coated beads were employed to collect 32P-labelled cells from single cell suspensions. Since they formed statistically uniform, large collecting surfaces, the collection of labelled cells was markedly improved as compared to the original assay. The cell-coated beads collected a large percentage of the labelled cells in a short time. The percentage of cells collected was independent of the concentration of labelled cells in the assay mixture, and the collection was linear for approximately 60 min. The variability between replicate assays was usually ± 5 %. The assay allows the rapid and precise determination of intercellular adhesion in large numbers of individual samples. These features make it useful to screen for effects of different treatments on intercellular adhesion.
Mechanisms of cell adhesion: Early-forming junctions between aggregating fibroblasts
Authors: Lloyd C. W. , Rees D. A. , Smith C. G. , Judge F. J. 
Published: April 2021

ABSTRACT
When cultured fibroblasts (16C) are mildly dissociated with EGTA or trypsin/EDTA, they aggregate rapidly. The formation of aggregates has been found to involve junctions of the gap and adhaerens types which are seen by electron microscopy within minutes of allowing cells to come together. The process of adhesion between freshly dissociated, transformed 16C fibroblasts is therefore organized and establishes its usefulness as a model for studying cellular interactions in relation to supracellular organization.
Biochemical studies of mammalian oogenesis: Protein synthesis during oocyte growth and meiotic maturation in the mouse
Authors: Schultz Richard M. , Wassarman Paul M. 
Published: April 2021

ABSTRACT
Using oocytes isolated from juvenile and adult mice, we have examined the qualitative patterns of protein synthesis during growth and during meiotic maturation of these oocytes. Oocytes were cultured in a defined medium in the presence of [35S]methionine and radioactively labelled proteins were separated by SDS-polyacrylamide gel electrophoresis and detected by fluorography. The results of these studies demonstrate that: (i) the patterns of protein synthesis are very similar in individual oocytes which are at the same stage of growth or of meiotic maturation, indicating a high degree of biochemical homogeneity in a given population of isolated mouse oocytes, (ii) the linear increase in protein content of growing mouse oocytes (with respect to oocyte volume) is accompanied by significant qualitative changes in the size classes of proteins synthesized, and (iii) meiotic maturation (germinal vesicle dissolution and nuclear progression to the second metaphase) is characterized by several discrete qualitative changes in the pattern of protein synthesis in the oocyte, especially during the period following germinal vesicle breakdown. Experiments carried out with oocytes cultured in the presence of drugs which have been shown to inhibit meiotic maturation at specific stages of nuclear progression suggest that: (i) protein synthesis is not required for germinal vesicle breakdown to take place; (ii) mixing of the oocyte’s nucleoplasm and cytoplasm must occur in order for those changes in the pattern of protein synthesis which characterize meiotic maturation to take place; and (iii) failure of nuclear progression to proceed beyond the circular bivalent stage does not prevent those changes in the pattern of protein synthesis which characterize meiotic maturation from taking place. The latter observations suggest that there are basic differences in the control of meiotic maturation in oocytes isolated from mammalian, as compared to non-mammalian, animal species.
The self-assembly of synthetic filaments of myosin isolated from Chaos Carolinensis and Amoeba Proteus
Authors: Condeelis John S. 
Published: April 2021

ABSTRACT
Synthetic myosin thick filaments were formed from preparations of electrophoretically homogeneous myosin isolated from Chaos carolinensis and Amoeba proteus when dialysed to physiological ionic strength and pH. Myosin dialysed directly against low ionic strength buffers formed native-like thick filaments in the presence and absence of exogenous divalent cations. The average dimensions of the synthetic filaments grown under these conditions were 455 nm long and 16 nm wide with a distinct bare central zone 174 nm long.
Myosin predialysed against EGTA-EDTA solutions at high ionic strength and then dialysed to low ionic strength formed native-like filaments only in the presence of 1 mM Mg2+. 1 mM Ca2+ could not be substituted for Mg2+ under these conditions to achieve native-like filaments. Filaments grown from predialysed myosin in the absence of Mg2+ resembled EGTA-dissociated myosin filaments observed in EGTA-treated cytoplasm and were highly branched, poorly formed filaments lacking a distinct bare central zone. The average dimensions of the filaments grown from predialysed myosin in the absence of Mg2+ were 328 nm long, 13 nm wide with a bare central zone 111 nm long.
Under the conditions tested, myosin isolated from these amoebae did not demonstrate a divalent cation requirement for thick filament formation. The results obtained with myosin isolated from the 2 organisms were identical.
Accumulation of gene products in the oocytes of the dragonfly Cordulia Aenea: II. Induction of annulate lamellae within dense masses during diapause
Authors: Halkka Liisa , Halkka O. 
Published: April 2021

ABSTRACT
During the 3 years of nymphal development of the dragonfly Cordulia aenea, gene products slowly accumulate in the cytoplasm of the previtellogenic oocytes. Nuclear extrusions separate into nematosome and dense-mass components. The dense masses, RNP-containing globules of tightly packed fibrillar material, disperse throughout the oocyte cytoplasm.
The last instar nymph experiences an obligatory diapause, after which oocyte development passes from mid to late previtellogenesis, and eventually to vitellogenesis proper in the adult. During diapause, annulate lamellae are induced within the dense masses. This process is continued during late previtellogenesis. The formation of annulate lamellae may be related to activation of some genetic message stored in the dense masses. The possibility of tubulin synthesis is discussed.
Cytochalasin B-induced pseudo cleavage of mouse oocytes In Vitro: II. studies of the mechanism and morphological consequences of pseudocleavage
Authors: Wassarman P. M. , Ukena T. E. , Josefowicz W. J. , Letourneau G. E. , Karnovsky M. J. 
Published: April 2021

ABSTRACT
Mouse oocytes are induced by cytochalasin B to undergo ‘pseudocleavage’ in vitro into 2 compartments, only one of which possesses microvilli. It has been found that this particular response to cytochalasin B is related to oocyte size and, possibly, to the acquisition of meiotic competence by the oocyte during its growth phase. Certain of the morphological events which characterize pseudocleavage have been determined using transmission and scanning electron microscopy. These events include : (i) an initial withdrawal of microvilli from the surface of the oocyte, together with the concomitant disappearance of microfilaments normally associated with the microvilli; (ii) the subsequent formation of a pseudocleavage furrow and contractile ring; and (iii) the reappearance of microvilli and associated microfilaments in one of the two resulting oocyte compartments. These changes in surface architecture are reflected in the distribution of fluorescein-conjugated lectins bound to the oocyte surface during pseudocleavage.
Electron-microscopic autoradiography of tritiated testosterone in rat testis
Authors: Frederik P. M. , Molen H. J. Van Der , Klepper D. , Galjaard H. 
Published: April 2021

ABSTRACT
The feasibility of a technique for autoradiography of diffusible substances has been further tested by analysing the localization of steroids in rat testes with the light- and electron-microscope. Testes of rats were perfused with tritiated testosterone (3 min) followed by 15-min perfusion with buffer containing a 100-fold excess of unlabelled testosterone. Tissue samples were frozen, freeze dried, fixed in osmium vapour and embedded in Epon. To exclude extraction of steroids, contact with water and other solvents was prevented during cutting of thin sections on an ultracryotome and further treatment for autoradiography. Light- and electron- microscopic observations indicate that the highest concentration of labelled testosterone was present within the basal parts of the Sertoli cell cytoplasm and in lipid inclusions of Sertoli cells within the seminiferous tubules. This is the first account of autoradiography of steroids at the electron-microscope level.
Mass isolation of polytene nuclei from Chironomus salivary glands
Authors: Mähr R. , Lezzi M. , Eppenberger H. M. 
Published: April 2021

ABSTRACT
In this paper we describe a method for the rapid mass isolation of polytene nuclei from Chironomus salivary glands. The procedure for the isolation of glands involves 5 principal steps; (a) freezing Chironomus larvae in liquid propane; (b) breaking open frozen animals in a precooled mortar; (c) thawing the fragments in sucrose medium, free of divalent cations; (d) pressing the suspension of broken animals through a system of regularly spaced capillary constrictions to free organs; and (e) enrichment of glands by differential sedimentation and removal of contaminating material under a dissecting microscope. The nuclear isolation procedure is a large scale modification of a method previously described by Robert, using digitonin as a non-ionic detergent to solubilize cytoplasma and secretion without affecting the nuclear membrane. Nuclei obtained by this method show structural integrity and an unchanged chromosomal banding pattern. Their incorporation of UTP is within the same range as reported by other authors for nuclei isolated by hand dissection.
The fixation of nuclei in glutaraldehyde
Authors: Skaer R. J. , Whytock Susan 
Published: April 2021

ABSTRACT
The production of an artifactual network in the nuclear sap of the salivary glands of Drosophila has been investigated. Mechanical stress to the cells, 3 % glutaraldehyde containing more than 4 mM calcium, tannins, or cacodylate buffer or whose temperature is above 10 °C all enhance this artifactual effect. Over the range pH 6· 65–7·4 there is no significant effect of pH. The inclusion of sucrose, and adenine nucleotides or other ‘chelating’ agents in the fixative reduces the effect, especially at low temperature (6–10 °C). These influences are additive and can abolish the artifactual effect. So too can 8 % glutaraldehyde, but this is irrespective of temperature.
Structural cross-bridges between microtubules and mitochondria in central axons of an insect (Periplaneta americana)
Authors: Smith David S. , Järlfors Ulla , Cayer Marilyn L. , Cameron Bruce F. 
Published: April 2021

ABSTRACT
The distribution of microtubules and mitochondria in central axons of an insect (Periplaneta americana) is assessed by comparison between counts on micrographs and computed axon random ‘models’. These studies show that the observed multiple association of microtubules with individual mitochondria is statistically highly significant. Electron micrographs of thin sections show that linkage is effected by physical cross-bridges, possibly comprising components from the microtubule and mitochondrion. Linear particle arrays are described on the outer mitochondrial membrane in freeze-fracture replicas, and tentatively related to the bridges seen in thin sections. The results are discussed in terms of proposed roles of microtubules in neurons and other cells.
Novel behaviour of the mitotic clock in physarum
Authors: Wille John J. , Scheffey Carl , Kauffman Stuart A. 
Published: April 2021

ABSTRACT
Surface plasmodia of the myxomycete, Physarum polycephalum were subjected to heat shocks at 38 °C for varying durations either in late G2, or at M + 4 h, and the excess delay to the next synchronous mitosis observed. Three-hour heat shocks applied in late G2 yielded mitotic excess delays which clustered at peaks of 4–5, 11–12 and 22–23 h. Hence plasmodia can skip part of a cycle, one full cycle, or even two full cycles, yet continue to count cycle times up to two cycles. This is one line of evidence that mitosis itself is not a necessary condition for timing the length of the mitotic cycle. In a large number of late G2 shocks, only a fraction of the nuclei divided at 4–5 h excess delay, and then went through their first full synchronous mitosis at 12 h excess delay. These partial mitoses also were observed for plasmodia which had their first full synchronous mitosis at 22–24 h excess delay. The fraction of nuclei which undergo partial mitosis is nearly independent of the mitotic interval occurring between the partial mitosis and the first full synchronous mitosis, indicating that nuclear:cytoplasmic ratio is unlikely to be the sole factor governing mitotic cycle length. The dependence of mitotic excess delay on: (1) the exact time at which heat shock began shortly before mitosis; (2) the condition of the culture from which a set of plasmodia were plated; (3) the average cycle length; (4) the occurrence of nucleolar breakdown; and (5) the extent of plasmodial death, is minimal. Six-hour heat shocks applied in late G2, also yielded rhythmical mitotic excess delay responses with peaks at 6–8, 14–16, and 26–27 h excess delay. Nine-hour heat shocks given in late G2 produced the greatest mean excess delays (17·5 h). Finally, plasmodia exposed to 12-h heat shocks in late G2, yielded mitotic excess delays with a mean of 10· 7 h, considerably less than either the 6–or 9–h heat shocks. In contrast, plasmodia given a 3–, 6– 9-, or 12–h heat shock at M+4 h showed only a monotonically increasing mitotic excess delay, which never exceeded one full cycle of delay.
The above results are consistent with and predicted by the mitotic oscillator model in which the periodicity of the mitotic cycle is underlain by a continuous biochemical limit cycle oscillation, which drives mitosis but which continues to oscillate even when mitosis is suppressed.
The abdominal epidermis of the blowfly Calliphora erythrocephala II. imaginal histoblasts during larval life
Authors: Pearson Murray J. 
Published: April 2021

ABSTRACT
Abdominal histoblasts in Calliphora (Díptera) are situated within the larval epidermis, and secrete larval cuticle throughout the 3 larval instars. An optical and electron-microscopic study of histoblasts and epidermal sensilla suggests that the latter have been previously confused with histoblast Anlagen in the first instar.
A steady rate of division until the mid-third instar leads to Anlagen growth, which is not seen in larval Drosophila. After a relatively quiescent period, division begins again, at a higher rate, at the time of pupariation (at the time when division first begins in Drosophila’). During prepuparial larval life, the ventral, dorsal, and postero-dorsal Anlagen increase from approximately 6, 8 and 4 cells to about 350, 500 and 150 cells respectively.
At the time of the second (puparial) mitotic phase there is also extensive reorganization of cellular fine structure in which large secondary lysosomes play an important part. The endoplasmic reticulum and Golgi subsequently present a different profile. At the same time numerous chromatic droplets appear in the rapidly dividing histoblast Anlagen. This division and the appearance of chromatic droplets are shown (and the subcellular reorganization is suggested) to depend upon the hormonal factors which are responsible for pupariation.
The dissociation of nuclear proteins from superhelical DNA
Authors: Levin Jeremy Max , Jost Erich , Cook Peter Richard 
Published: April 2021

ABSTRACT
Structures retaining many of the morphological features of nuclei may be released by gently lysing human cells in solutions containing non-ionic detergents and high concentrations of salt. These nucleoids contain superhelical DNA. Using a double-labelling procedure we have compared, at different salt concentrations, the amounts and types of protein associated with human nucleoids containing superhelical or relaxed DNA. We find that the slightly lysine-rich histones (H2A and H2B) but not the arginine-rich histones (H3 and H4) dissociate more slowly from nucleoids containing superhelical DNA than from those containing relaxed DNA. A protein of apparent molecular weight of 22000 also binds more tightly to superhelical DNA. We conclude that this protein and the slightly lysine-rich histones transmute free energy of supercoiling into binding energy when they bind to superhelical DNA.
Endocytosis and streaming of highly gelated cytoplasm alongside rows of arm-bearing microtubules in the ciliate Nassula
Authors: Tucker J. B. 
Published: April 2021

ABSTRACT
The microtubular cytopharyngeal basket acts as a jet engine when Nassula ingests filaments of blue-green algae. Prolonged and highly directed cytoplasmic streaming forms the main mechanical basis for propulsion of algal filaments through the basket. Cytoplasm surrounding such filaments streams at the same rate as that at which filaments travel through the basket’s interior. This cytoplasm appears to be very highly gelated. The arm-bearing surfaces of certain rows of microtubules seem to be located in the active shear zone where the forces responsible for cytoplasmic streaming are generated.
Algal ingestion represents a rapid and large scale form of endocytosis. An algal filament is contained in a long membranous invagination from the ciliate’s cell surface as it is drawn through the basket. The invagination moves through the basket at the same velocity as the algal filament and surrounding cytoplasm. The arm-bearing microtubules do not appear to bind directly to the invagination which consists of two unit membranes. One of these is probably an invagination of the cell surface membrane. The origin of the other membrane has not been ascertained.
There are indications that microtubule sliding and a contractile ring of microfilaments operate antagonistically during feeding to evert and re-invaginate a cell surface depression where the top of the basket is located.
Fine-structural aspects of fertilization in Chlamydomonas Reinhardi
Authors: Friedmann I. , Colwin A. L. , Colwin Laura H. 
Published: April 2021

ABSTRACT
Gametes of C. reinhardi lack the cell wall which vegetative cells possess. Just below the cell apex gametes form a. fertilization tubule which is up to 2 μ long and 0·2 μ in diameter; its plasma membrane and that of the apex have slender tubular projections. At the base of the fertilization tubule regularly lies the choanoid body, a collar-shaped cytoplasmic organelle; the plasma membrane overlying the body appears as an electron-dense ring. Gametes possess two ‘free’ basal bodies in addition to the basal bodies of the two flagella.
In the initial stage of union the conjugating cells are connected by the fertilization tubule whose plasma membrane is continuous with that of both copulants. At one end of the tubule lies a conspicuous choanoid body, but at the other end is a small structure which possibly is a homologue of the choanoid body. Subsequently, the fertilization tubule shortens and widens until finally no tubule exists and the apical ends of the two protoplasts adjoin. The merging cells then bend like a jack-knife and lateral alignment of the protoplasts occurs. This four-flagellated zygote becomes motile at about the time when the flagellar bases of the former gametes seem to approach each other and when fibrillar elements of the flagellar roots come into contact. In the motile zygote the nuclei do not fuse but remain ensheathed in the cup-shaped plastids of the two gametes.
A mating of plus (+) and minus (−) strains cultured, respectively, for high and low starch content suggested that gametes of only the plus (+) mating type contain the choanoid body. Since it appears that the gamete containing the choanoid body also produces the fertilization tubule, it is inferred that gametes of only the plus (+) mating type produce the fertilization tubule. Should further investigation support this inference, it would be established that there is a structural basis for designating the plus (+) mating type as male and the minus (−) type as female.
Fertilization involves fusion of the gamete membranes through the mediation of a specialized structure (the fertilization tubule) and in this respect there are similarities to certain aspects of fertilization in animal phyla. The relation of the fertilization tubule to the protoplasmic bridge of other species of Chlamydomonas is discussed.
The distribution of the protein-polysaccharide complex in the nucleus pulposus matrix in young rabbits
Authors: Smith J. W. , Serafini-Fracassini A. 
Published: April 2021

ABSTRACT
The distribution and relationship of the collagen and the proteinpolysaccharide complex in the extracellular matrix of the nucleus pulposus of the young rabbit were studied by electron microscopy. The polysaccharide was demonstrated by treatment of the tissue with either 0·5 % bismuth nitrate at pH 2 or a mixture of equal volumes of 1 % lead nitrate and 2 % osmium tetroxide at pH 5. The protein part of the complex was observed in tissue fixed in osmium tetroxide at pH 7·2 and stained with 1 % phosphotungstic acid. The collagen of the tissue was apparent in all preparations. The water-extracted proteinpolysaccharide was studied after coagulation of a concentrated solution in 0·5 % bismuth nitrate, whereas the isolated fibrous fraction was examined by negative staining of sprayed material.
Collagen is present in the intact tissues as native collagen fibrils of about 300 Å diameter, and as sheets, 400-Å thick, of parallel, separate, filaments of 50–60 Å diameter. Usually several such sheets lie close, and approximately parallel, to one another. After extraction of the proteinpolysaccharide from the tissue with water, all the collagenous components tend to aggregate into large native collagen fibrils.
Some of the proteinpolysaccharide complex of the intact tissue is free in the matrix. The polysaccharide moiety is visualized as 270 Å particles, serially attached to a protein core in the form of beaded filaments about 40 Å in diameter. The rest of the complex is attached to the sheets of collagen filaments in regular periodic zones which are 270 Å wide and centred 670 Å apart. None of the complex appears to be associated with the larger collagen fibrils.
The staining reactions of the polysaccharides in several connective tissues are discussed and the relationships of the proteinpolysaccharide complexes to collagen in cartilage, the vitreous body and the nucleus pulposus are compared.