bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclic membrane flow in the ingestive-digestive system of peritrich protozoans ii. cup-shaped coated vesicles
Authors: Mckanna J. A. 
Published: April 2021

ABSTRACT
As peritrich food vacuoles condense during the initial stage of digestion, excess membrane pinches off as cup-shaped vesicles which exhibit a structured coat on the non-cytoplasmic surface of the membrane. As the membrane cycles from cup-shaped vesicles to diskoidal vesicles to cytopharynx to food vacuoles, the coat undergoes structural transformations from the condensed form (5×16 nm peg-shaped elements) to an extended form (long thin filaments). Review of the literature reveals morphologically similar coats which undergo similar transformations in the digestive organelles of flagellate protozoa, Hydra absorptive cells, insect pericardial cells, ileal absorptive cells of suckling rats, cells of the guinea-pig placenta, mammalian Langerhans cells, and macrophages. The similar functional situation in which these coated membranes occur suggests that the coat is important to the recognition and binding of macromolecules.
Change in surface extensibility ofFundulusdeep cells during early development
Authors: Tickle Cheryll A. , Trinkaus J. P. 
Published: April 2021

ABSTRACTThe extensibility of the periphery of the deep cells of the Fundulus blastoderm was investigated by applying negative pressure to the cell surface in culture by means of a micropipette. The relative negative pressure required to produce standard deformations of the surface was measured for cells from embryos in 2 different stages of development. Less negative pressure was required to deform cells from early gastrulae than cells from early blastulae. This finding correlates with the behaviour of deep cells in vivo-, early blastula cells are rounded, form blebs, and do not engage in locomotion, whereas early gastrula cells form extended lobopodia and lamellipodia and engage actively in locomotion.
The patterned organization of thick and thin microfilaments in the contracting pseudopod of Difflugia
Authors: Eckert B. S. , Mcgee-Russell S. M. 
Published: April 2021

ABSTRACT
The lobopodial pseudopods of the shelled amoeba Difflugia undergo a rapid active contraction and length shortening which results in movement of the organism, or rapid pseudopod retraction. In polarized light, the pseudopod shows high birefringence before and during this normal contraction, suggesting a high degree of linear organization, and a complex pattern of changes. Immediately conventional fixation begins, pseudopods retract rapidly, and show changes in birefringence. When longitudinal sections are viewed in the electron microscope, such fixed, contracting pseudopods are seen to contain thick (14–16 nm) and thin (5–8 nm) microfilaments. Montages demonstrate that these microfilaments are found in close parallel association with each other, and lie parallel and peripheral to the longitudinal axis of the pseudopod, which is the axis of contraction. This distribution suggests that the patterned microfilaments could be involved in the shortening process and that they could account for the birefringence seen in the contracting pseudopod. Rapid alignment, or assembly, is also suggested.
A possible function of microtubules suggested by their abnormal distribution in rubbery wood
Authors: Nelmes Brenda J. , Preston R. D. , Ashworth Denise 
Published: April 2021

ABSTRACT
A difference in the distribution of microtubules in the peripheral cytoplasm of developing fibres has been observed between normal apple wood and that infected with ‘rubbery wood’ disease. In normal wood, where microtubules are abundant, the fibre wall is lignified, compact in texture and of limited thickness. In rubbery wood, where there are fewer microtubules, lignification is not complete in the fibre wall, which has a coarse, loose texture, and is abnormally thick. The whole stem is highly flexible. The pit membrane, which is unlignified in both normal and rubbery wood, has no microtubules adjacent to the plasmalemma.
It is suggested that microtubules are concerned in channelling into the wall substances, such as lignin precursors, which are essential for certain steps in the polymerization of the amorphous component of the wall.
Changes in structure of the disks of retinal rods in hypotonic solutions
Authors: Falk Gertrude , Fatt P. 
Published: April 2021

ABSTRACT
Changes in isolated frog rod outer segments, suspended in hypotonic solutions, have been examined by light and electron microscopy. Swelling of the disk occurs in hypotonic solutions. When one half or more NaCl is omitted from the Ringer solution used for suspending the rod outer segments, swelling is accompanied by the appearance of localized, irregular expansions projecting as buds from the disks. The axes of the buds tend to be in the plane of the disk, as can be seen in cross-sections of outer segments. In longitudinal sections of outer segments, the sectioned buds have profiles which were previously interpreted as vesicles. Attention is drawn to the properties of the disk edge, among which is a resistance to extension.
Dna replication in the chromosomes of the chicken, Gallus Domesticus
Authors: Mcfarlane Pamela W. , Callan H. G. 
Published: April 2021

ABSTRACT
DNA fibre autoradiography has been used to study the replication of chromosomal DNA from chicken cells in tissue culture at 37 °C. The S-phase is estimated to be about 7·5 h. Replication proceeds in the manner first described by Huberman & Riggs. Tandemly arranged units replicate bi-directionally from fork-like growing points, the times of initiation of individual repheating sections being staggered. Evidence against the existence of defined termini is presented. The rate of replication in these chicken cells is some 25–30 μm/h one-way. The mean interval between adjacent initiation points for replication is 63 μm, with a range of some 25–145 μm. Although initiation intervals vary in length, neighbouring intervals tend to be similar in length.
Proliferating hybrid cells formed between rat spermatids and an established line of mouse fibroblasts
Authors: Nyormoi Okot , Coon H. G. , Sinclair J. H. 
Published: April 2021

ABSTRACT
Proliferating hybrids were formed between rat spermatids and LM(TK−) cl 1 D, an established line of mouse fibroblasts. Spermatids were obtained from dissociated rat seminiferous tubules by differential attachment of testicular somatic cells to culture plates, followed by gravity velocity sedimentation into linear Ficoll gradients. Cells were fused with the aid of Sendai virus and hybrid selection was facilitated by the inability of cl 1 D cells to grow in HAT medium and the inability of spermatids to attach or proliferate in vitro. Three types of cells grew in fusion plates: (1) unfused contaminant rat testicular somatic cells; (2) rat testicular cell × cl 1 D hybrids and (3) rat spermatid × cl 1 D hybrids. Unfused rat testicular somatic cells were morphologically and karyologically different from either type of hybrid. The 2 hybrid classes were distinguished by the total number of chromosomes and the number of parental chromosome markers. Rat chromosomes are preferentially eliminated from haploid as well as diploid hybrids and at least 3 rat enzymes (lactate dehydrogenase, glucose phosphate isomerase and an unknown oxidase) are synthesized in hybrid clones of both types. The implications of partial haploid hybrids for genetic analysis are briefly discussed.
Sensitivity of the cell division cycle to α-amanitin in Allium root tips
Authors: De La Torre C. , Fernandez-Gomez M. E. , Gimenez-Martin G. , Gonzalez-Fernandez A. 
Published: April 2021

ABSTRACT
The effect of α-amanitin on the cell cycle in Allium cepa meristematic cells was studied: the G1 and G2 periods are prolonged respectively to 1·9 and 1·7 times the normal duration; the S-period is lengthened very little; and the prophase of mitosis is increased to twice the normal duration. It is postulated that real differences in the activity of the non-nucleolar RNA polymerase might exist in the course of the cell division cycle and that they would account for the higher sensitivities shown by G1, G2 and prophase.
On the other hand, the interphase nucleolus responds by segregation in the first few hours of α-amanitin treatment, but recovers its normal structure in continued presence of the drug; and nucleolar reorganization is inhibited in the first few hours in recently formed cells, but the process is subsequently speeded up to attain the same value 4 h after the treatment was begun as in untreated cells.
Arrangement of subunits in flagellar microtubules
Authors: Amos Linda A. , Klug A. 
Published: April 2021

ABSTRACT
Electron micrographs of outer doublet tubules from flagella have been analysed by methods which make use of the computed diffraction patterns of electron-microscope images. Analysis of singlet A-tubules in the tips of flagella has led to a determination of the helical surface lattice of the A-subfibre, confirming that there are 13 longitudinal protofilaments in the tubule wall and that dimers in neighbouring protofilaments form a staggered arrangement, equivalent to the lattice with an axial periodicity of 8 · 0 nm predicted in earlier work. A low-resolution 3-dimensional image of the A-tubule has been reconstructed, which supports the evidence for an 8 · 0-nm-long heterodimer oriented along the protofilaments. The heterodimer is identified as a pair of 4 · 0-nm morphological units, which appear to be globular at this resolution.
Filtered images have been obtained from doublet tubules which show that the B-subfibre is also made up of 8 · 0-nm dimers, but it differs from the A-tubule in that dimers in adjacent filaments are not in a staggered arrangement but are lined up obliquely at a shallow angle. Using the additional information about the hands of the lattices in the 2 subfibres which is presented in the accompanying paper, a model for the whole doublet has been proposed.
The hands of helical lattices in flagellar doublet microtubules
Authors: Linck R. W. , Amos Linda A. 
Published: April 2021

ABSTRACT
Negatively stained arrays of flagellar doublet microtubules have been tilted about an axis perpendicular to the tubule axes and imaged at angles of ± 20°. The images have been filtered to enhance the 4-nm periodicities in the tubulin lattice, and the resulting filtered images interpreted by comparison with simulated projections of tilted helical lattices. The different appearances of the edges of filtered doublet tubules for positive and negative tilt angles suggest that the 4-nm lattices of both subfibres are of the same hand, with the 3-start helices in each being left-handed. The information has been incorporated in a model proposed for the arrangement of subunits in doublet microtubules, which is described in the preceding paper.
An electron-microscope study of cell deletion in the anuran tadpole tail during spontaneous metamorphosis with special reference to apoptosis of striated muscle fibres
Authors: Kerr J. F. R. , Harmon B. , Searle J. 
Published: April 2021

ABSTRACT
The mechanism, of cell deletion responsible for involution of the anuran tadpole tail during spontaneous metamorphosis was studied by light and electron microscopy, attention being focused on epidermis and striated muscle.
The earliest indication of pending dissolution of epidermal cells was found to be aggregation of condensed chromatin beneath the nuclear envelope. This is followed by breaking up of the nucleus, and cytoplasmic condensation and budding with the production of a number of compact, membrane-bounded cell fragments with relatively well preserved organelles. These are then ingested and degraded by nearby viable cells, the majority by distinctive macrophage-like cells, which are scattered throughout the epidermis, and a few by epithelial cells. The morphological changes observed in the dying epidermal cells are the same as those described both in the ‘programmed cell death’ that plays an important role in the normal development of vertebrate embryos and in the type of cell death that has been shown to be involved in regulating the size of tissues in adult mammals under normal as well as pathological conditions; it has been suggested elsewhere that apoptosis might be a suitable name for the phenomenon.
Deletion of striated muscle fibres in the tadpole tail is accomplished by a process that appears to be a modification of classical apoptosis, in which dilatation and confluence of elements of the sarcoplasmic reticulum lead to internal fragmentation, the usual surface budding presumably being precluded by the large volume and specialized structure of these cells. The early and late nuclear changes, and the apparent ultrastructural integrity of organelles in the membrane-bounded muscle fragments are typical of apoptosis, and subsequent degradation within macrophages follows the standard stereotyped pattern. An essentially similar process has been described by others in the muscles of metamorphosing insect larvae, but whether striated muscle cells in adult higher vertebrates can undergo apoptosis is still uncertain.
The membranes of the basal labyrinth in kidney cells of the stickleback, Gasterosteus aculeatus, studied in ultrathin sections and freeze-etch replicas
Authors: Wendelaar Bonga S. E. , Veenhuis M. 
Published: April 2021

ABSTRACT
The structure of the basal labyrinth in kidney cells of freshwater sticklebacks was studied in ultrathin sections (after fixation with permanganate, osmium tetroxide, and combinations of glutaraldehyde with osmium tetroxide) and in freeze-etch replicas (after pretreatment with glutaraldehyde and/or glycerol, or without pretreatment). The structure of the basal labyrinth in sticklebacks, and probably in other teleost species, differs essentially from the type of labyrinth found in kidney cells of mammals like the rat. In the latter animals, the space enclosed by the membranes of the labyrinth is intercellular. In the stickleback the labyrinth consists of an intracellular system of branched membranes lining narrow saccular spaces. These spaces communicate with the exterior of the cells by means of small pores, located in the lateral and basal parts of the outer cell membranes.
All chemical fixation procedures used introduced specific structural artifacts. It is concluded that the structure of the basal labyrinth is relatively well preserved after fixation with potassium permanganate, with a mixture of glutaraldehyde and osmium tetroxide, or with osmium tetroxide when applied for 10 min only. The unit-membrane structure was, however, absent after all procedures involving osmium tetroxide.
In freeze-etch replicas determinations were made of the numbers of small particles covering the surfaces and fracture faces of the membranes of the basal labyrinth and of the outer cell membranes. The numbers per unit area of surface proved to be markedly constant and specific for each of the four faces of both types of membranes. Specific differences were found between the particle densities of the outer cell membranes and the membranes of the basal labyrinth. This finding points to functional differences between these types of membranes.
Particle densities were not influenced by pre-incubation with glycerol. After fixation with glutaraldehyde, the particles adhering to the outer and inner surfaces had decreased in number.
It is concluded from this study that membrane structure, as revealed in thin sections as well as in freeze-etch replicas, is consistent with Singer’s ‘fluid lipid-crystal protein’ model.
Growth and differentiation of the golgi apparatus in the red alga,Callithamnion roseum
Authors: Hawkins Eva Konrad 
Published: April 2021

ABSTRACTThe fine structure of the Golgi apparatus during development of tetrasporangia of Calli-thamnion roseum is described. Dictyosomes and associated vesicles of 4 developmental stages of sporangia are examined. The wall of sporangia exhibits a heretofore unseen cuticle in red algae. Development of the spore wall and a new plasma membrane around spores occurs through fusion of adjacent Golgi vesicles along the periphery of cells. Observations are discussed in relation to wall formation and expansion of tetrads and in comparison with other work on growth and differentiation of the Golgi apparatus.
Growth of human diploid fibroblasts in media with different amino acid composition
Authors: Litwin J. 
Published: April 2021

ABSTRACT
Human embryonic diploid lung fibroblasts were capable of growing in a medium consisting of Eagle’s MEM vitamins plus 0·1 μg/ml biotin, Earle’s salt solution, 4 mM glutamine, 0·4 mM cystine, 0·5 mM tyrosine, 10 % undialysed calf serum and 1 mM pyruvate. The growth rate and percent cell attachment in this medium was slightly less than in Eagle’s MEM but the longevity was about the same. Addition of 0· 5–1·0 mM histidine stimulated growth but addition of 0· 2 mM phenylalanine, methionine or valine decreased longevity markedly.
Maintaining a constant pH of about 7·5–7·6 with 20 mM of the organic buffers HEPES, TES or TRICINE yielded a growth rate equal to or better than that of cells growing in unbuffered medium. Some buffers gave good growth initially but eventually the longevity decreased (20mM BIS-TRIS, 20 mM BICINE, 10 mM TRIS). In almost all cases the initial exposure to the buffers yielded the best growth results.
Continuous nucleolar dna synthesis in late-interphase nuclei of Physarum polycephalum after transplantation into postmitotic plasmodia
Authors: Guttes E. 
Published: April 2021

ABSTRACT
In the myxomycete, Physarum polycephalum, nuclear DNA synthesis commences immediately upon completion of mitosis. While the synthesis of extranucleolar DNA is completed within a few hours, nucleolar DNA synthesis occurs during most of the S-phase and the entire G2 phase of the intermitotic period. When large (polyploid), late-interphase nuclei were allowed to bypass mitosis by transplantation into recipient plasmodia which were at early interphase and which belonged to a strain having smaller nuclei, the nucleolar DNA of the transplanted nuclei continued to be labelled (autoradiographs) after incubation of the host plasmodia with [3H] thymidine until they entered prophase along with the nuclei of the host plasmodium, approximately one intermitotic period later. This labelling was DNase-sensitive and RNase-resistant. When late-interphase nuclei were labelled with [3H]thymidine just prior to transplantation, there was no decrease of label after transplantation during the additional intermitotic period. We conclude from these experiments that there is no obligatory alternation between nucleolar DNA duplication and mitosis in Physarum polycephalum and that nucleolar DNA replication might exhibit amplification during an experimentally prolonged intermitotic period.
Nonhistone proteins of the oocyte nucleus of the newt
Authors: Hill R. J. , Maundrell K. , Callan H. G. 
Published: April 2021

ABSTRACT
Evidence has been obtained which indicates that disulphide bond crosslinks contribute to the morphological integrity of isolated lampbrush chromosomes (both chromomeres and lateral loops) and nucleoli. It is suggested that the progressive formation of these bonds in vitro by aerial oxidation may provide the basis for the previously recognized time-dependent hardening or ‘denaturing’ of these structures.
Manually isolated germinal vesicle nuclei have been massed and fractionated by low-speed centrifugation into nucleoplasm and chromatin. Phase-contrast microscopy demonstrates the chromatin to consist of nucleoli, lampbrush chromosomes and nuclear membranes.
Urea gel electrophoresis has been employed to resolve the reduced and S-carboxymethylated proteins of whole nuclei into some 12 components, negatively charged at pH 8. The nucleoplasm alone gives an essentially similar pattern, but with the distinct depletion of one component and slight depletion of another. Both of these components are much enriched in the chromatin pellet where they predominate over all other proteins.
The total chromatin has been subfractionated by microdissection, taking advantage of the differential attachment of nucleoli to the nuclear membrane at different stages of oogenesis. It is concluded that the nuclear membrane per se does not contribute to the major chromatin proteins. The two major polypeptides are components of the nucleoli. Preparations of isolated lampbrush chromosomes have not, to date, provided sufficient material to give a distinctive electropherogram; only one faint band, a major component of whole nuclei, was apparent.
Sodium dodecyl sulphate gel electrophoresis has resolved some 25 components in whole nuclei, and again demonstrates the enrichment of the two major species in the total chromatin fraction. The apparent molecular weights of these two species are 43 kilodaltons and no kilodaltons. Approximately 20 minor species are also present in the chromatin and are obviously good candidates as components of the nucleolar and chromosomal structures. Histones, at most, make only a minor contribution to the overall chromatin protein population.
Fusion of mouse fibroblasts with oleylamine
Authors: Bruckdorfer K. R. , Cramp F. C. , Goodall A. H. , Verrinder M. , Lucy J. A. 
Published: April 2021

ABSTRACT
As part of a search for chemical agents able to promote the fusion of mouse A 9 fibroblasts, oleylamine, a positively charged compound, has been investigated for its fusogenic properties. In the pH range 5·5–7·5 and in the presence of dextran, fibroblast polykaryons were produced on treatment of monolayers of cultured cells with oleylamine dispersed directly in a modified Eagle’s medium at concentrations of not less than 0·111 mg/ml. Electron microscopy demonstrated the absence of a dividing plasma membrane between the constituent nuclei of the polykaryons, and showed clustering of other subcellular organelles around their original parent nuclei.
Fusion, which was preceded by rounding and swelling of the cells, occurred between cells in contact after 10-15 min. Oleylamine in lipid droplets containing glyceryl mono- and dioleate also caused swelling and fusion but to a lesser extent. Phosphatidylcholine appeared to have an inhibitory effect on oleylamine-induced fusion : lecithin liposomes containing oleylamine were only weakly fusogenic. The fusion process, but not the preceding swelling, was calcium-dependent; fusion was inhibited by low concentrations of lanthanum ions.
While oleylamine inhibited cell division in monolayer cultures and prevented adhesion of fibroblasts in suspension to glass coverslips, oleylamine in lipid droplets was less toxic and is thus potentially more useful in this form for interspecific hybridization experiments.
Relationship between freezing rate, ultrastructure and recovery in a human diploid cell line
Authors: Beadle D. J. , Harris L. W. 
Published: April 2021

ABSTRACT
The relationship between freezing rate, ultrastructure and recovery in a human diploid cell line has been studied by freezing cells at rates that are known to give high and low recoveries and examining them immediately after thawing. Some correlation was found between structural damage and recovery. The main types of damage observed were loss of cytoplasm and nucleoplasm, indicating disruption of cellular membranes, and swelling of subcellular organelles due to osmotic changes during the freeze—thaw cycle. No simple correlation was found between freezing rate and structural damage. In the absence of a cryoprotectant both rapid and slow freezing produced similar types and amounts of damage resulting in low recovery. In the presence of 10 % dimethylsulphoxide, however, slowly frozen cells showed few signs of damage and recovery was high. DMSO had no such protective effect on rapidly frozen cells.