bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell to substratum contacts of chick fibroblasts and their relation to the microfilament system. a correlated interference-reflexion and high-voltage electron-microscope study
Authors: Heath J. P. , Dunn G. A. 
Published: April 2021

ABSTRACT
The interference reflexion microscope may be used to examine the pattern of cell-substratum separation of cultured cells. Earlier studies on chick fibroblasts using this technique identified 3 types of separation: (1) focal contacts, representing approx. 10—14 nm separation and which are sites of cell-substratum adhesion and form at the leading edge of a cell during locomotion; (2) close contacts, representing approx. 30 nm separation; and (3) regions of greater separation, generally 100 – 140 nm. Using light microscopy these studies described the association of the focal contacts with the distal ends of cytoplasmic fibres and noted their similarity to the adhesion plaques described in EM studies of thin vertical sections of fibroblasts.
In this investigation we have directly confirmed these earlier observations by using a correlated interference-reflexion and high-voltage stereo electron-microscopic study of cultured chick heart fibroblasts. The results show that focal contacts are always associated with the distal ends of linear bundles of microfilaments which pass centripetally and often obliquely through the cytoplasm. At their proximal ends the bundles insert into a loose matrix of microfilaments and organelles surrounding the nucleus. The close contacts are often associated with a meshwork of microfilaments.
The evidence supports the hypothesis that the microfilament bundles of a fibroblast form synchronously with the focal adhesions to the substratum. Our results are discussed with reference to the current evidence for the role of contractile proteins in cell locomotion.
The effects of tumour cells on embryonic cell aggregation, adhesion and detachment
Authors: Maslow D.E. , Weiss L. 
Published: April 2021

ABSTRACT
The presence of small numbers of tumour cells inhibits the aggregation of embryonic chicken neural retina cells grown in gyratory shaker culture. The aggregation of neural retina cells was also inhibited by ascites cell medium. We investigated whether the inhibitory effect of the tumour cells on aggregate size is effected by inhibition of the initial adhesion or by enhancement of their separation. The number of neural retina cells adherent to microtest plate surfaces was significantly reduced after incubation with either Ehrlich ascites cells or cell-free, conditioned medium, while the percentage of cells removed from glass by shearing was unchanged under those conditions. These results suggest that the reduction in neural retina cell aggregate size produced by Ehrlich ascites cells and their products is due to partial inhibition of neural retina cell adhesion processes, as distinct from enhancement of separation.
A morphological study of the cholinergic receptor protein from Torpedo marmorata in its membrane environment and in its detergent-extracted purified form
Authors: Cartaud Jean , Benedetti E. Lucio , Sobel André , Changeux Jean-Pierre 
Published: April 2021

ABSTRACT
The highly specialized structural features of the postsynaptic membrane of Torpedo mar-morata electric organ have been studied by freeze-fracturing, freeze-etching and negative staining applied both to intact electroplaques and to isolated purified excitable membrane fragments.
The external surface of the postsynaptic membrane, revealed by deep-etching and negative staining, is characterized by the presence of geometrically packed arrays of repeating particles having a subunit structure and a central pit. The isolated receptor protein molecules (molecular weight : 300 000) show structural features identical to those characteristic of the repeating particles visualized on the external surface of the postsynaptic membrane.
Freeze-fracture cleaves the postsynaptic membrane into 2 asymmetric halves, showing that numerous identical particulate entities are more strongly anchored to the cytoplasmic side of the bilayer. On the other hand, geometrically packed arrays of pits or depressions found on the external fracture face suggest that the receptor protein extends across the outer leaflet and is exposed to the external surface facing the synaptic cleft.
The homogeneous size-distribution of the particulate entities associated with the postsynaptic membrane element is consistent with the finding that the receptor protein accounts for at least 40% of the total protein of purified excitable membrane fractions. These results strongly favour the assumption that the particulate entities represent the receptor protein, which forms oligomeric complexes either of identical polypeptides or quasi-equivalently related proteins.
Thus, the cholinergic receptor oligomers forming a bidimensional lattice of repeating particles are exposed both to the synaptic cleft and to the cytoplasmic environment. It is proposed that the regulating properties of the excitable membrane depend upon oligomeric or polymeric associations of receptor proteins spanning the bilayer.
Duration of availability of tritiated thymidine following intraperitoneal injection
Authors: Blenkinsopp W. K. 
Published: April 2021

ABSTRACT
Much indirect evidence supports the assumption that tritiated thymidine does not label cells which enter the deoxyribonucleic acid synthesis phase (S(more than 1 h after injection. Direct evidence confirming this assumption was obtained by counting labelled epithelial nuclei in mice killed 1, 4 or 6 h after a single intraperitoneal injection of [3H]thymidine; colchicine was used to prevent the increase in number of labelled nuclei which would otherwise have occurred because of cell division. The proportion of cells labelled was the same at 1 h as at 4 or 6 h after injection of [3H]thymidine. Nuclei were regarded as labelled if they were overlaid by 4 grains or more; comparison of nuclear and background labelling indicated that nuclei overlaid by 3 grains or less represented background labelling.
Contractility and the fibre systems of Stentor Coeruleus
Authors: Bannister L. H. , Tatchell E. C. 
Published: April 2021

ABSTRACT
Observations of the microtubular ‘km’ system and filamentous ‘M’ systems in living specimens of Stentor coeruleus show that on contraction of the body both systems shorten, thicken and remain straight, but that on initial relaxation they behave differently: the km fibres begin to lengthen later than the M fibres, the latter being thrown into sinuous folds. Electron microscopy of specimens cooled before fixation appears to confirm this difference in behaviour in relaxing specimens.
The M fibres of the stalk region are discrete and prominent bundles, but in the adoral half of the body they are extensively linked together by side branches. There are diffuse filamentous attachments between the M fibres and the kinetosomes.
The vertical microtubular stacks which make up the km fibres are each linked with a pair of kinetosomes. Each stack contains about 21 microtubules grouped in a 2 + 19 pattern. Crossbridges are present between the microtubules of adjacent stacks. The number of stacks in each km fibre cross-section is smaller in extended specimens than in contracted ones, indicating that the stacks slide upon one another as the body changes its length.
On the effect of motor nerve degeneration on the fine-structural localization of esterases in the mammalian motor end-plate
Authors: Csillik B. , Knyihár Elizabeth 
Published: April 2021

ABSTRACT
Electron-microscopic localizations of acetylcholinesterase and non-specific esterases have been studied in the motor end-plates of the rat diaphragm, using a modified Koelle acetylthiocholine technique for acetylcholinesterase, the Holt technique for non-specific esterases (substrates: indoxyl acetate and indoxyl butyrate) and the Crevier-Bélanger technique for thiolacetic acid esterases. Acetylcholinesterase is located in the pre- and post-synaptic membranes and in the junctional folds built up by the latter. Indoxyl acetate esterase shows a homogeneous localization in primary and secondary synaptic clefts. Indoxyl butyrate esterase is located in the ‘middle dense layer’ of the synaptolemma. Thiolacetic acid esterase is predominantly post-synaptic, accompanied by a slighter pre-synaptic activity.
Eleven days after motor nerve transection, the synaptic gutter is occupied by a large number of collagenous fibres, and only small granular fragments of the degenerated nerve fibres remain. These fragments are devoid of acetyl- and non-specific esterases, but exert a thiolacetic acid esterase activity, probably demonstrating proteolytic enzymes. The post-synaptic membrane exhibits a slightly reduced enzyme activity without any major alteration in the fine-structural localization of acetyl- and non-specific esterases.
Plant protoplast agglutination by artificial carbohydrate antigens
Authors: Larkin P. J. 
Published: April 2021

ABSTRACT
The existence of β-lectins on protoplast surfaces is confirmed by the agglutination of proto-plasts by those Yariv antigens that have sugar specificities which also interact with isolated fi-lectins. Agglutination by β-mal tosyl but not by β-D-mannosyl Yariv antigens is used to identify some of the structural features required of the ligand for β-lectin binding. Inhibition of agglutination by phenolic glycosides and the effect of protoplast fixation are also investigated.
Induction of cleavage in nucleated and enucleated frog eggs by injection of isolated sea-urchin mitotic apparatus
Authors: Masui Y. , Forer A. , Zimmerman A. M. 
Published: April 2021

ABSTRACT
Mitotic apparatus (MA) were isolated in glycerol-dimethylsulphoxide solution (MTME) from zygotes of sea urchins (Strongylocentrotus purpuratus). Freshly isolated MA were stored in 1/10 strength MTME for varying periods of time and were then injected into unfertilized frog (Rana pipiens) eggs. These injections induced 40–60 % of the recipient frog eggs to initiate cleavage, resulting in the formation of blastula cell clusters. The cleavage-inducing activity of MA stored in 1/10 MTME at room temperature decreased with time of storage in 1/10 strength MTME, and disappeared by about 6 h. There was no change in the ultrastructure of MA during storage.
MA isolated and stored in MTME at room temperature had a constant level of cleavageinducing activity during the first 48 h of storage, but this activity slowly declined upon further storage; almost no activity was left after 3 weeks.
MA isolated in hexylene glycol (HG) and immediately transferred into MTME were compared with MA isolated in MTME; both MA had the same cleavage-inducing activity on the day of isolation, after which the MA isolated in HG quickly lost activity. On the other hand, MA isolated and stored in HG had little cleavage-inducing activity when tested 3 h following isolation.
Cleavage-inducing agent (CIA) isolated from frog brains induced cleavage and blastula formation when injected into nucleated frog eggs, but had no such activity when injected into enucleated frog eggs. MA isolated in MTME induced cleavage and blastula formation in enucleated frog eggs as well as in nucleated frog eggs. Cytological examination revealed that blastula cells which developed from MA-injected enucleated eggs contained Feulgen-negative nuclei, whereas cells which developed from CIA-injected nucleated eggs contained Feulgen-positive nuclei. These results suggest that sea-urchin nuclear materials participate in mitosis in frog eggs.
Isolated MA which had been stored in MTME for 3 weeks and which exhibited little cleavage-inducing activity were injected together with frog brain CIA into either normal or enucleated eggs; normal recipient eggs cleaved with significantly higher frequencies (70%) than those injected with CIA alone (40 %). Furthermore, enucleated eggs injected with CIA alone failed to cleave, while those injected with MA and CIA together cleaved with significant frequencies (overall 29 %). This result suggests a cooperative interaction between CIA and the inactivated MA to restore the cleavage-inducing activity of MA.
The role of phosphodiesterase in aggregation of Dictyostelium discoideum
Authors: Darmon Michel , Barra Jacqueline , Brachet Philippe 
Published: April 2021

ABSTRACT
The role of cAMP phosphodiesterase in the cAMP-mediated aggregation of the cellular slime mould Dictyostelium discoidettm was investigated with a morphogenetic mutant defective in phosphodiesterase production. Mutant cells become capable of aggregating normally when incubated in the presence of exogenous phosphodiesterase isolated from Dictyostelium or rat brain. Direct contact between enzyme and the cell membrane is not required for this phenotypic suppression. The aggregateless character of this strain presumably results from an over-accumulation of cAMP in the extracellular medium since aggregation can be induced in the absence of added phosphodiesterase under conditions facilitating diffusion of the nucleotide. This suggests that phosphodiesterase is not involved in the generation or recognition of cAMP signals, but that the enzyme is essential in the control of the cAMP signal-to-noise ratio.
Intracellular fibres in cultured cells: analysis by scanning and transmission electron microscopy and by sds-polyacrylamide gel electrophoresis
Authors: Trotter John A. , Foerder Beverly A. , Kellerj John M. 
Published: April 2021

ABSTRACT
The 3-dimensi0nal structure of the fibrous cytoskeleton of 3T3cells was examined by scanning electron microscopy of cells extracted with the non-ionic detergent Triton X-100. Detergent-extracted cells consist of the nucleus and an extensive system of fibres, the largest of which correspond to stress fibres visible by phase-contrast microscopy. The system of fibres, which is coterminous with the borders of the native cell, remains firmly adherent to the substratum. The major fibres branch into smaller fibrils which appear to end by ravelling out into fine filaments that constitute a matted network in a plane very close to that of the substratum. In the nuclear region all the major fibres pass over the top of the nucleus, where they may also branch into a system of fine fibrils. Thin-section transmission electron microscopy in conjunction with heavy meromyosin treatment of extracted cells shows the fibres to be composed of native F-actin. Intermediate filaments are also present, and are prominent in the matted network, together with actin filaments. The major proteins of the residue are identified by SDS-polyacrylamide gel electrophoresis as actin, a 56000 Dalton peptide, and histones. Also present are myosin heavy chain, peptides of 225000 and 250000, and minor bands at 60000 and 94000 Daltons. The non-ionic detergent extracts 70 % of the cellular protein, including 50 % of the actin and 75 % of the myosin. The Triton-insoluble fraction of 3T3cells appears to constitute, in addition to the nucleus, a stable cytoskeletal system, composed largely of contractile proteins and 10-nm filaments, which functions in maintenance of cell shape, in substratum adhesion, and in positioning the nucleus within the cell.
The arrangement of microtubules in serially sectioned spindles of the alga cryptomonas
Authors: Oakley Berl R. , Heath I. Brent 
Published: April 2021

ABSTRACT
Serial sections of mitotic spindles of the marine cryptophycean alga, Cryptomonas, were analysed to determine what types of microtubules they contained and which of these microtubules came close enough to each other (50 nm or less) for the commonly described crossbridging to be possible. Interpolar microtubules were rare (≤ 1 %) but from prometaphase through anaphase there was a substantial interpolar framework of free and polar microtubules which came close enough to one another to cross-bridge and generate anaphase spindle elongation by intermicrotubule sliding. However, such elongation would also require some concomitant polar microtubule polymerization. In contrast, only about 12% of the chromosomal microtubules came within bridging distance of interpolar framework microtubules. Thus, assuming that microtubules were accurately fixed in their in vivo positions, crossbridging between chromosomal and interpolar framework microtubules is unlikely to function in chromosome-to-pole movement. In all stages the great majority of chromosomal microtubules were found to extend all the way from the chromatin to the pole. Although the identification of intermicrotubular bridges in section is often ambiguous, the best and most frequent examples of bridges in the present material were between polar microtubules and between chromosomal microtubules but not between the 2 different categories. The spindles also contained 5-nm- diameter microfilaments associated mainly with chromosomal microtubules and occasionally with polar microtubules. A specific model for the possible involvement of these filaments in mitosis is presented.
Chromatin influence on the function and formation of the nuclear envelope shown by laser-induced psoralen photoreaction
Authors: Peterson Scott P. , Berns Michael W. 
Published: April 2021

ABSTRACT
Potorous tridactylis (PTK2) cells growing in culture were treated with psoralen derivatives and dividing cells were located by phase-contrast microscopy. Psoralens, light-sensitive DNA-photoadducting drugs, were reacted with mitotic chromosomes through exposure to 365-nm light from an argon laser microbeam system. It was found that following mitosis and photoreaction, cells without nuclear envelopes were produced when psoralen-treated cells received 60 light pulses over their entire chromosome complement. These ‘non-nuclear membrane* cells were found to incorporate PHjuridine and, to a lesser extent, [3H]thymidine by autoradiography. Reduction of the light exposure by half (30 near-u.v. pulses) over the entire chromosome complement in the presence of psoralen also produced non-nuclear-membrane cells as seen by light microscopy. Further examination of these cells (30 light pulses) by singlecell electron microscopy revealed that unlike the high light exposure (60 near-u.v. pulses), the low light dosage resulted in cells with membrane patches associated with their chrcmatin. Since neither actinomycin D nor cycloheximide impeded nuclear envelope reformation, the psoralen-DNA reaction is concluded to produce non-nuclear-membrane cells by a mechanism other than transcription or translation inhibition. The association of Golgi with areas of nuclear membrane patches gives indirect evidence of a possible Golgi contribution to the reformation of the nuclear envelope after mitosis. It is concluded that DNA plays a role in envelope reformation.
Genetic analysis of developmental mechanisms in hydra: V. cell lineage and development of chimera hydra
Authors: Sugiyama Tsutomu , Fujisawa Toshitaka 
Published: April 2021

ABSTRACT
Chimeric hydra were produced by making use of a strain (nf-1) which lacks interstitial cells, nerve cells and nematocytes. This strain arises by spontaneous loss of interstitial cells from its parental strain (sf-1) (Sugiyama & Fujisawa, 1978). Réintroduction of interstitial cells from other strains intonf-1 leads to the creation of chimeric strains that consisted of epithelial cells derived from strain sf-i and interstitial cells and their derivatives (nerves and nematocytes) from other strains.
In chimeras, interstitial or epithelial cells apparently maintain very stable cell lineages; no indication was obtained that suggested interstitial cell differentiation into epithelial cells or dedifferentiation in the opposite direction during the long courses of chimera cultures (up to one year).
Developmental characters of chimeras were examined and compared to those of the epithelial cell (sf-1) and the interstitial cell donors. Almost all of the chimera’s characters examined (growth rate, budding rate, tentacle numbers, polyp size, regenerative capacity, etc.) closely resembled those of the epithelial cell donor, but not of the interstitial cell donors. This suggests that epithelial cells, rather than interstitial or nerve cells, are the primary determinant of most, if not all, of hydra developmental characters.
Respiratory tract epithelium in primary culture: concurrent growth and differentiation during establishment
Authors: Heckman C. A. , Marchok Ann C. , Nettesheim Paul 
Published: April 2021

ABSTRACT
Studies of cellular function in the respiratory tract lining have traditionally been limited by the small tissue mass and functional diversity of the epithelium. Recent improvements in culture conditions have permitted long-term maintenance of epithelial cells derived from the upper respiratory tract of rats. The present study determined the extent to which proliferation and differentiation took place in such epithelial cell cultures. The labelling index obtained after ‘H-dThd administration was approximately 100-fold higher than that of the quiescent epithelium in vivo; therefore, a large proportion of the cells were probably in the cycling population.
Ultrastructural studies showed that features unique to the specialized mucous secretory cells and ciliated cells were lost rapidly with entry of these cells into the in vitro environment. With long-term maintenance, the cultures were reorganized into a stratified epithelium containing large, squamous, apical cells and small basal cells. The (Ultrastructural appearance of basal cells in vitro was nearly identical to that of basal cells in vivo. Squamous cells were frequently joined by tight junctions. Because hemicysts originated by detachment of squamous cells from the basal layers but not from adjacent squamous cells, they were considered to indicate stratification in the cultures. The proliferative and differentiative status of the mucociliary epithelium was altered by in vitro conditions, and came to resemble that of early squamous metaplasia in the respiratory tract epithelium.
Cell wall differentiation and stages involved with intercellular gas space opening
Authors: Roland J. C. 
Published: April 2021

ABSTRACT
The development of the intercellular gas system has been followed during the growth of Pisttm sativum root and Phaseolus aureus hypocotyl by means of ultrastructural cytochemistry.
The extension of the system is sequential and takes place according to a defined programme of cell wall reconstruction. Contrary to current views, the actual pectic middle lamella does not seem to be directly engaged in the initiation of the aerating system, which conversely appears subordinate to the presence of specialized substructures within the wall. The process is characterized by the early differentiation of a particular layer of wall called the ‘splitting layer’. The splitting layer differs from the pectic middle lamella particularly in its insolubility in an incubating medium which removes the wall subunits (EDTA, DMSO, pectinases, cellulases) and its non-reactivity to polysaccharide test involving periodic oxidation (PATAg staining). With ultracryotomy, it displays a distinctive β-glycerophosphatase activity.
The layer gradually splits apart from lateral sites in a manner which somewhat evokes the opening of a zip fastener. The primordial opening, and later the intercellular space, keeps a thin (10–20 nm) extramural coat which is apparently non-glucidic and derives from the splitting layer. Ultimately, local shifts and resorptions of the wall lead to fusion of the early intercellular channels.
One of the peculiarities of the opening of the air-space is that because of the mechanism involved the polysaccharides of the wall are not left naked. The processes observed are compared with other cases of cell wall separation.