bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reproductive history determines Erb
b
2 locus amplification, WNT signalling and tumour phenotype in a murine breast cancer model
Authors: Ordonez Liliana D. , Melchor Lorenzo , Greenow Kirsty R. , Kendrick Howard , Tornillo Giusy , Bradford James , Giles Peter , Smalley Matthew J. 
Published: April 2021

ABSTRACT
Understanding the mechanisms underlying tumour heterogeneity is key to the development of treatments that can target specific tumour subtypes. We have previously targeted CRE recombinase-dependent conditional deletion of the tumour suppressor genes Brca1, Brca2, p53 (also known as Trp53) and/or Pten to basal or luminal oestrogen receptor-negative (ER−) cells of the mouse mammary epithelium. We demonstrated that both the cell-of-origin and the tumour-initiating genetic lesions cooperate to influence mammary tumour phenotype. Here, we use a CRE-activated HER2 orthologue to specifically target HER2/ERBB2 oncogenic activity to basal or luminal ER− mammary epithelial cells and perform a detailed analysis of the tumours that develop. We find that, in contrast to our previous studies, basal epithelial cells are less sensitive to transformation by the activated NeuKI allele, with mammary epithelial tumour formation largely confined to luminal ER− cells. Histologically, most tumours that developed were classified as either adenocarcinomas of no special type or as metaplastic adenosquamous tumours. The former were typically characterized by amplification of the NeuNT/Erbb2 locus; in contrast, tumours displaying squamous metaplasia were enriched in animals that had been through at least one pregnancy and typically had lower levels of NeuNT/Erbb2 locus amplification but had activated canonical WNT signalling. Squamous changes in these tumours were associated with activation of the epidermal differentiation cluster. Thus, in this model of HER2 breast cancer, cell-of-origin, reproductive history, NeuNT/Erbb2 locus amplification and the activation of specific branches of the WNT signalling pathway all interact to drive inter-tumour heterogeneity.
Low-angle x-ray diffraction and electron-microscope studies of isolated cell membranes
Authors: Finean J. B. , Coleman R. , Green W. G. , Limbrick A. R. 
Published: April 2021

ABSTRACT
A sequence of low-angle X-ray diffraction patterns obtained during the controlled drying of a preparation of rat erythrocyte ghosts has been interpreted with the aid of corresponding electron micrographs and of a parallel study of myelin isolated from guinea-pig brain. A diffraction pattern that persists down to a level of 10–20 % hydration of the sample is believed to arise from the close packing of native erythrocyte membranes. Each membrane is about 100 Å thick and it is suggested that it consists of a predominantly continuous bimolecular layer of lipid, with non-lipid components associated with both surfaces. Further changes in diffraction pattern which accompany continued drying could be interpreted either as a change from a lamellar to a hexagonal structure or as the formation of a multiphase system. Evidence is put forward to support the latter interpretation.
An ultrastructural study of interspecific cell fusion induced by inactivated sendai virus
Authors: Schneeberger E. E. , Harris H. 
Published: April 2021

ABSTRACT
An electron-microscopic examination was made of the process of cell fusion induced by Sendai virus inactivated by ultraviolet light. Ehrlich ascites cells, HeLa cells, rabbit macrophages, rat lymphocytes and nucleated hen erythrocytes were chosen for study because it had previously been shown that these cells could be fused together, with varying degrees of facility, to form artificial heterokaryons. Cells which had large numbers of microvilli on their surfaces fused together more readily than those which had not, but the presence of microvilli was not essential for fusion to occur. Fusion appeared in all cases to be initiated by the formation of small cytoplasmic bridges between the cells ; but virus particles, although present elsewhere on the surface of the cells, were not detected at or near the cytoplasmic bridges. HeLa-hen erythrocyte heterokaryons were formed by the fusion of HeLa cells with red cell ghosts.
Movements of epithelial cell sheets in vitro
Authors: Vaughan R. B. , Trinkaus J. P. 
Published: April 2021

ABSTRACT
Chick embryo epithelial cells, cultured in vitro on a plane glass surface, show ruffled membrane activity like that seen in fibroblasts. When similar epithelial cells come into contact, long-lasting adhesions form, which are associated with the cessation of membrane activity. Movement of epithelial cell sheets is correlated with adhesion to the substratum of some or all of the marginal cells. Such adhesion does not occur in the absence of membrane activity. Non-marginal cells ordinarily appear to be non-adherent to the substratum; occasionally, however, they become adherent when attachments to neighbouring cells in a sheet are broken. This behaviour is accompanied by marked membrane activity. Mobilization and orientation of marginal cells are the vital steps in movements of coherent cell sheets.
The role of calcium in the isolation of brush borders from epithelial cells of rat small intestine
Authors: Millington P. F. , Critchley D. R. , Tovell P. W. A. 
Published: April 2021

ABSTRACT
A chelating agent such as EDTA or EGTA used with a dilute TRIS buffer at pH 7·2–7’5 was used in order to effect a good separation of brush borders from the epithelium of the small intestine. A good separation was not obtained in low concentrations of TRIS buffer or saline alone. Brush borders were not obtained when the calcium–chelate complex of EDTA or EGTA was used, and only a partial fractionation was obtained when the magnesium complex of EDTA was tried. The involvement of calcium was further illustrated by adding calcium salts directly to the fractionation medium ; separation was prevented when sufficient calcium had been added to saturate the chelating agent. It was found that there was no precise optimum concentration for EDTA but a separation could not be obtained below 2·4 mM/1. The effect of changing the pH of the buffer was also investigated and it was demonstrated that the onset of the ability to release brush borders coincided approximately with the ionization of the third acid radical of the chelating agent. This is in keeping with the suggested hypothesis that EDTA acts by chelating calcium ions.
From these and electron-microscope studies it is suggested that the binding of calcium ions is an important factor in the maintenance of the stability of the epithelial cell membrane.
Role of phragmoplast filaments in cell-plate formation
Authors: Bajer A. , Allen R. D. 
Published: April 2021

ABSTRACT
With the differential interference microscope (Nomarski system), it is possible to observe the interaction of filaments of the phragmoplast with micron-size refractile particles and vesicles, very close to the resolution limit of the microscope, during formation of the cell plate. Filaments occupying the birefringent zone of the phragmoplast (i.e. remnants of the continuous and interzonal fibres of the mitotic spindle) shorten and thicken in their mid-region to become spindle-shaped. The thickenings later fuse laterally to form the cell plate. During the process of thickening, vesicles can be seen to move toward the plate in close association with the filaments on both sides of the phragmoplast. These observations, taken together with information from electron micrographs of thin sections of Haemanthus endosperm and other dividing cells, confirm the notion that the fibrillar component of the phragmoplast has a transport function. The sizes of particles entering the phragmoplast region by saltation suggest that they correspond to Golgi bodies, which have been suspected of producing vesicles that contribute to cell-plate formation. Neither light nor electron micrographs have yet provided any insight into the mechanism of transport of these vesicles.
The function and fine structure of the cephalic airflow receptor in schistocerca gregaria
Authors: Guthrie D.M. 
Published: April 2021

ABSTRACT
Electron micrographs of parts of the sense organ showed that the dendritic axis consisted of a large and a small envelope containing microtubules as their main inclusion. The envelopes are supported by a thick-walled tube believed to be part of the ist-tier sheath cells. The small envelope is segregated from the large envelope near its apex by a fold of the tube wall. The packing of the neurotubular array within the small envelope is both more dense and more regular than within the large envelope. The tube is separated by an extracellular space from the trichogen-tormogen cell. Sections through the apex of the dendrite reveal a homogeneous cap unlikely to be part of a structure continued into the upper region of the hair shaft. No ciliary structures were visible within the dendrite, whose microtubules pass into the neuron cell body proximally. Sections through the neuron cell body reveal branched mitochondria, and numerous microtubules.
Rates of discharge in sensory axons from these hair organs produced by deflexion of the hair shaft were found to be within the range 300–100 impulses/sec. There is an initial phase of rapid adaptation which gives place to a steady rate.
It is suggested that the fine structure of the receptor may indicate mechano-electrical transduction at a more proximal level than is believed to be the case in some other types of receptor.
The diaphragms that support the hair shaft laterally can be seen to be composed of fine cuticular strands.
The interpretation of electron micrographs of negatively stained native collagen
Authors: Cox R. W. , Grant R. A. , Kent C. M. 
Published: April 2021

ABSTRACT
Deamination of native rat tail collagen followed by treatment with 1,2-cyclohexanedione removes the positive charge from the side chains of the lysine and hydroxylysine residues and blocks approximately 70 % of the positively charged side chains of the arginine residues. When such specimens are examined in the electron microscope after negative staining with 2 % potassium phosphotungstate at pH 6 ·8 –7 ·4 no change from the appearance of normal collagen is detectable. These findings suggest that electrostatic attraction does not occur between the stain and the side chains of the lysine, hydroxylysine and arginine residues of the collagen and justify the view that, at least with this stain and under these conditions, the effect is that of pure negative staining and not that of a mixture of positive and negative staining. Furthermore, the experiments indicate that possible electrostatic attractions between the positively charged side chains of lysine, hydroxylysine and arginine and the negatively charged side chains of residues such as aspartic acid and glutamic acid are relatively unimportant in the maintenance of the light cross-striations of negatively stained collagen. However, the loss of these light cross-striations after treatment of collagen with urea implies that they are mainly associated with intermolecular hydrophobic and, possibly, hydrogen bonding.
A study of terminal degeneration in the olfactory bulb of the rat
Authors: Pinching A. J. , Powell T. P. S. 
Published: April 2021

ABSTRACT
An ultrastructural study of degeneration in axon terminals of the glomerular layer of the rat olfactory bulb is described, concentrating particularly on the sequence of degeneration in the olfactory nerve terminals and the long-term events in the degeneration process in several terminal types. Olfactory nerve terminal degeneration is divided into 5 stages, representing parts of the sequential changes taking place in the terminal after fibre section. The main features in the sequence are as follows: I. Swelling of the terminal and its vesicles. II. Initial shrinkage of the terminal, while vesicles remain swollen and some are distorted. III. Further shrinkage and darkening of the terminal, distortion of many of the vesicles and some mitochondrial swelling. IV. Extreme shrinkage of the terminal and loss of cytoplasmic detail; synaptic contact still intact or partially separated. V. Disappearance of the presynaptic terminal and persistence of the post-synaptic thickening.
The validity of the observation of the persistence of post-synaptic membrane thickenings is considered and evidence adduced in its favour, both qualitative and quantitative. Characteristics of the newly apposed profiles are described, including cisternae and alveolate vesicles; the extracellular material of the synaptic cleft is considered in the light of its association with persisting thickenings. The relevance of these associated structures is discussed in terms of function and development. Spontaneous degeneration of olfactory nerves and the degeneration of the vomeronasal nerves in the accessory olfactory bulb are described, as well as Stage V in the degeneration of other terminal types of the glomeruli, following various lesions; persistence of post-synaptic thickenings after the degeneration of terminals showing symmetrical membrane thickenings is included. Observations on the persistence of post-synaptic thickenings in various sites in the central and peripheral nervous systems are reviewed in the context of the present study; the problems arising out of the morphological identification of apposition or reinnervations are discussed.
A new junctional structure in the epithelia of insects of the order dictyoptera
Authors: Flower N. E. 
Published: April 2021

ABSTRACT
The junctional complexes in the epithelia of insects of the order Dictyoptera have been investigated using the freeze-etch technique. As well as septate junctions, a new type of junction has been identified and the name ‘inverted gap junction’ proposed. The patch-like distribution of the inverted gap junctions basal to and often closely associated with septate junctions is very similar to the form of gap junctions and their relationship to tight junctions in vertebrates. This suggests that the inverted gap junctions, like normal gap junctions, could perform a communicating function between epithelial cells. The following features distinguish inverted gap junctions from normal gap junctions in freeze-etch preparations: (i) the arrays of particles and holes within inverted gap junctions appear on B- and A-type faces respectively, i.e. on the opposite faces to the particles and holes in gap junctions; (ii) the particles within inverted gap junctions appear to lie in rows which anastomose to form an irregular net, and not in an hexagonal array, as occurs in gap junctions.
A new specialization of the granular endoplasmic reticulum in the uterine glands of the pig in the later stages of pregnancy
Authors: Crombie Paula R. 
Published: April 2021

ABSTRACT
A new specialization of the granular endoplasmic reticulum (GER) which develops within the uterine gland cells of the pig during the final third of pregnancy is described.
The ‘tubular bodies ‘are interpreted as sheets of GER rolled up to form open-ended cylinders enclosing cytoplasm which is distinctly less electron-dense than the surrounding external cytoplasm, and in which large clear vesicles and free ribosomes are frequently found.
The tubular bodies are not present during the first two thirds of pregnancy, but by day 100 of gestation they are readily discerned. They increase in number within the last week of pregnancy and are still found in glands from the day 1 post-partum uterus. They are distributed, either singly or in groups of up to 30 or more units, throughout the cells. The cisternal space which surrounds them is continuous with that of the granular endoplasmic reticulum.
A tentative developmental sequence is suggested, based on morphological similarities between the wall structure of the early tubular body and the paired cistemae, which are seen scattered as single, short strands within the gland cells. The final form is achieved by modification of the inner apposed, ribosome-free cisternal membranes into the straightened-out, thickened membranes characteristic of the tubular body wall, together with a rolling-up of the ‘sheet’ of paired GER cistemae. Subsequent loss of the innermost unmodified cisternal membrane which is now in contact with the centrally enclosed cytoplasm results in the characteristic tubular body wall structure.
The characteristic appearance of the central cytoplasm and the presence of modified surrounding membranes suggests the possibility of a localized, modified internal environment required for some unspecified functional activity; possibly a synthetic process or some type of ionic regulation.
Action of rifampicin on the liverwort Marchantia polymorpha
Authors: Mache R. , Loiseaux S. 
Published: April 2021

ABSTRACT
The effect of rifampicin was studied on a multicellular plant in comparison with its effect on unicellular organisms. Marchantía polymorpha L. is sensitive to rifampicin and was chosen as the material. The inhibitory dose on the growth of young gemmae was established. The effect of rifampicin on the ultrastructure of the cells was investigated and it was found to inhibit the formation of plastid ribosomes and dissociate existing ribosomes into their subunits, but probably does not inhibit the synthesis of some plastid proteins, which remain visible as small granules in the stroma. The effect of rifampicin on the chlorophyll content and on the absorption of C02 by intact thalli and isolated chloroplasts has also been studied. Little or no change was observed.
Microtubule-arms and propulsion of food particles inside a large feeding organelle in the ciliate Phascolodon vorticella
Authors: Tucker J. B. 
Published: April 2021

ABSTRACT
Attention is drawn to the apparently invariable presence of rows of arm-bearing microtubules lining the sucking mouthparts of ciliates. Their arrangement inside the cytopharyngeal basket of Phascolodon is described and compared with that in the tentacles of suctorians and the sucking tubes and baskets of other ciliates. It is suggested that arms are involved in the propulsion of materials alongside microtubules when these ciliates ingest food. Mechanisms by which arms may accomplish this are outlined. The different functions of links and other intertubular materials in the several microtubular basket components of Phascolodon are considered. The form and arrangement of microfilaments and pointed, sharp-edged structures around the mouth are also described. The possibility that the pointed structures are used for biting is discussed.
Cytoplasmic nucleoloids of Lilium male reproductive cells contain rDNA transcripts and share features of development with nucleoli
Authors: Sato S. , Jones K. , Alche J. De Los Dios , Dickinson H. G. 
Published: April 2021

ABSTRACT
Nucleolus-like inclusions in the meiocytes of Lilium sp. have been investigated at the light and electronmicroscope levels, with respect both to their composition and their formation during the meiotic divisions. Those present in the cytoplasm (cytoplasmic nucleoloids) first appear as small structures late in anaphase I. Coincidentally, small nuclear nucleoluslike inclusions (NLBs) develop on the surface of the chromosomes, and sometimes in the region between chromosomes as they are carried into the daughter nuclei. The cytoplasmic nucleoloids increase in size from late anaphase I to the dyad stage, but disappear before metaphase II. They redevelop late in anaphase II and persist, increasing in size, until the tetrad stage. The NLBs also increase in size over this period. Ultrastructural investigation indicates that both the nascent nucleoloids and NLBs are fibrous in texture as they arise in late anaphase. Elsewhere in the cytoplasm, however, large accumulations of amorphous electron-opaque material also aggregate. This material becomes associated with the nucleoloids and the NLBs during the period of their enlargement. Nucleoloids late in development, and post-telophase nucleoli are not invested by these amorphous masses. Interestingly, cytoplasmic nucleoloids and NLBs react in an identical fashion to a range of cytochemical treatments and, using in situ hybridisation at the electron-microscope level, they have been demonstrated to contain RNA sequences homologous with a wheat ribosomal gene probe. Cytoplasmic nucleoloids are thus interpreted as following an identical developmental pathway to nucleoli except in that, perhaps owing to high levels of rDNA transcription during meiosis, they condense in the cytoplasm rather than the nucleoplasm.
Biogenesis of the apical endosome–lysosome complex during differentiation of absorptive epithelial cells in rat ileum
Authors: Wilson Jean M. , Whitney J. Andrew , Neutra Marian R. 
Published: April 2021

ABSTRACT
Absorptive cells of the neonatal rat ileum have an elaborate apical endocytic complex consisting of tubular and vesicular endosomes, multivesicular bodies (MVB), and a giant lysosomal vacuole. This system develops rapidly over the last 3 days (20–22) of gestation. We followed the assembly of this complex by ultrastructural analysis and immunocytochemistry using antigenic markers for microvilli, endosomal tubules and lysosomal membranes. At 19 days gestation, low levels of lactase appeared on microvilli but specialized apical endosomal tubules and lysosomes were absent. At 20 days, expression of microvillar lactase increased and the endosomal marker entubin appeared, in parallel with the appearance of specialized apical endosomal tubules. The compartments of the apical endosomelysosome system were assembled sequentially after differentiation of the apical plasma membrane domains; first endosomal tubules and vesicles, followed by MVB, and ending with the assembly of the giant lysosome shortly after birth. During early stages of the assembly process, membrane components. of the tubular endosomes and lysosomes appeared in the apical plasma membrane before being restricted to their respective intracellular compartments
Comparison of biological and immunochemical properties indicates that scatter factor and hepatocyte growth factor are indistinguishable
Authors: Furlong Robert A. , Takehara Toyohiro , Taylor William G. , Nakamura Toshikazu , Rubin Jeffrey S. 
Published: April 2021

ABSTRACT
Scatter factor, a stimulant of epithelial cell motility, and Hepatocyte Growth Factor (HGF) were compared by cross-biological studies using naturally occurring and recombinant proteins in four bioassays. Both scatter factor and HGF produced similar effects in cell motility and DNA synthesis assays. Antibodies to scatter factor or HGF neutralized the biological activities of each cytokine, and in immunoblotting reacted with species of the same Mr. These results, together with the available sequence data, suggest that scatter factor and HGF are the same protein.