bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell size and proportional distance assessment during determination of organelle position in the cortex of the oliate Tetrahymena
Authors: Lynn D. H. , Tucker J. B. 
Published: April 2021

ABSTRACT
Developing oral organelles of dividing Tetrahymena corlissi appear to be positioned by mechanisms which assess distances as a proportion of the organism’s overall dimensions. In some respects, the cortex of this protozoan obeys the ‘French flag’ rule formulated by Wolpert for describing regulation of spatial proportions during differentiation of metazoan embryos.
Dividing Tetrahymena of markedly different sizes occur when division is synchronized by starvation and refeeding. At the start of cell division, the distance between old and new mouthparts varies proportionately with respect to cell length. In addition, determination of the site where new oral organelles will develop is apparently not directly related to the number of ciliated basal bodies which separate the 2 sets of mouthparts; the greater the distance between the old and developing sets of mouthparts, the greater the number of ciliated basal bodies in the rows between them.
It is suggested that 2 distinct mechanisms are largely responsible for defining organelle position in ciliates. The new terms structural positioning and chemical signalling are defined to describe these mechanisms.
The chitin crystallite in arthropod cuticle
Authors: Neville A. C. , Parry D. A. D. , Woodhead-Galloway J. 
Published: April 2021

ABSTRACT
Electron microscopy has revealed that chitin from a representative selection of insect orders (plus one crustacean and one arachnid) is localized in crystallites about 2’8 nm across. Furthermore, these crystallites are arranged on an hexagonal or pseudo-hexagonal lattice, the lateral order of which varies considerably. The lattice becomes secondarily reoriented during cuticle expansion following an ecdysis. The size of the ‘unit cell’ has been measured both by optical diffraction and direct measurements of the micrographs, permitting an estimate of the chitin and resilin content for locust rubberlike cuticle. The number of poly-N-acetyl-glucosamine chains per sheet and sheets per crystallite can be estimated from the physical dimensions of the crystallite. Each crystallite is unlikely to comprise more than 3 sheets and 6 chains per sheet. The calculated and measured density of α-chitin can be shown to be in close agreement.
A three-dimensional reconstruction of the polygonal pattern on placental coated-vesicle membranes
Authors: Ockleford C. D. 
Published: April 2021

ABSTRACTThere is a surface structure on the coated vesicles of human placenta. Some features of this structure have been examined. Measurements of the polygonal network seen in surface views have been made and compared with measurements of structures projecting from vesicle walls in median sections. A 3-dimensional reconstruction of the vesicle shows the pattern to be one of raised ridges.Use of a goniometer to tilt the specimens has confirmed the assumption that both types of image obtained are from one structure.Although it is usually the case that vesicles are approximately spherical, some are definitely irregularly shaped. For this reason it is suggested that the walls of the polygons need not always be packed into a structure with a regular and precisely maintained pattern.Consideration of the surface structure in the light of current understanding of the cell membrane as a dynamic system leads to a possible explanation of the process of vesicle formation in this context and of the selective nature of uptake by micropinocytosis.
Species-specific aggregation factor in sponges: VI. aggregation receptor from the cell surface
Authors: Müller W. E. G. , Müller I. , Zahn R. K. , Kurelec B. 
Published: April 2021

ABSTRACTAn aggregation receptor from the siliceous sponge Geodia cydonium has been isolated and purified in an almost pure form. It sediments at about 2·6 s, has a buoyant density of 1·51 g/ml in CsCl and elutes from Sephadex G-50 at a Ve/0 value of 1·311. Chemical analysis revealed that the receptor consists of 81 % neutral carbohydrate and 7·5 % protein. The activity of the receptor is rapidly destroyed by Na-periodate.The receptor is released from the cell surface after removal of Ca2+ from the medium or after incubation of the cells with trypsin. The depleted cells can be charged again with isolated receptor molecules. The binding of the receptor molecules on the cell surface is prevented in the presence of trypsin. For optimal binding, physiological salt concentrations with respect to NaCl (540 rπmM NaCl) and Cas+ ions are necessary.The receptor whose isolation is described in this report, is involved in secondary aggregation processes, which are initiated by a soluble aggregation factor. The primary aggregation of the cells is not influenced by the receptor.Time-course studies with receptor-depleted cells revealed that new aggregation receptor molecules are formed during the aggregation process.By competition experiments it could be shown that high concentrations of soluble aggregation receptor molecules inhibit secondary aggregation. The soluble receptor molecules can compete with surface-bound receptor molecules only if these are not linked with the aggregation factor.
Spore germination promoter of dictyostelium discoideum excreted by aerobacter aerogenes
Authors: Hashimoto Yohichi , Tanaka Yoshimasa , Yamada Takuzo 
Published: April 2021

ABSTRACT
The nutrient medium in which Aerobacter aerogenes was grown, contains a spore germination promoter (SGP) for the cellular slime mould Dictyostelium discoideum. SGP can cause synchronous spore germination in a short time, and triggers the germination process in just a few minutes. Germination-promoting capacity of SGP decreases as it comes in contact with increasing number of spores. When spores activated by SGP are stored at 4 °C, they gradually return to the dormant state. SGP is comparatively heat-stable, but is unstable at pH above 10 or under 3.
Apparent amitosis in the binucleate dinoflagellatePeridinium Balticum
Authors: Tippit D. H. , Pickett-Heaps J. D. 
Published: April 2021

ABSTRACTMitosis and cytokinesis in the free-living binucleate dinoflagellate Peridinium balticum are described. P. balticum contains 2 nuclei; one is a typical dinoflagellate nucleus and the other resembles the interphase nuclei of some eucaryotic cells and is here named the supernumerary nucleus (formerly called the eucaryotic nucleus). The dinoflagellate nucleus divides in the characteristic manner already described for certain other dinoflagellates. The supernumerary nucleus does not undergo normal mitosis; its chromatin does not condense, a spindle is not differentiated for its division, nor are any microtubules present inside the nucleus during any stage of its division. Instead the supernumerary nucleus divides by simple cleavage, which is concurrent with cytoplasmic cleavage. The nucleus cleaves first on its side facing the wall, but later it cleaves circumferentially as the cytoplasmic cleavage furrow draws closer. Invariably at late cytokinesis, a portion of the dividing nucleus passes through the only remaining uncleaved area of the cell. The final separation of the supernumerary nucleus is probably accomplished by the ingrowing furrow pinching the nucleus in two. There is no apparent precise segregation of genetic material during division, nor are there any structural changes inside the dividing nucleus which distinguish it from the interphase nucleus. Certain aspects of amitosis, and previously postulated theories concerning the endosymbiont origin of the second nucleus, are discussed.
Pollen-wall proteins: quantitative cytochemistry of the origins of intine and exine enzymes in Brassica Oleracea
Authors: Vithanage H. I. M. V. , Knox R. B. 
Published: April 2021

ABSTRACT
Simultaneous coupling methods for detection of acid phosphatase and non-specific esterase produce a coloured reaction product that is quantitatively related to enzyme content in freeze-sectioned Brassica pollen and tapetal cells.
The intine-located acid phosphatase has 2 periods of synthesis: the first in late vacuolate period, associated with the completion of deposition of the intine polysaccharides; the second during pollen maturation, apparently reflecting cytoplasmic synthesis. Esterase activity accumulates in the tapetal cells until dissolution at early maturation period, when there is a dramatic rise in pollen-wall esterase activity, reflecting the transfer from tapetum to exine cavities. These quantitative studies confirm the gametophytic and sporophytic origins of the intine and exine proteins.
Cell surface saccharides ofTrypanosoma lewisi.: II lectin-mediated agglutination and fine-structure cytochemical detection of lectin-binding sites
Authors: Dwyer D. M. 
Published: April 2021

ABSTRACTBloodstream (BSF) and culture forms (CF) of Trypanosoma lewisi were specifically agglutinated with the plant lectins concanavalin A (Con A), soybean agglutinin (SBA), wheat germ agglutinin (WGA), and fucose-binding protein (FBP). Lectin-mediated cell agglutination was inhibited, and reversed in the presence of specific lectin-binding saccharides. Cells were agglutinated randomly with all lectins suggesting a uniform distribution in the trypanosome cell surface of the lectin-binding saccharide ligands. The BSF and CF were not agglutinated with phytohaemagglutinin-M, phytohaemagglutinin-P, or influenza virions. Living trypsinized BSF, which lacked a surface coat, gave agglutination results with the lectins identical to those obtained with living intact BSF. Glutaraldehyde- or formalin-fixed intact and trypsinized BSF gave results similar to those obtained with living cells and SBA, WGA, and FBP. However, intact, fixed BSF gave much lower agglutination levels with Con A than trypsinized-fixed, living intact, or living trypsinized BSF cells. Intact and trypsinized living and fixed CF gave identical agglutination results with each of the lectins. Living and fixed cells treated extensively with the glycoside hydrolases a-amylase, dextranase, and neuraminidase gave results with the lectins identical to those obtained with untreated cells.Con A bound at the cell surface was visualized with an iron-dextran (Fe-Dex) conjugate. Dense iron marker particles were distributed randomly in the intact BSF surface coat. The Con A-bound Fe-Dex marker was present on the pellicular and flagellar membrane outer lamina of trypsinized BSF and intact CF cells. Horseradish peroxidase (HRPO)-diamino-benzidine (DAB) coupled reactions also were used to visualize surface-bound Con A. Dense Con A-HRPO-DAB deposits were present uniformly in the BSF surface coat, and on the membranes of trypsinized BSF and intact CF trypanosomes.SBA and WGA were conjugated to HRPO and these used in DAB-coupled reactions at the ultrastructure level. Results obtained with the HRPO-conjugated lectins were similar in surface localization and distribution to those obtained with the Con A-HRPO-DAB preparations.Treatment of BSF and CF with the several glycoside hydrolases produced no apparent enhanced or reduced reactivity for the lectins in any of the fine-structure cytochemistry experiments.The cumulative results indicate that ligands similar or identical to α-D-mannose, N- acetylgalactosamine, and N-acetylglucosamine, and α-L-fucose are constituents in the extracellular surface coat matrix of T. lewisi BSF. Similar conclusions also pertain to the pellicular and flagellar membrane ligands of the BSF and CF cells. Moreover, results obtained with the glycoside hydrolases and influenza virions suggest that the T. lewisi cell surface ligands are not associated directly with repetitively bonded α-1,4- and α-1,6-D-glucans or sialic acid moieties.
Studies on the mechanism of circus movement in dissociated embryonic cells of a teleost,Oryzias latipes:Fine-structural observations
Authors: Fujinami Noboru 
Published: April 2021

ABSTRACTThe fine structure of lobopodia in dissociated embryonic cells of the freshwater fish, Orysias talipes, was observed with the electron microscope in order to understand the mechanism of the circus movements which they display. Dense material (granular or fibrillar) is present in the zone between the lobopodium and the endoplasm, as well as in the cortical layer around the cell circumference. The direction of lobopodial movement is related to the distribution of this dense material. The band between the lobopodium and the endoplasm is conspicuous and is connected to the cortical dense layer around the cell periphery at the advancing front of the lobopodium, while the dense material is usually almost absent beneath the cell membrane in the anterior region of the lobopodium. The band between lobopodium and endoplasm is blurred or disrupted near the hind end of the lobopodium, where the peripheral dense layer is well developed.In situ localization of actin/heavy meromyosin complexes in the cell showed that the dense material has actin-like properties. Cytochalasin B (0·5 μg/ml) induced constriction of the neck of the bleb, shrinkage of the endoplasm, and herniation of the endoplasmic contents to the enlarged hemispherical bleb, and thus arrested the circus movement.On the basis of these results, an hypothesis concerning the mechanism of circus movement is proposed and discussed.
Sulphur in epidermal keratohyalin granules: A quantitative assay by x-ray microanalysis
Authors: Jessen H. , Peters P. D. , Hall T. A. 
Published: April 2021

ABSTRACT
The elemental composition of different types of keratohyalin granules from the epidermis of newborn and adult rats was studied by means of an EMMA-4 analytical electron microscope, equipped with an energy-dispersive X-ray spectrometer. An absolute quantitation of the sulphur concentration in keratohyalin granules was performed.
The results demonstrate that epidermal keratohyalin granules are chemically heterogeneous. A type of keratohyalin granule present in the nuclei and cytoplasm of epidermal cells from both newborn and adult rats - termed single granules - is rich in sulphur, having a content of 2·5-3·6%. Other types of keratohyalin granules, which differ in newborn and adult rats, contain a sulphur-poor component; they often have a sulphur-rich component as well. The sulphur-poor keratohyalin contains 0·6-0·9% sulphur.
It is suggested that the sulphur-rich keratohyalin granules are the source of the peripheral envelope protein of cornified cells.
Heterogeneity of phospholipid synthesis in rat liver endoplasmic reticulum during proliferation of smooth membranes
Authors: Higgins Joan A. 
Published: April 2021

ABSTRACT
During proliferation of smooth endoplasmic reticulum (SER) induced by phenobarbital the specific activity of acyl transferases of the smooth microsomes increases, there is a transient rise in the phospholipid/protein ratio of these membranes, and an increased incorporation of [14C]glycerol into smooth-membrane phospholipid. Microsomes separated into subfractions on 2 gradients exhibited a heterogeneous distribution of these characteristics, indicating a nonuniform distribution of the site of phospholipid synthesis in the ER under these conditions. Cytochemical localization of acyltransferases on whole liver and smooth and rough microsomes confirmed this heterogeneity, and indicated that the distribution of this- activity was not restricted to any morphologically distinct site in the ER of the intact cell. After 4 days of phenobarbital treatment the increased membrane is restricted to lighter subfractions and is similar in distribution to that of increased acyltransferase activity. These results indicate that the synthesis of membrane phospholipid and the growth of the SER in response to phenobarbital is not uniform but occurs at randomly dispersed sites in the SER while proteins may be added preferentially at these sites resulting in a final uniform distribution.
Rapid modification of the morphology of cell contact sites during the aggregation of limpet haemocytes
Authors: Jones G.E. , Gillett R. , Partridge T. 
Published: April 2021

ABSTRACT
Haemocytes suspended in the blood of the limpet Patella vulgata rapidly form microspikes and aggregate in response to withdrawal from the haemocoel. It has previously been suggested that the contacts between colliding cells in shaken suspension are stabilized by the rapid spreading of participant cells over each other’s surfaces by a microspike-dependent process. In this communication we report that an electron-microscopic study of the contacts formed between cells in the early stages of aggregation suggests that intercellular contact elicits a rapid response from the organelles concerned with cell motility. This response leads to the rapid progression of each initial collision through 3 major categories of contact morphology, namely cell body/lamella, lamella/lamella and cell body/cell body. There is a concomitant increase in the area of mutually contacting surface between participating cells.
On the basis of these results, a model is constructed for the participation of sub-surface components in the process of cellular aggregation. The sequence of development of contact found between aggregating cells is envisaged to be a consequence of cellular locomotory activities resembling those by which these cells spread on to a solid substrate. Included in this process is an element of intercellular recognition. It is suggested that the involvement of motile elements in cell aggregation is a general feature of aggregating cells. This would permit a re-interpretation of aggregation experiments which show specificity of cell adhesion, for total adhesive interactions between cells would depend not only on the adhesiveness per unit area of contacting cell surface but also on the extent or rate of formation of flat contact areas. The latter element could be regulated by a recognition system between contacting cells independently of the force per unit area which holds the 2 surfaces together.
The control of mitosis in Physarum polycephalum: The effect of delaying mitosis and evidence for the operation of the control mechanism in the absence of growth
Authors: Sudbery P. E. , Grant W. D. 
Published: April 2021

ABSTRACT
Possible mechanisms coordinating the control of mitosis and DNA synthesis with growth were experimentally tested in Physarum polycephalum by the response of plasmodia to 2 different kinds of perturbation of the DNA:mass ratio. Mitosis and DNA synthesis were delayed without stopping growth either by the use of fluorodeoxyuridine (FUdR) or puro- mycin, in both cases the delayed mitosis was followed by a single shortened intermitotic period, as predicted by all the mechanisms considered and substantiating a basic assumption made that the time of mitosis is homeostatically controlled to maintain a constant DNA:mass ratio. When more than 50% of the DNA was destroyed by ultraviolet irradiation 2 consecutive mitoses could occur even when growth was completely stopped by starvation. This result can only be accounted for by 2 of the 5 models considered, a finding which agrees with the results of previous experiments which were also consistent with only these 2 mechanisms.
Some ultrastructural aspects of mitosis and early differentiation in human foetal lung
Authors: Mcdougall Jennifer 
Published: April 2021

ABSTRACT
In rapidly dividing human foetal lung cells there is evidence of synthesis of extra membrane prior to mitosis. During prophase the nuclear envelope breaks down and is conserved as long double or complex stacks during the following stages of mitosis. It is suggested that the membrane is retained partly for incorporation into the daughter cell nuclear envelopes and partly for the formation of RER. The relevance of the observations to the biochemical data in the literature concerning the formation of intracellular membranes is discussed briefly.
The nucleolus organizer and the synaptonemal complex inEndymion non-scriptus(L.)
Authors: Jordan E. G. , Luck B. T. 
Published: April 2021

ABSTRACTStages of meiosis from the bluebell Endymion non-scriptus (L.) were studied by electron microscopy. The nucleolus went through the process of segregation at the beginning of meiosis with the movement to its surface of a pale-staining region. This region was shown to be the same as that called the ‘L zone’ or lacunae of nucleoli. Its chromosomal nature was strongly suggested by the presence of the synaptonemal complex within it. This demonstrated that the pale-staining region of nucleoli is the nucleolus organizer and almost certainly the chromosome region containing the ribosomal cistrons, and justifies the use of these terms to describe the structure when seen inside the nucleolus. The relationship between this zone and the heterochromatic knob called the nucleolar organizing body in maize by other workers is discussed.
Observations on intranuclear crystal and nucleolar size at different stages of cell differentiation in the midgut epithelium of several insects
Authors: Gouranton J. , Thomas D. 
Published: April 2021

ABSTRACT
Based on an inverse size relationship between nuclear crystal and nucleolus in different cells it has been postulated by several authors that the crystal develops from nucleolar materials. The purpose of the present paper is to investigate the validity of this argument. Intranuclear proteinaceous crystals appear in differentiating midgut cells of Gyrinus marinus and Tenebrio molitor. In an autoradiographic study we have previously demonstrated in these two species that the crystals do not develop from nucleolar materials. However, an inverse relationship with regard to size is observed between these 2 structures during the cell differentiation: the crosssectional area of the nucleolus decreases when the cross-sectional area of the crystal increases. But a decrease in size of the nucleolus is also observed during the differentiation of the midgut cells of Gyrinus natator where the crystals are not present. Consequently an inverse size relationship cannot be a sufficient argument to postulate that intranuclear crystals and nucleoli are interconvertible structures; decrease in size of the nucleolus is not related to development of the intranuclear crystal.
Perturbation of mammalian cell division: III. the topography and kinetics of extrusion subdivision
Authors: Mullinger Ann M. , Johnson R. T. 
Published: April 2021

ABSTRACT
If mitotic-arrested, cold-stored HeLa cells are incubated at 37 °C a proportion of the population divides by an aberrant process which we have called subdivision by extrusion. This process has been studied by time-lapse photography and shown to differ from normal cleavage in several respects. The cell surface becomes more generally mobile and, instead of producing the precisely localized furrowing activity of cytokinesis, gives rise to multiple surface protrusions. These protrusions enlarge at the expense of the parent cell and develop into a cluster of small daughter cells (mini segregants). The surface structure of the cell, as seen by scanning electron microscopy, also changes; the microvilli characteristic of interphase, metaphase and cleaving HeLa cells are lost during extrusion and the cell surface becomes smooth. Extrusion activity is much more variable than division by cleavage in terms of both topography and kinetics, and in general takes longer to complete.
Some cells in the cold-treated populations divide by mixtures of cleavage and extrusion or by cleavage alone. The relative numbers of cells dividing in different ways vary with the conditions of pretreatment and incubation of the mitotic cells. The greater the perturbation (e.g. longer cold storage), the greater the proportion of extruding rather than cleaving cells. Human diploid cells can also be induced to subdivide by extrusion. Possible mechanisms underlying the different types of division activity are discussed.