bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell surface lipids and adhesion: III. the effects on cell adhesion of changes in plasmalemmal lipids
Authors: Curtis A. S. G. , Chandler C. , Picton N. 
Published: April 2021

ABSTRACT
The two preceding papers of this series suggest that the state of the plasmalemmal lipids affects cell adhesion. Plasmalemmal composition was altered by the experimental incorporation of fatty acids into R1 and R2 positions in the phosphatidyl components of the cell surface. In this paper we report that: If the incorporation is of long chain length fatty acids (saturated) cell adhesion rises.If the incorporation is of unsaturated fatty acids cell adhesion falls as the unsaturation increases.Incorporation has to be extensive to produce a large change in adhesion.Changes in adhesion parallel the plasmalemmal incorporation but do not follow the total cell incorporation.
Item (4) argues that it is plasmalemmal and not other membrane lipids that are involved in cell adhesion. Item (3) suggests that bulk membrane properties and not some very specific grouping are involved in the effects of lipids on adhesion. The similar extents of incorporation of the various different fatty acids and the negligible amounts of lysophospholipids in the membranes of cells that have incorporated fatty acids argue that the effects are not due to differential accumulations of these lysolipids when incubations are done with different fatty acids. The changes in adhesion cannot be accounted for by changes in surface charge density since the electrophoretic mobility of the cells is unchanged by these incubations.
It is suggested that these effects on adhesion due to changes in plasmalemmal lipids can be explained either in terms of the action of intermembrane van der Waals-London (electrodynamic) forces in cell adhesion or of changes in surface fluidity. These alternatives are discussed.
The induction of dna synthesis in the chick red cell nucleus in heterokaryons during the first cell cycle after fusion with hela cells
Authors: Johnson R. T. , Mullinger A. M. 
Published: April 2021

ABSTRACT
Induction of DNA synthesis in embryonic chick red cells has been examined during the first and second cell cycles after fusion with HeLa cells synchronized in different parts of G1 and S-phase. The data indicate that: (i) the younger the embryonic blood the more rapidly the red cells are induced into DNA synthesis; (ii) the greater the ratio of HeLa to chick nuclei in the heterokaryon, the more rapidly the induction occurs; (iii) DNA synthesis in the chick nucleus can continue after the HeLa nucleus has left S-phase and entered either G2 or mitosis; (iv) the induction potential of late S-phase HeLa is somewhat lower than that of early or mid S-phase cells; (v) less than 10 % of the chick DNA is replicated during the first cycle after fusion and only a small proportion (15 %) of the chick nuclei approach the 4C value of DNA during the second cycle after fusion; (vi) the newly synthesized DNA is associated either with the condensed regions of the nucleus or with the boundaries between condensed and non-condensed regions; (vii) the chick chromosomes at the first and second mitoses after fusion are in the form of PCC (prematurely condensed chromosomes); they are never fully replicated and are often fragmentary; (viii) DNA synthesis in the chick nucleus is accompanied by an influx of protein (both G1 and S-phase protein) from the HeLa component of the heterokaryon.
The growth of the pollen tube wall in Oenothera organensis
Authors: Dickinson H. G. , Lawson Janice 
Published: April 2021

ABSTRACT
The growth of the pollen tube wall of Oenothera is effected by the expulsion of fibrillar material from the cytoplasm into the developing wall. This material may also be seen in the cytoplasm, contained in membrane-bound vesicles. It is not clear how the content of the vesicles is discharged, but it appears not to involve the participation of microtubules.
The source of the cytoplasmic fibrillar bodies depends upon the stage of development of the pollen tube. The earliest growth is derived from the inclusion into the wall of vesicles containing pre-formed materials present in the grain on pollination. During the next stage of growth the wall is derived from the content of double-membraned inclusions also present in the pollen. The content of the former vesicles is not so similar to the wall as the latter, but intermediates between the 2 types of vesicle may be seen in the cytoplasm, indicating that the former are formed from the latter. Most of the tube wall is derived from the products of dictyosomes in the pollen grain or tube. These dictyosomes are few in number and they must be exceedingly active. This, and the observation that dictyosome vesicles are frequently associated with banked complexes of mitochondria, indicates that some steps in the metabolism of the vesicular content, perhaps phosphorylation, take place distant from the dictyosomes.
These different sources of fibrillar material presumably permit the rapid starting of tube growth, without any attendant metabolism. However, it would be impossible to include enough pre-formed wall material in the grain to enable the full growth of the tube, so once started, it seems that the tube then relies on the elaboration of simple reserves for the construction of its wall. These reserves are likely to be held in the pollen, and may be the large numbers of starch grains characteristic of the pollen cytoplasm.
Hepatocyte function in long-term organ culture of Amphiuma means liver
Authors: Fleming N. , Brown D. , Balls M. 
Published: April 2021

ABSTRACT
Fragments of liver from the adult urodele Amphiuma means, the Congo eel, were maintained in organ culture for up to 70 days. The normal electrophoretic patterns of several enzymes were retained. The activities of ornithine transcarbamylase, arginase, glutamate oxalacetate transaminase and glutamate pyruvate transaminase, and urea production, glucose uptake and tissue glycogen content remained relatively constant throughout the culture period. Histological organization and hepatocyte ultrastructure were also retained. Liver fragments survived better in media based on MEM or BME than in medium based on Leibovitz L15. Since many aspects of tissue-specific structure and function are retained, long-term amphibian organ culture is well suited to studies on the control of hepatocyte function and on the effects of metabolites, hormones, drugs and toxins.
An electron-microscope study of the intranucleolar chromatin during nucleologenesis in root meristematic cells ofAllium cepa
Authors: Chouinard L. A. 
Published: April 2021

ABSTRACTThe various states of condensation of the chromatin material, contained inside the lacunar regions of the reforming nucleolus in Allium cepa, have been investigated by means of conventional electron-microscope techniques. The observations reveal that, in the emerging early to late telophase nucleoli, the intralacunar chromatin material in question appears both in an extended and a condensed condition; from late telophase to the mid G1 period of interphase, the intralacunar chromatin material of the rapidly growing and developing nucleoli is present in an extended state only.An attempt is made to interpret these morphological findings in the light of current knowledge concerning the structural relationship of the nucleolar organizing region of the nucleolar chromosome with the interphase nucleolus in plant cells. The relevant observational evidence would be consistent with the view that the chromatin-containing lacunar regions of the reforming nucleolus in Allium cepa correspond, in fact, to cross- or oblique sections of a meandering channel through which the nucleolar organizing segment of the nucleolar chromosome passes. Assuming the applicability to intranucleolar chromatin of the general concept of condensed-inactive versus extended-active chromatin, it is concluded that gradual uncoiling and subsequent decondensation of the chromatin of the nucleolar organizing region in the form of a convoluted loop structure are key morphological and functional events associated with the process of nucleologenesis in the species investigated.
Spontaneous and lectin-induced redistribution of cell surface receptors on embryonic chick neural retina cells
Authors: Mcdonough J. , Lilien J. 
Published: April 2021

ABSTRACT
The mobility of plant lectin receptors in the plane of the membrane is examined for cells prepared from embryonic chick neural retinas by a variety of procedures. Cells liberated from the intact tissue by trypsin treatment followed by mechanical dissociation are able to redistribute their receptors into ‘caps ‘both spontaneously and in the presence of a multivalent lectin. These cells, dispersed by trypsinization, upon repair in culture for a suitable period of time lose their ability to redistribute lectin receptors. Cells dispersed by mechanical means without prior trypsin treatment are unable to undergo ‘cap’ formation. In addition, cells within intact tissues are also unable to redistribute their lectin receptors into ‘caps. ‘Based on these observations we propose that within solid tissues which have assumed their characteristic architecture, cell surfaces are immobilized, and that this phenomenon may be a critical parameter in determining the potential of a cell to undergo morphogenetic rearrangements.
Fine structure of the nucleolus in normal and mutant Xenopus embryos
Authors: Hay Elizabeth D. , Gurdon J. B. 
Published: April 2021

ABSTRACT
Mutant and normal Xenopus laevis embryos (o-nu, 1-nu, 2-nu) were examined in the electron microscope after glutaraldehyde and/or osmium-tetroxide fixation. During cleavage both 0-nu and wild-type embryos contain multiple small nucleolar bodies, less than 1 μ in diameter, composed mainly of a fibrous material. By the end of cleavage or beginning of gastrulation, granular caps develop on the fibrous nucleolar bodies. In 1- and 2-nu cells, the multiple nucleolar bodies are replaced during gastrula and neurula stages by definitive nucleoli (2–5 Å in diameter) which contain abundant small (150 Å) granules intermingled with fibrous material. In o-nu cells, one or two pseudonucleoli (1–3 μ in diameter) appear at about the same time that definitive nucleoli develop in wild-type cells. The multiple small nucleolar bodies disappear as the pseudonucleoli enlarge. Pseudonucleoli differ from definitive nucleoli in having a much smaller amount of the granular component, which is located as a cap on the periphery of the fibrous component and not mingled with it. The granular component of the 0-nu pseudonucleoli, however, is not distinguishable in its fine structure from the same component of normal nucleoli. In many o-nu tadpoles at stage 41, the granular component of the nucleolus is entirely absent and the fibrillar component is very prominent. Both granular and fibrous components of the o-nu pseudonucleoli contain RNA as judged by RNase sensitivity and staining affinity for basic dyes.
A study of mitochondrial membranes in relation to elementary particles
Authors: Malhotra S. K. , Eakin R. T. 
Published: April 2021

ABSTRACT
Elementary particles that commonly have been seen by electron microscopy to be attached by stalks to mitochondrial cristae in negatively stained preparations, were not apparent in similarly stained mitochondria from exponentially growing wild-type Neurospora crassa when these were isolated in sucrose solution containing 1 × 10−3 M EDTA. However, elementary particles were easily demonstrable in electron micrographs if the mitochondria were isolated without EDTA in the sucrose solution. A biochemical study indicated that both kinds of mitochondrial preparations, isolated in the presence or absence of EDTA, had about the same capacity for oxidative phosphorylation. Observations on rat-liver mitochondria also suggested that the stalked elementary particles were more easily demonstrated if the preparation was made in the absence of EDTA. It was difficult to demonstrate elementary particles in wild-type Neurospora mitochondria isolated with or without EDTA and subsequently prepared for electron microscopy by spreading on the surface of an aqueous solution of potassium phosphotungstate. Elementary particles could be demonstrated in poky Neurospora mitochondria isolated with EDTA if the mitochondria were spread on the surface of an aqueous solution of phosphotungstate. It was concluded that biochemical functions associated with elementary particles are independent of structural configuration as seen by electron microscopy.
Factors affecting the tertiary structure of resilin in locusts
Authors: Neville A. C. 
Published: April 2021

ABSTRACT
Autofluorescent daily growth zones in locust resilin provide a detailed record of cross-linking of the polypeptide chains, since the fluorescence is caused by the tertiary cross-links, dityrosine and trityrosine. Environmental temperature changes are the main cause of autofluorescent daily growth layers in resilin, fluorescence increasing with temperature. Microdensitometric scans show that this rhythmicity is superficial, in harmony with the optical and mechanical isotropy of resilin. The molecular structure and properties of resilin appear to be homeo-statically controlled by the cells. With suitable rearing conditions, resilin ligaments were produced with half or twice as many fluorescent growth layers as usual, or with them almost absent. Evidence for a weak circadian rhythm influencing cross-linking is presented. A marked drop in fluorescence followed by a sharp rise occurs at adult emergence and is metabolically triggered. A metabolic control also operates to make the resilin grown before the moult less fluorescent than resilin grown after it. Further evidence for the very rapid cross-linking of resilin during its formation is discussed.
An electron-microscope study of the in vitro transformation of human leucocytes: II. transformation to macrophages
Authors: Chapman J. A. , Gough J. , Elves M. W. 
Published: April 2021

Abstract
Macrophages which develop in cultures of human peripheral blood have the typical ultrastructural features of macrophages occurring in other situations, in vivo and in vitro. The cultured cells usually have irregular nuclei and the cytoplasm possesses numerous digestion vacuoles containing debris; the cell outline is irregular with many filopodia. Other cells were laden with membrane-bounded granular bodies containing periodic-structured material of regular outline. Although it is concluded that no evidence about cell ancestry can be adduced from this morphological study, it seems likely from other work that many of these macrophages arise from lymphocytes.
Fine-Structural Studies of the Gametes and Embryo of Fucus Vesiculosus L. (Phaeophyta): II. The Cytoplasm of the Egg and Young Zygote*
Authors: Brawley Susan H. , Wetherbee Richard , Quatrano Ralph S. 
Published: April 2021

ABSTRACT
Following fertilization, there are rapid changes in the appearance of the Fucus egg. Large electron-translucent vesicles (V1) accumulate fibrillar material, and following pronuclear fusion, they are largely electron-opaque. These vesicles (V1) are formed originally in unfertilized eggs by smooth endoplasmic reticulum (SER) after release of the eggs from the oogonium. Golgi complex hypertrophy follows fertilization, and this increased activity continues throughout early embryogenesis. Wall formation begins after penetration of the egg by the sperm. Vesicles (V2) of unknown origin, which have homogeneously fibrillar contents, and Golgi vesicles (V3) merge with SER-derived vesicles (V1) after wall formation begins. Osmiophilic bodies are a prominent feature of the egg and embryo. They are penetrated by SER, and subsequently there is a loss of electron-opaque material. Alternatively, they discharge concentrically whorled material into the cytoplasm. The nuclear surface of the egg is convoluted in the period close to fertilization, and electron-opaque material is segregated in the cytoplasmic matrix lying within the nuclear invaginations.
Cytochalasin b-induced pseudo-cleavage of mouse oocytes in vitro: Asymmetric localization of mitochondria and microvilli associated with a stage-specific response
Authors: Wassarman P. M. , Albertini D. F. , Josefowicz W. J. , Letourneau G. E. 
Published: April 2021

ABSTRACT
Mouse oocytes are induced by cytochalasin B to undergo ‘pseudo-cleavage’ in vitro into 2 equally sized and separable compartments. This response to the drug is dependent upon the meiotic state of the oocytes, as well as upon the presence of an intact zona pellucida. The resulting 2 cellular compartments can be completely separated from one another and cultured in vitro. Each of the compartments possesses characteristic structural features. The most pronounced structural differences include: (i) the presence of a nucleus (germinal vesicle) and nucleolus in one compartment; (ii) the presence of microvilli on the surface of the anucleate, but not the nucleate, compartment; and (iii) the localization (segregation) of mitochondria at the periphery of the anucleate, but not the nucleate, compartment. The results presented suggest that pseudo- cleavage induced by cytochalasin B arises as a consequence of a limited interaction of the drug with the oocyte surface and/or cortex and that it may represent a topographical dissociation of transporting and non-transporting regions of the membrane. These and other features of mouse oocytes treated with cytochalasin B are of interest in view of the involvement of the oocyte zona pellucida and plasma membrane during meiotic maturation, fertilization, and early embryogenesis.
Pollen ultrastructure in anther cultures of Datura innoxia: I. Division of the presumptive vegetative cell
Authors: Dunwell J.M. , Sunderland N. 
Published: April 2021

ABSTRACT
Ultrastructural features of embryogenic pollen, in Datura innoxia are described, just prior to, during, and after completion of the first division of the presumptive vegetative cell. In anther cultures initiated towards the end of the microspore phase and incubated at 28 °C in darkness, the spores divide within 24 h and show features consistent with those of dividing spores in vivo. Cytokinesis is also normal in most of the spores and the gametophytic cell-plate curves round the presumptive generative nucleus in the usual highly ordered way. Further differentiation of the 2 gametophytic cells does not take place and the pollen either switches to embryogenesis or degenerates. After 48–72 h, the remaining viable pollen shows the vegetative cell in division. The cell, which has a large vacuole and thin layer of parietal cytoplasm carried over from the microspore, divides consistently in a plane parallel to the microspore division. The dividing wall follows a less-ordered course than the gametophytic wall and usually traverses the vacuole, small portions of which are incorporated into the daughter cell adjacent to the generative cell. The only structural changes in the vegetative cell associated with the change in programme appear to be an increase in electron density of both plastids and mitochondria and deposition of an electron-dense material (possibly lipid) on the tonoplast. The generative cell is attached to the intine when the vegetative cell divides. Ribosomal density increases in the generative cell and exceeds that in the vegetative cell. A thin electron-dense layer also appears in the generativecell wall.
It is concluded that embryogenesis commences as soon as the 2 gametophytic cells are laid down. Gene activity associated with postmitotic synthesis of RNA and protein in the vegetative cell is switched off. The data are discussed in relation to the first division of the embryogenic vegetative cell in Nicotiana tabacum.
Pollen ultrastructure in anther cultures of Datura innoxia: III. Incomplete microspore division
Authors: Dunwell J. M. , Sunderland N. 
Published: April 2021

ABSTRACT
During the microspore division in Datura innoxia, the mitotic spindle is oriented in planes both perpendicular (PE) and oblique (OB) to the spore wall against which the nucleus is situated. However, irrespective of polarity, the usual type of hemispherical wall is laid down at cytokinesis and isolates the generative cell from the rest of the pollen grain (type A). In PE spores the vegetative nucleus initially occupies a central position in the pollen grain, whereas in OB spores the vegetative nucleus lies at the periphery of the grain close to the generative cell. In anther cultures initiated just before the microspore division is due to take place, no marked change can be observed in either orientation or symmetry of the mitotic spindle when the spores divide. In some, however, cytokinesis is disrupted and deposition of the hemispherical wall arrested. In the absence of a complete wall, differentiation of the generative cell cannot take place and binucleate pollen grains are formed having 2 vegetative-type nuclei (type B). The 2 nuclei in the B pollens are always situated against the pollen-grain wall, suggesting that the disruption phenomenon is related to the OB spores. The incomplete wall always makes contact with the intine on the intine-side of the spindle. Wall material may be represented merely as short stubs projecting out from the intine into the cytoplasm, in which event the 2 nuclei lie close to each other and are separated by only a narrow zone of cytoplasm. In other grains the wall is partially developed between the nuclei and terminates at varying distances from the tonoplast; in these, the nuclei are separated by a wider zone of cytoplasm. The significance of these binucleate grains in pollen embryogenesis is discussed.
Meiotic maturation of mouse oocytes In Vitro: inhibition of maturation at specific stages of nuclear progression
Authors: Wassarman P. M. , Josefowicz W. J. , Letourneau G. E. 
Published: April 2021

ABSTRACT
In vitro studies of meiotic maturation of mouse oocytes have been carried out in the presence of several drugs. The individual steps of nuclear progression, including dissolution of the nuclear (germinal vesicle) membrane, condensation of dictyate chromatin into compact bivalents, formation of the first metaphase spindle, and extrusion of the first polar body, are each susceptible to one or more of these drugs.
Germinal vesicle breakdown, the initial morphological feature characteristic of meiotic maturation, is inhibited by dibutyryl cyclic AMP. However, even in the presence of dibutyryl cyclic AMP, the nuclear membrane becomes extremely convoluted and condensation of chromatin is initiated but aborts at a stage short of compact bivalents. Germinal vesicle breakdown and chromatin condensation take place in an apparently normal manner in the presence of puromycin, Colcemid, or cytochalasin B. Nuclear progression is blocked at the circular bivalent stage when oocytes are cultured continuously in the presence of puromycin or Colcemid, whereas oocytes cultured in the presence of cytochalasin B proceed to the first meiotic metaphase, form an apparently normal spindle, and arrest. Emission of a polar body is inhibited by all of these drugs. The inhibitory effects of these drugs on meiotic maturation are reversible to varying degrees dependent upon the duration of exposure to the drug and upon the nature of the drug.
These studies suggest that dissolution of the mouse oocyte’s germinal vesicle and condensation of chromatin are not dependent upon concomitant protein synthesis or upon microtubules. On the other hand, the complete condensation of chromatin into compact bivalents apparently requires breakdown of the germinal vesicle. Failure of homologous chromosomes to separate after normal alignment on the meiotic spindle in the presence of cytochalasin B suggest that microfilaments may be involved in nuclear progression at this stage of maturation. Cytokinesis, in the form of polar body formation, is blocked when any one of the earlier events of maturation fails to take place.