bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell cycle kinetics and development of Hydra attenuata: III. nerve and nematocyte differentiation
Authors: David C. N. , Gierer A. 
Published: April 2021

ABSTRACT
The differentiation of nerve cells and nematocytes in Hydra attenuata has been investigated by labelling interstitial cell precursors with [3H]thymidine and following by autoradiography the appearance of labelled, newly differentiated cells. Nematocyte differentiation occurs only in the gastric region where labelled nematoblasts appear 12 h and labelled nematocytes 72—96 h after addition of [3H]thymidine. Labelled nerves appear in hypostome, gastric region, and basal disk about 18 h after addition of [3H]thymidine. The lag in the appearance of labelled cells includes cell division of the precursor as well as differentiation since nerves and nematocytes have 2n postmitotic nuclear DNA content.
A cell flow model is proposed for interstitial cells and their differentiated products. Stem cells occur as single interstitial cells or in pairs. Per cell generation about 60 % of the daughter cells of stem cell divisions remain stem cells and about 40 % differentiate nerves and nematocytes. Nerves differentiate directly from stem cells in about 1 day. Nematocyte differentiation requires 5-7 days including proliferation of a cluster of 4, 8, 16 or 32 interstitial cells and differentiation of a nematocyst capsule in each cell. The numbers of interstitial cells and nematoblasts predicted by the cell flow model from the rates of nerve differentiation (900 nerves/day/ hydra), nematocyte differentiation (1760 nematocyte nests/day/hydia) and stem cell proliferation (stem cell cycle = 24 h), agree with the numbers of these cells observed in hydra. The number of stem cells per hydra is 3000-6000 depending on assumptions about the time of determination. The ratio of nematocyte to nerve differentiation averaged over the whole hydra is 3:1. In the hypostome and basal disk interstitial cell differentiation occurs exclusively to nerve cells while in the gastric region the ratio of nematocyte to nerve differentiation is about 7:1.
Limpet haemocytes: III. effects of cytochalasin b and colchicine on cell spreading and aggregation
Authors: Jones G. E. , Partridge T. 
Published: April 2021

ABSTRACTLimpet blood cells are suitable for the study of a number of interdependent features of cell behaviour; microspike formation, spreading and locomotion on a solid substrate, and aggregation. The effects of cytochalasin B (CCB) and colchicine on each of these activities is studied with a view (a) to determining with which functions these 2 reagents interfere; and (b) to gaining information on the relationships between these functions in normal cell behaviour.Rapid spike formation and fast aggregation in a shaker system, which are normal features of the behaviour of amoebocytes in limpet blood or in seawater, are totally but reversibly inhibited by the presence of low concentrations of CCB (e.g. 0·5 μg/cm3). Similarly, the spreading of amoebocytes on to a solid substrate is greatly inhibited by CCB, both in rate and extent, and the rapid locomotion on a solid substrate of normal amoebocytes is completely abolished by CCB. The first observable effects of CCB on spread amoebocytes are loss of optical integrity of the spikes and retraction of parts of the anterior cell margin. The loss of distinctive cell shape, the inhibition of spreading on to a glass surface and the lack of motility on such a surface may all be immediate consequences of the disruption of spike structure.CCB inhibits aggregation but does not disrupt preformed contacts between cells, which suggests that it acts on an early stage in the formation of stable contact rather than on the adhesiveness per unit area of contacting cell surface. A possible link between the effects of CCB on spikes and on aggregation is the proposal that low-diameter projections are needed to establish initial contact between cells. Alternatively, the spikes may be required for the rapid spreading of cells, not only on to glass but also over the surfaces of other cells, enabling them to increase their mutual contact area very rapidly and thus stabilize an adhesion.Amoebocytes maintained in the presence of 50 μg/cm3 colchicine for a number of hours gradually lose their bipolar form and the entire cell margin becomes occupied by the spike-supported lamella which normally constitutes the leading edge of the cell. Thus microtubules are probably not necessary for the skeletal functions of spikes or for their roles in spreading and aggregation, but they do appear to play a part in the control of spike orientation.Macrophages, cells lacking obvious spikes and showing little sign of bipolarity, appear unaffected by CCB or colchicine and spread normally on to a glass slide in the presence of either reagent. This, together with the limited spreading of amoebocytes in CCB, suggests that at least 2 distinct mechanisms may operate in the spreading of cells on to a solid substrate.
Contact inhibition of overlapping and differential cell adhesion: A sufficient model for the control of certain cell culture morphologies
Authors: Martz E. , Phillips H. M. , Steinberg M. S. 
Published: April 2021

ABSTRACTUsing intuitive arguments, several investigators have proposed that the relative strengths of adhesion of cell to cell and of cell to substratum could determine whether or not monolayering – and specifically contact inhibition of cell overlapping – will occur. In the present communication, these ‘strengths of adhesion’ are given precise physical definitions, and the adhesive relationships which would promote spontaneous cell monolayering are rigorously derived, using the thermodynamic approach embodied in the differential adhesion hypothesis. This analysis verifies that contact inhibition of overlapping could, in principle, be a result solely of differential adhesion. In addition, it is demonstrated that for homogeneous populations of uniform cells cultured on a solid, uniform substratum, eleven distinct equilibrium configurations (cell population morphologies) could be generated merely by varying the relative values of cell-to-cell and cell-to-substratum adhesiveness. Most of these configurations have been observed previously in actual cell cultures.
Effects of hormones on the polysaccharide-synthesizing membrane systems of lettuce pith
Authors: Wright K. , Bowles D. J. 
Published: April 2021

ABSTRACT
Changes have been induced in the polysaccharides laid down in the cell walls of lettuce pith by administration of the hormones auxin and zeatin. This polysaccharide derives from the membrane systems of the cells and radioactive precursor has been used to follow the accompanying changes which occurred in the polysaccharide contained within isolated Golgi and endoplasmic reticulum fractions. Zeatin-induced division and differentiation was accompanied by up to 12-fold increases in the amount of radioactivity in polysaccharide of isolated membrane fractions, and the pattern of distribution of label between the sugars of this polysaccharide was qualitatively different in the presence of zeatin. The change in this pattern was evident in the Golgi fraction at an earlier stage in the induction of the response than that in the endoplasmic reticulum.
Distribution of microtubules and microfilaments in developing vestibular sensory epithelium of mouse otocysts grown in vitro
Authors: Heywood P. , Van De Water T. R. , Hilding D. A. , Ruben R. J. 
Published: April 2021

ABSTRACT
Otocysts explanted from 12th-gestation-day mice and maintained in organ culture under went a series of developmental changes which paralleled those that occurred in vivo and which resulted in the formation of a sensory epithelium of the vestibular type. At the time of explantation presumptive vestibular sensory epithelium consisted of cells that were undifferentiated, pseudostratified and rapidly proliferating. The only microtubules present were those of the mitotic apparatus. After 4 days of in vitro development cells comprising the presumptive vestibular sensory epithelium were less pseudostratified and more elongate; their nuclei had assumed a basal orientation and there was a clear marginal velum. Longitudinally oriented cytoplasmic microtubules were present at the apices of some cells; they were often grouped around a centriole which may have served as a nucleation centre for their assembly. After 7 days of in vitro development mitosis had ceased and supporting cells and innervated hair cells were present: both types of cells were always longer than they were broad and were often highly asymmetrical. Hair cells were flask- or columnar-shaped, with a nucleus situated in the basal third of the cell. Most mitochondria in hair cells were located in the apical third of the cell. The same distribution of mitochondria and nuclei was evident in supporting cells. Microtubules occurred throughout the length of the supporting cell and were always parallel to its longitudinal axis. In hair cells microtubules were more frequent than in supporting cells: the majority were parallel to the longitudinal axis of the cell but there were two exceptions. First, at the apex of hair cells some microtubules were oriented transversely and diagonally: these were probably involved in the development and maintenance of the constricted apex of these cells. Secondly, microtubules appeared to be randomly arranged in the narrow region of the cytoplasm between the ventral surface of the nucleus and the base of the hair cells. Microfilaments were confined to the basal third of hair cells where their orientation paralleled that of the microtubules. The possible functions of microtubules and microfilaments in the development of hair cells and supporting cells of the mouse vestibular epithelium are discussed.
Observations on the ultrastructure of the choanoflagellate Codosiga botrytis (Ehr.) saville-kent with special reference to the flagellar apparatus
Authors: Hibberd D. J. 
Published: April 2021

ABSTRACT
The ultrastructure of the choanoflagellate Codosiga botrytis is described with particular reference to the flagellar appendages, the flagellar rootlet system, the transition zone, the basal body and accessory centrioles, and the stalk. The controversial early reports of flagellar appendages in this species have been confirmed and they have been detected in 2 further species, Salpingoeca frequentissima and Monosiga sp. The appendages consist of a delicate bilateral vane 2 am wide on either side of the axis, composed of extremely fine overlapping or interwoven fibrils.
The flagellar root system consists of a large number of radiating microtubules associated with bands of electron-dense material near the basal body; striated roots are absent. The microtubules extend from several separate foci, those in any one group originating near a composite electron-dense band, and for a distance of 300 nm from the basal body they are separated by blocks of interstitial material.
The flagellar basal body forms one of a diplosome pair of centrioles. The triplet microtubules of the accessory centriole are embedded in amorphous electron-dense material and the whole is enveloped in a sheath of similar appearance. The existence of a third centriole close to the diplosome pair is also reported. The relatively complex structure of the flagellar transitional zone is described.
The stalk is composed of a core of circular lacunae, which may or may not contain finger-like protoplasmic extensions of the posterior end of the cell, surrounded by a continuation of the sheath material which encloses the remainder of the protoplast. In the stalk only there is a further closely sheathing layer about 15 nm thick which is regularly striated, the spacing of the striations in shadowcast material and sections being about 3 times that measured by negative staining.
The structure of choanoflagellates differs widely from that of the algal class Chrysophyceae, the group in which they are included in some classifications, and from the remainder of the algae; they do not appear to have a place in either the algae or the plant kingdom. The structure of Codosiga botrytis is briefly compared with that of sponge choanocytes and collared cells in the Metazoa and some of the possible phylogenetic implications of this are indicated.
Linkage of the loci for glucose-6-phosphate dehydrogenase and for inosinic acid pyrophosphorylase to the x chromosome of the field-vole Microtus agrestis
Authors: Cook P. R. 
Published: April 2021

ABSTRACT
It has been proposed that there are strong selective pressures which have acted during the evolution of mammals to conserve the linkage of genes on the X chromosome. If so, loci that are known to be X-linked in one mammalian species should be X-linked in others. The loci for glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49) and for inosinic acid pyrophosphorylase (E.C. 2.4.2.8) are known to be X-linked in a variety of mammals. The linkage of these loci to the X chromosome of the field-vole, Microtus agrestis, is indicated by the pattern of segregation of these loci in hybrid cells derived by fusion of mouse cells with vole lymphocytes.
Drosophila cell fusion induced by wheat germ agglutinin
Authors: Rizki Rose M. , Rizki T. M. , Andrews C. A. 
Published: April 2021

ABSTRACT
The effects of wheat germ agglutinin on Drosophila embryonic cell lines growing on coverglasses was examined by scanning electron microscopy. At low concentrations of the lectin (5-10 μg/ml), cells spread against the glass surface and fused to form syncytia. At high concentration, damage to the cell surface was evidenced as extensive membrane shrivelling and loss of surface microfilaments. Fusion also occurred under these conditions. There was some indication that the morphology of cells in division remains undisturbed by wheat germ agglutinin. The coalescence of cells and morphologic distortion induced by wheat germ agglutinin were not inhibited by N-acctylglucosamine, the hapten inhibitor of the lectin, under the conditions utilized in this study.
Insect peripheral nerves: Accessibility of neurohaemal regions to lanthanum
Authors: Lane Nancy J. , Leslie R. A. , Swales Lesley S. 
Published: April 2021

ABSTRACT
During incubation in vivo, exogenously applied ionic lanthanum comes to surround the numerous neurosecretory terminals which are found lying within or immediately beneath the acellular neural lamella ensheathing the nerves from fifth instar and adult specimens of Rhodnius prolixus. The lanthanum does not penetrate beyond the cellular perineurium, which completely surrounds the non-neurosecretory axons in these nerves and constitutes a form of ‘blood-brain barrier’. In some cases, however, lanthanum is found in the vicinity of a neurosecretory axon lying beneath the perineurium, where it can be assumed to have leaked in from the neurosecretory terminal lying free in the neural lamella.
When nerves are incubated in calcium-free media, regions with an attenuated perineurium become ‘leaky’, in that lanthanum is found lying in those extracellular spaces between axons and glia which lie immediately below the thin part of the perineurial layer. Bathing solutions made slightly hyperosmotic to the haemolymph with sucrose have no apparent disruptive effects on the barrier. When the tissues are incubated in more hypertonic solutions, the perineurial barrier becomes ‘leaky’ throughout, and tracer pervades beyond its cells into all the intercellular spaces between glia and axons.
The possible role of the zonulae occludentes in both the maintenance of the perineurial barrier and in the formation of interglial occlusions to local penetration of exogenous substances is considered.
Fine structure of the cytoplasm in salivary glands of simulium
Authors: Macgregor H. C. , Mackie J. B. 
Published: April 2021

ABSTRACT
The salivary glands of 3rd or 4th instar larvae of Simulium mditifrons are about 5 mm long and up to 400 μ wide. They have a capacious lumen which is normally filled with secretion.
The apical (luminal) plasmalemma of the gland cells is thrown into numerous microvilli. The basal plasmalemma is usually straight but is infolded in places. The infoldings may be complex near to cell junctions. There is a thick, uniform basement membrane. Contact surfaces of adjacent cells often interdigitate. A septate junction extends inwards from the lumen for one-quarter the depth of the cells. Rough endoplasmic reticulum is distributed evenly throughout the cytoplasm. Many Golgi complexes with dark membrane-bounded granules are scattered throughout the cytoplasm. Solitary granules, often more than 1 μ in diameter, lie in the apical cytoplasm, especially near the apical border of the cell. These granules resemble the larger Golgi granules and the contents of the lumen. Solitary granules consisting of 2 components have been seen in various stages of passage through the cell membrane. The 2 components are present in roughly constant proportions and can be identified in the larger Golgi granules and in the secretion in the lumen. The nucleus is spherical. The nuclear envelope is smooth in the larger cells of a gland but may be folded in the smaller cells. There are 80–100 pores/μ2 of nuclear envelope. Each pore appears to have a small granule at its centre. Microtubules, about 180 A thick, are numerous in the apical cytoplasm, particularly near the luminal border. Tubules which lie deep in the cytoplasm are flanked by a clear area 100–200 Å wide.
The fine structure of a salivary gland cell of Simulium appears to indicate that the major components of the salivary secretion are synthesized in association with the ribosomes on the rough endoplasmic reticulum, concentrated in the Golgi regions, formed into secretion granules, and passed out of the cell into the lumen of the gland by reverse phagocytosis.
The reactivation of the red cell nucleus
Authors: Harris H. 
Published: April 2021

ABSTRACT
When the nucleus of a mature hen erythrocyte is introduced into the cytoplasm of a HeLa cell it resumes the synthesis of RNA and DNA. This reactivation of the red cell nucleus in the heterokaryon is associated with a marked increase in its volume. There is a direct relationship between the volume of the nucleus and the amount of RNA which it makes. The nuclear enlargement is not a consequence of increased RNA synthesis, or of DNA synthesis : enlargement is the primary event, and the increase in RNA synthesis is determined by it. The possibility is considered that changes in nuclear volume may regulate not only the amount of RNA made in the nucleus but also the areas of chromatin on which it is made.
Mast cell proliferation in adult rats
Authors: Blenkinsopp W. K. 
Published: April 2021

ABSTRACT
Mast cell proliferation was investigated in adult male rats using continuous infusions of tritiated thymidine to label deoxyribonucleic acid. The results indicate that the total number of mast cells increases as body weight increases (though at a lower rate) and that there is no mast cell turnover in the sense of discard and replacement. No evidence was found of mast cell formation from ‘stem’ cells.
The influence of indol-3yl acetic acid and sugar on the pattern of induced differentiation in plant tissue culture
Authors: Jeffs R. A. , Northcote D. H. 
Published: April 2021

ABSTRACT
The induction of vascular differentiation in callus tissue of Phaseolus vulgaris by the application of indol-3yl acetic acid (IAA) and sucrose has been studied by cytological methods. The application of radioactive IAA and sucrose in the induction experiments has enabled the concentration of these substances, which move through the callus tissue mass by simple diffusion, to be estimated.
Various monosaccharides, disaccharides, trisaccharides and sugar derivatives have been used instead of sucrose in order to study the biological role of the sugar molecule in the induction process. The results indicate that sucrose and certain other α-glucosyl disaccharides have a specific action in inducing differentiation into nodules containing xylem, phloem and meristematic activity.
Evidence is also presented to show that possibly only very young cells, immediately following division, can be induced to differentiate.
Cytoplasmic streaming and microtubules in the coenocytic marine alga, Caulerpa prolifera
Authors: Sabnis D. D. , Jacobs W. P. 
Published: April 2021

ABSTRACT
Two distinct patterns of cytoplasmic streaming in the leaf of Caulerpa prolifera are described. Broad, longitudinally running, two-way streams are restricted to the endoplasm of one leaf surface. Also present are large numbers of narrow, two-way streams that coil helically through-out the endoplasm surrounding the central vacuole. Numerous unique bundles of aggregated, evenly spaced, oriented microtubules are distributed within the inner cytoplasm some distance from the cell wall. Cortical microtubules, as described for other plant material, have been only very infrequently encountered in Caulerpa and appear to be sparsely distributed. Apart from the prominent bundles of oriented microtubules, no other significant ultrastructural differences were noted between the stationary ectoplasm and streaming endoplasm. The possible cyto-skeletal role of the oriented microtubules in the development and maintenance of asymmetries in organ differentiation is discussed in relation to their direct or indirect influence on the directional migration of cytoplasmic components.
Sites of protein synthesis in nucleoli of root meristematic cells ofAllium cepaas shown by radioautography with [3H]arginine
Authors: Chouinard L. A. , Leblond C. P. 
Published: April 2021

ABSTRACTThe interphase nucleolus in root meristematic cells of Allium cepa may be divided into four regions, three of which are always present: the fibrillar, granular and lacunar regions, while the fourth or vacuolar region may be missing. The sites of protein synthesis in nucleoli were investigated by means of light and electron-microscope radioautography after a 5-min immersion of the roots in a solution of [3H]arginine.The radioautographs of interphase nucleoli showed many silver grains over both the fibrillar and the granular regions. Occasional silver grains were also recorded over, or close to, the lacunar regions, but none were over the vacuolar regions. A 15-min chase period did not change the radioautographic pattern. It is concluded that the three permanent regions of the interphase nucleoli, namely the fibrillar, the granular and the DNA-containing lacunar regions, are sites of protein synthesis.
Photoinduction of plastids and of chlorophyll in a Chlorella mutant
Authors: Bryan G. W. , Zadylak Arlene H. , Ehret C. F. 
Published: April 2021

ABSTRACT
Stage-characterized populations of dark-grown heterotrophs of an asexually reproducing, unicellular alga, Chlorella mutant C-10, have been studied to determine light-induced ultra-structural changes in plastids and in chlorophyll synthesis. C-10 requires light to synthesize chlorophyll and to produce a photosynthetically potent chloroplast. Thylakoid development is followed through a series of stages from prethylakoidal tubules to primary thylakoids which produce blebs. The blebs expand and slide over the primary thylakoid, and then form a secondary thylakoid; the process continues until the characteristic stacks of tertiary thylakoids are present in the mature chloroplast. A dramatic decrease in the rate of chlorophyll synthesis (‘ early-rate-decline’) is observed approximately 1 h after the onset of induction. This early-rate-decline correlates with the appearance of blebs on the primary thylakoid. Twelve hours after the onset of induction, the photosynthetically impotent proplastid develops into a mature plastid containing stacks of disc-like thylakoids. The application of chloramphenicol, puromycin and actinomycin D suggests that the early-rate-decline is associated with an insufficient rate of synthesis of the holochrome proteins.