bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gland cells in Hydra: Cell cycle kinetics and development
Authors: Schmidt Tobias , David Charles N. 
Published: April 2021

ABSTRACT
The proliferative capacity of gland cells in Hydra attenuata was investigated. The results indicate that both gland cell proliferation and interstitial cell differentiation to gland cells contribute to the maintenance of the whole population. On the basis of [3H]thymidine incorporation and nuclear DNA measurements, gland cells consist of at least three different populations. One population consists of rapidly proliferating cells with a cell cycle of about 72 h. These cells are distributed throughout the body column. In the lower gastric region there is a population of non-cycling cells in G2 while in the upper gastric region there is a population of noncycling cells in G1. About half the G1 population becomes a new antigen, SEC 1, which is typical of mucus cells.
Change in the rate of CO2 production in synchronous cultures of the fission yeast Schizosaccharomyces pombe: A periodic cell cycle event that persists after the DNA-division cycle has been blocked
Authors: Novak B. , Mitchison J. M. 
Published: April 2021

ABSTRACT
CO2 production has been followed by manometry in synchronous and asynchronous cultures of Schizosaccharomyces pombe prepared by elutriation from the same initial culture. The rate of production follows a linear pattern in synchronous cultures with a rate change once per cycle at the time of cell division. This pattern is most clearly shown in oscillations of the difference between values of the second differential (acceleration) for the synchronous and asynchronous cultures. The association between the rate change and the time of division is maintained during growth speeded up in rich medium and slowed down in poor medium and at lower temperature. It is also maintained after a shift-up in temperature. Results with wee mutants suggest that the association is with the S period rather than division itself. The rate and acceleration of CO2 production are approximately proportional to cell size (protein content) in asynchronous cultures.
When synchronous cultures of the temperature-sensitive mutants CdC 2.33 and CdC 2.33 wee 1.6 are shifted up to the restrictive temperature, the DNA-division cycle is blocked. The oscillatory pattern of CO2 production, however, continues for one to two cycles until the acceleration reaches a constant value, after which the oscillations are undetectable. This point is reached later in the double mutant and there is a phase difference in the oscillations compared to those in the single mutant. With both blocked mutants the ‘free-running’ oscillations are about 15 % shorter than the normal cycle time. There are well-known examples of such oscillations in eggs but they are rare in growing systems.
Cytoskeletons from a mutant of Dictyostelium discoideum with flattened cells*
Authors: Claviez M. , Brink M. , Gerisch G. 
Published: April 2021

ABSTRACT
Development of a mutant of Dictyostelium discoideum, HG403, is described whose cells spread strongly on a substratum. Although the mutant cells were less clearly polarized into the front and rear ends, and usually less extensively elongated than wild-type cells, their aggregation pattern was only slightly less regular. Cells of the mutant responded well to cyclic AMP by chemotaxis, although their capability of stabilizing cell shape and maintaining dominance of a single moving front appeared to be reduced. Mutant HG403 proved to be ideal for the preparation of cytoskeletons in which the organization of the microtubular system, the network of filaments between them, the dense texture of the microfilament network at the periphery of the cells, as well as the bundling of microfilaments in spike-like extensions, could be observed.
Development of microtubule capping structures in ciliated epithelial cells
Authors: Portman R. W. , Lecluyse E. L. , Dentler W. L. 
Published: April 2021

ABSTRACT
Although capping structures are present at the tips of microtubules in both growing cilia and mature cilia, previous work has not determined the time of cap formation. The results reported here reveal that the large caps of mature palate cilia appear in cilia with lengths as short as 1·75 μm. In the growing palate cilium, a diskshaped plate is formed at the tip during the first gm of growth. As the cilium elongates to 1·5–2·0μm, a small plate forms underneath the disk-shaped plate that gives an asymmetrical appearance to the whole cap structure. The structure of the cap is complete in cilia longer than 2·0 μm. The hair-like structures that form the extraciliary crown appear on the membrane at the ciliary tip at the same time as the mature cap is forming. The formation of a cap structure is discussed in relation to microtubule assembly during ciliogenesis.
Periodic cell cycle changes in the rate of CO2 production in the fission yeast Schizosaccharomyces pombe persist after a block to protein synthesis
Authors: Novak B. , Mitchison J. M. 
Published: April 2021

ABSTRACT
CO2 production has been followed by manometry in synchronous and asynchronous control cultures of Schizosaccharomyces pombeprepared by elutriation from the same initial culture. Earlier results showed a periodic change in the rate of production, which took place once per cell cycle. These changes were most clearly shown as oscillations in the difference between values of the second differential (acceleration) for the synchronous and asynchronous cultures. This paper shows that the oscillations continue for atleast three cycles in the presence of cycloheximide (with and without chloramphenicol). Protein synthesis is virtually absent and there is no cell division. The control of this metabolic oscillation is therefore not directly dependent on translation. The period of the oscillation under these conditions is about 60 % of the normal cycle time.
Incompatibility in Populus: Structural and cytochemical characteristics of the receptive stigmas of Populus alba and P. nigra
Authors: Villar M. , Gaget M. , Said C. , Knox R. B. , Dumas C. 
Published: April 2021

ABSTRACT
Structural and cytochemical characteristics of stigmas of Populus alba (section Leuce) and P. nigra (section Aigeiros) have been studied to provide an understanding of the cell biology of the interspecific incompatibility reactions between these two species. In addition to specific morphological characteristics, stigma surfaces differ in the presence of an exudate studied by ultrastructural and stigma print techniques. P. nigra shows features of a dry-type stigma covered by a pellicle, whereas P. alba has a copious exudate typical of a wet-type stigma that contains unsaturated lipids.
Signal-Induced Reorganization Of The Microtubular Cytoskeleton In The Ciliated Protozoon Euplotes Octocarinatus
Authors: Jerka-Dziadosz Maria , Dosche Christine , Kuhlmann Hans-Werner , Heckmann Klaus 
Published: April 2021

ABSTRACT
A predator-released substance induces the freshwater ciliate Euplotes octocarinatus to undergo, within a few hours, a drastic change in cell form that makes engulfment by the predator more difficult or even impossible. During this transformation, the outline of the cell changes from ovoid to circular and the size increases considerably. The cells cease dividing while they transform, but later continue divisional morphogenesis and maintain the circular form for many cell generations if the concentration of the predator factor is maintained
The microtubular cytoskeleton of Euplotes was studied by transmission electron microscopy of cells from which the cytoplasm had been extracted by mild treatment with Triton X-100. This procedure increased the visibility of microtubules, especially single microtubules located in the endoplasm. In transformed cells, a considerable increase in number of microtubular triads on the dorsal and ventral surfaces and the appearance of extra single microtubules between the dorsal triads was observed. However, certain interconnected groupings of microtubules located on the dorsal surface were greatly diminished after transformation. Intracytoplasmic microtubules were also more abundant in the enlarged cells than in the untreated ovoid ones. The spacing and general pattern of microtubules, however, appears to be the same in untreated and treated cells.
We conclude from these observations that the transformation of Euplotes cells from their typical ovoid form into the enlarged circular form is accompanied by the mobilization and utilization of microtubules already present in subcortical regions and an assembly of new microtubules needed for support of the expanding cell cortex.
Distribution of an endogenous β-galactoside-specific lectin during foetal and neonatal rabbit development
Authors: Catt James W. , Harrison F. Lynne , Carleton J. Susan 
Published: April 2021

ABSTRACT
The tissue concentration of an endogenous β-galactoside-specific lectin is developmentally regulated in rabbit tissues during foetal and neonatal development. Immunoassay data and localization studies both indicate that the lectin is particularly associated with late embryonic and early postnatal development. No lectin could be detected in embryos prior to 21 days of gestation, whereas many tissues showed an increase in lectin around the time of birth. It is likely that in most tissues the high concentrations of lectin are largely due to increased synthesis by fibroblasts, which are particularly abundant and active in connective tissue during the extensive tissue reorganization taking place at this time. The lectin appears to be synthesized by other differentiated cell types also, notably myoblasts, alveolar cells and erythroblasts. The peak of lectin concentration seen in foetal liver probably reflects lectin associated with foetal erythropoiesis. The rabbit lectin has a low specific activity but its tissue concentration is correspondingly higher than lectin concentrations in other mammals. This conservation of total lectin activity suggests a fundamental role for the lectin dependent upon its saccharide binding activity. This and other indirect evidence suggests that these lectins are involved in the synthesis, secretion or organization of extracellular matrix components.
General electromagnetic theory of total internal reflection fluorescence: the quantitative basis for mapping cell-substratum topography
Authors: Gingell D. , Heavens O. S. , Mellor J. S. 
Published: April 2021

ABSTRACT
Total internal reflection fluorescence (TIRF) has recently been used to look at the contacts made between cells and a glass surface on which they are spread. Our method utilizes the fluorescence of a water-soluble dye that acts as an extracellular aqueous volume marker. Fluorescence is stimulated by the short-range electric field near the glass surface that exists under conditions of total internal reflection. Since fluorescence is normally generated beneath a spread cell and not beyond it, the fluorescence of the image is related to the size of the cell-glass water gap. The images obtained are remarkable for their detail, contrast and the absence of confusing granularity due to cytoplasmic heterogeneity, which is commonly seen in interference reflection (IRM) images.
We here develop a rigorous electromagnetic theory of total internal reflection in layered structures appropriate for cell contacts and apply it to quantitative TIRF. We show that: (1) TIRF, unlike IRM, can report cell-glass gaps in a way that is practically independent of the detailed physical properties of the cell; (2) TIRF is also far more sensitive than IRM for measuring cellglass water gaps up to ≈100 nm. These striking results explain the image quality seen by TIRF. As the initial step towards verifying our theory we show that measurement of the fluorescence stimulated by total internal reflection at a simple glass-water interface matches theoretical predictions.
Biochemical and ultrastructural data on Tetrahymena pyriformis treated with copper and cadmium
Authors: Piccinni E. , Irato P. , Coppellotti O. , Guidolin L. 
Published: April 2021

ABSTRACT
The addition of copper (10 μgml−1) or cadmium (5 μgml−1) to the medium is well tolerated by Tetrahymena pyriformis GL. Both metals are accumulated by cells, cadmium to a greater extent than copper. The growth rate is not affected and from the micrographs it is evident that the ultrastructure is not altered by the treatments. After 3 days of culture the macronucleus contains dense masses of chromatin and numerous nucleolar fusion bodies. Granules, cytolysomes and many food vacuoles are present in both control and treated cells. Cadmium induces the formation of a chelating protein; the amino acid analyses and the ultraviolet spectrum indicate that it is similar to the metallothionein isolated by higher organisms.
The molecular weight of native protein is about 27 000. After treatment by sulphitolysis or oxidation we obtained a peak of molecular weight at about 6000.
The treatment with copper does not appear to induce metallothioneins or other chelatins. The high tolerance of Tetrahymena towards cadmium is believed to be due to the formation of a Cd-Zn metallothionein.
The different chelating proteins induced by copper and cadmium in other groups of Protozoa and the different detoxification mechanisms present in these organisms are discussed.
Hydrostatic pressure in epidermal cells is dependent on ca-mediated contractions
Authors: Strohmeier Renate , Bereiter-Hahn Jürgen 
Published: April 2021

ABSTRACT
Volume/osmotic pressure relationships were compared in Xenopus epidermal cells treated with the calcium antagonist lanthanum and in control cells. In lanthanum-treated cells the volume was found to be proportional to the reciprocal of the osmotic pressure in the hypotonic range, but not in the control cells. This difference is interpreted as being caused by contractions of the actomyosin system in control cells, which require external calcium. On the basis of the different slopes of the measurements under these two conditions the contractile force of the cells in isotonic conditions was calculated to be 0-96× 105 Nm-2.
The observation that in hypotonic media the cell body is enlarged in the direction of movement provides evidence that the cell body/lamella transition region is the part of the cell that contracts most during locomotion.
By analysing cell speed in media with varying osmotic pressures, the relationship between internal pressure and cell locomotion was revealed.
Development of macrociliary cells in Beroë II. Formation of macrocilia
Authors: Tamm Sidney L. , Tamm Signhild 
Published: April 2021

ABSTRACT
Two patterns of macrociliary growth occur in Beroë. Early differentiation described previously (Tamm & Tamm, 1988) leads to the first pattern of ciliogenesis. A tuft of 10–20 single cilia initially grows out from basal bodies that have migrated to the cell surface and are axially aligned. Ciliary membranes then begin to fuse along their length, except at the base, resulting in thicker groups of cilia on each cell. Progressive fusion of ciliary membranes, together with addition and elongation of new axonemes, finally results in mature macrocilia, 5 μm thick and 40 μm long, enclosed by a single membrane distally. The second pattern of ciliogenesis begins with the simultaneous appearance of several hundred ciliary buds on the apical surface. The short cilia possess individual membranes with bulbous tips, and are not axially aligned. Subsequent elongation is accompanied by progressive fusion of neighbouring ciliary membranes, except at the base, leading to flat-topped ‘stumps’ surrounded by a single membrane distally. Further elongation then proceeds asymmetrically within each stump. Axonemes on the aboral side of the macrocilium stop elongating, while those towards the oral side increase progressively in height, resulting in a slanted profile. Basal feet and central-pair microtubules are now uniformly aligned. Unequal elongation of axonemes on the oral and aboral sides of the macrocilium continues until the macrocilium resembles a lobster’s claw, with a long slender shaft projecting from a broad base. Finally, the polarity of unequal growth reverses: the shorter axonemes on the aboral side elongate and almost catch up with the longer ones on the opposite side, resulting in a mature macrocilium of uniform diameter. The unusual membrane architecture of the macro-cilium is thus a consequence of selective fusion of the distal regions of originally separate ciliary membranes. The polarized, asymmetrical growth of axonemes on the two sides of the macrocilium illustrates a remarkable control of microtubule elongation at the subcellular level.
Fertilization in ascidians: Apical processes and gamete fusion in Ciona intestinalis spermatozoa
Authors: Fukumoto Makoto 
Published: April 2021

ABSTRACT
This paper describes the fine structure of the spermatozoan apex and its morphological changes during the process of fertilization in Ciona intestinalis.
At the apex of the head an acrosome is present in the form of a flattened vesicle containing moderately electron-dense material with an electron-dense plate in its centre. Contiguous to the acrosome, an apical substance is located in the anterior-most tip of the sperm head.
The spermatozoa that bind to and penetrate the chorion of both normal and caffeine-treated eggs have an intact acrosome and do not show an observable alteration of the plasmalemma enclosing the apex of the head. On the other hand, spermatozoa in the perivitelline space of both normal and caffeine-treated eggs lack an acrosome. Instead of an acrosome, apical processes are observed at the apex of the spermatozoa in the perivitelline space of both normal and caffeine-treated eggs. Gamete fusion seems to occur between the egg membrane and some of these apical processes at the tip of the sperm head. The apical process reported here is thought to be analogous to the acrosomal process in other marine invertebrates. The apical processes that are induced in the perivitelline space have not been previously described in ascidians.
Aggregative behaviour of embryonic chick cells in the presence of anti-bodies directed against actomyosins
Authors: Kemp R. B. , Jones B. M. , Gröschel-Stewartf U. 
Published: April 2021

ABSTRACT
Skeletal muscle and liver tissue from 9-day-old chick embryos were dissociated into separate cells using 0·25 % (w/v) crude trypsin. The effect of rabbit anti-actomyosin sera on the aggregation of these cells was estimated by the gyratory shaker and turbidimetric methods. Studies were also undertaken on the ability of fluorescein isothiocyanate-labelled rabbit anti-uterine actomyosin serum (FITC-labelled anti-UAM) to stain the cell surface and on the type specificity and species specificity of rabbit anti-chicken actomyosin sera.
Antisera against chicken gizzard smooth-muscle actomyosin (anti-GAM) and against chicken pectoralis striated muscle actomyosin (anti-PAM) both gave single precipitin bands with their respective actomyosins on diffusion through agar. The antisera neither reacted with their heterologous actomyosin nor with gizzard tropomyosin; they were type-specific. Serial sections of human cervix were stained in a similar pattern with both anti-UAM and anti-GAM, showing that anti-smooth muscle actomyosin sera were not species-specific. The fibrocytes of the human umbilical cord and human platelets were stained by FITC-labelled anti-UAM serum but not by labelled anti-human PAM.
The aggregation of muscle and liver cells over a 24-h period in the presence of antisera against human or chicken PAM was not significantly different from the controls incubated on a gyratory shaker in Eagle’s minimum essential medium (MEM) containing 10% (v/v) rabbit non-immunized serum (NIS) or calf serum. However, anti-UAM and anti-GAM inhibited both the rate of aggregation of liver and muscle cells and the size of aggregates attained in 24 h. This effect could not be simulated with specific rabbit antisera against human plasma proteins.
The globulin-enriched fraction of anti-GAM markedly inhibited the aggregation of liver and muscle cells in a range of concentrations between 50 and 500 μg per 2×106 cells/ml Eagle’s MEM. In contrast, the aggregation of cells incubated with globulin-enriched anti-PAM was similar to the controls. The addition of anti-GAM globulins at 1 or 2 h to muscle cells rotated by the turbidimetric method reduced the aggregative competence of the cells over the remainder of a 4-h period.
The possibility that the inhibitory effect of anti-UAM and anti-GAM on cell aggregation is due to impurities in the antisera or to a general reaction with cell surface ATPases is discussed but, in the light of evidence, rejected in favour of a reaction between the antisera and an actomyosin of the smooth-muscle type at the cell surface.
The fine structure of Gonyaulax polyedra, a bioluminescent marine dinoflagellate
Authors: Schmitter Ruth E. 
Published: April 2021

ABSTRACT
An electron-microscope study of Gonyaulax polyedra, a holophytic marine dinoflagellate which is bioluminescent, has revealed 2 structures not previously described in free-living dino flagellates: a polyvesicular body occurring at intervals along the cell’s periphery, and a large spherical body which may function in intracellular digestion. Coated vesicles were found in the nuclear-Golgi region. Chloroplast lamellae were widely and regularly spaced in portions of the chloropla8t8 at the interior of cells harvested during the light period of the culture cycle. The lamellae were closer together and not so regularly arrayed in peripherally located chloroplast branches, or in chloroplasts harvested during the dark period. Other aspects of the ultrastructure of G. polyedra are described and discussed.