bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations on the fine structure and development of the spindle at mitosis and meiosis in a marine centric diatom (Lithodesmium Undulatum): II. the early meiotic stages in male gametogenesis
Authors: Manton Irene , Kowallik K. , Von Stosch H. A. 
Published: April 2021

ABSTRACT
Various cytoplasmic phenomena, including spindle structure and development during prophase of the first meiotic division, are described and illustrated. The living culture is represented by a timed sequence of photographs continuing those previously published with respect to mitotic stages in the same filament. The meiotic preliminaries include the so-called swelling phase, by which the parental frustule is forced open, liberating the contained spermatocytes. This occurs during pachytene on evidence of chromosome structure which is illustrated. A spindle precursor is shown to be present before opening of the frustule; this resembles structurally the mitotic equivalent though the ground plan is oblong instead of square. Growth of the precursor continues until after opening of the frustule, when the spindle itself begins to be laid down. Two stages of developing spindles during the later prophases are illustrated by sections cut in three planes and by serial sections. Preliminary comparisons are made with metaphase I and with mitosis, both qualitatively and quantitatively, but a full discussion is deferred pending completion of the record for the later meiotic stages.
The classes of endosymbiont of Paramecium Aurelia
Authors: Beale G. H. , Jurand A. , Preer J. R. 
Published: April 2021

ABSTRACT
The endosymbionts of Paramecium aurelia appear to consist of a number of different Gram-negative bacteria which have come to live within many strains of paramecia. It is not known whether in nature this relationship is mutually beneficial or not. The symbionts from one paramecium may kill other paramecia lacking that kind of symbiont. We identify the following classes of endosymbiotic organisms. First, kappa particles (found in P. aurelia, syngens 2 and 4) ordinarily contain highly characteristic refractile, or R, bodies, which are associated with the production of a toxin which kills sensitive paramecia. In certain mutants of kappa found in the laboratory both R bodies and ability to kill have been lost. Second, mu particles (in syngens 1, 2 and 8) produce the phenomenon of mate-killing. Third, lambda (syngens 4 and 8) and sigma particles (syngen 2) are very large, flagellated organisms which kill only paramecia of syngens 3, 5 and 9, and are enclosed in membrane-bound vacuoles. Fourth, gamma particles (syngen 8) are minute endosymbionts, surrounded by an additional membrane resembling endoplasmic reticulum. They have strong killing activity but no R bodies. Fifth, delta particles (syngens 1 and 6) possess a dense layer covering the outer membrane. At least one of the two known stocks is a killer. Sixth, nu particles are a heterogeneous group of particles (syngens 2 and 5) which do not kill or possess distinctive morphological characteristics. Seventh, alpha particles (syngen 2) are the only known nuclear symbionts of P. aurelia; they are found in the macronucleus. Alpha is also exceptional in being the only particle which is highly infectious, though certain of the other symbionts can also be taken up by paramecia lacking them, under special conditions.
The synthesis of deoxyribonucleic acid and nuclear histone of the X chromosome of the Rehnia Spinosus spermatocyte
Authors: Bloch D. P. , Teng Christina 
Published: April 2021

ABSTRACT
The X chromosome of the Rehnia spinosus (Orthoptera) spermatocyte exists in a vesicle separate from the rest of the nucleus during its replication. This chromosome is typically heterochromatic, and late replicating. After replication the chromosome vesicle fuses with the nucleus. Cytophotometric determination of DNA and histone during replication of the chromosome revealed two types of histone. One class increases in amount in proportion to the DNA. The second class remains constant as DNA doubles, and probably increases later. Autoradiographic studies of incorporation of amino acids indicates that histone labelling occurs during chromosome replication. However, a lag in amino acid incorporation suggests that DNA replication in the X chromosome, while accompanied, or closely followed, by complexing with histone, is not necessarily coupled with its synthesis.
Movement of cytoplasmic proteins into nuclei induced to enlarge and initiate dna or RNA synthesis
Authors: Merriam R. W. 
Published: April 2021

ABSTRACT
In other studies it has been shown that somatic cell nuclei, which normally do not divide, are induced to enlarge and synthesize DNA when introduced into the cytoplasm of egg cells of Xenopus laevis. Introduction of such nuclei into the cytoplasm of large oocytes, however, causes nuclei to enlarge in a different way and to synthesize RNA but not DNA.
In this study the proteins of eggs and oocytes were labelled with radioactive amino acids. Brain or blastula nuclei were then injected into cells containing labelled proteins under conditions in which protein synthesis was inhibited. Movement of cytoplasmic proteins was studied by observing the increase in acid-insoluble label over the injected nuclei by quantitative autoradiography.
To prevent nuclear protein synthesis during the experiments, puromycin was injected with the nuclei. An estimation of the size of the labelled amino acid pool, a demonstration of the inhibitory effects of puromycin, and comparison of the amount of labelled material with and without puromycin all showed that protein synthesis in the nuclei played an insignificant role during the course of the experiments.
A movement of acid-insoluble label from cytoplasm of egg cells into injected brain nuclei was noted even before they had begun to swell or synthesize DNA. In the initial period of nuclear enlargement there was a disappearance of the heterochromatic clumps characteristic of brain nuclei. This period coincided with a very rapid uptake of label to concentrations about twice that of the surrounding cytoplasm. A subsequent phase of nuclear swelling was characterized by a dilution of stainable nuclear material, loss of basophilia, and establishment of acidophilia of the nuclear contents. Cytoplasmic proteins continued to enter nuclei during this phase, but at a slower rate. Extraction of the soluble materials of labelled eggs with 0·01 M NaCl at pH 7·8 and a subsequent fractionation of the extract showed that there were many radioactive compounds present with molecular weights greater than 5000.
The synthesis of DNA was initiated even before nuclear swelling could be detected, proceeding at least through the early stages of swelling.
The induction of enlargement in blastula nuclei by oocyte cytoplasm containing labelled proteins was also accompanied by an uptake of label from the cytoplasm. In this case, although the uptake of unlabelled acidophilic material was much greater, the uptake of labelled proteins was much slower than that observed in the egg.
The results are discussed in terms of chromosomal changes which occur during nuclear enlargement and during concomitant changes in nucleic acid metabolism.
Action of colchicine and heavy water on the polymerization of microtubules in wheat root meristem
Authors: Burgess J. , Northcote D. H. 
Published: April 2021

ABSTRACT
The effects of colchicine and heavy water on cell division in wheat roots have been examined by means of mitotic index measurements correlated with an electron-microscope examination of the tissue. Heavy water alone caused an arrest of mitosis both in normal tissue and in roots which had been brought into partial synchrony of division by means of 5-aminouracil. Colchicine alone caused an accumulation of cells at c-metaphase in the synchronized tissue. Colchicine dissolved in heavy water showed variable effects; at high heavy water concentrations (greater then 70 %) mitosis was arrested; when the heavy water concentration was less than 70%, the mitotic index was approximately equal to that obtained by treatment of the tissue with colchicine dissolved in ordinary water.
These actions of colchicine and heavy water on the mitosis of the cells have been related to the formation and organization of the microtubules in the dividing cells. Heavy-water treatment was characterized by an increase in the number of microtubules found in the preprophase band and in the mitotic spindle. The microtubules of the preprophase band in cells treated with heavy water were arranged in a highly disoriented manner. After colchicine treatment the numbers of microtubules at the preprophase band and in the mitotic spindle were depleted. The preprophase band consisted of a few microtubules situated close to the wall. In the mitotic spindle the microtubules were either not present or visible only in the vicinity of profiles of endopla8mic reticulum or the chromosomes. When the cells were exposed to a solution of colchicine in 70 % heavy water microtubules were absent from the mitotic spindle and the preprophase band consisted of a few microtubules which were sometimes found scattered both along the wall and dispersed further into the cytoplasm.
Observations on the central pair of microtubules from the cilia of Tetrahymena Pyriformis
Authors: Chasey D. 
Published: April 2021

ABSTRACT
Frayed cilia from Tetrahymena pyriformis have been examined in the electron microscope using both uranyl acetate and phosphotungstic acid as negative stains. Observations on the central microtubules show that one member of the pair exhibits two rows of short projections. These are about 18 nm long, and are spaced longitudinally at 16-nm intervals. In many specimens the projections are separated from the tubule wall and appear as a ladder-like structure linked by one or more longitudinal filaments. These results are related to some recent work on sectioned material; it is likely that the projections are independent of any central sheath holding the two tubules together.
Mitotic delay following inhibition by 5’-fluorodeoxyuridine of S-phase in Physarum is not due to delay in termination of S-phase
Authors: Kauffman Stuart A. , Shymko Ronald M. 
Published: April 2021

ABSTRACT
It has been known for several years that inhibition by 5′-fluorodeoxyuridine (FdUrd) of DNA synthesis in plasmodia of Physarum polycephalum delays subsequent nuclear mitosis. To test whether this delay is due to delay in the termination of 5-phase, we blocked DNA synthesis with FdUrd + uridine for 3 h at different stages of S-phase, and in plasmodia with different cycle times. The results show that in short-cycling plasmodia the delay in mitosis can be as long as 9 h, despite little delay in termination of S-phase, and is longest when plasmodia are blocked in early S-phase. In plasmodia with long cycle times, no mitotic delay following 3 h inhibition by FdUrd of.S’-phase is observed. Our results suggest that mitotic delay after pulses of FdUrd is not due to delay in termination of S-phase, which therefore does not appear to ‘gate’ entry into a G1 period of fixed length. The fact that delay is longest after FdUrd blocks in early S-phase suggests that normal progress through S-phase, not its termination, is critical for the timing of the subsequent mitosis. This may reflect an obligate coupling between replication and transcription of specific genes needed for progress toward mitosis. The lack of mitotic delay in long-cycling plasmodia shows that S-phase-coupled processes need not act as ‘timers’ if other processes become rate-limiting.
Effect of colcemid on the centriole cycle in chinese hamster ovary cells
Authors: Kuriyama Ryoko 
Published: April 2021

ABSTRACT
The structural changes in the centrioles in Chinese hamster ovary cells were monitored by electron microscopy of whole mount preparations to investigate the effects of colcemid on the events in the centriole cycle. The population of mitotic cells increased with time of incubation with colcemid, but the arrest at mitosis by this drug was soon overcome, resulting in the formation of nuclei and a change in the shape of the cells again spreading over the substrate. The maximal mitotic index was reached every 25 h in the presence of either 0·10 or 0·91 μg/ml of colcemid. During this time, cells became multinucleated, increased greatly in size, and accumulated 8 to 10-nm filamentous bundles in the cytoplasm instead of microtubules, almost all of which had been depolymerized after exposure to colcemid.
In the cells that were continuously treated with colcemid, a pair of centrioles became disoriented and each subsequently produced a daughter centriole. However, these daughter centrioles elongated to only half their full length; many unusual figures in the centriolar pairs resulted from their proceeding normally to the phases for disorientation and nucleation for centrioles in the next cycle. Although the rate of centriole elongation and the frequency of formation of the daughter centrioles were decreased by increasing the concentration of colcemid, the disorientation of the centrioles was not disturbed by this drug. The inhibitory effect of colcemid on centriolar nucleation and elongation was found to be totally reversible; the formation and elongation of new daughter centrioles occurred again just after removal of the drug.
Prolonged treatment of cells with colcemid caused ultrastructural changes in the centrioles, such as the outgrowth of microtubules from the wall of centriolar triplets or the formation of unusual bundles of microtubules around the centrioles.
Coated vesicle-mediated transport and deposition of vitellogenic ferritin in the rapid growth phase of snail oocytes
Authors: Bottke W. , Sinha I. , Keil I. 
Published: April 2021

ABSTRACT
The main yolk component in oocytes of the pulmonate freshwater snails Planorbarius cometa L. and Lymnaea stagnalis L. consists of the iron storage protein ferritin and iron-free apoferritin. Both compounds are deposited in the yolk in the form of large paracrystalloids, tubular structures and randomly dispersed particles. In addition, the plasm contains lysosomelike inclusions with depositions of haemosiderin. Haemosiderin is interpreted as the product of proteolytic degradation of ferritin. During the rapid growth phase of the oocytes vitellogenic ferritin is transported across the basement lamina and taken up by adsorptive endocytosis via coated pits and vesicles. Formation of yolk bodies occurs by fusion of ferritin-containing vacuoles and empty vesicles that are probably derived from the Golgi apparatus. Uptake of ferritin is restricted to the basal region of the oocyte. No involvement of the follicle cells in synthesis and deposition of ferritin could be detected. Secretory cells of the midgut gland are the most likely site of synthesis of vitellogenic ferritin.
Under conditions of iron overload large masses of ferritin are encountered in the basement lamina of the oocytes. However, no significant increase in the uptake of ferritin could be observed. With the use of a tannic acid-glutaraldehyde fixation procedure a hitherto unobserved filamentous or rod-like material was detected inside the lamina and in coated pits. This material is probably also taken up by the oocytes and integrated into yolk platelets.
Though ferritin is a rather unusual vitellogenic protein, the mode of its uptake and deposition in the oocyte plasm is highly reminiscent of that of typical hormone-induced vitellogenins in other animal groups.
Morphology and physiology of gamete mating and gamete fusion in the fungus Allomyces
Authors: Pommerville Jeffrey 
Published: April 2021

ABSTRACT
New structural features of gametes are presented and several physiological aspects of mating and gamete fusion in the fungus Allomyces macrogynus are described. In the posterior region of the male gametes, where fusion is thought to occur, thin-section electron microscopy demonstrated the presence of microfilaments that were associated with a ruffling of the otherwise smooth plasma membrane. When the cells were treated with the microfilament-disruptive drug cytochalasin B, fusion was inhibited due to the interaction of the drug with the female gamete. Freeze-fracture replica analysis of the posterior region of the gamete plasma membrane showed an area devoid of membrane particles (termed the flagellar collar) at the basal end of the flagellum. Physiological analysis of gamete mating and fusion showed a requirement for divalent cations, and the time required for gamete mating could be lengthened or shortened by decreasing or increasing, respectively, the divalent cation concentration. Diphenhydramine and chloroquine also increased the time required for mating or completely prevented fusion. Tertiary amine local anaesthetics produced the same type of results, as did trypsin and Pronase. Phospholipases were without an inhibitory effect. When the gametes were washed free of the drugs prior to mating, it was seen that the female gametes were more sensitive to cell surface changes than the males. In addition, 2-h-old female gametes showed a 70% loss of fusion ability with young male gametes while the reverse experiment showed only a 20% decrease. These observations support the concept that gamete mating and fusion may occur at the flagellar collar area and that mating in A. macrogynus is governed, at least in part, by cation and protein interactions.
The relationship of fibroblast translocations to cell morphology and stress fibre density
Authors: Lewis L. , Verna J.-M. , Levinstone D. , Sher S. , Marek L. , Bell E. 
Published: April 2021

ABSTRACT
Translocation of human fibroblasts in culture was studied using techniques of time-lapse cinemicrography, indirect immunofluorescence, and computer analysis. An inverse relationship between the velocity of cells during the last hour of life and the density of stress fibers seen by immune staining was demonstrated. Translocating cells generally assumed one of two interconvertible morphologies: a triangular tailed shape or tailed fibroblast (TF), and a tailless form that resembled a half-moon, which we call a half-moon fibroblast (HMF). The tail of TFs formed only on regions of substrate that had been previously traversed by cells. The halfmoon morphology developed either on previously used or on virgin substrate. Cells adopted the HMF rather than the TF morphology with a four-fold greater frequency. HMFs translocated slightly faster than TFs. The foregoing observations suggest that the fibroblast tail is not an organelle essential for translocation. Since our technique allowed us to distinguish between cells which were cycling and those which had left cycle, we compared their velocities and found them to be similar. Also the average velocities of cells of different population-doubling levels (10th, 30th and 40th) were approximately equal.
Fine structural changes in the fat body cells of Rhodnius (hemiptera) during extreme starvation and recovery
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACT
The fate of lipid-rich components in the fat body cells of Rhodnius during extreme starvation and recovery is described. The mitochondria (along with ER etc.) degenerate to form large cytolysomes whose amorphous contents are dispersed after feeding to yield watery vacuoles with lipofuscin in their walls. Surviving mitochondria become swollen, with reduced cristae and conspicuous deposits of residual lipid or lipofuscin. In extreme starvation chromatin is progressively dispersed and discharged from the nucleus.
After feeding, damaged mitochondria recover very slowly before multiplying ; there seems to be no new formation of mitochondria. New ER is formed within the first hour after feeding by the escape of lipid-rich material from the nucleolus, which leads to expansion of the outer nuclear membrane to form blisters; these are budded off to form cysts and their surface is evaginated repeatedly to form laminated ER. New lipid droplets in the fat body appear to arise from the condensation of clusters of lipid-rich particles which are derived from the ER.
Relation of cytoplasmic calcium to contractility in Physarum polycephalum
Authors: Kuroda Ritsu , Kuroda Hideyo 
Published: April 2021

ABSTRACT
In a dumbbell-shaped plasmodium of Physarum polycephalum showing active shuttle streaming Ca was precipitated with potassium pyroantimonate (K[Sb(OH)6]), and the distribution of Ca between the cytoplasm and cellular organelles, especially vacuoles, was examined by electron microscopy. The contracting half-mass, where many empty vacuoles were present, was rich in the small Ca precipitates located in the cytoplasm. The relaxing half-mass, where many Ca-containing vacuoles were present, was poor in the cytoplasmic Ca precipitates. One half-mass of a dumbbell-shaped plasmodium was treated with Ca ionophore, X-537A, and its effect on the motive force for endoplasmic streaming and the distribution of Ca was investigated. The motive force was increased by X-537A, but the period of shuttle streaming was not changed. X-537A also induced a significant increase in the number of the cytoplasmic Ca precipitates in the X-537A-treated contracting half-mass, so that the asymmetry of the distribution of cytoplasmic Ca precipitates was enhanced. A large portion of the vacuoles were empty in the contracting half-mass, and Ca-containing in the relaxing one as in the case of the untreated plasmodium.