bluuebunny/crossref_metadata_2025_split huggingface dataset:
Protease secretion during onset of development in Dictyostelium discoideum
Authors: Rossomando Edward F. , Maldonado Barbara , Crean Edmund V. , Kollar Edward J. 
Published: April 2021

ABSTRACT
At the onset of development, the single cells of the eukaryotic micro- organism Dictyostelium discoideum secrete proteolytic activity which can be assayed using the insoluble substrate remazolbrilliant blue hide. The activity is not secreted by exponentially growing cells, but does appear extracellularly at the onset of the stationary growth phase. When growth phase cells are resuspended in non-nutrient buffer, proteolytic activity begins to appear outside the cells. It accumulates in the buffer at a rate similar to that observed for 2 glycosidases of lysosomal origin and reaches a maximum after about 2 h of incubation. After 3–4 h incubation, centrifugation of the non-nutrient buffer removes the cells, producing a supernatant which we refer to as conditioned medium.
Subsequent experiments with conditioned medium showed: (a) its incubation with purified plasma membranes results in the release of polypeptides which can be recovered and, when displayed on polyacrylamide gels, can be shown to be stage specific; and (b) that conditioned medium can decrease the rate of detachment of cells from a collagen substratum. Both effects can be prevented by the addition of remazolbrilliant blue hide suggesting that they are due to proteolytic activity present in the conditioned medium.
Finally, we were able to show that conditioned medium contains components which, when spread over the bottom of plastic Petri dishes, enhance the rate of multicellular structure formation. Additional studies showed that this effect of conditioned medium could also be brought about by components which remained behind on uncoated plastic dishes after the removal of a D. discoideum cell layer. These data may be accommodated to a model in which the protease secreted during the onset of development acts on the cell membrane releasing components which coat the substratum and facilitate migration and multicellular structure formation.
pH oscillations in cell suspensions of Dictyostelium discoideum: Their relation to cyclic-amp signals
Authors: Malchow D. , Nanjundiah V. , Gerisch G. 
Published: April 2021

ABSTRACT
Cells of Dictyostelium discoideum known to release cyclic AMP (cAMP) rhythmically in the form of pulses, change with the same period of about 8 min the pH of their medium. The pH is used here as an indicator to investigate the effect of externally added cAMP pulses on the oscillations. Both a temporary increase in amplitude and a permanent phase shift can be induced. The phase-response curve indicates that the period can be increased and decreased by rhythmic stimulation with cAMP pulses.
Intracellular motility of mitochondria: Role of the inner compartment in migration and shape changes of mitochondria in xth-cells
Authors: Bereiter-Hahn J. 
Published: April 2021

ABSTRACT
Mitochondrial movements have been followed by phase-contrast microscopy in living XTH-cells (Xenopus laevis tadpole-heart cells) in tissue culture. The same organelles have been viewed subsequently in electron micrographs. Locomotion of mitochondria proceeds at velocities up to 100 μm/min. Formation of branches of mitochondria and other shape changes may occur with the same speed. Mitochondrial motility can be classified into 4 types: (1) Alternating extension and contraction at the two ends of rod-shaped mitochondria. (2) Lateral branching. (3) Alternate stretching and contraction of arbitrary parts of a mitochondrion amounting to a kind of peristaltic action. (4) Transverse wave propagation along the organelle. Types 1 to 3 can be reduced to the same underlying principle; they cause locomotion. Formation of mitochondrial extensions is due to elongation of cristae.
The observations are discussed in terms of 4 specific proposals. (1) Intracellular locomotion of mitochondria is caused by local enlargements and contractions of the organelles. (2) The shape changes are correlated with alterations in the arrangement of the cristae. (3) Such arrangements are not associated with overall swelling or shrinkage of the mitochondrion; they are local features. (4) Estimates of the time required for rearrangement of the inner compartment amount to less than 0·3 s for single crista arrangements during the fastest shape changes, and less than 1–3 s during slower alterations. This high velocity is in good accord with the hypothesis of energy conservation by conformational events during oxidative phosphorylation.
The ultrastructure of cell division inEuglena gracilis
Authors: Gillott Marcelle A. , Triemer Richard E. 
Published: April 2021

ABSTRACTThe ultrastructure of mitosis in Euglena gracilis was investigated. At preprophase the nucleus migrates anteriorly and associates with the basal bodies. Flagella and basal bodies replicate at preprophase. Cells retain motility throughout division. The reservoir and the prophase nucleus elongate perpendicular to the incipient cleavage furrow. One basal body pair surrounded by a ribosome-free zone is found at each of the nuclear poles. The spindle forms within the intact nuclear envelope. Polar fenestrae are absent. At metaphase, the endosome is elongated from pole to pole, and chromosomes are loosely arranged in the equatorial region. Distinct, trilayered kinetochores are present. Spindle elongates as chromosomes migrate to the poles forming a dumb-bell shaped nucleus by telophase. Daughter nuclei are formed by constriction of the nuclear envelope. Cytokinesis is accomplished by furrowing. Cell division in Euglena is compared with that of certain other algae.
Ultrastructure of mitosis in the chloromonadophycean algaVacuolaria virescens
Authors: Heywood Peter 
Published: April 2021

ABSTRACTDuring preprophase in the chloromonadophycean alga Vacuolaria virescens microtubules are present around the flagellar basal bodies and extend over the anterior surface of the nucleus. These microtubules assist in the separation of the flagella and later enter the nucleus through polar gaps. During prophase the nucleoli begin to disperse and the chromosomes become condensed. At metaphase the nucleus assumes an elliptical shape and an equatorial plate of chromosomes becomes aligned across the long axis of the nucleus; kinetochores are recognizable on some of the chromosomes. The nuclear envelope remains intact over most of the surface and in places it forms folds. During anaphase chromosomes are less distinct and vesicles are present in the elongating nucleus. Most of the new nuclear envelope around the progeny nuclei is formed by coalescence of these membrane vesicles during late anaphase and telophase, although some of the original nuclear envelope may also become incorporated. During telophase disintegration of the original nuclear envelope becomes pronounced and portions of this structure are recognizable in the cytoplasm after completion of mitosis.It is suggested that this unusual type of nuclear envelope behaviour may be important in ensuring the segregation of the Golgi apparatus and contractile vacuole to progeny cells. Interphase cells contain a single extensive Golgi apparatus which is located between the anterior surface of the nucleus and the contractile vacuole. The Golgi apparatus and contractile vacuole act as an osmoregulatory system and their presence is presumably essential to the existence of the organism. Formation of a new contractile vacuole and division of the Golgi apparatus occur early in mitosis and thereafter a Golgi apparatus and contractile vacuole become associated with each of the poles of the nucleus. They retain this location throughout mitosis and during cytokinesis, with the result that an osmoregulatory system is present in each of the daughter cells. In a similar manner, microbody-like organelles are associated with the nuclear envelope during mitosis but not at interphase. Growth of the nuclear envelope during mitosis may serve as the means of partitioning these organelles to the progeny cells. Thus mitosis in Vacuolaria virescens is responsible not only for the equal segregation of the genetic material but also for the correct distribution of some of the cytoplasmic components.
The histochemical localization of acrosin in guinea-pig sperm after the acrosome reaction
Authors: Green D. P. L. , Hockaday A. R. 
Published: April 2021

ABSTRACT
The protease acrosin is widely considered to be an essential component of a zona lysin which enables sperm to penetrate the zona pellucida of the egg. Sperm form a characteristic penetration slit little wider than the sperm head itself and this has long suggested that any zona lysin is attached to the sperm surface after an acrosome reaction. This paper provides the first ultrastructural evidence that this is the case.
The protein acrosin inhibitor, Kunitz soybean trypsin inhibitor, has been covalently attached to the electron-dense marker, ferritin, and the conjugate incubated with guinea-pig sperm which have undergone an Az3i87-induced acrosome reaction. Electron microscopy shows that ferritin is distributed unevenly over the outer surface of the newly exposed inner acrosomal membrane but does not extend to the equatorial segment. This is further evidence that acrosin can be considered as a candidate for the role of zona lysin. The mechanism of sperm penetration of the zona is discussed in the light of these observations.
Meiosis in Coprinus: IX. the influence of premeiotic s-phase arrest and cold temperature on the meiotic cell cycle
Authors: Lu B. C. , Chiu S. M. 
Published: April 2021

ABSTRACT
Arrest of premeiotic 5 phase by high temperature and light causes the meiotic cell cycle time to become shortened by 4 h after release of the arrest. Genetical and cytological evidence shows that diplotene is drastically reduced from 4·5 h to less than 1 h. Cycloheximide (50 μg/ml) treatment of early and late diplotene cells in normal cultures prevents the meiotic divisions even though the chromosomes are condensed. The same treatment given within 1 h of metaphase I allows both divisions to be completed but fails to allow sporulation. This is interpreted to mean that the cellular programme for meiotic division (division programme) is made during diplotene. In the arrest-release cultures, however, the division programme is made during pachytene. This finding is interpreted to mean that the cellular programme in meiosis is prepared one step at a time. When the nuclear cycle is arrested, the cytoplasmic programmes continue. As a result, the division programme is precociously induced at pachytene. Since the diplotene programme is complete, the cells proceed directly from pachytene into metaphase I with the diplotene stage drastically reduced. Cold treatment at 5 °C at pachytene temporarily suspends the progress of meiosis and hence prolongs the pachytene stage. This prolongation causes an increase in recombination frequency. This finding supports the argument that recombination frequency is a function of time.
The role of golgi bodies in polysaccharide sulphation in Fucus zygotes
Authors: Callow Maureen E. , Coughlan S. J. , Evans L. V. 
Published: April 2021

ABSTRACT
The cell wall of 24-h zygotes of Fucus serratus is composed of 3 layers -an inner fibrillar layer (sulphated fucan), an outer fibrillar layer (alginic acid/cellulose) and an exterior amorphous layer (sulphated fucan, alginic acid). The 2 layers containing sulphated fucan are preferentially thickened at the rhizoid pole.
Light- and electron-microscope autoradiographic pulse-chase experiments on 22-h zygotes using 56SO3-show the Golgi bodies to be the sites of fucan sulphation. The isolation and characterization of isolated organelle fractions from 22-h zygotes is described. Biochemical analysis of isolated Golgi-rich fractions from 22-h zygotes shows that the first detectable labelled macromolecule is associated with these fractions 2 min after addition of 56SO24-. The sulphate acceptor molecule has been partially characterized. 56S-APS and 56S-PAPS are detectable in the soluble fraction 0·5 min after addition of 56SO24-.
The results are discussed in relation to other published work on the differentiation of Fucus embryos and on polysaccharide sulphation.
Structural differences contrast higher plant and animal golgi apparatus
Authors: Mollenhauer Hilton H. , Morré D. James 
Published: April 2021

ABSTRACT
The intercistemal spacings between cistemae of dictyosomes of higher plants differ from those of mammalian dictyosomes. In plants, the spacings increase from an average of about 8·0 nm at the forming face to about 14·0 nm at the maturing face. The increase in spacing coincides with the appearance within the intercistemal space of parallel filaments called intercistemal elements. In mammals, the intercistemal spacings are more nearly constant, and intercistemal elements have not been observed. Plant and animal dictyosomes may differ as well in the relative widths of the cisternal lumina, the widths of the intercistemal spacings, and in more subtle ways involving the appearance of the membranes. These structural differences may be indicative of some functional differences that contrast higher plant and animal Golgi apparatus.
Non-reciprocal contact inhibition of locomotion of chick embryonic choroid fibroblasts by pigmented retina epithelial cells
Authors: Parkinson E. K. , Edwards J. G 
Published: April 2021

ABSTRACT
Using light and electron microscopy, we have confirmed an earlier observation that chick embryonic pigmented retina epithelial cells (PRE cells) seeded in vitro on cultured sheets of choroid fibroblasts, are able to spread. Spreading is as rapid (and shows the same dependence on lateral contact between PRE cells) as on a serum-coated culture substrate. After 1 h most cells are spreading on the upper surface of the choroid sheet, but after 4 h, some PRE cells can be found sandwiched between overlapping choroid cells, and thus have invaded the sheet. Choroid fibroblasts underlie PRE in vivo, but the ability of PRE cells to spread on cultured fibroblasts is not specific for choroid, since PRE cells spread also on BKH21 hamster kidney fibroblasts, and on fibroblasts from chick embryonic heart.
As reported by others for various fibroblastic cells, choroid cells seeded on to choroid sheets or on to cultured PRE are unable to spread. A possible explanation is that spreading of adherent cells is contact-inhibited by the cells in the sheet, just as their leading edges are paralysed on contact, and thus locomotion is inhibited, when fibroblasts collide on a plane substratum. If spreading of seeded cells and cell locomotion are inhibited by the same mechanism, PRE cells should contact-inhibit choroid fibroblasts with which they collide, but not themselves be so inhibited. Using time-lapse cinemicrography, we have found this to be the case.
We first established that in homotypic collisions, choroid fibroblasts do show contact inhibition of locomotion, despite the criss-cross (not well monolayered) appearance of confluent cultures. In heterotypic collisions between choroid and PRE we found the predicted nonreciprocal behaviour: the choroid leading edge is paralysed on collision, and the cell subsequently retracts, whereas the active PRE margin appears to be completely unaffected. Speed measurements from a series of such collisions show that the speed of choroid cells is markedly reduced on collision with PRE, whereas the slight slowing of PRE is not statistically significant.
We have observed similar behaviour in heterotypic collisions between various epithelial and fibroblastic cells, and so it seems possible that non-reciprocity may prove general for this interaction. If so, it has important implications for the role of contact inhibition of locomotion in phenomena such as morphogenesis, wound healing and the invasiveness of carcinoma cells. On the one hand, non-reciprocal contact-inhibition of locomotion may permit the spreading of epithelia over mesenchymal cells, thus generating or restoring an epithelial bounding membrane. On the other hand, in the absence of other interactions, it would fail to inhibit the invasion of mesenchymal territory by aberrant epithelial cells, or presumably by epithelial free edges.
Cyclic production of tension force in the plasmodial strand of Physarum polycephalum and its relation to microfilament morphology
Authors: Nagai Reiko , Yoshimoto Yasuaki , Kamiya Noburô 
Published: April 2021

ABSTRACT
Cyclic contraction and relaxation of plasmodial strands of Physarum polycephalum were measured under both isotonic and isometric conditions, and their relation to changes in microfilament (MF) morphology was investigated. The contraction-relaxation rhythm of a strand segment was insignificant and irregular immediately after isolation from the mother plasmodium. It became regular half an hour later when local minute rhythms were synchronized spontaneously. If a strand kept under isotonic conditions was loaded with a heavier weight or a strand kept under isometric conditions was stretched a few times, the amplitude of each contraction wave was enhanced. After a strand had been thus conditioned, it was fixed at a selected phase of the contraction-relaxation cycle under both isotonic and isometric conditions.
The state of MFs changed strikingly according to the phase of the contraction cycle. In the shortening phase of the strand under isotonic contractions, MFs with a diameter of 6-7 nm were arranged parallel to each other to form large compact bundles in which adjacent filaments were bridged with cross linkages. Among these MFs, thicker filaments were sporadically scattered. At about the phase of minimal strand length, most of the MFs became kinky and formed networks. In the elongating phase, new loose bundles of MFs developed from the network. These loose bundles became compact again when the strand reached its maximal elongation phase. In the isometric contraction, MFs in the increasing tension phase were nearly the same as those in the shortening phase in isotonic contraction. Around the maximal tension phase, dense areas of MFs appeared along the bundles in place of the network formed in the isotonic contraction phase. These areas were closely packed, with MFs arranged parallel to each other. In the decreasing and minimal tension phases in isometric contraction, MFs were arranged similarly to those in the elongating and maximally elongated phases, respectively, in isotonic contraction. Alternation between the straight bundle and fine network configuration of the MFs observed in isotonic contraction was inconspicuous in isometric contraction. This was probably due to spatial restriction of shortening under isometric contraction. The results are interpreted in terms of cyclic changes of the aggregation pattern of the MFs in the form of F-actin, as opposed to the possibility that the contraction-relaxation cycles depend on cyclic G-F transformation of actin.
Isolated flagellar apparatus of Chlamydomonas: characterization of forward swimming and alteration of waveform and reversal of motion by calcium ions in vitro
Authors: Hyams Jeremy S. , Borisy Gary G. 
Published: April 2021

ABSTRACT
The control of flagellar activity in the biflagellate green alga, Chlamydomonas reinhardtii was investigated by the in vitro reactivation of the isolated flagellar apparatus (the 2 flagella attached to their respective basal bodies plus accessory structures). The waveform and beat frequency of the isolated apparatus in the presence of 1 mM adenosine triphosphate (ATP) were comparable to those recorded for living cells. Equimolar concentrations of adenosine diphosphate (ADP) could be substituted for ATP with little change in beat frequency and no apparent change in waveform, suggesting that the latter is converted to ATP by axonemal adenylate kinase. No reactivation occurred in adenosine monophosphate (AMP). Beat frequencies in cytidine, guanosine and uridine triphosphates (CTP, GTP and UTP) were approximately 10% that obtained in ATP. Reactivation was optimal over a broad pH range between pH 6·4 and pH 8 9 in both ATP and ADP.
Isolated flagellar apparatus could be induced to change from forward to reverse motion in vitro by manipulation of exogenous calcium ions. The 2 types of motion were directly comparable to recorded responses of living cells. Forward swimming occurred at levels of calcium below 10−6 M, the isolated apparatus changing to backward motion above this level. Motility was inhibited at concentrations above 10−3 M. The threshold for reversal of motion by calcium was lowered to 10−7M when the flagellar membranes were solubilized with detergent, indicating that the flagellar membranes are involved in the regulation of the level of calcium within the axoneme. The reversal of motion by calcium was itself freely reversible. The relationship of these observations to the known tactic responses of Chlamydomonas is discussed.
Carbon dioxide evolution during the cell cycle of the fission yeast Schizosaccharomyces pombe
Authors: Creanor James 
Published: April 2021

ABSTRACT
The rate of CO2 evolution was measured in synchronous cultures of the fission yeast Schizosaccharomyces pombe growing in a minimal medium. The rate of CO2 evolution was found to double sharply at about the time of nuclear division (0·75 of the way through the cell cycle). For the remainder of the cell cycle the rate remained constant.
Addition of inhibitors of DNA synthesis or nuclear division did not affect the pattern of CO2 evolution in synchronous cultures. Similarly, in an induced synchronous culture, in which DNA synthesis, nuclear division and cell division -but not growth, were synchronized, CO2 evolution showed a continuous pattern and not the step-wise increase associated with the normal synchronous cultures.
When S. pombe was grown in a complete medium, the evolution of CO2 in synchronous cultures was shown to increase in a continuous manner but at a rate faster than the growth of the culture.