bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations on the number of nuclei within the fibres of some red and white muscles
Authors: Burleigh I. G. 
Published: April 2021

ABSTRACT
Nuclei have been enumerated in muscle fibres of different physiological properties within adult rats and rabbits. Almost invariably, and regardless of muscle type, there is a direct relationship between the cross-sectional area (or fibre breadth2) of muscle fibres and the number of nuclei within them. The one exception occurred in muscles of older rats where increased nuclear numbers do not always appear to result in broader muscle fibres.
The greater complement of nuclei in broader fibres is accompanied by larger amounts of cell substance per nucleus.
Confirming early observations in the literature, red fibres of the slow-phasic type have more nuclei than have white, fast-phasic fibres of similar breadth. These conclusions are not vitiated by differences in the number of nuclei within capillaries or in satellite cells, by differences in nuclear length or by variation in the degree to which fibres are contracted.
In respect of their complement of nuclei, and the average amount of cell substance formed per nucleus the small red fibres that occur within muscles of predominantly fast-phasic character appear to be fast- rather than slow-phasic in type.
When the number of nuclei observed per fibre is plotted against fibre cross-sectional area, the shapes of the resulting distributions suggest that estimates of muscle nuclei may be valuable not only as an index of growth potential, but of the extent to which that potential is expressed. In one muscle, the above distribution was of a form which indicated that some fibres may have formed abnormally large amounts of protein per nucleus. However, this was not adequately confirmed.
Various factors have been investigated that are relevant to the accuracy of enumerating nuclei and measuring fibre breadths.
Spermiogenesis in the fern Marsilea: Microtubules, nuclear shaping, and cytomorphogenesis
Authors: Myles Diana Gold , Hepler Peter K. 
Published: April 2021

ABSTRACT
Spermiogenesis in Marsilea is a complex series of events, including the formation of a helically wound organelle coil. The coil begins to appear in early development when a multilayered structure (MLS) is formed de novo in association with a mitochondrion. The outermost layer of the MLS is a ribbon of microtubules. As the microtubules grow out from the MLS, they grow along the nuclear envelope. The nucleus elongates parallel to the longitudinal axis of the microtubule ribbon until it makes 4-5 gyres. The coil mitochondrion associated with the MLS grows until it completes approximately 9 gyres, following the path of the nucleus in its posterior gyres. The microtubule ribbon is associated with both of these organelles along their exterior edge and separates them from the developing flagellar band. This band arises from dense material that is associated with the basal bodies from early development, increases in volume, and finally condenses into a solid band, interconnecting the 100-120 basal bodies of the sperm. The flagella are distributed along the entire organelle coil.
Besides the microtubules of the ribbon, a set of cytoplasmic tubules is seen during spermiogenesis. These microtubules radiate in bundles from a region of dense nodules located near the MLS.
Late in development there is a gross rearrangement of the cytoplasm. This rearrangement begins as the outgrowth of a ring of cytoplasm from the posterior end of the sperm, and continues to grow down around the organelle coil in the anterior end, and fuses to form a bridge, enclosing the anterior end and all the flagella. This bridge fills with cytoplasm that migrates from the posterior region, including many mitochondria and ribosomes, and is finally shed by the sperm when it is released from the microspore and becomes motile.
The possible involvement of chromatin condensation and/or microtubules in nuclear morphogenesis is considered. Because much of the shaping of the nucleus occurs before bulk chromatin condensation, the possibility that it is the cause of shaping is ruled out. We postulate that microtubules are involved, not in providing the mechanical force, but as a guide along which shape formation occurs. Furthermore, microtubules of the ribbon were observed to have a close structural relationship to the condensing chromatin.
Spatial distribution of lamin A/C determines nuclear stiffness and stress-mediated deformation
Authors: Srivastava Luv Kishore , Ju Zhaoping , Ghagre Ajinkya , Ehrlicher Allen J. 
Published: April 2021

ABSTRACT
While diverse cellular components have been identified as mechanotransduction elements, the deformation of the nucleus itself is a critical mechanosensory mechanism, implying that nuclear stiffness is essential in determining responses to intracellular and extracellular stresses. Although the nuclear membrane protein lamin A/C is known to contribute to nuclear stiffness, bulk moduli of nuclei have not been reported for various levels of lamin A/C. Here, we measure the nuclear bulk moduli as a function of lamin A/C expression and applied osmotic stress, revealing a linear dependence within the range of 2–4 MPa. We also find that the nuclear compression is anisotropic, with the vertical axis of the nucleus being more compliant than the minor and major axes in the substrate plane. We then related the spatial distribution of lamin A/C with submicron 3D nuclear envelope deformation, revealing that local areas of the nuclear envelope with higher density of lamin A/C have correspondingly lower local deformations. These findings describe the complex dispersion of nuclear deformations as a function of lamin A/C expression and distribution, implicating a lamin A/C role in mechanotransduction.
This article has an associated First Person interview with the first author of the paper.
Upregulation of APP endocytosis by neuronal aging drives amyloid-dependent synapse loss
Authors: Burrinha Tatiana , Martinsson Isak , Gomes Ricardo , Terrasso Ana Paula , Gouras Gunnar K. , Almeida Cláudia Guimas 
Published: April 2021

ABSTRACT
Neuronal aging increases the risk of late-onset Alzheimer's disease. During normal aging, synapses decline, and β-amyloid (Aβ) accumulates intraneuronally. However, little is known about the underlying cell biological mechanisms. We studied neuronal aging using normal-aged brain and aged mouse primary neurons that accumulate lysosomal lipofuscin and show synapse loss. We identified the upregulation of amyloid precursor protein (APP) endocytosis as a neuronal aging mechanism that potentiates APP processing and Aβ production in vitro and in vivo. The increased APP endocytosis may contribute to the early endosome enlargement observed in the aged brain. Mechanistically, we showed that clathrin-dependent APP endocytosis requires F-actin and that clathrin and endocytic F-actin increase with neuronal aging. Finally, Aβ production inhibition reverts synaptic decline in aged neurons, whereas Aβ accumulation, promoted by endocytosis upregulation in younger neurons, recapitulates aging-related synapse decline. Overall, we identify APP endocytosis upregulation as a potential mechanism of neuronal aging and, thus, a novel target to prevent late-onset Alzheimer's disease.
This article has an associated First Person interview with the first author of the paper.
Ribosome quality control activity potentiates vaccinia virus protein synthesis during infection
Authors: Sundaramoorthy Elayanambi , Ryan Andrew P. , Fulzele Amit , Leonard Marilyn , Daugherty Matthew D. , Bennett Eric J. 
Published: April 2021

ABSTRACT
Viral infection both activates stress signaling pathways and redistributes ribosomes away from host mRNAs to translate viral mRNAs. The intricacies of this ribosome shuffle from host to viral mRNAs are poorly understood. Here, we uncover a role for the ribosome-associated quality control (RQC) factor ZNF598 during vaccinia virus mRNA translation. ZNF598 acts on collided ribosomes to ubiquitylate 40S subunit proteins uS10 (RPS20) and eS10 (RPS10), initiating RQC-dependent nascent chain degradation and ribosome recycling. We show that vaccinia infection enhances uS10 ubiquitylation, indicating an increased burden on RQC pathways during viral propagation. Consistent with an increased RQC demand, we demonstrate that vaccinia virus replication is impaired in cells that either lack ZNF598 or express a ubiquitylation-deficient version of uS10. Using SILAC-based proteomics and concurrent RNA-seq analysis, we determine that translation, but not transcription of vaccinia virus mRNAs is compromised in cells with deficient RQC activity. Additionally, vaccinia virus infection reduces cellular RQC activity, suggesting that co-option of ZNF598 by vaccinia virus plays a critical role in translational reprogramming that is needed for optimal viral propagation.
Secreted C-type lectin regulation of neuromuscular junction synaptic vesicle dynamics modulates coordinated movement
Authors: Bhimreddy Meghana , Rushton Emma , Kopke Danielle L. , Broadie Kendal 
Published: April 2021

ABSTRACT
The synaptic cleft manifests enriched glycosylation, with structured glycans coordinating signaling between presynaptic and postsynaptic cells. Glycosylated signaling ligands orchestrating communication are tightly regulated by secreted glycan-binding lectins. Using the Drosophila neuromuscular junction (NMJ) as a model glutamatergic synapse, we identify a new Ca2+-binding (C-type) lectin, Lectin-galC1 (LGC1), which modulates presynaptic function and neurotransmission strength. We find that LGC1 is enriched in motoneuron presynaptic boutons and secreted into the NMJ extracellular synaptomatrix. We show that LGC1 limits locomotor peristalsis and coordinated movement speed, with a specific requirement for synaptic function, but not NMJ architecture. LGC1 controls neurotransmission strength by limiting presynaptic active zone (AZ) and postsynaptic glutamate receptor (GluR) aligned synapse number, reducing both spontaneous and stimulation-evoked synaptic vesicle (SV) release, and capping SV cycling rate. During high-frequency stimulation (HFS), mutants have faster synaptic depression and impaired recovery while replenishing depleted SV pools. Although LGC1 removal increases the number of glutamatergic synapses, we find that LGC1-null mutants exhibit decreased SV density within presynaptic boutons, particularly SV pools at presynaptic active zones. Thus, LGC1 regulates NMJ neurotransmission to modulate coordinated movement.
Direct evidence of cellular transformation by prion-like p53 amyloid infection
Authors: Navalkar Ambuja , Pandey Satyaprakash , Singh Namrata , Patel Komal , Datta Debalina , Mohanty Bhabani , Jadhav Sachin , Chaudhari Pradip , Maji Samir K. 
Published: April 2021

ABSTRACT
Tumor suppressor p53 mutations are associated with more than 50% of cancers. Aggregation and amyloid formation of p53 is also implicated in cancer pathogenesis, but direct evidence for aggregated p53 amyloids acting as an oncogene is lacking. Here, we conclusively demonstrate that wild-type p53 amyloid formation imparts oncogenic properties to non-cancerous cells. p53 amyloid aggregates were transferred through cell generations, contributing to enhanced survival, apoptotic resistance with increased proliferation and migration. The tumorigenic potential of p53 amyloid-transformed cells was further confirmed in mouse xenografts, wherein the tumors showed p53 amyloids. p53 disaggregation rescued the cellular transformation and inhibited tumor development in mice. We propose that wild-type p53 amyloid formation contributes to tumorigenesis and can be a potential target for therapeutic intervention.
This article has an associated First Person interview with the first author of the paper.
Red blood cell adhesion: III. Analysis of forces
Authors: Parsegian V. Adrian , Gingell David 
Published: April 2021

ABSTRACT
The results of experiments on the adhesion of glutaraldehyde-fixed red blood cells to both polarizable metal/saline and liquid hexadecane/saline interfaces have been analysed in terms of physical forces. The results show that the electrostatic repulsions sufficient to prevent adhesion to these test surfaces are remarkably similar, and that a force-balance condition is predicted at cell-substratum separations ∼ 100 nm in 0 ·4 MM NaCl as found by interferometry. From the repulsive force the size of the attractive force can be found. If this is viewed as an electrodynamic attraction, the force coefficient is found to lie between 5 and 8 × 10−14 erg (5 and 8 × 10−21 J), a range in reasonable correspondence with measurements in physical systems.
Motive force of the migrating pseudoplasmodium of the cellular slime mould Dictyostelium discoideum
Authors: Inouye Kei , Takeuchi Ikuo 
Published: April 2021

ABSTRACT
Motive forces of migrating pseudoplasmodia (slugs) of Dictyostelium discoideum were determined by application of a double-chamber method. The motive force of a whole slug was proportional to its volume, the value per unit volume being 5 ·85 × 106 dyne/cm3 (58·5 N cm-3). The motive force was independent of temperature (13·5 —26 °C) and decreased during prolonged migration. Motive force per unit volume of an anterior isolate of a slug was much larger than that of a posterior isolate, their weighted mean being approximately equal to that of a whole slug. These results agree well with the predictions previously made using a model based on analyses of migrating velocities of slugs. The motive force per unit volume of either isolate was soon regulated to reach the normal value of an intact slug after several hours of isolation, concurrently with conversion of cell types between prestalk and prespore cells. The possibility that motive force of each cell is determined by its cell type is discussed in relation to cell sorting.
Membrane recycling and endocytosis in Paramecium confirmed by horseradish peroxidase pulse-chase studies
Authors: Allen Richard D. , Fok Agnes K. 
Published: April 2021

ABSTRACT
Paramecium caudatum cells were pulse-chased in horseradish peroxidase (HRP) using pulses of 30 s to follow endosome (endocytotic vesicle) formation from defaecating digestive vacuoles and 3-min pulses to follow the movement and fate of these vesicles in the cell. Endosomes formed during the 30 s in HRP are heavily labelled with HRP reaction product and are mostly flattened. Some align along microtubules that point toward the cytopharynx. Diskoidal vesicles at the cytopharynx are unlabelled in unchased cells. Cells exposed to a 3-min HRP pulse contain varied amounts of HRP-labelled diskoidal vesicles at the cytopharynx but no labelled vesicles near their closed cytoprocts. Labelled vesicles are also found aligned along the cyto-pharyngeal microtubular ribbons. Diskoidal vesicles are no longer labelled after a 47-min chase. Use of pulse-chase HRP cytochemistry supports the hypothesis that the membrane of digestive vacuoles retrieved at the cytoproct is moved along microtubular ribbons directly to the cytopharynx where the membrane enters the diskoidal vesicle pool. This membrane appears to enter neither the Golgi nor lysosomal systems in its passage. HRP reaction product is also found in vesicles near the parasomal sacs, in some secondary lysosomes and in small spherical vesicles that are probably trichocyst membrane fragments. Possibly some membrane from parasomal sacs or condensing digestive vacuoles may also enter the diskoidal vesicle pool but apparently not membrane from trichocysts.
Role of concanavalin a as an endocytic modulator in chinese hamster ovary cells
Authors: Storrie Brian , M. Maurey Karen 
Published: April 2021

ABSTRACT
The effect of the lectin, concanavalin A (Con A), on pinocytic uptake and pinosome-lysosome fusion in Chinese hamster ovary (CHO) cells, a fibroblast line, was investigated. The glycosylated protein, horseradish peroxidase (HRPase), and the non-glycosylated protein, 125I-labelled bovine serum albumin ([125I]BSA), were used as endocytic tracers. Con A at high concentrations (⩾ 50 μg/ml) promoted the uptake of HRPase and inhibited the degradation of ingested HRPase. Con A inhibited the degradation of HRPase whether the two were added simultaneously or at different times to the cultures. Fusion of HRPase-positive pinosomes with secondary lysosomes was observed by electron microscopy in Con A-treated CHO cells. Con A at 200 μg/ml had no effect on either the uptake or degradation of [125I]BSA. Together these observations strongly suggest that the effects of high Con A concentrations on the uptake and degradation of HRPase are a consequence of direct complex formation between lectin and glycoprotein. Con A does not appear to have a general modulating effect on the dynamics of endocytic membrane in CHO cells.
Functional interdependence of pseudopodia in Amoeba proteus stimulated by light-shade difference
Authors: Grębecki Andrzej , Klopocka Wanda 
Published: April 2021

ABSTRACT
Polytactic cells of Amoeba proteus were exposed to localised photic stimulation. When a pseudopodium is stimulated to advance, by shading it, other pseudopodia are retracted. Activation of the shaded front is the primary response, and contraction of other fronts the secondary one. When a pseudopodium is inhibited by illuminating its frontal segment, or when it is allowed to enter the bright zone in the course of migration, it slows down and stops but its eventual retraction depends on the existence of other possible directions for the endoplasmic flow. Therefore, if other active pseudopodia are lacking, the front suppressed by light cannot retreat effectively until new fronts arise in other body regions kept in shade. In all experimental situations the development of new fronts or the activation of forward flow in lateral pseudopodia precedes the contraction of the former leading pseudopodium. Also the reversal of direction of the endoplasmic streaming begins at the new front, and then it gradually extends until it reaches the former front.
The results confirm the interdependence of different pseudopodia in the same individual and they contradict the concept that pseudopodia behave as separate functional units. On the other hand, they indicate that formation of new pseudopodia should not be explained as a simple secondary effect of contraction of the older ones but, on the contrary, as a phenomenon that initiates the changes in the pattern of flow in amoeba. The general interpretation is based on this variant of the pressure-flow theory of amoeboid movement, which attributes the motive power to the contractile activity of the whole cell cortex and the steering role to events taking place in the front of the migrating cell.
Gene expression in Acetabularia: III. Comparison of stained cytosolic proteins and in vivo and in vitro translation products
Authors: Shoeman Robert L. , Neuhaus Gunther , Schweiger Hans-Georg 
Published: April 2021

ABSTRACT
A comparison of stained cytosolic proteins, in vivo 80 S ribosome translation products and in vitro translation products of poly(A)+ RNA from three species of Acetabularia was performed after characterization of their molecular weights and isoelectric points via two-dimensional electrophoresis. A total of 803 stained proteins, and 121 in vivo and 77 in vitro translation products, representing the most abundant proteins in each category, were analysed. In interspecies comparisons, approximately 10% of the stained proteins were common to all three species and more than 50% were found to be species-specific. Approximately 25% of the in vivo translation products were common to all three species and more than 30% were found to be species-specific. The majority of the in vivo and in vitro translation products were detected by one or both of the other methods employed. Even though the analysis was limited to the most abundant proteins detected by each of the three methods and to one stage of development, the results suggest that the translation of some proteins is not regulated, that the in vivo translation of others, whose mRNA is present and translated in vitro, is turned off while the translation in vivo of others is enhanced relative to the total. This feature makes them candidates for stage-specific proteins. The results provide a firm basis for the extended analysis of the biological activity of heterologous messenger RNA in Acetabularia cytoplasm and for a more complete cataloguing of the mRNA population and translational activity at different stages in the development of Acetabularia.
Functional design of microvilli in the malpighian tubules of the insect Rhodnius prolixus
Authors: Bradley Timothy J. 
Published: April 2021

ABSTRACT
The Malpighian tubules of Rhodnius prolixus are divided into two regions; the upper tubule, which is the site of isosmotic secretion and haemolymph filtration, and the lower tubule where water and KC1 are resorbed.
In the upper tubule the microvilli are arranged in clumps consisting of several hundred microvilli lying closely parallel. The microvillar plasma membranes do not touch but are held ≈l6nm apart along the full length of the microvilli. As a consequence, the extracellular space between the microvilli consists of long narrow channels. A morphometric analysis of extracellular, cytoplasmic, endoplasmic reticular and mitochondrial volume within the clumps was conducted. Using the secretion rate of the epithelium and the channel dimensions, it was calculated that the mean residence time for secreted fluid in the intermicrovillar spaces was ≈0·4s. In view of our current knowledge of the physiology and morphology of the upper tubule, it is argued: (1) that osmotically driven water passes principally through the cells, not the junctional spaces; and (2) that the microvillar clumps are a morphological specialization, which serves to maximize solute-water coupling in the upper tubule.
The microvilli in the lower tubule are free-standing, with no pattern of clumping as in the upper tubule. The axopods are about twice as long as the microvilli (10-14 μm) and are found in all regions of the lower tubule. This is in agreement with the proposal that the motile axopods serve to propel uric acid crystals through the lower tubule. No morphological difference was found between the upper and lower halves of the lower tubule, although the two portions are known to be physiologically distinct.
Macrocyst development in Dictyostelium discoideum: II. mating-type-specific cell fusion and acquisition of fusion-competence
Authors: Saga Y. , Okada H. , Yanagisawa K. 
Published: April 2021

ABSTRACT
The early events of macrocyst development in Dictyostelium discoideum have been investigated using a new culturing system. When cells of opposite mating-types, HM1 and NC4, are cultured together at the appropriate temperature in the dark, giant cells appear, ingest the surrounding amoebae, and develop into macrocysts. Although these giant cells have been assumed to be the products of the fusion of opposite mating-type cells, no experimental evidence to prove this assumption has been obtained using such mixed-culture systems. In order to avoid the complexities involved in mixed-culturing, we have developed a new system involving the separate culture, and later mixing, of opposite mating-type cells. This has enabled us to obtain direct evidence that giant cells are produced by fusion between opposite mating-type cells. Cell fusion occurs immediately after mixing and is completed within 30 min. As a number of cells fuse simultaneously, giant cells produced by this method are very large multinucleated cells, and not binucleated zygotes. Using this system we also discovered the following facts related to giant cell formation: (1) cells can acquire their fusion competence without the presence of cells of the opposite mating-type; (2) only HM1 cells require darkness to acquire their fusion competence; (3) the restrictive temperature, 25°C, inhibits the induction of fusion competence in HM1 cells, but not in NC4 cells.