bluuebunny/crossref_metadata_2025_split huggingface dataset:
A massive system of microtubules associated with cytoplasmic movement in telotrophic ovarioles
Authors: Macgregor H. C. , Stebbings H. 
Published: April 2021

ABSTRACT
The telotrophic ovary of Notonecta glauca glauca consists of 7 ovarioles. Each ovanole comprises, from front to rear, a terminal filament, a trophic region, a prefolhcular region, and a series of 10-15 follicles of progressively increasing size The trophic region is largely syncytial and is made up of polyploid trophic nuclei packed around a central trophic core The cytoplasm of the trophic core is continuous with the cytoplasm of each oocyte through a system of trophic tubes. There is one trophic tube per oocyte. The trophic nuclei have large nucleoh. There are a few small nucleoh in the oocyte nuclei The cytoplasm of the trophic core, the trophic tubes, and the oocytes is rich in RNA. Autoradiographs of sections of ovarioles fixed 2 h after injection of PHjundine into animals show label over the trophic nuclei only. Eight-hour autoradiographs show heavy labelling of the trophic region and label over the front ends of the trophic tubes, but little label over the posterior regions of the tubes or the oocyte cytoplasm. Later autoradiographs indicate that label gradually spreads backwards from the trophic core, along the trophic tubes, and progressively builds up in the oocyte cytoplasm These observations are thought to indicate synthesis of RNA in the trophic region and movement of RNA from the trophic core along the trophic tubes to the oocytes The trophic core and tubes show brilliant positive form birefringence with respect to their lengths. This birefringence can be reduced by keeping animals at 2 °C for 12 h, and eliminated by placing ovanoles in 1 % colchicine for 6 h. Electron micrographs of thin sections of ovanoles show that trophic core and tubes are densely and uniformly packed with nbosomes and microtubules The latter are lined up along the trophic tubes. There are about 30000 microtubules evident m a TS through a trophic tube 15 fim wide. Lengths of microtubules up to 2 /*m have been observed. Ribosomes are packed between the microtubules but are excluded from regions where the spacing between adjacent microtubules is less than 25 ran The contribution of the trophic region to the oocytes and the role of the microtubules in maintaining or facilitating the movement of nbosomes along the trophic tubes is discussed
Genetic recombination in Coprinus II. its relations to the synaptinemal complexes
Authors: Lu B. C. 
Published: April 2021

ABSTRACT
The frequency of genetic recombination in Coprinus lagopus may be modified by heat and cold shock. By removal of samples from a fruiting body before and after temperature treatment, it is possible to study the ultrastructure of chromosomes at the time recombination frequency (between den+ × +me—1) can be modified. The sensitive period for temperature effects and, therefore, probably the time of crossing over, commences with the formation of the synaptinemal complex (s.c.) and ends with its disappearance, i.e. during the entire existence of the s.c. It is concluded that recombination is an event subsequent to the formation of the s.c. and is independent of the process of its formation. It is suggested that the event takes place at the synaptic centre.
Absence of step changes in activity of certain enzymes during the cell cycle of budding and fission yeasts in synchronous cultures
Authors: Creanor J. , Elliott S. G. , Bisset Y. C. , Mitchison J. M. 
Published: April 2021

ABSTRACT
Synchronous cultures prepared by selection from an elutriating rotor were used to measure activity changes during the cell cycle of the following enzymes: acid phosphatase in Schizosac-charomyces pontbe and Saccharomyces cerevisiae, a-glucosidase in S. cerevisiae and /Lgalacto-sidase in Kluyveromyces lactis. There was no sign of step rises in activity in acid phosphatase but there were indications in S. cerevisiae of the linear pattern with rate doublings once per cycle that had been found previously in S. pombe. There was also no sign of step rises in the other two enzymes, in contrast to earlier results using different techniques. Asynchronous control cultures showed little or no perturbations after the first hour.
Stromal colonies from mouse marrow: Characterization of cell types, optimization of plating efficiency and its effect on radiosensitivity
Authors: Xu C. X. , Hendry J. H. , Testa N. G. , Allen T. D. 
Published: April 2021

ABSTRACT
Modifications to the colony assay in vitro for stromal progenitor cells in mouse femoral marrow have been studied so as to optimize the efficiency of colony formation (CFE). The highest reproducible concentration achieved was about 30 colonies (containing fibroblasts, macrophages and endothelioid cells) per 106 nucleated marrow cells (range 20—50) in mice 3—4 months old, and higher by 50% in mice 14–15 months old. Each of many slight technical modifications could reduce these values by more than 30%.
The importance of optimization was demonstrated by a reduced radiosensitivity when the CFE was reduced by a factor of 3 using a-medium stored at 4°C for 15 days. The Do value was 3·9 ± 0·8 Gy compared to 1·6 ± 0·1 Gy using freshly prepared medium, and this could be due to the selection of a radioresistant subpopulation.
The modifications studied may partly explain the marked variations in CFE and in radiosensitivity reported in the literature.
Circadian rhythm of protein synthesis activity in the exocrine pancreas of fed and starved rats
Authors: Völkl A. , Poort C. 
Published: April 2021

ABSTRACT
Rats, either fed a solid standard chow ad libitum or starved for 24 h prior to the beginning of the experiments, were kept in a normal light-dark cycle of 12 h. At certain times over a total period of 24 h, three animals of each group were killed, their pancreata were excised and the protein synthetic capacity was determined, measuring both the amount of cellular RNA and the percentage of ribosomes active in protein synthesis. A clear-cut circadian rhythm in the synthetic activity was found, well expressed in the fed animals but less evident and shifted in time in the starved ones. The RNA/DNA ratios in the two sets of animals remained fairly constant throughout the day, but were somewhat lower in the fasted rats.
Higher-Order Structure Of Chromatin From Resting Cells : Ii. High-Resolution Computer Analysis Of Native Chromatin Fibres And Freeze-Etching Of Nuclei From Rat Liver Cells
Authors: Nicolini C. , Cavazza B. , Trefiletti V. , Pioli F. , Beltrame F. , Brambilla G. , Maraldi N. , Patrone E. 
Published: April 2021

ABSTRACT
Non-destructive electron microscopy of native chromatin from rat liver nuclei reveals that the 30 nm fibre is formed of four 11 nm nucleofilaments, arranged in a coiled-coil (or rope-like) conformation. At low ionic strength, native fibres show an alternating pattern of compact and unwound regions. Freeze-etching experiments carried out on the same nuclei are compatible with the existence of periodic attachments of the fibres to the nuclear envelope near the pores in a regular, drapery-like fashion.
For the first time, computer image analysis has been applied to electron micrographs of giant chromatin fibres and a few essential geometrical parameters characterizing the conformation of the higher-order structures have been determined. No significant difference has been found between calf thymus and rat liver chromatin.
Changes In Poly(A)+ Rna During Male Meiosis In Lilium
Authors: Porter E. K. , Parry D. , Dickinson H. G. 
Published: April 2021

ABSTRACT
Levels of poly(A)+ RNA have been investigated at each stage of male meiosis in Lilium (var. Firecracker). Two methods were employed in this work: in one extracts from labelle’d meiocytes were passed through oligo(dT) columns, while in the other the specific probe [3H]poly(U) was hybridized in situ with resin-embedded sections of pollen mother cells. The label contained in the eluate from the oligo(dT) columns was measured by liquid scintillation, and the quantity of [3H]-poly(U) hybridized was determined by statistical analysis of light microscopic autoradiographs. Both techniques revealed a dramatic decline in detectable poly(A)+ RNA during prophase. Lowest levels are reached in the pachytene stage, following which a gradual restoration of this species of RNA takes place in both nucleus and cytoplasm. The data presented here provide no clear indication as to whether this fall in RNA levels is caused by the action of novel enzymes specific to the meiotic prophase, by a cessation of synthesis and the activity of normal turnover processes, or by a combination of the two. Although there is some evidence from the [3H]poly(U) hybridization study that a small peak of poly(A)+ RNA synthesis may take place in leptotene, both methods indicate that there is a very low level of poly(A)+ RNA synthesis throughout prophase. The presence of poly(A)+ RNA was not detected in either the accessory nucleoli or the cytoplasmic nucleoloids that characterize the nucleus and cytoplasm of these cells. These events are considered in terms of the juncture at which they occur in the plant life-cycle.
Dna density in mitotic and meiotic metaphase chromosomes of plants and animals
Authors: Bennett M. D. , Heslop-Harrison J. S. , Smith J. B. , Ward J. P. 
Published: April 2021

ABSTRACT
Studies of chromosome disposition at metaphase using serial thin-sectioning and threedimensional reconstruction techniques have produced accurate estimates of the total volume of chromosomes per cell in 15 plant and two animal species. Comparing this character with the 4C DNA amount showed no indication of systematic differences in DNA density between either organisms with widely different (&gt;200-fold) C values or different groups or organisms. For example, there was no significant difference between the density of DNA in somatic metaphase chromosomes of man (0·141 pg/ μm3) and its mean in 14 angiosperm plant species (0·182pg/ μm3), or between four dicotyledons (0·180 pg/ μm3) and 10 monocotyledons (0–182pg//tm3). However, evidence was found showing that DNA density can vary significantly within a species. Thus, although the total chromosome volume per cell was closely correlated (r&gt;0·97) with 4C DNA amount in somatic and meiotic cells, the density of DNA in metaphase chromosomes was significantly lower in meiocytes (0·131 pg/ μm3) than in somatic metaphase cells (0·179pg/ μm3).
Actin in xenopus yolk platelets: A peculiar and debated presence
Authors: Colombo Roberto 
Published: April 2021

ABSTRACT
Our previous work showed that Xenopus yolk platelets exhibited, when reacted with actin antibodies or fluorescent DNase 1, a shiny halo of fluorescence, which revealed an external actin cover around the platelets themselves. This structure was named the ‘actin-shell’. Now we have demonstrated the actin-containing coat of Xenopus yolk platelets by agglutination tests, using anti-Xenopus-muscle-actin rabbit serum, and by indirect immunofluorescence microscopy, when the platelets reacted with antibodies directed against DNase 1. We chose these procedures to minimize the difficulties of the techniques used previously and to confirm the data obtained.
Involvement of the n-terminal polypeptide of vimentin in the formation of intermediate filaments
Authors: Traub Peter , Vorgias Constantin E. 
Published: April 2021

ABSTRACT
The potential to form intermediate filaments of a 54 × 103 molecular weight (Mr) polypeptide derived from vimentin by cleavage by the intermediate filament-specific, Ca2+-activated proteinase was investigated. Under physiological conditions of assembly, the breakdown product did not form intermediate filaments. Electron microscopy revealed short, rod-like structures similar to those described by Geisler et al. for a 38 × 103Mr, α-helical core particle derived from desmin. Since the specific, Ca2+ -activated proteinase degrades vimentin preferentially from its N terminus, this result suggests the involvement of the basic, N-terminal polypeptide of vimentin in the assembly of intermediate filaments. This was supported by the observation that arginine inhibits the formation of intermediate filaments from intact vimentin. Whereas lysine had very little effect on the assembly process, guanidinium hydrochloride was effective at the same concentration as arginine. On the basis of these findings, an affinity chromatography method for the identification and isolation of intermediate filament subunit proteins was developed. Beside vimentin, desmin, the 68 × 103Mr neurofilament triplet protein, the glial fibrillary acidic protein and cytokeratins also bound to arginine methylester Sepharose 4B in a salt-stable manner and could be eluted with arginine. The 145 × 103Mrneurofilament triplet protein exhibited reduced binding activity, whereas the 210 × 103Mr subunit did not bind to the affinity matrix. Among the degradation products of vimentin produced by the specific, Ca2*-activated proteinase, only those with molecular weights higher than 40 ×103 bound to arginine methylester Sepharose 4B. The same applied to the high molecular weight degradation products of desmin with a proteinase-resistant 37 × 103Mr, polypeptide as the major component. The results suggest that arginine residues of the non-α-helical, N-terminal polypeptides of intermediate filament subunit proteins play an important role in filament assembly.
Cyclic cytoplasmic activity of nonnucleate egg fragments of Xenopus controls the morphology of injected sperms
Authors: Sakai Masao , Shinagawa Atsunori 
Published: April 2021

ABSTRACT
Triton X-100-treated sperms were injected into non-nucleate egg fragments of Xenopus laevis to determine whether the structure of the injected sperm nucleus is affected by the cyclic activity of the cytoplasm.
Swollen vesicular nuclei were very frequently observed when the sperms were injected and incubated during the ‘rounding-up’ phase of the recipient fragment, whereas no such structures were found when they were incubated during the ‘relaxing’ phase.
Morphological and temporal sequence of meiotic prophase development at puberty in the male mouse
Authors: Goetz P. , Chandley Ann C. , Speed R. M. 
Published: April 2021

ABSTRACT
The correct sequence of meiotic prophase development in the male mouse has been established by the use of pubertal males. The first wave of spermatogenesis at this time provides a unique opportunity to study progressive meiotic development in a direct way. Air-dried and micro-spread analyses have been carried out. Temporal and morphological progression at this time is entirely consistent with that occurring in the later waves of meiosis of the adult male. Morphological detail shows delayed pairing of the X and Y chromosomes relative to the autosomes. The longest XY synaptonemal complex is seen in early pachytene cells, occupying up to 72% of the length of the Y and 22% of the length of the X axis. By late pachytene, end-to-end pairing in the XY bivalent is established, the autosomal axes remaining fully paired. Desynapsis of the autosomes commences at early diplotene. A ‘diffuse’ diplotene stage in the male, comparable to the dictyate stage of the female, could not be found. Marked lengthening of the XY and autosomal axes did, however, occur through the diplotene stage.
The apical structure in Perophora annectens (tunicate) spermatozoa: Fine structure, differentiation and possible role in fertilization*
Authors: Fukumoto Makoto 
Published: April 2021

ABSTRACT
The apical structure in Perophora annectens spermatozoa is approximately 4 μm in length and it is helically coiled. Its major component is a striated structure, which may be analogous to a perforatorium. The plasmalemma enclosing the anterior quarter of the apical structure is covered by extracellular materials, the anterior ornaments.
During spermiogenesis, the apical structure is first recognized as a small blister of the plasmalemma at the apex of the young spermatid. It develops into a conical protrusion and then into a fingerlike process (approximately 1 μm in length). This process is transformed into an elongated process (approximately 4 μm in length) with electron-dense material in its core. Finally, the elongated process is helically coiled to form an apical structure in which electron-dense material forms dense striations.
Vesicles (50–70nm in diameter), presumably derived from the Golgi apparatus, have been recognized in the blisters of younger spermatids, and can be followed through to the finger-like process. In the finger-like process these vesicles are transformed into smaller vesicles (20–30 nm in diameter), which probably fuse with the anterior plasmalemma of the finger-like process. This suggests that chorion lysin(s) is associated with the anterior membrane enclosing the apical structure in these spermatozoa.
An analysis of in vivo cell migration during teleost fin morphogenesis
Authors: Wood Andrew , Thorogood Peter 
Published: April 2021

ABSTRACT
In the teleost embryo the pectoral fin bud initially displays an apical ectodermal ridge along its entire distal margin. The ridge subsequently becomes transformed into an apical fold as the distal ectodermal epithelium grows and folds to enclose an extracellular space between the apposed basal surfaces of the epithelium. Collagen fibrils up to 2μm in diameter, termed ‘actinotrichia’, are deposited along the proximo-distal axis in two (dorsal and ventral) arrays. The actinotrichia are aligned parallel to one another with a regular spacing along the greater part of their length. Mesenchymal cells migrating distally from the base of the fin bud encounter the dorsal and ventral arrays of actinotrichia and move between them apparently using the fibrils as a substratum. The entire structure is transparent and, using the killifish Aphyosemion scheeli, we have investigated the migration of the mesenchymal cells between 135 and 220 h of development, using Nomarski interference contrast microscopy and time-lapse video recording. The number of cellular processes per cell increased significantly during the period of observation. These processes could be graded according to their diameters. Processes of diameter greater than 2 μm were not usually aligned along actinotrichia and arose at any aspect of the cell body. In contrast, processes with diameters less than 2 μm appeared to be confined to the distal aspects of the migrating cells and showed an increasing tendency to become aligned as development progressed. Time-lapse video recordings revealed that such aligned processes move faster (mean speed 17·98(±2·25) μm/h) than non-aligned processes (mean speed 4·66(±0·67) μm/h). Whole cell translocation was generally slower than rates of process movement: the lowest mean value (1 ·52(±0·36) μm/h) was recorded between 135 and 160h of development rising to a maximum mean rate (4·72(±0·42) μm/h) between 195 and 220h; the period of the fastest rate of cell translocation correlated with maximum process alignment along actinotrichia. Thin 1 μm plastic sections revealed that, generally, aligned processes were in close association with the surface of the actinotrichial fibrils and not the spaces between them.
Distribution of concanavalin a binding carbohydrates during mating in Chlamydomonas
Authors: Millikin Blake E. , Weiss Richard L. 
Published: April 2021

ABSTRACT
Cell surface carbohydrates, detected by fluorescein isothiocyanate/concanavalin A (F1TC-ConA), were identified at four locations on gametes of Chlamydomonas reinhardtii. (1) The cell wall: uniform labelling with FITC-ConA was observed; a substantial number of sites were localized in the sodium dodecyl sulphate-insoluble inner wall, which contains the flagellar collars. (2) The periplasm-, a crescent-shaped area was visualized with FITC-ConA and localized by ferritin-ConA. We were able to recover autolytic activity on a ConA affinity column from the mating medium of wild-type cells after the release of these periplasmic sites. The cell-wall-less mutant CW15 displays no periplasmic sites and demonstrates a corresponding inability to release autolytic activity after mating for 60 min. A model for wall lysis is presented, which considers the involvement of these sites in the lytic process. (3) The mating structure: during mating a small fluorescent plaque-like site was observed on cells at a location corresponding to the carbohydrate-like zone of the mating type minus mating structure and may indicate the involvement of ConA binding material in gametic cell fusion. (4) Secreted products: following cell fusion zygotes begin to secrete ConA positive material at about . After 24 h a ConA positive zygote wall and pellicle appear.
Effect of cell–substrate interaction time and shearing force on adhesion of L1210 cells to collagen and glass
Authors: Kowalczyńska Hanna M. , Nowak Małgorzata 
Published: April 2021

ABSTRACT
The early adhesive interaction of living cells with substrates was examined. L1210 cells were allowed to interact with collagen or glass in serum-containing medium (time of cell–substrate interaction, tint, under stationary conditions, was within 2–2 5 min) or in serum-free medium (tintwas 58–1 5 min). The relative number A of cells adhering under stationary conditions, and remaining adherent to the substrate despite experiencing a shearing force F, was determined.
The following was found for cells adherent to collagen and glass, both in the presence and absence of serum in the medium. The number A increases with the value of tint and tends to reach a plateau. The plateau value depends on adhesion conditions (presence or absence of serum).When adhesion occurred in serum-containing medium (F ≃ 0·1 × 10−l3 N), function A(tint) increased up to 15 min. The plateau values were in the ratio of 2: 1 for cells adherent to collagen and glass, respectively.When adhesion took place in serum-free medium, the function A(tint) increased within the first 20 or 130 s for cells adhering to glass or collagen, respectively. The value of A(tint) increased up to the effective interaction time, teff int, i.e. the time after which a plateau was reached at 100% adhesion. This meant that after tint≥teff int all cells were in adhesion with glass and collagen despite the application of the greatest shearing force, F= 2 × 10−9 N. The values of teff int for cells adherent to collagen and glass were in the ratio of 6:1, respectively.The value of A decreases with the value of F for cells adherent to substrate in the absence of serum when tint&lt; teff int. The function A(F) for cells adherent to collagen and glass in the presence of serum, but not in the absence of serum, can be described by the equation: , where a and c = constant &gt; 0. The values of a were in the ratio of 2: 1 for cells adherent to collagen and glass, respectively.The Brownian motion of cells interacting with both substrates in the absence of serum ceased. The times during which cell motion persisted for cells interacting with collagen and glass, respectively, were in the ratio of 2·5: 1.