bluuebunny/crossref_metadata_2025_split huggingface dataset:
An autoradiographical study of amino acid and nucleoside incorporation during the cell cycle of Amoeba proteus
Authors: Mills K. I. , Bell L. G. E. 
Published: April 2021

ABSTRACT
The incorporation of tritiated thymidine, uridine and leucine, into the acid-precipitable material of DNA, RNA and proteins, respectively, was studied by autoradiography throughout the cell cycle of Amoeba proteus. DNA synthesis occupied the first 17 h of the cycle (57 h long) and 2 peaks between 0·5–7 and 9–13 h accounted for the majority of the thymidine incorporation. RNA synthesis was represented by a series of peak uridine grain counts, the 3 major peaks occurring at to, 26–27 and 47–48 h. The incorporation of leucine also followed a pattern of peaks and dips, the main peaks occurring 1-2 h after the major increases in uridine incorporation. The fraction of label present over the nucleus decreased during the cell cycle, and this was probably due to a lowered incorporation of the leucine label by proteins synthesized in the cytoplasm and destined to become nuclear proteins. The incorporation patterns of 6 amino acids (arginine, aspartic acid, leucine, lysine, serine and valine) were studied individually during 3 periods of the cell cycle: 0–10 h (S phase); 20–30 h (early G 2); and 40-50 h (mid-late G 2). Variations in the intensity and timings of the incorporation maxima of the amino acids were observed, although the timings of increased grain counts of some of the amino acids frequently coincided. ‘Unique’ incorporation peaks (i.e. only observed in one of the amino acids studied) possibly indicate the synthesis of phase-specific proteins. The amino acid and nucleoside incorporation profiles presented in this paper will enable the results obtained from future studies on amoebae to be related to the macromolecular synthesis patterns.
Electron microscopic studies of silver-stained proteins in nucleolar organizer regions: location in nucleoli of rat sympathetic neurons during light and dark periods
Authors: Pébusque Marie-Joséphe , Seïte Raymond 
Published: April 2021

ABSTRACT
Ag-AS staining of nucleolar organizer regions was carried out on interphasic superior cervical ganglia neurons of rats sacrificed during light and dark periods. While the Ag-AS technique has mostly been used on monolayer cell lines or cell suspensions, the present study showed that in electron microscopy this technique is also applicable to small pieces of tissues. The finest pictures are obtained when (1) all solutions used for the staining procedure are at pH 4·5–4·7 and (2) the second step of the reaction involving ammoniacal silver and formalin developing solutions does not exceed 3 min. The results indicate that in the 2 time periods studied, a positive reaction took place exclusively in nucleolar fibrillar centres and in the fibrillar ribonucleoprotein (RNP) component (dense fibrillar component). The other nucleolar components, i.e. granular and vacuolar, were devoid of silver deposits. As previously shown in sympathetic neurons, the fibrillar centres of the nucleoli show a 10-fold increase in volume during the dark period. In this period, silver grains were located on both ‘giant’ and smallsized fibrillar centres. The fibrillar RNP component seen either at the periphery of fibrillar centres or in the form of a well-delimited network showed the strongest reaction. The same distribution of silver grains was observed in the sympathetic neurons of rats sacrificed during the light period. Here again, silver accumulation occurred exclusively in the fibrillar centres and the fibrillar RNP component. The same difference in reactivity was observed as for the dark period, the fibrillar RNP component being the main site of the reaction.
Structural heterogeneity of endocytic membranes in macrophages as revealed by the cholesterol probe, filipin
Authors: Montesano Roberto , Vassalli Pierre , Orci Lelio 
Published: April 2021

ABSTRACT
The polyene antibiotic, filipin, by specifically interacting with cholesterol, produces ∼ 25-nm protuberances (filipin-sterol complexes) in freeze-fractured membranes, and the addition of filipin to aldehyde fixatives has been recently introduced as a cytochemical technique for the localization of cholesterol in cell membranes. In a previous study we showed that, in fibroblasts, filipin-sterol complexes are absent from endocytic coated pits. To establish whether the absence of filipin-sterol complexes is a phenomenon restricted to coated pits or is correlated with endo-cytosis in general, we applied the filipin probe to cultured mouse peritoneal macrophages, in which different forms of endocytosis take place. The macrophages were incubated with bovine albumin or concanavalin A (Con A) to induce pinocytosis, and with heat-killed staphylococci or opsonized erythrocytes to induce phagocytosis, then fixed in glutaraldehyde/filipin and freeze-fractured. Filipin-sterol complexes were plentiful on the plasma membrane, on the smooth-membrane invaginations and vesicles induced by albumin, on the large endocytic vacuoles induced by Con A, and on the membrane of phagosomes but, in contrast, they were absent from coated pits and vesicles, as well as from coated segments of invaginations or vesicles. These results indicate that the membranes involved in different types of endocytosis do not react in the same way with filipin and may, therefore, have a different cholesterol content. This could reflect different mechanisms of formation for the various types of endocytic vesicles.
Acetylcholinesterase in mammalian erythroid cells
Authors: Keyhani Ezzatollah , Maigne JoËlle 
Published: April 2021

ABSTRACT
The biosynthesis of acetylcholinesterase in mammalian erythroid cells during differentiation and maturation was studied using a cytochemical method. Acetylcholinesterase was actively synthesized in basophilic erythroblasts I and II, and polychromatophilic erythroblasts, where it was present in the nuclear membrane, endoplasmic reticulum and Golgi apparatus. In orthochromatophilic erythroblasts the enzyme was present only in the Golgi apparatus, thus suggesting the end of the biosynthesis of acetylcholinesterase at this stage of maturation. In mouse and human marrow, evidence was also found suggesting the secretion of acetylcholinesterase into the extracellular compartment. No acetylcholinesterase reaction product was found in cat erythroblasts.
Polygonal networks in living chick embryonic cells
Authors: Ireland Grenham W. , Voon Frank C. T. 
Published: April 2021

ABSTRACTRegular polygonal networks have been found in explants and dissociated cells of early chick embryos. These networks are readily observable in live cells with phase-contrast optics thus allowing time-lapse cinemicroscopy. They consisted of a regular pattern of nodes and radiating struts found predominantly in the lamelliplasm of the free edges of the cells bordering expiants. At the outer edge, the network was terminated by radial struts associated with substrate-attached retraction processes whilst toward the centre of the cells it faded out.The network was also associated with stress fibres running across the cell and with microextensions on the dorsal surface. Even within one cell the network varied in size. Time-lapse films showed that microvilli were protruded from the dorsal surface over the nodes. Although the cells containing the networks were poorly motile the network itself was a mobile structure.Many explants from regions differing in prospective fates developed these networks after 2–4 days in culture. They appeared earlier in the smaller less yolky cells of definitive endoblast and epiblast. Experiments with dissociated and reaggregated cells confirmed their occurrence mainly in free edges of cells. The relationship between these networks seen in living chick embryo cells and those seen in other cell types using immunofluorescent techniques is discussed and a mechanism is proposed for their formation.
Nuclear crystalloids in sieve elements of species ofEchium(Boraginaceae)
Authors: Esau Katherine , Thorsch Jennifer 
Published: April 2021

ABSTRACTUltrastructural studies of differentiating phloem of the midvein in 15 species of Echium (Boraginaceae) have shown that in every species one or more crystalloids develop in sieve-element nuclei. These inclusions appear as soon as the cell begins to differentiate from a procambial derivative. Small at first, they enlarge later, particularly in length. The crystalloid may extend end-to-end in the correspondingly elongated nucleus. When the nucleus disin-tegrates in the maturing cell the crystalloid is released into the cell lumen where it remains intact or becomes fractured into large pieces. No dissociation into. subunits was observed. The crystalloids are composed of tightly packed narrow rods (tubules) forming a two-dimensional lattice of squares in transections and a system of parallel striations in longitudinal sections. The similarities of these inclusions to the crystalline form of P-protein in Fabaceae raises the question of terminological delimitation of P-protein, a common component of angiospermous sieve-element protoplasts. The occurrence of nuclear crystalloids in another previously investigated genus in the Boraginaceae, Amsinckia, suggests that this inclusion should be explored in boraginaceous representatives for its possible value as a systematic character.
Localization of mitotic factors on metaphase chromosomes
Authors: Adlakha Ramesh C. , Sahasrabuddhe Chintaman G. , Wright David A. , Lindsey William F. , Rao Potu N. 
Published: April 2021

ABSTRACT
The objective of this study was to determine whether the mitotic factors of HeLa cells, which induce meiotic maturation, i.e. germinal vesicle breakdown (GVBD) and chromosome condensation, when injected into fully grown Xenopus laevis oocytes, were localized in the cytoplasm or associated with the metaphase chromosomes. Cytoplasmic extracts Were prepared by lysing mitotic HeLa cells in low-salt hypotonic buffer and separating the chromosomes by centrifugation. The mitotic factors bound to chromosomes were extracted with high-salt (0·2 M-NaCl) buffer. Both the cytoplasmic and chromosomal protein fractions were evaluated for their maturation-promoting activity (MPA) in the Xenopus oocytes. The results of this study indicate that both the cytoplasmic and chromosomal fractions are identical in many respects, including their ability to induce GVBD, but the specific activity of the chromosomal fraction was at least threefold greater than that of the cytoplasmic fraction. These data suggest that a major portion of the mitotic factors is localized on the metaphase chromosomes. This association does not appear to be due to adventitious binding of mitotic proteins to chromosomes during the extraction procedures. Furthermore, when extracts were prepared in a similar way from early- and mid-G2-phase HeLa cells, only the nuclear extracts had MPA and no activity was found in the cytoplasmic fraction. Both the cytoplasmic and nuclear extracts of late-G2 cells exhibited MPA. These data support the conclusion that the mitotic factors become preferentially bound to chromatin as soon as they are synthesized, and as the cell synthesizes more of these factors in preparation for mitosis, increasing amounts of them are retained in the cytoplasm.
Dna repair synthesis in subpopulations of human lymphocytes
Authors: Lewensohn R. , Ringborg U. , Baral E. , Lambert B. 
Published: April 2021

ABSTRACT
Human peripheral blood lymphocytes enriched in T or B cells were exposed to ultraviolet irradiation, nitrogen mustard or methylmethane sulphonate and investigated regarding their capacity for DNA repair synthesis. The DNA repair synthesis, measured as [3H]thymidine incorporated, was determined by autoradiography as unscheduled DNA synthesis (LIDS). No systematic difference could be found in the capacity for UDS between the T- and B-cell-enriched fractions. A larger individual variation in UDS was found in the B-cell-compared to the T-cell-enriched lymphocytes.
Changes in the fine structure of the apical plasma membrane of endometrial epithelial cells during implantation in the rat
Authors: Murphy C. R. , Swift J. G. , Mukherjee T. M. , Rogers A. W. 
Published: April 2021

ABSTRACT
In previous work we have shown that ovarian hormones, when injected into ovariectomized rats, alter the fine structure of the plasma membrane of endometrial epithelial cells. In this paper freeze-fracture techniques have been used to study the apical plasma membrane of endometrial epithelial cells of rats during the period of blastocyst implantation of normal pregnancy. On day 1 of pregnancy there were 2354 ±114 intramembranous particles (IMPs) per μm2 of membrane. The particles were spherical and randomly distributed. On day 5 of pregnancy IMP density rose to 2899 ± 289 per μm2 and some rod-shaped particles were also visible. By day 6 of pregnancy IMP density had risen to 4014 ±206 per μm2 and there were more rod-shaped IMPs than before. In addition, on day 6 IMPs were also present as rows of particles and some gap-junction-like arrays of particles were also seen.
Our findings indicate that there are fine-structural alterations in the apical plasma membrane of endometrial epithelial cells, the site of first contact between maternal and embryonic cells, during the period of early pregnancy. The findings are discussed in the light of suggested mechanisms of blastocyst attachment to the uterine epithelium at implantation.
Macrocyst development in Dictyostelium discoideum: I. Induction of synchronous development by giant cells and biochemical analysis
Authors: Saga Y. , Yanagisawa K. 
Published: April 2021

ABSTRACT
In Dictyostelium discoideum, cytological and physiological studies on macrocyst formation revealed that this process consists of at least two steps: the production of giant cells, which are believed to be formed from the fusion of cells of two opposite mating types, and the subsequent induction of macrocyst development by the giant cells. The conditions that had been considered formerly to be required for macrocyst formation, such as darkness and the presence of two cells of complementary mating types in heterothallic strains, were actually required only for the production of the giant cells. Once giant cells are produced, the surrounding cells can aggregate and form macrocysts even in the light. Furthermore, it was demonstrated that giant cells can switch the developmental mode of the surrounding cells to macrocyst formation. That is, if a critical number of the isolated giant cells are introduced into a cell population of a single strain of NC4, which normally would produce only fruiting-bodies, macrocysts are formed instead. When in the presence of giant cells, the development of macrocysts may be initiated by starvation. Therefore, if all cells are made to starve simultaneously development begins and proceeds synchronously. Using this technique of synchronous development, the developmental kinetics of enzyme activities were assayed during macrocyst and fruiting-body formation. Considerable differences in the patterns of those enzyme activities were demonstrated between the two developmental modes of D. discoideum.
The motive force of the migrating pseudoplasmodium of Dictyostelium discoideum under dark and light conditions
Authors: Kitami Masanobu 
Published: April 2021

ABSTRACT
As a contribution to the understanding of the mechanism of the collective motion of the cell mass in the migrating pseudoplasmodium its motive force has been determined. The measurements in the present paper were made by an original method using centrifugal force. The maximum value of the motive force of a migrating pseudoplasmodium in the dark was estimated as 0·6–1·6 dyn. This value is comparable to the motive force of protoplasmic streaming in Physarum polycephcdum. In addition, the motive force in phototactic migration, which has not previously been estimated, was measured. Illumination from the front increased the motive force, whereas illumination from the back produced the opposite results. That is to say, illumination could directly influence the motive force. Furthermore, some interesting results were obtained by measuring the changes in the velocity of the pseudoplasmodia placed under four conditions (combinations of illuminated or non-illuminated, and parallel or antiparallel to the direction of the external force). These results suggest the necessity of taking into consideration the direct effect of light upon the motility of the cells in the migrating pseudoplasmodium.
Spreading of blastomeres from eight-cell mouse embryos on lectin-coated beads
Authors: Kimber S. J. , Surani M. A. H. 
Published: April 2021

ABSTRACT
Single blastomeres from 8-cell embryos adhere to lectin-coated agarose beads. The cells spread over the surface of peanut lectin (PNA), wheat germ lectin (WGA) and concanavalin A (Con A)-coated agarose beads, and this was prevented by sugars with high affinity for the appropriate lectin. Spreading was also prevented by cytochalasin D at a concentration (0·5-1·0 Ag/ml) known to inhibit compaction of whole 8-cell embryos. Colcemid (1–2 μg/ml) only depressed spreading, as measured by linear contact distance, to 70–80 % of that for the controls, while removal of calcium from the medium with EDTA had little effect on spreading. Fucose promoted spreading on WGA beads. Cells from 8-cell embryos will not adhere to negatively charged G-Sephadex and CM-Sephadex beads. They do adhere to positively charged DEAE-Sephadex beads but do not spread on them.
In an attempt to inhibit cell spreading at compaction in intact 8-cell embryos, these were disaggregated in the presence of various (34) saccharide-containing molecules. Neither any sugar-containing molecules alone, nor combinations of N-acetyl-glucosamine, galactose and mannose, fucose and galactose, and fucose and lactose were able to inhibit compaction at physiological concentrations. However, blastocyst formation was inhibited to various extents by high non-physiological concentrations (50 mm) of D-glucose, D-mannose, L-fucose, D-arabinose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, α-lactose, 25 mM-α-meliblonic acid and by 2 mg/ml fucoidin, ovine mucin and desialylated ovine mucin. Our results indicate that interaction of PNA, WGA and Con A with molecules on the cell surface that bind these lectins can trigger the cells to spread. However, a simple lectin-sugar interaction alone may not account for the spreading of cells on one another at compaction in whole 8-cell embryos.
Movement and guidance of migrating mesodermal cells in Ambystoma maculatum gastrulae
Authors: Nakatsuji Norio , Gould Andrew C. , Johnson Kurt E. 
Published: April 2021

ABSTRACT
A scanning electron microscopic study in early gastrulae of Ambystoma maculatum showed that migrating presumptive mesodermal cells were strongly oriented toward the animal pole. They had lamellipodia and filopodia at their leading edges, and rounded or tapering, tail-like, trailing edges. Of the cells whose polarization could be determined unequivocally, 81 % appeared to be directed in a quadrant toward the animal pole, and 93 % were directed to some extent away from the blastopore. This strong orientation suggests that specific mechanisms direct cell movement, in addition to the non-specific dispersive mechanism of the contact inhibition of cell movement. There is a network of fine extracellular fibrils that covers the inner surface of the ectodermal layer. Filopodia of the migrating cells frequently attach to and appear to follow the fibrils, suggesting that the fibrils serve as a guiding substratum for cell attachment and movement. There are areas where the fibrils are apparently aligned along the blastopore - animal pole axis, and a preliminary statistical analysis using micrographs at high magnification showed a significant alignment parallel to the blastopore - animal pole axis. This fibril alignment could cause the strong orientation of the mesodermal cells by means of contact guidance.
Ascospore development in the fission yeasts Schizosaccharomyces pombe and S. japonicus
Authors: Tanaka Kenji , Hirata Aiko 
Published: April 2021

ABSTRACT
The fine structure of ascospore formation in the fission yeasts Schizosaccharomyces pombe and Schizosaccharomyces japonicus var. japonicus was studied by serial thin-sectioning and electron microscopy. The morphogenetic events were almost the same in both species. Ascospore development was initiated by the formation of the forespore membrane on the cytoplasmic side of the differentiated nucleus-associated organelle (NAO) in the interval between meiosis I and II in S. pombe, or during the post-meiotic nuclear division in S. japonicus, and the process proceeded almost synchronously through the two or four nuclei in the ascus. The forespore membrane developed by fusion of the cytoplasmic vesicles and this was clearly demonstrated in S. japonicus where the behaviour of vesicles involved in the forespore membrane development could be traced as they were marked by the presence of electron-dense granules. The staining technique, by phosphotungustic acid-chromic acid (PTA-CA) after treatment with periodic acid, was used to attempt to elucidate the origin and the nature of the forespore membrane. The method specific to plasmalemma-type membranes stained both ascus and ascospore plasmalemmas; the forespore membrane was not stained at first but developed the same affinity for stain as the plasma membrane in the course of ascospore development. The results suggest that the forespore membrane did not come directly from the ascus plasma membrane, but from another membrane system such as the endoplasmic reticulum. Spore wall material was deposited in the space between the inner and outer leaflets of the forespore membrane.
The detergent-resistant cytoskeleton of higher plant protoplasts contains nucleus-associated fibrillar bundles in addition to microtubules
Authors: Powell Andrew J. , Peace Geoffrey W. , R. Slabas Antoni , Lloyd Clive W. 
Published: April 2021

ABSTRACT
Cytoskeletons prepared from carrot protoplasts often retain the nucleus, which is associated with bundles of 7 nm fibrils. These were also seen in cytoskeletons from oil palm, maize and Italian rye grass cells. By examining such cytoskeletons by immunofluorescence, negative staining and stereo scanning electron microscopy it appears that the bundles could be part of a more delicate system of fibrils distal to the nucleus. Optical diffraction of the bundles, staining with heavy meromyosin, drug treatments and phalloidin-staining all confirm that the bundles are not composed of actin. Bundles could not be isolated from such cytoskeletons in quantities sufficient for analysis, but by disrupting protoplasts prepared from stationary-phase cells it was possible to purify fibrillar bundles that appeared in the lysate. These were similar in size and properties to the nucleus-associated bundles. The former were shown by sodium dodecyl sulphate/polyacrylamide gel electrophoresis to be composed of several proteins and were sensitive to reducing agents. Since they are not composed of actin, the possibility was explored that these fibrils are related to the P-proteins of phloem sieve tube and accessory cells.