bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fixation of the central nervous system by perfusion with aldehydes and its effect on the extracellular space as seen by electron microscopy
Authors: Johnston Patricia V. , Roots Betty I. 
Published: April 2021

Abstract
Rat brains fixed by perfusion with glutaraldehyde and prepared for electron microscopy under certain conditions showed an abundance of very closely apposed or completely fused surface membranes in some areas. This apparent lack of extracellular space was most consistently observed in the lateral geniculate body and the superior colliculus and less consistently in the cerebellum and parietal cortex. Lowering the temperature of the perfusate from body temperature (38–39 °C) to room temperature (19–20 °C) and/or lowering the pressure at which it was delivered (from 140 to 70 cm of water) led to the appearance of more extracellular space. A striking change in the amount of extracellular space was observed when ethanol was used for dehydrating the samples instead of acetone. When ethanol was employed a space of approximately too A was seen between most cellular elements, whereas acetone dehydration led to an abundance of closely apposed or fused surface membranes. It is suggested that if glutaraldehyde acts by cross-linking proteins in apposing membranes, this reaction is more effectively completed in the presence of acetone and that this may be due to depolymerization of glutaraldehyde by the solvent. It is also suggested that the variation in the amount of extracellular space seen in brains fixed by perfusion with aldehydes may reflect real differences in distances between membranes at the time of fixation.
Critical density for relaying in Dictyostelium discoideum and its relation to phosphodiesterase secretion into the extracellular medium
Authors: Gingle A. R. 
Published: April 2021

ABSTRACT
The critical cell density for relaying in D. discoideum, N*, has been measured as a function of cell density, N, and time after harvesting, t. It has logarithmic dependence on N for 2·5 × 104/cm2 &lt; N &lt; 7·5 × 105/cm2 and saturates for N &gt; 1·0 × 106/cm2. N* is an increasing function of time after harvesting. The phosphodiesterase (PDE) secretion rate on which N* depends is a constant. Expressions were derived which relate N* to PDE secretion and diffusion. They have been fitted to the data from time delay experiments yielding values of the PDE diffusion constant in 2% buffered agar, Dp = (2·25 ± 0·15) × 10−9 cm2/s, and the ratio of relaying threshold concentration to signal pulse size, C*/η = (1·4 ± 0·05)× 105cm-3. N* has also been measured in the presence of various amounts of added beef heart PDE. The cAMP relaxation rates, 1/τ0, due to beef heart PDE were calculated from the N* measurements and found to be proportional to amounts of added PDE for (1/τ0)max &lt; (10 s-1). Finally, two kinds of inhibition have been observed in the PDE secretion. The PDE activity per cell is constant for N &lt; 8·0 ×104/cm2, and decreases for larger N. It depends only on N for 1/τ0 &lt; 10 s-1 and is strongly inhibited by extracellular PDE activity above this relaxation rate.
Flagellar Doublet Microtubules: Fractionation of Minor Components and α-Tubulin from Specific Regions of the A-Tubule
Authors: Linck R. W. 
Published: April 2021

ABSTRACT
Proteins occurring in minor amounts with purified sperm flagellar doublet microtubules were identified and studied by SDS-gel electrophoresis. Methods were developed to solubilize selectively these minor components; electron microscopy (EM) of the fractionated products revealed possible locations of these proteins in the tubule.
Doublet microtubules were prepared from sea-urchin (Echinus esculentus and Strongylo-centrotus droebachiensis) and scallop (Pecten maximus) sperm by dialysing flagellar axonemes against 2 mM Tris-0·2 mM EDTA-0·5 rπM DTT. EM indicates that these doublet tubule preparations retain at least 70% of their radial spokes; cross-sections show a globule or fibre applied to the inside wall of the A-tubule, across from the inner B-tubule junction. On SDS-gels these preparations separate into at least 10 minor bands, accounting for 20–30% of the total protein; the remaining 75 ±4% migrates as tubulin. For E. esculentus the molecular weights and relative amounts of these components are: Component Ee 8 (150000 Daltons; 1 %), 11 (114 000; 2·5%), 15 (8 9 000; 2%), 16 (8 0 000; 2·5%), 17 (7 4 000; 2%), 18 (6 9 000; 2%), 19 (66 000; 2 %), 21 (48 000; 4·5 %), 22 (45 000; 3 %) and 23 (44 500; 3 %).
Treatment of sea-urchin tubules with 0·1–0·5 % sarkosyl, 0·1–0·3 M KSCN or 0·3–0·6 M KI results in the selective solubilization of: first, component 8 and some B-subfibre tubulin; second, components 11 and 23 and the remaining B-subfibre tubulin; third, most of the A-subfibre tubulin and components 17, 18 and 19. Thermal fractionation extracts none of these components, suggesting they are principally associated with the A-tubule. Finally 25–35 % of the original protein is resistant to solubilization, and appears in the EM as ribbons of 3 protofilaments with 16-nm axial repeats. The resistant ribbons contain components 15, 16, 21 and 22 (plus component 20 in S. droebachiensis) in addition to 25 ±4% of the total tubulin. The data support the existence of two stable moieties in each doublet tubule: (1) a ribbon of 3 protofilaments and (2) either a second ribbon of 3 protofilaments or an equivalent amount of tubulin in some other form. EM images suggest that one ribbon forms the lateral side of the A-tubule (e.g. protofilaments A1,2,3 or A13,1,2 in the model) and that the globule applied to A13 may be a multisubunit complex of remaining minor components.
Treatment of scallop tubules with 0·3 M KSCN preferentially extracts α-tubulin, yielding ribbons 1–4 protofilaments wide. The significance of this finding is discussed.
Cell wall development of Micrasterias americana, especially in isotonic and hypertonic solutions
Authors: Ueda Katsumi , Yoshioka Sachiyo 
Published: April 2021

ABSTRACT
The cell wall development of Micrasterias americana was investigated by light and electron microscopy. From digestion experiments with pectinase and cellulase, and from fluorescence spectra in Calcofluor and Coriphosphin solution, it was concluded that pectic substances were the main component of the young developing cell wall and that cellulose was synthesized after the daughter hemicell was well developed. In 016 M mannitol, wall materials accumulated and were incompletely incorporated into the wall at the region where wall growth would be expected. The plasma membrane was in close contact with the cell wall at the sinus, and this contact was assumed to prevent penetration of wall material at this region, resulting in the accumulation of wall material at regions other than the sinus. The cellulosic wall layer was formed after the production of pectic substances in the 0 · 16 M mannitol. In 0 · 3 M mannitol neither a definite wall layer of cellulose nor a pectic wall was produced, presumably due to extensive dilution of the wall materials in the plasmolysed space between the cell wall and the plasma membrane. Under normal circumstances, the shape of the daughter cell is assumed to be determined by the shape of the developed primary wall, which is induced by precocious differentiation of the wall at the sinus.
The redevelopment of heteropolar doublets and monster cells of Oxytricha fallax after cystment*
Authors: Hammersmith Robert L. 
Published: April 2021

ABSTRACT
Heteropolar doublets of the hypotrichous ciliate Oxytricha fallax can encyst, as can monster cells containing multiple copies of at least part of the ciliature. The resulting cysts excyst as heteropolar doublets or monster cells, respectively. Transmission electron microscopy of resting cysts derived from monster cells and from singlets, however, indicates a complete loss of the ciliature - all kinetosomes, ciliary axonemes, and microtubules. Thus, the determination of each ciliature of a monster cell cannot be attributed to the persistence of any visible part of the ciliature.
Transmission electron microscopy of monster and singlet cysts suggests that the information for a ciliature may be related to the system of cyst wall grooves and possibly to differentiations in the inner cell membrane which separates the cyst cytoplasm from the cyst wall.
The redevelopment of heteropolar doublets upon excystment indicates that the anterior-posterior polarity is independently determined for each ciliature and is maintained through cystment. This polarity is not, however, reflected in a recognizable anterior-posterior polarity of any visible structure of the resting cyst.
The number of adoral zones of membranelles (AZMs) may increase or decrease in some excysting monster cells compared with that observed in the encysting cells. Possible explanations for these changes are offered in the Discussion.
Gap junctions in the differentiated neural retinae of newly hatched chickens
Authors: Fujisawa H. , Morioka H. , Nakamura H. , Watanabe K. 
Published: April 2021

ABSTRACT
Gap junctions in the neural retinae of newly hatched chickens were examined in thin section and by freeze cleaving.
Unusual gap junctions containing linear arrays of intramembrane particles are found between principal and accessory cones which form a double cone at the region of the outer limiting membrane. These unusual gap junctions are often continuous with macular aggregates of hexagonally packed intramembrane particles which are characteristic of a typical gap junction.
Typical gap junctions are also found in both the outer and the inner plexiform layers and in the outer nuclear layer, but are not so abundant as in the outer limiting membrane region.
The sizes of intramembrane particles and their centre-to-centre spacing within the macular aggregate of a gap junction in differentiated neural retinae are slightly larger than those in undifferentiated neural retinae.
Tight junctions are not found in differentiated neural retinae.
Different cation requirements for aggregation of BHK cells and their transformed derivatives
Authors: Urushihara Hideko , Takeichi Masatoshi , Hakura Akira , Okada T. S. 
Published: April 2021

ABSTRACT
BHK21 cells singly dissociated by trypsin aggregate in medium with calcium ions, but not in medium with magnesium ions. Their malignant derivatives (pyBHK) induced by polyoma virus, after dissociation with trypsin, aggregate equally well in medium with either calcium or magnesium ions. When EDTA is used for dissociation of cells from culture on a substrate, neither BHK21 nor pyBHK. cells require addition to the medium of divalent cations for rapid aggregation. Trypsin-dissociated BHK21 cells become aggregative in medium without divalent cations, when they are incubated for 60 min in dispersion with medium containing calcium ions before aggregation. In the case of pyBHK cells, incubation in dispersion in the medium with calcium or magnesium ions is effective in this respect. Calcium and magnesium ions are equally effective for adhesion of both BHK21 and pyBHK cells to non-cellular substrate or to a cell monolayer. We discuss the different cation requirements for aggregation of BHK21 and their transformed derivatives in relation to the recovery process of cell surfaces after exposure to trypsin.
Separation and biochemical characterization of the two cell types present in the pseudoplasmodium of Dictyostelium mucoroides
Authors: Oohata Akiko , Takeuchi Ikuo 
Published: April 2021

ABSTRACT
The pseudoplasmodium (slug) of the cellular slime mould, Dictyostelium mucoroides consists of prestalk and prespore cells. These 2 differentiated types of cells were separated by modification of the previous methods using density-gradient centrifugation. Major improvements made in the present study were the use of a density column of different specific gravities and the use of a discontinuous gradient rather than a continuous one. With these improvements, it became possible to obtain efficiently a large number of prestalk and prespore cells. After separation of the 2 types of cells, activities and electrophoretic patterns of some developmentally regulated enzymes were compared. The hydrolases such as β-glucosidase, β-galactosidase, acetylglucosaminidase and alkaline phosphatase showed higher activities in the prestalk than in the prespore cells. The results are consistent with the fact that more autophagic vacuoles are present in the prestalk than in the prespore cells. On the other hand, UDP-galactose polysaccharide transferase was almost exclusively found in the prespore cells. Electrophoresis on polyacrylamide gels of slug, prestalk and prespore extracts showed that one among 4 isozymes of β-galactosidase recognized in the slug extract was present only in the prestalk extract. Electrophoretic patterns of acid phosphatase revealed that one of the two isozymes present in the slug was specifically found in the prestalk cell. Finding of such prestalk specific isozymes was significant, since no specific markers have been known for the prestalk cell.
Quantitative studies of rDNA in amphibians
Authors: Vlad M. 
Published: April 2021

ABSTRACT
The proportion, of the genome that is complementary to 18 and 28 s has been determined for 12 species of amphibians. The group of species chosen for the experiment includes 5 related species belonging to the same genus (Plethodon) as well as species belonging to distant taxonomic groups whose C-values range from 3 to 62 pg.
Hybridization of rRNA (18 S + 28 S) to whole chromosomal DNA to saturation level indicates that the proportion of rDNA decreases with increasing DNA content.
The results presented in this paper do not support the hypothesis of Nardelli, Amaldi & Lava-Sanchez that the number of ribosomal cistrons in various amphibians can always be expressed as a power of 2.
Quantitative assay to study cell movement in the myxobacteria
Authors: Lonski Joseph , Heromin Ronald , Ingraham David 
Published: April 2021

ABSTRACT
A simple quantitative assay has been developed to test the rate of cell movement of myxo-bacteria. The assay employs an agar surface and at no time are the cells cultured in a liquid environment. Isolation of a rate-increasing substance(s) from fruiting Myxococcus xanthus is reported. The understanding of the aggregative process in these bacteria will be aided by characterization of the chemotactic system.
Computer evidence concerning the chemotactic signal in Dictyostelium Discoideum
Authors: Parnas Hanna , Segel Lee A. 
Published: April 2021

ABSTRACT
Observed pulsatile aggregation of cellular slime mould amoebae is simulated on a computer. One spatial dimension is considered. In the simulation, attractant is rapidly secreted by the cells, after a delay period, when a superthreshold attractant concentration is sensed. Cells are refractory to further signals after secretion. Once secreted, the attractant diffuses and is hydrolysed.
Movement results if a cell’s extending pseudopods sense a supercritical increase of attractant; if increases are sensed on both sides, a sufficiently large difference can also initiate movement. The movement continues for a period independently of further signals, but then can be reversed by an attractant increase (at the back of the cell) that surpasses a high threshold. After 100s, motion stops and the threshold for movement reverts to normal.
With the above rules, and with parameter values taken, as far as possible, from the literature, the simulation provides the observed pattern of aggregation. Outward moving waves of attractant and organized inward pulsatile ‘steps’ of cell movement surround a cell that secretes autonomously every few minutes. Other rules fail to give this picture, or give it only for a relatively narrow range of parameter values. It appears that of the various possible signals for chemotaxis, the most likely to be used by the amoebae is a temporal increase of attractant as sensed by extending pseudopods. Nonetheless, we cannot rule out the ‘classical’ hypothesis that cells directly sense concentration differences.
Response of preimplantation rat blastocysts In Vitro to extracellular uterine luminal components, serum and hormones
Authors: Surani M. A. H. 
Published: April 2021

ABSTRACT
The influence of extracellular environmental factors on preimplantation rat blastocysts was tested by determining the number of embryos which escaped from their zonae pellucidae, followed by attachment and outgrowth of trophoblast giant cells, after 72 h in culture Uterine luminal components from individual females, or hormones, were included in Dulbecco’s medium which contained 4 mg/ml bovine serum albumin. In about 20% of cases, uterine fluids were embryotonic. However, uterine fluids from day-5 pregnant females, the day of implantation in the rat, were more potent in these tests than uterine fluids obtained from ovariectomized females treated with progesterone alone. The potency of a mixture of the 2 fluids was also high. Uterine fluids obtained at 14 h after an injection of oestradiol and progesterone to the ovariectomized females, were also effective in these tests. Rat serum and foetal calf serum were effective too, but steroids or insulin alone in the medium had no detectable influence on embryos. Serum or uterine luminal proteins appear to be essential for maintaining the viability of the blastocysts and for inducing the responses observed here. In the uterine fluids, some proteins released into the lumen after treatment of females with oestradiol and progesterone appear to be the biologically active components. Differences in the responses of blastocysts in vitro are compared with those in vivo.
Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos : III. characterization of galactose- and glucosamine-labelled materials
Authors: Johnson Kurt E. 
Published: April 2021

ABSTRACT
Normal Rana pipiens gastrulae show more incorporation of isotopically-labelled galactose and glucosamine into TCA-insoluble materials than blastulae. Interspecific hybrid embryos which undergo developmental arrest at the onset of gastrulation often synthesize reduced amounts of galactose- and glucosamine-labelled materials. These materials are high-molecular weight, but not collagen. After pronase digestion, labelled materials elute in the void volume of Sephadex G-50. Labelled materials migrate slowly on cellulose acetate, bind to several kinds of anion exchangers and elute at low ionic strength, are precipitated by cetyl pyridinium chloride (CPC) when mixed with carrier compounds, and are not degraded by Clostridium neuraminidase or Streptomyces, leech, and bovine testicular hyaluronidases.
Some clues as to the formation of protrusions byFundulusdeep cells1
Authors: Tickle C. , Trinkaus J. P. 
Published: April 2021

ABSTRACTOne of the ways in which Fundulus deep cells move in vivo is by putting out long, fingerlike protrusions. This involves a change in the shape of the cell as a whole, with cytoplasmic flow, and is not just a local phenomenon. Moreover, particles on the cell surface move toward a protrusion as it is forming, suggesting surface flow. The role of surface flow is discussed both on a gross level and in respect to molecular fluidity. Long, stable protrusions can be pulled from cells by the application of negative pressure at a constant rate and these behave in a similar way to those formed during cell locomotion. Such long protrusions must be structured. The importance of contractile properties of the cytoplasm in the formation of protrusions was studied by treating cells with media that modify cellular contractility.
Plant protoplast agglutination and membrane-bound β-lectins
Authors: Larkin P. J. 
Published: April 2021

ABSTRACT
Plant protoplast agglutination caused by normal and immune serum and by artificial carbohydrate antigens is described. Evidence is presented that the new class of lectins, called all-β lectins by previous authors, are present on protoplast membranes and responsible for both forms of agglutination. Some non-specific serum component and the artificial antigens are the 2 respective passive ‘bridge’ molecules between agglutinating protoplasts.
Mitotic activity of differentiated goldfish erythrophoresin culture
Authors: Ozato Kenjiro 
Published: April 2021

ABSTRACT
Integumental erythrophores on the scales of xanthic goldfishes were dissociated and cultured in a monolayer for about 30 days. The proportion of erythrophores in the culture was about 50% at the beginning of cultivation. Erythrophores in culture were characterized by the aggregate of orange-coloured pigment in the centre of the cell body. With the progress of culture the erythrophores developed a few elongated dendritic processes and came to rest on a monolayer sheet of coexisting non-pigmented cells. The erythrophores responded to adrenocorticotropic hormone (ACTH) by producing reversible pigment dispersion and this response was retained throughout the whole period of culture. Dividing erythrophores were found first within 3 days of cultivation and at all times after that. The number of the erythrophores doubled within 9 days of cultivation and trebled within 16 days. Thus, evidence was provided that differentiated erythrophores of the goldfish still showed mitotic activity in vitro, in contrast to the generally accepted view that fish chromatophores are a kind of terminally differentiated cell.
A light- and electron-microscope study of nuclear structure throughout the cell cycle in the euglenoid Astasia longa (jahn)
Authors: Chaly N. , Lord A. , Lafontaine J.G. 
Published: April 2021

ABSTRACT
The structure of nuclei of Astasia longa in synchronized cultures was examined at the light- and electron-microscope levels. Three types of nuclei, differing mainly in chromatin conformation, were observed during interphase and were tentatively classed in the G1S and G2-periods. The fibrillar nucleolar regions exhibited a most complex organization and appeared to consist of convoluted, coarse filaments or nucleolonemata approximately 0·15 μm in diameter. Chromosome condensation was evidenced first by the longer, thicker profiles of chromatin observed in late prophase. Furthermore, the nucleolus, that persists throughout mitosis, began to elongate at this stage, simultaneously with the appearance of short, unoriented profiles of intranuclear microtubules. Chromosome condensation was complete by mid-metaphase and the nucleolus was elongated into a cylindrical shape with irregular extremities. Microtubule profiles were longer than in prophase; they were now oriented parallel to the nucleolus and frequently lay closely appressed to its sides. In anaphase, the chromosomes segregated into 2 groups, one towards each extremity of the dumb-bell-shaped nucleolus. The telophase chromosomes assumed a random orientation with respect to the still intact nucleolus. Throughout the division stages the persisting nucleolus maintained its ultrastructural organization and consisted partly of conspicuous nucleolonemal profiles which tended to be oriented along the major axis of this organelle. Nucleolar separation into 2 fragments occurred late in telophase and was followed by a reformation of daughter nuclei and initiation of cell fission during cytokinesis.