bluuebunny/crossref_metadata_2025 huggingface dataset:
Trypsinized bhk21 cells aggregate in the presence of metabolic inhibitors and in the absence of divalent cations
Authors: Edwards J. G. , Campbell Janice A. , Robson R. T. , Vicker M. G.
Published: April 2021

The rapid formation of adhesions in suspension by lightly trypsinized BHK21 cells is not dependent on protein synthesis, and only in part on cellular metabolism, although it is completely inhibited by heat- and aldehyde-fixation of the cells. A requirement for protein synthesis becomes evident only if cells are exposed to high levels of trypsin for long periods. Formation of adhesions does not require addition to the medium of divalent cations, although it is increased by divalent manganese and cobalt ions. It is promoted by cytochalasin B and by cyclic AMP and is not inhibited by p-mercuriphenylsulphonate. We discuss a possible relationship between aggregation and the formation of gap junctions.
The fine structure of oogonia and oocytes in human ovaries
Authors: Baker T. G. , Franchi L. L.
Published: April 2021

Twenty-eight foetal and post-natal human ovaries (6 weeks post conception to 11 years post partum) have been examined with the electron microscope. Stages in the normal differentiation of germ cells (oogonia; oocytes at the pre-leptotene, leptotene, zygotene, pachytene, and diplotene stages of meiotic prophase) were identified by comparison with (a) corresponding cells in histological and squash preparations, and (b) similar cells in the rat ovary. Atretic cells (oogonia in mitosis ; oocytes at pachytene and diplotene) were also examined.

The nuclei of oogonia contain an evenly dispersed fibrillar matrix which becomes organized into irregular strands in oocytes at pre-leptotene. At leptotene these strands become the sheaths surrounding unpaired, electron-dense axial threads or ‘cores’, which become associated in pairs during the transitory zygotene stage, and tend to be polarized within the nucleus. Single and paired threads are replaced by ‘tripartite ribbons’ (synaptinemal complexes) at pachytene; longitudinal subdivision of the lateral components of the ribbon is observed in some nuclei and may represent a later stage. At diplotene, essentially unpaired cores are observed as at leptotene, although they are thicker and more intimately related to the surrounding fibrillar sheath. The latter is also more highly organized than at earlier stages. This chromosomal structure is retained in oocytes in promordial follicles in post-natal ovaries. The dictyate stage observed in rat ovaries is not found in man.

The organization of the cytoplasm does not change markedly as oogenesis advances, although organelles become more numerous, and the internal structure more complex, as the cells enlarge towards the diplotene stage.

Oogonia degenerating during mitosis differ from normal cells in that the chromosomes become fused to form an irregular mass. Abnormal membrane-bound areas are also observed in the cytoplasm. Atretic oocytes at pachytene coalesce to form ‘pools’ of cytoplasm containing several nuclei in various stages of pyknosis. Atretic cells at diplotene may contain grossly swollen cytoplasmic organelles and clumped, homogeneous chromosomes. The ‘atretic divisions’ appear to be phagocytosed by somatic cells, but the means of elimination of degenerating meiocytes was not determined.
Cytological changes in the fat body of Rhodnius during starvation, feeding and oxygen want
Authors: Wigglesworth V. B.
Published: April 2021

Fourth-stage larvae of Rhodnius survive starvation for 7–9 months. The filamentous mitochondria in the fat-body cells become reduced to granules and short rods (say 16 weeks). By 25 weeks the granules are swollen to form spheres which still contain NAD-diaphorase. By 30–35 weeks many mitochondria break down to osmiophil spheres or cytolysomes containing acid phosphatase. The origin of these spheres agrees with that of ‘protein droplets’ in holometa-bolous insects.

After feeding, the nucleus and nucleolus enlarge, RNA begins to accumulate in the cytoplasm and both the granular and the enlarged spherical mitochondria develop into filaments which break up into rows of granules. Within 2 days the fat-body cells become distended with watery vacuoles. All these changes are arrested or delayed if the oxygen supply to the fat body is reduced by tracheal section. Mitosis is hardly affected.

Accumulation of reserves of fat and glycogen takes place later.
The fine structure of the eye of the leech, Helobdella stagnalis
Authors: Clark A. W.
Published: April 2021

The eye of the rhynchobdellid leech, Helobdella stagnalis, has been examined with the electron microscope. The eye is composed of a cup of pigment cells surrounding a compact mass of photoreceptor cells. In addition to pigment granules, the pigment-cell cytoplasm is characterized by mitochondria, a Golgi complex, and profiles of rough-surfaced endoplasmic reticulum. The photoreceptor cell contains a microvillous rhabdomere. The microvilli arise from the membrane of a large intracellular vesicle and obliterate much of its lumen. No connexion between the lumen of the intracellular vesicle and the extracellular space has been observed. The plasmalemma of the photoreceptor cell is folded to form thin pleats of cytoplasm which separate adjacent receptor cells from each other. No glial-like cells have been seen in the receptor cell mass. Directly subjacent to the microvilli and surrounding the intracellular vesicle is a tortuous and predominantly smooth-surfaced endoplasmic reticulum. A pair of centrioles is found near the rhabdomere. The cytoplasm around the nucleus is characterized by smooth- and rough-surfaced elements of endoplasmic reticulum, many mitochondria, and a Golgi complex. Proximally, the receptor cell narrows to form a nerve fibre which joins those from other cells to form the optic nerve.
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

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

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 < N < 7·5 × 105/cm2 and saturates for N > 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 < (10 s-1). Finally, two kinds of inhibition have been observed in the PDE secretion. The PDE activity per cell is constant for N < 8·0 ×104/cm2, and decreases for larger N. It depends only on N for 1/τ0 < 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

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

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

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

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

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

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

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

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

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

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

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

One 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

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

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

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.
An intracellular pool of a cell-surface ligand which inhibits lectin-induced capping
Authors: McDonough James , Rutz Richard , Lilien Jack
Published: April 2021

It has previously been established that cells dissociated from embryonic chick neural retina tissues redistribute their cell surface Concanavalin A receptors into patches and caps upon treatment with the lectin. During 4 h in continuous culture the cell population progressively loses the capacity to cap Con A receptors. In the presence of cycloheximide this decrease occurs for only the first 2 h of incubation. Concomitant with this loss in the ability to redistribute Con A receptors, cells become agglutinable by a tissue-specific component first described in 1975.

The results of our experiments assaying inhibition of capping by tissue culture supernatant solutions and loss of capping ability through cellular repair processes are interpreted in terms of an endogenous pool of one or more species, which, when displaced to the cell surface, inhibit the capping of Con-A receptors and permit tissue-specific cell agglutination. Once present at the cell surface, these species are released into the culture medium, either during continuous culture or during an incubation in fresh medium containing cycloheximide. Subsequent to release of these species, the cells regain their capacity for cap formation and lose agglutinability. In addition, the components released from the cells inhibit capping of Con A receptors when added to freshly dissociated cells.

The assay methods were also used to determine parameters governing mobilization of the pool of capping inhibitors to the cell surface.
Distribution of anionic sites on surface of b cell granule and plasma membranes: a study using cationic ferritin
Authors: Howell S. L. , Tyhurst Margaret
Published: April 2021

The distribution of anionic sites on the membranes of rat pancreatic B cells and of their storage granules has been studied by the use of a visual probe of cationic ferritin. Membranes of isolated storage granules possessed a net negative charge which was apparently evenly distributed; the number of anionic sites was not markedly altered by prior incubation of the granules with neuraminidase or with 10−6 to 2 × 10−3 M calcium chloride. Distribution of charges along B cell plasma membranes was less uniform but was similarly unaffected by alterations of calcium concentration, or by neuraminidase treatment. However, during the fusion of plasma membrane and granule membrane which occurs in exocytosis, the emerging granule membrane was found to be devoid of anionic sites. The implications of these findings for the regulation of insulin secretion by exocytosis are discussed.
Endotoxin-induced platelet aggregation and secretion I. morphological changes and pharmacological effects
Authors: Macintyre D. Euan , Allen Anthony P. , Thorne Kareen J. I. , Glauert Audrey M. , Gordon John L.
Published: April 2021

Endotoxin lipopolysaccharide (LPS) from Acinetobacter 199 A induced aggregation of blood platelets from immune adherence-positive species (rat, rabbit) but not from immune adherencenegative species such as pig and man. Aggregation occurred in 2 phases: the first was not accompanied by secretion of platelet constituents, was apparently a consequence of C3 activation, and was selectively inhibited by EGTA. The second phase of aggregation was associated with secretion of platelet granule contents, and with a lesser amount of cytoplasmic leakage. Secondary aggregation was abolished by the sulphydryl alkylating agent N-ethyl maleimide, and by agents which increased the level of cyclic AMP in platelets, such as prostaglandin Et (a stimulator of adenylate cyclase) and methyl xanthines (inhibitors of phosphodiesterase). Secondary aggregation was partly inhibited by agents which block platelet prostaglandin biosynthesis (e.g. aspirin, indomethacin). Primary aggregation was unaffected by these inhibitors at concentrations which blocked secondary aggregation.
Endotoxin-induced platelet aggregation and secretion. II. changes in plasma membrane proteins
Authors: Thorne Kareen J. I. , Oliver Rhonda C. , Macintyre D. Euan , Gordon John L.
Published: April 2021

Responses of blood platelets to bacterial endotoxin lipopolysaccharide (LPS) have been correlated with changes in the molecular organization and composition of the platelet plasma membrane proteins. Binding of LPS, which occurred in the absence of Ca2+, was distinguished from platelet aggregation and degranulation, which required Ca2+ and plasma proteins.

Changes in membrane organization were detected by double-labelling with [l25I] and [131I] iodide, mediated by lactoperoxidase and hydrogen peroxide. Changes in total membrane composition were detected by gel electrophoresis of isolated membranes. Binding of LPS was associated with increased accessibility of a protein of mol. wt. 80000 to iodination. After aggregation and degranulation there was, in addition, increased accessibility of proteins of mol. wt. 68000 and 48000. Isolated membranes from LPS-stimulated platelets contained more of a protein of mol. wt. 200000 and less of a protein of mol. wt. 220000 than control membranes prepared from unstimulated platelets in the presence of cAMP and aminophylline.

The relationship of the modified plasma membrane proteins to the contractile proteins of the platelet and their possible redistribution in the cell during aggregation and secretion is discussed.
Interaction of glycosaminoglycan and adenylate cyclase at the surface of cultured human diploid fibroblasts (HLM15)
Authors: Kelley Robert O. , Palmer Gene C. , Crissman Harry A. , Nilson John H.
Published: April 2021

To determine whether glycosaminoglycan-containing (GAG) components of embryonic cell surfaces are associated with adenylate cyclase, human limb mesenchymal cells (HLM15) in exponential and stationary conditions were incubated in testicular hyaluronidase (300 lU/mg) prior to analysis of enzyme activity (stimulated with 10−4 M norepinephrine, NE). Treatment with NaF revealed an active catalytic component of the adenylate cyclase system. However, little activity of adenylate cyclase was observed after incubation of exponential growth control groups with NE. Removal of GAG increased enzyme activation by NE over that of controls, suggesting the presence of a developed but masked receptor component. Untreated, stationary cells after incubation in NE showed enzyme activity similar to that of hyaluronidase-treated cells in exponential growth. Patterns of distribution in G1S and G2+ M after enzyme treatment were identical to controls. In addition, cells incubated for 4 h in growth medium containing NE had normal cell cycle distributions. HLM15 cells incubated in medium containing dibutyryl cyclic AMP (dbcAMP: 10−5 to 10−8 M) had population doubling times of 40 + h (in contrast to a 24-h generation time for controls) and exhibited a consistent perturbation of S. Cells incubated in hyaluronidase and cultured for 4 additional hours in NE show a pattern of perturbation in S identical to that of cells cultured in dbcAMP. Furthermore, these cells exhibit increased incorporation of [3H]uridine into RNA when compared to untreated cells. We conclude that HLM15 cells have developed both receptor and catalytic components of the adenylate cyclase system and that enzyme receptivity to hormone stimulation is enhanced when cell-surface GAG is reduced.
Association of membrane cisternae and macrotubules in vinblastine-treated histiocytes
Authors: Schliwa Manfred
Published: April 2021

Resting histiocytes within the dermis and epidermis of the cichlid fish Pterophyllum scalare exhibit an unusual association between stacks of lamellar cistemae and tubular structures greater in diameter than ordinary microtubules (macrotubules) after treatment with 2 × 10−4 M vinblastine. Macrotubules are found in the intercistemal spaces in a regular side-by-side orientation and extend the entire length of the cisternae. The lamellae seem to be formed as a result of increased membrane proliferation of the outer nuclear membrane; in some instances, cistemae have been observed to be continuous with the nuclear envelope. Since blebbing of the outer nuclear membrane is also observed in untreated histiocytes, lamellae formation is envisaged as hypertrophy of a normally occurring process. The association of lamellae with macrotubules possibly indicates a relationship between membranes and microtubule proteins.
Cell contact-induced inhibition of division in Dictyostelium
*
Authors: Kopachik Will J. , Gregg James H.
Published: April 2021

The developmental stage at which Dictyostelium discoideum strain v12/M2 cells was inhibited in resuming cell division was monitored by a Coulter counter. Neither vegetative nor preaggregating v12/M2 amoebae used as inocula in liquid growth cultures exhibited a delay in recommencing cell division. Inocula prepared from aggregates were delayed for 3 h before the onset of division. Although cyclic AMP had no effect upon vegetative or preaggregating stages the aggregating amoebae were inhibited for 9 h before resuming division. Following the onset of division by both controls and cyclic AMP-treated cells the normal growth rate of vegetative amoebae (3·2 h/generation) was attained. Aggregateless mutant vegetative amoebae and those of comparable ages to v12/M2 aggregates were not inhibited in the rate of cell division by cyclic AMP.

Cyclic AMP sustains the delay in cell division only among amoebae derived from aggregates. Cyclic AMP induces structural components in the plasma membranes which may be necessary in cell adhesion and interactions. Consequently interactions between the membranes of apposing cells may transmit stimuli intracellularly to inhibit cell division.
Fluorescent staining of fungal nuclei with a benzimidazol derivative
Authors: Lemke Paul A. , Kugelman Bertha , Morimoto Hideo , Jacobs Ernest C. , Ellison John R.
Published: April 2021

A direct staining procedure is described for fluorescence microscopy of fungal nuclei, chromosomes and mitochondria. The fluorochrome is a benzimidazol derivative (33258 Hoechst) known to bind selectively to deoxyribonucleic acid at neutral pH. The advantages of 33258 Hoechst relative to Feulgen compounds used previously to stain these structures include a greater intensity of fluorescence, the absence of fading or rapid quenching of the fluorescence, and the omission of acid hydrolysis from the procedure for removal of ribonucleic acid. 33258 Hoechst has been evaluated as a nuclear stain with a yeast (Saccharomyces cerevisiae) and a filamentous fungus (Agaricus bisporus) and appears to penetrate easily vegetative cells and spores of both fungi.
Studies on the incorporation of dna into Paramecium Aurelia
Authors: Gibson I.
Published: April 2021

Attempts have been made to transform the cell Paramecium aurelia with DNA preparations. No success was achieved for the genes concerned with maintenance of killer particles or surface antigens. Using radioautography, density gradient ultracentrifugation and nucleic acid hybridization it was shown that extracellular DNA was taken up by paramecia and remained as long nucleotide sequences. Possible reasons for the failure of transformation in the face of such observations are given.
Sarcomere length during post-natal growth of mammalian muscle fibres
Authors: Goldspink G.
Published: April 2021

The length of the sarcomeres, the A- and the I-filaments and their percentage overlap were measured in the fibres of the biceps brachii muscle from mice of different ages. The sarcomere length with the limb in the fully extended position was found to increase from 2·3 μ in the newborn animal to 2·8 μ in the adult. This increase was due to a decrease in the percentage overlap of the filaments and not to any change in the filament lengths. The sarcomeres at the ends of the fibres were found to be shorter than those in the middle of the muscle, at all ages. When the muscles were stretched beyond their resting length, only about the middle 60 % of the sarcomeres in the young muscles increased in length. Length/tension plots were obtained for young and old muscles and the difference in the shape of these plots could be explained as being due to the non-functional terminal sarcomeres of the young muscles. The maximum tension developed by the young muscles was found to be attained at an initial muscle length about 10 % greater than their length at maximum limb extension. The adult muscles developed maximum tension at their length at maximum limb extension.
The response of human cultured lymphocytes to cytochalasin b
Authors: Ridler M. A. C. , Smith G. F.
Published: April 2021

The cytochalasins are a new group of compounds which have been recently isolated from moulds. Some of their properties are of interest in the study of cytoplasmic and nuclear division since they have been shown to inhibit motility, produce nuclear extrusion and prevent cytoplasmic cleavage with the production of multinucleated cells. The present study is a report of the effects of cytochalasin B on cultured human lymphocytes.

After exposure to cytochalasin B, a proportion of the cultured human lymphocytes became multinucleate. The magnitude of this effect was related to the concentration and the length of time of exposure to the compound. Cells with from one to eight nuclei were identified. Progressive variation in nuclear morphology became apparent as the number of nuclei in a cell increased. Examination of the chromosomes showed only diploid, tetraploid and a few octa-ploid cells. No obvious chromosomal abnormalities were detected, except in octaploid cells. It is suggested that in multinucleated cells there may be a failure of mitotic control leading to variations in size and shape of interphase nuclei.
The effect of antrycide on patterns of rna synthesis in Amoeba discoides
Authors: Summers Julie M. , Hawkins Shirley E.
Published: April 2021

Antrycide is an aminoquinaldine whose inhibitory action on the growth of Trypanosoma and Crithidia is not fully understood at the cellular level. The growth of Amoeba discoides in concentrations of antrycide between 0·5 and 2 was reduced considerably, while cells failed to divide in 4 μg/ml. The effects on growth rate were reversible at least up until 7 days in antrycide.

In order to assess the action of this synthetic drug on RNA synthesis in amoebae, the pattern of synthesis in normal cells was investigated using polyacrylamide gel electrophoresis. The profile of high molecular weight RNAs observed depended on the length of time in [3H]uridine, and was only fully developed after 66 h, when 5 peaks could be seen. The relative molecular weights of these peaks (I-V) were 2·45, 1·55, 1·13, 0·8 and 0·52×106 Daltons respectively. Those of 1·55 and 0·8 × 106 corresponded to ribosomal RNAs, the identity of the other peaks is unknown.

After growth in 2 μg/ml antrycide for 4 days, no high molecular weight RNA was found. Use of [14C]adenine/[3H]uridine showed that after 17 h in antrycide there was a loss of ribo-somal RNA and increased levels of low molecular weight RNAs, due either to lack of synthesis or to degradation of newly synthesized material. Incorporation of [3H]leucine into hot acid-precipitable protein was inhibited in antrycide-treated cells by at least 50%. A possible explanation of the effect of antrycide on A. discoides was the inhibition of mRNA synthesis for ribosomal proteins, leading to degradation of newly synthesized rRNA. Reduced growth would continue on pre-existing ribosomes and previously synthesized long-lived mRNAs.
Membrane junctions in the myelin sheath of goldfish lateral nerve
Authors: Bertaud W. S.
Published: April 2021

The myelin sheath of the goldfish lateral line nerve has been studied by means of the freezeetch technique. Fracture faces of the myelin lamellae reveal linear structural elements which in some respects resemble those of tight junctions. In unfixed myelin rows of particles on the ef face are matched by narrow grooves on the pf face. Fixation with glutaraldehyde produces a partitioning of junctional particles between the 2 fracture faces. These elements are observed most frequently in the outer layers of the sheath where their arrangement is predominantly more or less parallel and longitudinal, merging in places into a more reticulate organization. They also occur at other levels in the myelin and in association with Schmidt-Lantermann clefts. Orientation in these cases appears to be predominantly longitudinal, though circumferentially running elements have been observed. The possible functional significance of these structures and their implications for tissue development, maintenance and growth are discussed.
Direct visualization of the 10-nm (100- Å)-filament network in whole and enucleated cultured cells
Authors: Small J. V. , Celist J. E.
Published: April 2021

Following extraction of actomyosin and tubulin from cultured cells treated with Triton X-100, a cytoskeleton remains which is composed predominantly of the cell nucleus encompassed by a network of 10-nm filaments. After negative staining the dense perinuclear region appears as a densely woven filament net punctuated by patches of high electron density. Enucleation of 3T3cells with cytochalasin B gives rise to karyoplasts surrounded by 10-nm filaments and cytoplasts in which 10-nm filaments remain situated in the central region of the cytoplasm. While the 10-nm filaments occurred mainly as single filaments in human skin fibroblasts and 3T3cells, in epithelioid PtKi and PtK2 cells they were commonly associated in prominent meandering bundles. In addition, in these latter cells after Triton extraction the remaining ribosomes were bound specifically to the 10-nm-filament net.

After exposure of 3T3cells to cytochalasin B the 10-nm filaments formed branches that radiated from the perinuclear region into the immobile cell extensions. Concavalin A had no marked effect on the distribution of the 10-nm-filament net.

The results suggest that the 10-nm filaments act primarily as structural elements, serving, in particular, to support and constrain the nucleus in its position in the cell.
The induction of the acrosome reaction in guinea-pig sperm by the divalent metal cation ionophore a23187
Authors: Green D. P. L.
Published: April 2021

The divalent metal cation, ionophore A23187 induces an acrosome reaction in guinea-pig sperm which is dependent on external calcium. Examination of this acrosome reaction by electron microscopy shows that it is morphologically normal. The known properties of A23187 and the morphological similarity between the acrosome reaction and the secretory discharges of other secretory cells suggests that the immediate cause of the acrosome reaction is an increase in the cytoplasmic free calcium concentration.