bluuebunny/crossref_metadata_2025 huggingface dataset:
On the differential divisions and preprophase microtubule bands involved in the development of stomata of Vigna Sinensis
Authors: Galatis B. , Mitrakos K.
Published: April 2021

The manifestation of premitotic cell polarity and the resultant structural asymmetry of the differential divisions participating in the development of stomata of Vigna sinensis vary considerably. However, two morphologically distinct types of differential division were distinguished : (a) ‘asymmetrical differential divisions ‘, in which the premitotic polarization of the cell, the eccentric position of the nucleus during division and the differences in size and organization of the daughter cells are obvious; and (b) differential divisions in which the above features are inconspicuous or almost absent. The former occur in the ordinary protodermal cells, the latter in some meristemoids.

The organization of a sharply demarcated preprophase microtubule band (PMB) precedes, all differential and non-differential divisions. In the first type of differential division the PMB is formed eccentrically, while in the second it may display either an approximately symmetrical or a clearly asymmetrical disposition, always indicating with surprising accuracy the sites where the succeeding cell plate will join the parent walls. The PMB foreshadowing the highly curved cell plates in meristemoids I of the mesoperigenous process, as well as in meristemoids I and II of the mesogenous one, are apposed only on one anticlinal wall and therefore do not encircle the nucleus or traverse the cell.

In the symmetrical divisions of guard cell mother cells (GMC), as well as in those of proto-dermal cells, the PMB runs right round the internal plasmalemma surface in an equatorial position, coinciding with that of the future cell plate. In the former cells the wall abutting the cortical cytoplasm traversed by the band becomes locally thickened. The variability in the pattern of the microtubules of the band along the walls of the GMC is directly mirrored in the pattern of the thickening. It seems that in GMC the PMB mediates a directed exocytosis of dictyosome vesicles.

In contrast to what is now generally accepted in dicotyledonous plants, each meristemoid I of both the mesogenous and mesoperigenous stomata in Vigna sinensis leaves does not inhibit but induces the formation of other meristemoids close to it.
Cell-to-substratum contacts in living cells: A direct correlation between interference-reflexion and indirect-immunofluorescence microscopy using antibodies against actin and A-actinin
Authors: wehland Jürgen , Osborn Mary , weber Klaus
Published: April 2021

Rat mammary cells growing on glass coverslips were photographed first using interferencereflexion microscopy and then after processing for indirect-immunofluorescence microscopy with antibodies to actin or to α-actinin. A comparison of the images of the same cell given by the 2 microscopical procedures indicates that the focal contacts between the cell and the substratum correspond to distal ends of microfilament bundles, and that these bundles are only in limited areas close to the substratum. The focal contacts are rich in α-actinin which has been proposed as a membrane-anchorage protein for microfilament bundles. Use of stereo immunofluorescence microscopy allows a direct comparison between the interference-reflexion image, and the underside of the cell after staining with antibodies to actin or α-actinin.
A morphological study of the interaction between Trypanosoma Cruzi and rat eosinophils, neutrophils and macrophages In Vitro
Authors: Sanderson Colin J. , Souza Wanderley de
Published: April 2021

The interaction between trypomastigotes of T. cruzi and purified rat eosinophils, neutrophils and macrophages has been studied. Macrophages induced by dextran, became infected and the parasites multipliedasamastigotes, eventually beingreleased as trypomastigotes into the medium. Eosinophils show an antibody-dependent phagocytosis, while neutrophil phagocytosis is enhanced by antibody. Electron microscopy showed that once inside the granulocyte phagosome, the trypomastigotes transform to amastigotes as a prelude to degeneration. This occurs as material apparently of granule origin accumulates in the phagosome. Eosinophils have the capacity to eject incompletely degenerated amastigotes into the medium. This phenomenon is discussed in relation to previous time-lapse cinematography studies of the lysis of chick erythrocytes by eosinophils, and reports that eosinophils release granule contents by means of a secretory vesicle.
An ultrastructural study of the effects of wheat germ agglutinin (WGA) on cell cortex organization during the first cleavage of Xenopus Laevis eggs: I. inhibition of furrow formation
Authors: Geuskens M. , Tencer R.
Published: April 2021

Xenopus laevis fertilized eggs have been treated with wheat germ agglutinin (WGA) before the onset of the first cleavage, at the stripe stage and during groove deepening. The ultrastructure of the animal cortex of the arrested embryos has been compared with that of the same region of control embryos at different stages of first furrow formation and of cytochalasin B-treated embryos. The outer side of the plasma membrane of WGA-treated embryos is covered with a coat which is different from the diffuse material observed in either control or cytochalasin B-treated embryos and which is distributed in patches in the groove region. Narrow indentations of the plasma membrane in the cortex of WGA-treated eggs have been observed, particularly in the blocked or regressed groove. In WGA-treated eggs, a few bundles of microfilaments are located under the plasma membrane at the animal pole, but they are never arrayed in a continuous layer as in the control eggs. In the latter, many microtubules are located in close proximity to the microfilament layer at the beginning of cleavage, but they are only occasionally observed in the same region of WGA-treated eggs.

It is concluded that the binding of WGA molecules to their receptors on the surface of the Xenopus zygote interferes with the alignment of microfilaments in the furrow region and provokes the disorganization of the aligned microfilaments once the cleavage has begun. Internalization of portions of the nascent membrane in the groove could play an important part in the arrest of cleavage.
Transfer of mouse nuclear envelope specific proteins to nuclei of chick erythrocytes during reactivation in heterokaryons with mouse a9 cells
Authors: Jost Erich , d’arcy Allan , Ely Susan
Published: April 2021

When chick erythrocyte nuclei are introduced into the cytoplasm of mouse A9 cells by cell fusion, proteins present in a fraction of the mouse nuclear envelope begin to appear in the envelope of the chick erythrocyte. The protein uptake was examined using antisera raised in chickens against the 3 major polypeptides of the nuclear pore complex-fibrous lamina fraction from rat liver nuclei. In indirect immunofluorescence studies these antisera give a strong envelope-specific Staining with various mammalian but not chicken cells.

Eighteen hours after cell fusion the first murine antigens can be observed in the erythrocyte nucleus. Two days after cell fusion the vast majority of the erythrocyte nuclei in cell hybrids contain some antigen and by 3 days the fluorescence of the reactivated erythrocyte nuclei reaches a level comparable to that of the mouse A9 nuclei. The rate of appearance of fluorescence in the chick nuclei depends upon the ratio of A9 cytoplasm to chick nuclei. Antigen uptake by the erythrocyte envelope is inhibited when protein synthesis is blocked suggesting that synthesis of mouse antigen, rather than a redistribution, determines the velocity of erythrocyte envelope reactivation. The early uptake of nucleospecific protein into the reactivating chick erythrocyte may not require any alteration in the nuclear envelope.
Cytology, growth characteristics and cellular alterations following SV40-induced transformation of human foetal brain cells derived from a Gm2 gangliosidosis and control
Authors: Brooks Steven E. , Amsterdam Daniel , Hoffman Linda M. , Adachi Masazumi , Schneck Larry
Published: April 2021

Cell cultures were derived from the cerebra of a control and a Gm2 gangliosidosis (Tay-Sachs disease (TSD)) foetus. Both cell lines were identified as astrocytic, based on the ultrastructural demonstration of glial fibres. The control culture exhibited morphological differentiation when exposed to dibutyryl cAMP, a finding which was not observed with the TSD cells. The TSD culture demonstrated the pathobiological features of the disease, which included the absence of hexosaminidase A, increased concentration of Gm2 ganglioside and the detection of membranous cytoplasmic bodies by electron microscopy.

Control and TSD cells were exposed to SV40 virus, resulting ultimately in the isolation of transformants which differed from the parental cell types in morphology, growth rate and greatly accelerated cell death. Both control and TSD cell lines have been in propagation for over 200 subcultures and the transformants were identified as astrocytic, based on the retention of characteristic glial fibres. The control culture demonstrated a chromosome range of 34-63, with a mean of 47. In contrast, the TSD transformants exhibited a range of 50-107 and a mean of 74. Transformed lines retained their parental hexosaminidase isoenzyme profiles; Hex A and B in control, and Hex B in TSD cells. Membraneous cytoplasmic bodies persisted in the TSD line. Neither line could be induced to differentiate after exposure to cAMP. Additionally, they had a population doubling time of under 85 h and failed to release infectious virus particles.

Significant alterations in the total quantity and distribution profile of gangliosides were noted following viral transformation. A large increase in the percentage of Gm3 and a more modest increase in Gm2 were detected. In contrast, transformed lines were characterized by substantial reduction in the percentage of glucosamine-containing Gm2 and polysialoganglioside. Additionally, cultures exhibited a characteristic reduction in gangliosidc content after trans formation.

The in vitro transformation of human brain cells has resulted in the derivation of permanent astrocytic lines which arc, by virtue of their rapid growth rate and long-term survival, uniquely suited and adapted to the large scale in vitro production of substantial quantities of cells required for extensive biochemical study. Significantly, those characteristics which are unique to the Gm2 gangliosidosis storage disease have been retained in a permanent model CNS cell line.

*All correspondence should be addressed to: Dr Daniel Amsterdam, Kingsbrook Jewish Medical Center, Rutland Road & East 49th Street, Brooklyn, New York, n203, U.S.A.
Detection of small amounts of human DNA in human−rodent hybrids
Authors: Rodgers A.
Published: April 2021

A method of measuring semi-quantitatively small amounts of human DNA in irradiated human × mouse and irradiated human × Chinese-hamster somatic cell hybrids is described. One method uses molecular hybridization of cell DNA bound to nitrocellulose filters with a cRNA probe to Cot 0–1 human DNA. Alternatively hybrid cell DNA is reassociated in solution with a Cot 0-1 fraction of nick-translated human DNA. Formamide buffers give specificity to the reaction. The detection limit of the filter method is 0·2–0·5 % equivalents and reassociation kinetics 0·005−0·01 % equivalents of a human genome.

Experiments with cell hybrids suggest that a fragment of repetitive DNA may be retained along with the selected genes after a cell fusion. In one case however, of a hybrid cell in which malignancy is suppressed, highly repetitious sequences were not found.
Structural changes in the pollinated and unpollinated avocado stigma and style
Authors: Sedgley Margaret
Published: April 2021

Structural changes in the pollinated and unpollinated avocado (Persea americana Mill) stigma and style up to 42 h after first opening of the flower were investigated using light and electron microscopy. The pollen tubes grew in the stigma secretion and intercellular substance and initial contact occurred between the plasma membrane of the male and the cuticle and stigma secretion of the female. The pollen tube wall started to develop 15 min after pollination and increased in thickness up to 24 h after pollination.

By 18 h after first opening of the flower, starch had disappeared and cell wall thickenings were present in both the pollinated and unpollinated stigma and style. The wall thickenings developed more slowly in the upollinated than in the pollinated tissue. They contained lipid and were bounded by callose. Degeneration of the cytoplasm of some of the papilla and transmitting tissue cells occurred only following the passage of the pollen tubes and may be of importance in tube nutrition. There was no degeneration in the unpollinated stigma and style and the cytoplasm did not start to lose clarity until 42 h after first opening of the flower.
Ultrastructural localization of calcium-binding sites in the electrocyte of electrophorus electrices (L.)
Authors: Jorge T. C. De Araujo , Souza W. De , Machado R. D.
Published: April 2021

Calcium-binding sites were detected in the electrocyte of Electrophorus electricus (L.) using the Oschman & Wall technique, in which CaCl2 was added to the fixative and washing solutions. Deposits were seen scattered along the plasma membrane of the electrocyte, inside mito-chondria, associated with the post-synaptic membrane and the membrane of synaptic vesicles.
Epithelial-fibroblastic organization in cultures grown from human embryonic kidney: its significance for morphogenesis in vivo
Authors: Bard Jonathan B. L.
Published: April 2021

The morphological behaviour of explants of human embryonic kidney has been studied in order to investigate the rules governing interactions between epithelial and fibroblastic cells from the same tissue. When the fragments are cultured, epithelia migrate out first and are followed, a few days later, by cables which grow out from the fragments and which are composed of multilayered fibroblasts. These cables extend through the epithelia to reach the substratum, to which they adhere. The epithelia maintain an upper surface free of spread fibroblasts and are unable to multilayer, although occasional rounded-up cells adhere to this surface. Fibroblasts, however, not only multilayer in the cables but can act as a substratum for epithelial cells which migrate on the cable surface. Fibroblasts and epithelia from kidney thus follow the same behavioural rules that govern the interactions between kidney epithelia and fibroblasts from different tissues. The suggestion that these rules derive from tissue differences and that cells from the same tissue are more tolerant of one another is not borne out. These observations and those reported by others are interpreted in terms of the functional properties of the cells in vivo. It is further pointed out that only those epithelia that maintain a free surface in vivo would be expected to show this property in vitro. Finally, the implications of cells with essentially the same properties generating more than one structure are considered.
Sodium and potassium in oocytes of Triturus cristatus
Authors: Riemann W. , Muir C. , Macgregor H. C.
Published: April 2021

Newt oocytes were dissected under liquid paraffin and known volumes of clean nucleoplasm and cytoplasm were obtained from oocytes in different stages of oogenesis. The samples were digested in redistilled nitric acid, diluted with deionized water, and their Na and K contents were measured by flame spectrophotometry. The results were expressed as micro-equivalents of Na and K per millilitre of nucleoplasm or cytoplasm. In oocytes of 0·3—0·5 mm diameter nucleoplasm and cytoplasm have similar Na and K concentrations, and the molar K:Na ratio is about 3:1. As the oocyte grows to maturity the nucleoplasmic Na and K concentrations do not change, but the cytoplasmic K concentration falls steadily until, in nearly mature oocytes, the cytoplasmic K:Na ratio is near 1:1. Measurements of Na and K concentrations in yolky and clear cytoplasm show that both fractions have the same K content and the concentration of K decreases in both fractions as the oocyte grows. The significance of these results is discussed in terms of the possible effects of changes in the intracellular ion balance on the morphology and synthetic activity of the chromosomes.
The fine structure of photoreceptors in Mitopus morio (phalangida)
Authors: Curtis D. J.
Published: April 2021

Fine structural studies on the eyes of the harvestman Mitopus morio revealed the presence of microvilli in the rhabdom. The microvilli vary in length between 1 μand 2 μ, are about 800 Å wide, and curved or straight. They derive from the plasma membranes of the four retinula cells which surround the rhabdom. Approximately cylindrical in shape, the rhabdoms are about 40 μ long by about 4–6 μ in cross-diameter. Each rhabdom is situated at the centre of a retinula, and these retinulae are packed in a hexagonal array to form the retina. Distally, rhabdom fusion occurs to form a rhabdom network. The retina lies beneath the dioptric apparatus which consists of a single lens, surmounting a glassy body composed of lentigen cells.

The cytoplasmic organelles of the retinula cells include mitochondria, lysosomes, sparse elements of endoplasmic reticulum, vesicular components, prominent Golgi complexes and pigment granules which possess a laminated structure. An important feature of the retinula cell is the presence of many small vesicles, about 0·1μin diameter, clustered beneath the rhabdom. Incubation of glutaraldehyde-fixed eyes in a Gomori medium with acetylthio-choline as substrate, coupled with inhibition of controls by 62C47, indicates the presence of a presumed acetylcholinesterase in these vesicles. Similar vesicles also occur in the proximal cytoplasm of the retinula cells. Other larger vesicles, often with a core of whorled membranes, as well as dense bodies, also show acetylthiocholine-splitting activity. This latter activity is not inhibited by 62C47 and is probably the effect of lysosomal non-specific esterase. These bodies also exhibit acid phosphatase activity when incubated in a Gomori medium with β-glycerophosphate as substrate.

The presence of acetylcholinesterase activity, as distinct from non-specific esterase, in vesicles closely associated with the rhabdom and in more proximally situated vesicles is significant. It would point to the presence of an acetylcholine/acetylcholinesterase system involved in the generation and/or propagation of the sensory impulse arising from photo-stimulation of the rhabdom.
Changes in extracellular space of the mouse cerebral cortex during hydroxyadipaldehyde fixation and osmium tetroxide post-fixation
Authors: Harreveld A. Van , Khattab F. I.
Published: April 2021

Perfusion of the cerebral cortex of mice with a 4·5 and 12·5 % hydroxyadipaldehyde (HAA) solution in a cacodylate buffer caused a biphasic change in the tissue conductivity. After a latency of a fraction of a minute the cortical conductivity dropped markedly, reaching a minimum in 1·5–2 min. Then the conductivity increased again. Electron micrographs (EMs) of material perfused with HAA for 1 5—20 min and post-fixed with osmium tetroxide showed electron-transparent swollen structures, some of which could be identified as dendritic. The extracellular space consisted of 100–200 Å slits between the tissue elements and larger spaces in bundles of small profiles (unmyelinated axons). Cortex frozen after 2 min perfusion with HAA and subjected to substitution in acetone containing 2 % OsO4 at—85 °C showed swollen (dendritic) structures and a paucity of extracellular material in accordance with the conductivity drop. Often tight junctions between the tissue elements were present. Tissue frozen after 15–20 min of HAA perfusion when the conductivity had increased again yielded EMs which were characterized by an abundance of extracellular space between the small profiles. The mitochondria in the swollen (dendritic) structures were enormously enlarged. Cortex perfused for 15–20 min with HAA, post-fixed with OsO4 and then freeze substituted produced EMs resembling those of tissue fixed in the same way but not subjected to freeze substitution. The examination of the fixation process by freeze substitution demonstrated a sequence of major changes in the fluid distribution of the tissue which precludes any direct relationship between the spaces in the normal and fixed tissue.
Some evidence for the continuity of ciliary fibrils and microtubules in the insect sensory dendrite
Authors: Slifer Eleanor H. , Sekhon S. S.
Published: April 2021

Evidence has been obtained that the microtubules of the insect sensory dendrite may originate from the nine pairs of peripheral fibrils in the ciliary portion of the dendrite and retain direct continuity with them. The peripheral fibrils separate and each of the single fibrils resulting appears to divide one or more times. The number of microtubules within the dendrite distal to the ciliary region often lies close to 18 or to a multiple of 18, such as 36 or 72. If our interpretation is correct, the basal bodies, their rootlets, the ciliary fibrils and microtubules of the insect sensory dendrite form a continuous structure with the probable function of a cytoskeleton.
The fine structure of Cricosphaera carterae: I. external morphology
Authors: Pienaar R. N.
Published: April 2021

The external morphology of Cricosphaera carterae is demonstrated using shadow, replicating and thin section techniques. The covering of the cell was found to be composed of three forms of scales which differ from one another in size and ornamentation. The largest of the three scales serves as the organic matrix on which the calcium carbonate is deposited to form the characteristic coccolith. The structure of these scales is discussed.
The regulation of amounts and proportions of genetic elements in the macronuclei of Tetrahymena thermophila strains of diverse karyotype
Authors: Seyfert Hans-Martin , Preparata Rosa Maria
Published: April 2021

Measurements of the micronuclear DNA content of clones with assumed different degrees of micronuclear ploidy confirmed the triploid nature of one clone. The micronuclear DNA content of a presumptive haploid clone was found to be slightly higher than expected, whereas one of two aneuploid clones had an unexpectedly low micronuclear DNA content.

The macronuclear DNA content of cells with macronuclei which had developed from triploid, diploid and probably haploid and aneuploid macronuclear-Anlagen is very similar. Specifically, the smallest individual macronuclear DNA contents are consistently found within the same size class in all clones tested.

Cell volumes, RNA and protein contents are alike in all clones tested. Only the growth rate and maximal density reached of one out of two aneuploid clones is reduced in comparison with the very similar other clones.

The results are discussed with reference to the regulation of macronuclear DNA content, and to the compensation of gene-dosage.
Quantitative replicon analysis of dna synthesis in cancer-prone conditions and the defects in bloom’s syndrome
Authors: Ockey C. H.
Published: April 2021

A quantitative method of replicon analysis of DNA fibre autoradiographs has been used to study the relationship between mean rate of DNA chain growth (R) and distance between adjacent replicons (ID) in fibroblasts from cancer-prone conditions. Results are expressed in terms of the mean linear regression R = δ + (K.ID) 10−2. When replicon behaviour was examined in cells from patients with ataxia telangiectasia, basal cell naevus and Bloom’s syndromes grown at high density after 48 h in culture, no significant differences could be found in replicon behaviour between these syndromes and normal cultures. How ever when Bloom’s cells were grown at low density and examined 24 h earlier, the mean rate of chain growth R was reduced compared to normal cells at the same density. Both cell types at high densities at 24 h showed equal but lower R values than at 48 h after plating the cultures. The lower rate of chain growth in Bloom’s was accompanied by a longer S-period and cell cycle.

Studies of cell proliferation kinetics using consecutive mitoses after bromodeoxyuridine (BUdR) incorporation and harlequin banding showed that Bloom’s cells at low cell density require a longer period to recover a normal cell cycle length after plating than do normal cells at the same density. Plating at higher densities and using conditioned media shorten the recovery period in Bloom’s cells, and when foetal calf serum/MEM is replaced by human AB serum/McCoy 5a medium as the growth media, cell cycle behaviour of low density Bloom’s and normal cells are equal at a much earlier time. It is concluded that the slow rate of DNA chain growth in Bloom’s cells is an artefact introduced by culture conditions and also may be present in normal cells at an earlier period. The behaviour of replicons during this recovery period appears to be similar in Bloom’s and normal cells except for the time lag. As recovery proceeds, the DNA chain growth in the associated replicon pairs recover progressively. This alters both the mean R value from 0·4 to 0·8 μm/min, the slope of the regression K from < 1·0 1·0 ∼ 1·0 while the distance between initiation sites (ID) remains constant throughout. Pretreatment of all cultures with fluorodeoxyuridine (FUdR) produced the same differential effect on release from DNA synthesis inhibition, that is a similar increase in the activation of normally inactive replicons and a slightly slower rate of chain growth over all replicons.

No evidence of a substance released by Bloom’s cells in culture capable of increasing the sister-chromatid frequency in normal cells could be found. Since SCE frequencies were found to increase with fixation time after BUdR introduction it is concluded that some of the reported changes could be due to differences in cell cycle kinetics brought about by the different media conditions.
Pigment mutants of Chlamydomonas with deformed plastids and increased levels of chloroplast nucleic acids
Authors: Wilson Ronald E. , Swift Hewson , Chiang Kwen-Sheng
Published: April 2021

The chloroplast ultrastructure of two Chlamydomonas rcinhardtii pigment variant mutants, U3N and U3A, is strikingly different from that of the wild type. The mutant chloroplast has greatly lowered levels of chlorophyll a and b, and lacks the usual ordered thylakoid membrane structure. The amount of chloroplast ribosomes is increased, but the pyrenoid and surrounding starch grains appear to be unaltered.

Our biochemical analyses have shown that, while the properties of chloroplast DNA, ribosomal RNA, and ribosomes in these mutants appeared to be normal, their relative amounts per cell increased markedly when compared to the wild type. In U3N these increases were approximately 60% for chloroplast DNA and 80% for chloroplast ribosomes. However, the ratio of chloroplast rDNA genes to total chloroplast DNA remained unchanged as shown by DNA–rRNA hybridization.

We propose that (1) The enhanced level of chloroplast ribosomes in these mutants is a direct consequence of the elevated amount of chloroplast DNA. Both of these increases may, in turn, arise from defective mechanism for their control. (2) These mutants grow successfully in the absence of functional photosynthesis, provided an external carbon source is available to them, but functional plastid DNA, ribosomes and protein synthesis may still be a requirement for normal starch metabolism.
The junctional complex in the intestine of Sagitta setosa (chaetognatha): The paired septate junction
Authors: Duvert Michel , Gros Daniel , Salat Christiane
Published: April 2021

The junctional complex of the intestine of Sagitta setosa has been studied in tissues stained with uranyl acetate or after lanthanum impregnation, and by freeze-cleaving. All types of junctions have been characterized in both perpendicular and tangential planes. From the apex to the base of the cell the following junctions occur in this order: a zonula adhaerens; a septate junction where the septa occur in pairs; a pleated sheet septate junction; and numerous gap junctions of the A-type. From the upper part of the cells inwards to the septate junction, the membranes follow a relatively straight path. In the lower part of the cells the membranes are deeply interdigitating. At the intersection between 3 cells a very different junction is to be observed where small units, periodically disposed, bind the membranes of the 3 adjoining cells. Each unit is composed of 3 short segments which bind the cell membranes to a central ring 16 · 6±2 · 3 nm in outer diameter.

The paired septate junction constitutes a new type. Its main features are that the septa are paired and occur in 2 formations, one the ‘loose formation’, with elements between the septa of each pair, and the other, a ‘tight formation’. After lanthanum impregnation, the thickness of each septum is seen to be about 3 nm and the undulation period 12 · 6 ± 1 · 6 nm. On freezefractures 10-nm particles are found on crests on the PF face and in furrows on the EF face. The possible significance of this type of junction is discussed.

The junctional complex described is analogous to those found in various invertebrate epithelia.
Pollen-stigma interaction in Brassica oleracea: The role of stigmatic proteins in pollen grain adhesion
Authors: Stead A. D. , Roberts I.N. , Dickinson H.G.
Published: April 2021

The adhesion of pollen grains to the stigmas of Brassica oleracea was assayed after treatment of the stigmas with protease and/or cycloheximide. Treatment with protease alone adversely affected pollen grain adhesion. However, the adhesive properties of the stigma recovered fully if the stigmas were not pollinated until 2 h after treatment. Immersion of the stigmas in cycloheximide after protease treatment prevented any recovery of the stigmas’ adhesive properties. Cycloheximide treatment alone prevented pollen grain adhesion when pollination occurred later than 1-2 h after treatment but did not affect pollen grain adhesion if pollination occurred immediately after treatment. These results indicated not only that the surface-held proteins of the stigma are involved in pollen grain adhesion, but also that their turnover rate is rapid. Isoelectric focusing of extracts derived from stigmas after protease and cycloheximide treatment showed a marked decrease in staining intensity of 3 protein bands, one of which, a glycoprotein, is known to be present only when the self-incompatibility system is fully functional. These observations suggest a specificity of adhesion between higher plant cells in the presence of the cell wall.
The deformability of bhk cells and polyoma virus-transformed bhk cells in relation to locomotory behaviour
Authors: Erickson C. A.
Published: April 2021

Several aspects of the behaviour of polyoma virus-transformed BHK cells in culture have suggested that they are more deformable than BHK cells. This possibility was tested by applying negative pressure at the cell surface by means of a micropipette. It was found that PyBHK cells in early mitosis are twice as deformable as BHK cells in the same stage. In addition, the taut, non-ruffling margins of both cell types when fully spread are much less deformable than the extending, ruffling leading lamella. The degree of deformability of these cells is correlated with the distribution and organization of microfilaments and, consistent with this, deform-ability increases greatly in the presence of cytochalasin B. The significance of deformability studies such as these is discussed.
The effect of fibronectin and substratum-attached material on the spreading of chick embryo mesoderm cells in vitro
Authors: Sanders E. J.
Published: April 2021

Endoblast and hypoblast tissue, dissected from early chick embryos, was explanted and cultured on glass or plastic substrata. These tissues grew rapidly to form epithelial sheets. Under the same conditions, mesoderm, dissected without the aid of dissociating agents, grew poorly. After 24 h in culture, the mesoderm explants consisted of a sparse outgrowth of fibroblast-like cells. When pieces of mesoderm were seeded onto the dorsal surface of the epithelia, however, the cells penetrated the sheet and rapidly spread on the substratum within 4 h. If the epithelial sheet was detached from the substratum and the mesoderm then seeded onto areas of substratum previously occupied by epithelium, similar rapid spreading occurred. This effect could be produced in the absence of serum. The method used to remove the epithelium (EDTA, detergent or manual dissection) did not influence the result. When the substratum-attached material (SAM) was examined by scanning electron microscopy, 2 types of material were seen. One type appeared to be the remains of detached filopodia and cytoplasmic lamellae, while the other appeared to be of extracellular origin. Both these types reacted positively by immunofluorescence using anti-fibronectin serum. SAM derived from mesoderm reacted negatively. When mesoderm was cultured in the presence of plasma fibronectin on unmodified plastic or glass, spreading was complete in 4–5 h and thus was similar to mesoderm seeded onto SAM. The morphology of mesoderm expiants on SAM or in the presence of plasma fibronectin was more epithelial than on untreated substratum in normal medium. Hypoblast and endoblast cultured in the presence of anti-fibronectin serum failed to spread normally, apparently being unable to attach to the substratum. Mesoderm did not spread rapidly on SAM in the presence of this antiserum. Cycloheximide reversibly inhibited the spreading of hypoblast and endoblast, and this effect could be eliminated, at least for hypoblast, by the addition of plasma fibronectin. Covering attachment sites on the substratum with bovine serum albumin, thereby preventing the attachment of SAM or fibronectin, also inhibited spreading. It is proposed that mesoderm cells have low levels of surface fibronectin in comparison with endoblast and hypoblast, and that this results in a comparatively low adhesiveness, which is important for its morphogenetic activity within the embryo.
The oral apparatus of Tetrahymena: V. oral apparatus polypeptides and their distribution
Authors: Gavin R. H.
Published: April 2021

Two-dimensional electrophoresis was used to resolve approximately 162 polypeptides from the isolated oral apparatus of Tetrahymena thermophila. The molecular weight range was between 110000 and 15000 Daltons. The polypeptides had apparent isoelectric points between pH 3·3 and pH 7·2. Electrophoretic analysis of isolated ciliary axonemes and fractionated oral apparatuses made possible the assignment of polypeptides to structures within the oral apparatus. Approximately 24 polypeptides, including α and β tubulins, are probable components of the basal body-basal plate complex. At least 5 of the oral apparatus polypeptides, including a and β tubulin, are components of the oral apparatus ciliary axonemes. Approximately 138 polypeptides are components of the oral apparatus framework.
Similarities of membrane structure in freeze-fractured Xenopus laevis kidney collecting tubule and urinary bladder
Authors: Brown Dennis
Published: April 2021

The collecting tubule of Xenopus laevis kidney is formed of two main types of cell: the socalled flask cells (or mitochondria-rich cells) and the remaining, more cuboidal epithelial cells. It has previously been shown that the flask-cell plasma membrane contains a population of elongated intramembrane particles similar to those found in mitochondria-rich cells of the toad bladder. It is now clear that the structure of the apical membrane of the remaining epithelial cells of the collecting duct is similar to the apical membrane of the amphibian urinary bladder granular cells. The P-face of the apical membrane has relatively few particles, whereas the E-face has many more. The E-face particles are of large diameter (16 nm), and many of them have an apical dense spot, which may represent a pit or depression in the particle. Such particles are not found on the lateral E-face below the level of the tight junctions. At the present time, the functional significance of these particles is unknown, but since vasopressin fails to elicit a hydrosmotic response in Xenopus laevis they are probably not involved in transepithelial water permeability. The fact that the different membrane specializations which characterize these mitochondria-rich and non-mitochondria-rich cells are found both in the bladder and the collecting tubule suggests that, at least in Xenopus, the 2 epithelia may share some common functions at the level of the apical membranes of their constituent cells.
Changes of the dna content of differentiating and adult macronuclei of the ciliate Loxodes magnus (karyorelictida)
Authors: Bobyleva N. N. , Kudrjavtsev B. N. , Raikov I. B.
Published: April 2021

The DNA content of isolated micronuclei, differentiating macronuclei (macronuclear Anlagen), and adult macronuclei of Loxodes magnus was measured cytofluorimetrically in preparations stained with a Schiff-type reagent, auramine-SO2following hydrochloric acid hydrolysis. The DNA content of the youngest macronuclear Anlagen proved to be the same as that of telophasic micronuclei (2 c). The Anlagen thus differentiate from micronuclei which are still in G1. The quantity of DNA in the macronuclear Anlagen thereafter rises to the 4-c level, simultaneously with DNA replication in the micronuclei which immediately follows mitosis. In non-dividing animals most micronuclei are already in Gt. Adult macronuclei here contain on average 1·5 times more DNA than the micronuclei; their DNA content is about 5–6 c (in some individual nuclei, up to 10 c). These data are consistent with autoradiographic evidence indicating a weak DNA synthesis in the macronuclei of Loxodes and make likely the existence of partial DNA replication (e.g. gene amplification) in the macronuclei.

The DNA content of adult macronuclei isolated from dividing animals proved to be significantly smaller than that of macronuclei isolated from non-dividing specimens of the same clone. In 3 clones studied, the former value amounted on average to 71–79, 78 and 95 % of the latter, respectively. This drop of DNA content cannot be explained by ‘dilution’ of the old macro-nuclei with newly formed ones. The quantity of DNA in adult macronuclei thus seems to undergo cyclical changes correlated with cytokinesis, despite the fact that, in Loxodes magnus, the macronuclei themselves never divide and are simply segregated at every cell division. The macronuclei of Loxodes can be termed paradiploid or hyperdiploid.
Effects of insulin and anchorage on hepatocytic protein metabolism and amino acid transport
Authors: Poli Alessandro , Gordon Paul B. , Schwarze Per E. , Grinde Bjørn , Seglen Per O.
Published: April 2021

Insulin partially inhibits endogenous protein degradation in isolated hepatocytes. The inhibition seems to specifically affect the lysosomal pathway of degradation, since it is not additive to the effects of lysosome inhibitors such as propylamine and leupeptin. The insulin effect is potentiated by intermediate concentrations of amino acids, but is largely abolished at high amino acid concentrations which suppress degradation maximally, suggesting that the hormone may exert its effect indirectly by acting upon the more basal amino acid control mechanism. Glucagon, which stimulates protein degradation, similarly displays its effect only in the presence of intermediate amino acid concentrations.

The insulin inhibition is not affected by the aminotransferase inhibitor, aminooxyacetate, indicating that it is not due to interference with amino acid metabolism. Protein synthesis furthermore does not seem to be required, since a significant insulin effect can be seen in the presence of the protein synthesis inhibitor, cycloheximide. The issue is, however, complicated by the fact that cycloheximide itself inhibits protein degradation to approximately the same extent as does insulin.

Insulin stimulates uptake of the amino acid α-aminoisobutyrate (AIB), but not the uptake of valine, indicating a specific stimulation of ‘A’-type transport. Cycloheximide similarly stimulates AIB uptake, without completely obfuscating the transport effect of insulin.

Neither protein synthesis, protein degradation, amino acid transport, nor the effects of insulin were affected by cell-to-substratum anchorage (attachment and spreading) in any detectable way.
Ultrastructural organization, sites of transcription and distribution of fibrillar centres in the nucleolus of the mouse oocyte
Authors: Mirre C. , Stahl A.
Published: April 2021

The emergence of newly formed nucleoli and their development have been studied in mouse oocytes from pachytene to diplotene stages. At mid-pachytene, the nucleolus first appears as a fibrillar centre surrounded by a layer of electron-dense fibrils and penetrated by chromatin fibres emanating from the secondary constriction region of the nucleolar bivalent. Since this bivalent contains 2 paired nucleolar organizers, 2 nucleoli are formed in a symmetrical fashion. At advanced pachytene, the nucleoli are extended by strands of fibrillar component which become fibrillogranular distally. The 2 nucleoli fuse together at late pachytene. At diplotene, the nucleolus becomes large and reticulated. The development of the nucleolonema coincides with the appearance of numerous secondary fibrillar centres. Three-dimensional reconstruction of the reticulated nucleolus shows that the number of fibrillar centres largely exceeds that of nucleolar organizers. Radioautography after [‘HJuridine incorporation demonstrates that during the first step of nucleologenesis the labelling is limited to the layer of electron-dense fibrils surrounding the fibrillar centre. Study of the time course of tritiated uridine incorporation from pachytene to diplotene shows that the labelling extends with the extending strands of fibrillar component. In the fully developed nucleolus, all fibrillar strands are labelled and contain, therefore, actively transcribed rDNA. These observations suggest that the rDNA, which is initially compacted in the primary fibrillar centre at the onset of nucleogenesis, progressively unravels and becomes distributed throughout the fibrillar parts of the nucleolonema. The lack of labelling of the secondary fibrillar centres suggests that they are zones of inactivity of the ribosomal genes where the rDNA remains locally compacted. A model of the ultrastructural organization of the nucleolus is proposed based on our observations.
Inverse correlation between neutrophil microtuble numbers and enhanced random migration
Authors: Rich A. M. , Hoffstein S. T.
Published: April 2021

The random migration of neutrophils under agarose as measured by the number of cells leaving the well, is enhanced when the pH or the osmolality of the medium is reduced or when microtubule agents are used. Concentrations of colchicine above 5 × 10−7 M increased the number of cells migrating and decreased the mean number of centriolar microtubules in a dosedependent fashion from 16 to 4 per 4 μm2 at 10−5 M. The distance that colchicine-treated neutrophils migrated from the well was not different from the control. Lowering the pH from 7·4 to 6·o also increased random migration and decreased pericentriolar microtubules from a mean of 16 to a mean of 10. At pH 6· 0, both the number of cells that migrated and the distance the cells forming the leading edge travelled from the well were increased. Since peripheral microtubules may play a greater role in cell migration than centriolar ones, we examined the numerical density of microtubules in the peripheral cytoplasm. Lowering the medium pH reduced the mean number of microtubules per 10 μ m ;3; from 6 to 2. Colchicine reduced microtubules in the same area to 1. At the low pH, colchicine reduced even further the numbers of both centriole-associated and peripheral microtubules but the migration pattern was the same as that seen at pH 6-0 without colchicine. Lowering medium osmolality from 280 to 230 m-osmol increased random migration but did not affect microtubule numbers. The addition of colchicine to this system decreased microtubule numbers and increased migration even further. Conditions that enhanced neutrophil migration also affected cell shape. Whereas cells at pH 7-4 were generally fan-shaped with a broad, smooth leading edge, cells at pH 6’0 with or without colchicine were long and narrow. Neutrophils at pH 7·4 but 230 m-osmol had a scalloped ege, which often appeared thickened. This too was not altered by colchicine. The morphology of cells treated with colchicine was similar to controls except for the more frequent presence of long retraction fibres. Each of these treatments thus appears to act on a different aspect of the cell’s locomotory apparatus. The mechanisms by which colchicine and lowered pH enhance migration may partially overlap since both significantly decrease peripheral microtubules. The data suggest that microtubules play a constraining role within the cell, limiting the ability of the cell to move and change direction.
Inhibition of cell division by interferon: Changes in cell cycle characteristics and in morphology of ehrlich ascites tumour cells in culture
Authors: Richard L. , Panniers V. , Clemens Michael J.
Published: April 2021

The rate of division of Ehrlich ascites tumour cells in culture is inhibited by mouse interferon. A 75 % reduction in cell number is achieved after 3 days and this effect is species specific. The growth inhibition is associated with a marked increase in modal cell volume and with extensive changes in cellular morphology. The cells also become more resistant to detachment from the substratum by mild trypsin treatment.

Analysis of the duration of specific phases of the cell cycle indicates prolongation of mitosis (by 150 %), G2 (by 44 %) and S-phase (by too %), but a slight shortening of G1, as a result of interferon treatment. There is also a dramatic rise in the proportion of cells in culture which contain 2 or more nuclei. As a result of these changes, together with the increase in cell size, the mean cellular contents of protein, RNA and DNA are considerably elevated.

There is a small but significant increase in 3′5′ cyclic AMP (cAMP) content of Ehrlich cells after exposure to interferon, and exogenous cAMP or its analogues cause morphological changes similar to those elicited by interferon. However, many of the other effects of the latter are not mimicked by the cyclic nucleotide, suggesting that cAMP is only involved in part of the complex pattern of responses of cells to interferon which result in inhibition of growth and division.
Effects of disuse on growing and adult chick skeletal muscle
Authors: Shear Charles R.
Published: April 2021

The effects of long-term muscle inactivity, throughout post-hatching development, have been examined. Continuous immobilization of the chicken posterior latissimus dorsi (PLD) muscle from the first hour after hatching for varying periods up to 330 days, resulted in a significantly greater decrease in myofibre size (40―64 % less than control) than occurred when adult muscles were immobilized for similar periods (20―40 % less than control). The myofibre atrophy resulting from long-term immobilization of adult muscle is reversible, after removal of the plaster cast. In contrast, the myofibres immobilized immediately after hatching, for similar periods of time, were unable to recover once the casts were removed. On the basis of myofibre cross-sectional area, 2 populations of cells were seen in muscles immobilized during postnatal development: small myofibres of 0·5―200 µm2 and larger myofibres of 500―800 µm2. The distribution of fibre cross-sectional area within immobilized adult muscles was similar to controls, suggesting a uniform response (i.e. atrophy) by all of the myofibres within the muscle. Immobilization in both newly hatched and adult PLD muscles did not appear to alter the pattern of motor endplate distribution within the muscle. Small, multiple motor endplates were observed associated with immobilized and control myofibres near their terminal ends. This finding suggests that the embryonic pattern of myofibre innervation is not entirely lost from all the fibres during postnatal development.