bluuebunny/crossref_metadata_2025 huggingface dataset:
SPRR4, a novel cornified envelope precursor: UV-dependent epidermal expression and selective incorporation into fragile envelopes
Authors: Cabral Adriana , Sayin Arzu , de Winter Sandrine , Fischer David F. , Pavel Stan , Backendorf Claude
Published: April 2021

The cornified cell envelope (CE), a structure formed in the outermost layers of stratified squamous epithelia, provides a physical barrier against environmental insults. It is composed of several structural proteins, which are irreversibly crosslinked by calcium-activated transglutaminases. The small proline rich proteins (SPRRs) are one set of CE precursors. SPRR4, a novel member of this gene family, displayed very low or undetectable expression levels in normal human skin or other stratified squamous epithelia, but was clearly induced by UV light both in vivo and in vitro. High epidermal expression of SPRR4 was monitored only after chronic UV exposure and was concomitant with a thickening of the stratum corneum, which is believed to provide protection against subsequent damage. The calcium-dependent translocation of an SPRR4-GFP fusion protein to the cell periphery in living keratinocytes and its integration into both rigid and fragile cornified envelopes proved that SPRR4 is a novel CE precursor. Interestingly, after UV irradiation, SPRR4 was selectively incorporated into fragile CEs. Our results show for the first time that UV-induced cornification is accompanied by qualitative changes in CE precursor assembly. SPRR4 is part of an adaptive tissue response to environmental stress, which is likely to compensate for UV induced impairment of the epidermal barrier function.
The role of lipid rafts in signalling and membrane trafficking in T lymphocytes
Authors: Alonso Miguel A. , Millán Jaime
Published: April 2021

Combinatorial association of different lipid species generates microheterogeneity in biological membranes. The association of glycosphingolipids with cholesterol forms membrane microdomains – lipid rafts – that are involved in specialised pathways of protein/lipid transport and signalling. Lipid rafts are normally dispersed in cellular membranes and appear to require specialised machinery to reorganise them to operate. Caveolin-1 and MAL are members of two different protein families involved in reorganisation of lipid rafts for signalling and/or intracellular transport in epithelial cells. T cell activation induces a rapid compartmentalisation of signalling machinery into reorganised rafts that are used as platforms for the assembly of the signalling complex. Costimulatory molecules participate in this process by providing signals that mobilise raft lipids and proteins, and remodel the cytoskeleton to the contact site. As in epithelial cells, rafts are used also as vesicular carriers for membrane trafficking in T lymphocytes. Furthermore, there are potential similarities between the specialised protein machinery underlying raft-mediated processes in T lymphocytes and polarised epithelial cells.
Complexes of tetraspanins with integrins: more than meets the eye
Authors: Berditchevski Fedor
Published: April 2021

The transmembrane proteins of the tetraspanin superfamily are implicated in a diverse range of biological phenomena, including cell motility, metastasis, cell proliferation and differentiation. The tetraspanins are associated with adhesion receptors of the integrin family and regulate integrin-dependent cell migration. In cells attached to the extracellular matrix, the integrin-tetraspanin adhesion complexes are clustered into a distinct type of adhesion structure at the cell periphery. Various tetraspanins are associated with phosphatidylinositol 4-kinase and protein kinase C isoforms, and they may facilitate assembly of signalling complexes by tethering these enzymes to integrin heterodimers. At the plasma membrane, integrin-tetraspanin signalling complexes are partitioned into specific microdomains proximal to cholesterol-rich lipid rafts. A substantial fraction of tetraspanins colocalise with integrins in various intracellular vesicular compartments. It is proposed that tetraspanins can influence cell migration by one of the following mechanisms: (1) modulation of integrin signalling; (2) compartmentalisation of integrins on the cell surface; or (3) direction of intracellular trafficking and recycling of integrins.
Interactions of a hemidesmosome component and actinin family members
Authors: Gonzalez Annette M. , Otey Carol , Edlund Magnus , Jones Jonathan C. R.
Published: April 2021

Hemidesmosomes are multimeric protein complexes that attach epithelial cells to their underlying matrix and serve as cell surface anchorage sites for the keratin cytoskeleton. Two hemidesmosome components, the α6β4 integrin heterodimer and a human autoantigen termed BP180, are transmembrane proteins that link the extracellular matrix to the keratin network in cells. Here, we report that actinin-4, an actin-bundling protein, is a potential binding partner for BP180. Using yeast two-hybrid, we have mapped the binding site for BP180 to the C-terminal region of actinin-4. This site contains two EF-hand, Ca2+ regulation domains and shares 87% sequence homology with the same region in actinin-1. Consistent with this, BP180 can bind actinin-1 in both the yeast two-hybrid assay and in immunoprecipitation assays. To determine whether the EF-hand domain is a consensus binding sequence for BP180, we tested whether other proteins with this domain bind BP180. None of the proteins tested including calmodulin, with 4 EF-hand domains, and myosin regulatory light chain, with 1 EF-hand domain, interacts with BP180 in yeast two-hybrid system and immunoprecipitation studies, suggesting that the interaction between BP180 and actinin family members is specific. We have compared the distribution of actinin-1 and actinin-4 with that of BP180 in MCF-10A and pp126 cells. Surprisingly, BP180 localizes not only to sites of cell-substratum interaction, but is also present at sites of cell-cell contacts where it co-distributes with both actinin-1 and actinin-4 as well as other adherens junction proteins. In oral tissues, BP180 is present along the basement membrane and at cell-cell contact sites in basal epithelial cells where it co-distributes with adherens junction proteins. Since BP180 antibodies inhibit association of junction proteins at sites of cell-cell contact in oral keratinocytes, these results suggest that BP180 may play a role in establishing cell-cell interactions. We discuss a role for BP180 in crosstalk between cell-matrix and cell-cell junctions.
Microtubule-associated protein 1B phosphorylation by glycogen synthase kinase 3β is induced during PC12 cell differentiation
Authors: Goold Robert G. , Gordon-Weeks Phillip R.
Published: April 2021

In recent studies we have demonstrated that glycogen synthase kinase 3β (GSK3β) and its substrate microtubule-associated protein 1B (MAP1B) regulate the microtubule cytoskeleton during axon outgrowth. To further examine the role GSK3β plays in axon outgrowth we investigated the expression of GSK3β and its activity towards MAP1B during nerve growth factor (NGF)-stimulated PC12 cell differentiation. Levels of GSK3β expression increase relatively little during the course of differentiation. However, the expression of a novel GSK3β isoform characterised by a reduced mobility on SDS gels is induced by NGF. Expression of this isoform and the GSK3β-phosphorylated isoform of MAP1B (MAP1B-P) are induced in parallel in response to NGF. This increase lags behind initial neurite formation and the expression of MAP1B in these cells by about two days and coincides with a period when the majority of cells are extending existing neurites. MAP1B and GSK3β are expressed throughout the PC12 cell but MAP1B-P expression is restricted to the growth cones and neurites. Consistent with these observations, we find that neurite extension is more sensitive to the GSK3 inhibitor Li+ than neurite formation and that this correlates with an inhibition of MAP1B phosphorylation. Additionally, GSK3β from PC12 cells not exposed to NGF can not phosphorylate MAP1B in vitro. However, a soluble factor in differentiated PC12 cell extracts depleted of GSK3β can activate MAP1B phosphorylation from undifferentiated cell extracts otherwise devoid of kinase activity. These experiments provide evidence for an NGF-mediated regulation of MAP1B phosphorylation in growing neurites by the induction of a novel isoform of GSK3β.
TheS. pombeaurora-related kinase Ark1 associates with mitotic structures in a stage dependent manner and is required for chromosome segregation
Authors: Petersen Janni , Paris Jeannie , Willer Martin , Philippe Michel , Hagan Iain M.
Published: April 2021

Metazoans contain three aurora-related kinases. Aurora A is required for spindle formation while aurora B is required for chromosome condensation and cytokinesis. Less is known about the function of aurora C. S. pombe contains a single aurora-related kinase, Ark1. Although Ark1 protein levels remained constant as cells progressed through the mitotic cell cycle, its distribution altered during mitosis and meiosis. Throughout G2 Ark1 was concentrated in one to three nuclear foci that were not associated with the spindle pole body/centromere complex. Following commitment to mitosis Ark1 associated with chromatin and was particularly concentrated at several sites including kinetochores/centromeres. Kinetochore/centromere association diminished during anaphase A, after which it was distributed along the spindle. The protein became restricted to a small central zone that transiently enlarged as the spindle extended. As in many other systems mitotic fission yeast cells exhibit a much greater degree of phosphorylation of serine 10 of histone H3 than interphase cells. A number of studies have linked this modification with chromosome condensation. Ark1 immuno-precipitates phosphorylated serine 10 of histone H3 in vitro. This activity was highest in mitotic extracts. The absence of the histone H3 phospho-serine 10 epitope from mitotic cells in which the ark1+ gene had been deleted (ark1.Δ1); the inability of these cells to resolve their chromosomes during anaphase and the co-localisation of this phospho-epitope with Ark1 early in mitosis, all suggest that Ark1 phosphorylates serine 10 of histone H3 in vivo. ark1.Δ1 cells also exhibited a reduction in kinetochore activity and a minor defect in spindle formation. Thus the enzyme activity, localisation and phenotype arising from our manipulations of this single fission yeast aurora kinase family member suggest that this single kinase is executing functions that are separately implemented by distinct aurora A and aurora B kinases in higher systems.
Properties of lamin A mutants found in Emery-Dreifuss muscular dystrophy, cardiomyopathy and Dunnigan-type partial lipodystrophy
Authors: Östlund Cecilia , Bonne Gisèle , Schwartz Ketty , Worman Howard J.
Published: April 2021

Autosomal dominant Emery-Dreifuss muscular dystrophy is caused by mutations in the LMNA gene, which encodes lamin A and lamin C. Mutations in this gene also give rise to limb girdle muscular dystrophy type 1B, dilated cardiomyopathy with atrioventricular conduction defect and Dunnigan-type partial lipodystrophy. The properties of the mutant lamins that cause muscular dystrophy, lipodystrophy and dilated cardiomyopathy are not known. We transfected C2C12 myoblasts with cDNA encoding wild-type lamin A and 15 mutant forms found in patients affected by these diseases. Immunofluorescence microscopy showed that four mutants, N195K, E358K, M371K and R386K, could have a dramatically aberrant localization, with decreased nuclear rim staining and formation of intranuclear foci. The distributions of endogenous lamin A/C, lamin B1 and lamin B2 were also altered in cells expressing these four mutants and three of them caused a loss of emerin from the nuclear envelope. In the yeast two-hybrid assay, the 15 lamin A mutants studied interacted with themselves and with wild-type lamin A and lamin B1. Pulse-chase experiments showed no decrease in the stability of several representative lamin A mutants compared with wild-type. These results indicate that some lamin A mutants causing disease can be aberrantly localized, partially disrupt the endogenous lamina and alter emerin localization, whereas others localize normally in transfected cells.
Nuclear envelope disorganization in fibroblasts from lipodystrophic patients with heterozygous R482Q/W mutations in the lamin A/C gene
Authors: Vigouroux Corinne , Auclair Martine , Dubosclard Emmanuelle , Pouchelet Marcel , Capeau Jacqueline , Courvalin Jean-Claude , Buendia Brigitte
Published: April 2021

Dunnigan-type familial partial lipodystrophy (FPLD), characterized by an abnormal body fat redistribution with insulin resistance, is caused by missense heterozygous mutations in A-type lamins (lamins A and C). A- and B-type lamins are ubiquitous intermediate filament proteins that polymerize at the inner face of the nuclear envelope. We have analyzed primary cultures of skin fibroblasts from three patients harboring R482Q or R482W mutations. These cells were euploid and able to cycle and divide. A subpopulation of these cells had abnormal blebbing nuclei with A-type lamins forming a peripheral meshwork, which was frequently disorganized. Inner nuclear membrane protein emerin, an A-type lamin-binding protein, strictly colocalized with this abnormal meshwork. Cells from lipodystrophic patients often had other nuclear envelope defects, mainly consisting of nuclear envelope herniations that were deficient in B-type lamins, nuclear pore complexes, lamina-associated protein 2 beta, and chromatin. The mechanical properties of nuclear envelopes were altered, as judged from the extensive deformations observed in nuclei from heat-shocked cells, and from the low stringency of extraction of their components. These structural nuclear alterations were caused by the lamins A/C mutations, as the same changes were introduced in human control fibroblasts by ectopic expression of R482W mutated lamin A.
Regulation of functional nuclear pore size in fibroblasts
Authors: Feldherr Carl M. , Akin Debra , Cohen Robert J.
Published: April 2021

Protein-NLS-coated gold particles up to approximately 250 Å in diameter are transported through the nuclear pores in normal, proliferating BALB/c 3T3 cells. This size can increase or decrease, depending on cellular activity. It has been suggested that increases in functional pore size are related to a reduction in the amount of available p53. To further test this hypothesis, we investigated the effects of cycloheximide and pifithrin-α, which inhibits p53-dependent transcriptional activation, on nuclear transport. After 3 hours in cycloheximide, there was a significant increase in the size of the gold particles that entered the nucleoplasm. When the incubation period was extended to 6 hours or longer, transport capacity returned to the control level. By using proteasome inhibitors, it was shown that the cycloheximide-dependent increase in functional pore size was due to the inhibition of protein synthesis, consistent with the fact that p53 is a short-lived protein, and requires the activity of at least two different factors. Although cycloheximide increases the functional diameter of the channel available for signal-mediated transport by approximately 60 Å, it had no significant effect on either the import rate of small NLS-containing substrates (FITC-BSA-NLS), or passive diffusion of fluorescent-labeled proteins across the envelope. This suggests that changes in transport capacity were not caused by an increase in overall pore diameter but instead are due to a transient increase in pore size that accompanies signal-mediated transport. Pifithrin-α also caused an increase in functional pore diameter without altering the import rate of FITC-BSA-NLS, providing further support for the view that p53 can initiate changes in nuclear transport capacity.
Formation of the milk fat globule membrane without participation of the plasmalemma
Authors: Wooding F. B. P.
Published: April 2021

In goat mammary tissue under certain conditions perfusion fixation produces a considerable swelling of the rough endoplasmic reticulum and the appearance, in a small number of cells, of intracellular vacuoles which contain lipid globules and casein particles. The morphological evidence suggests that these vacuoles form by fusion of Golgi vesicles. By this process the characteristic structure of the milk fat globule membrane (MFGM) is produced around the lipid globules without any contribution from the plasmalemma. This corroborates the earlier suggestion that normal MFG secretion involves the Golgi vesicles directly.
Stimulation of DNA synthesis by prolactin in rabbit mammary tissue
Authors: Bourne R. A. , Bryant J. A. , Falconer I. R.
Published: April 2021

The capacity of mammary gland tissue slices to incorporate [3H]thymidine into DNA was studied at intervals after intraductal injection of prolactin. Prolactin markedly increased the rate of incorporation of thymidine into DNA (as extracted by HClO4 or by sodium dodecyl sulphate). The increase in incorporation rate occurred within 6 h of prolactin injection. Autoradiography of mammary tissue, after administration of [3H]thymidine in vivo, showed that the increased rate of incorporation of thymidine was caused by an increase in the number of alveolar cells entering 5-phase. These results are discussed in relation to current theories concerning functional differentiation of mammary tissue.
Patterns of incorporation of [3H]galactose by cells of Zea mays root tips
Authors: Dauwalder Marianne , Whaley W. G.
Published: April 2021

[3H]galactose shows a selective pattern of uptake distribution in the apical portion of the root tip of Zea mays. In cells entering division it is incorporated into the Golgi apparatus within 10 min and is transferred from that organelle to the forming cell plate.

The pattern of uptake suggests a specific biochemical activity on the part of the Golgi apparatus at the time of division so far as the incorporation of galactose is concerned. Apparently little galactose is converted to glucose in the most apical portion of the root. In normal secretory cells, the heaviest uptake is found in the sieve tube elements, epidermal cells and the outer cells of the root cap.
Cytochalasin B and embryonic heart muscle: Contractility, excitability and ultrastructure
Authors: Sachs H. G. , Mcdonald T. F. , Springer M.
Published: April 2021

The effect of cytochalasin B (CB) on beating, electrical activity and cytological ultrastructure of embryonic hearts and tissue-cultured heart preparations was investigated. The inhibition of spontaneous pulsation and the subsequent recovery after drug washout were found to be dosedependent and to be a function of the type of preparation. In the presence of CB, spontaneous action potentials can be recorded from all three (intact hearts, isolated myocytes, reaggregated cells) after cessation of all visible contractions, although the action potential duration is reduced. CB at 0·5–10 μg/ml was found not to uncouple heart cells electrically nor to prevent cells from aggregating and establishing new electrical coupling. In all 3 systems, however, CB does result in disruption of myofibrillar organization. After 30 h in CB (2 μg/ml) bundles of myofilaments are found to be randomly oriented, with Z-band material condensed into amorphous bodies, no longer aligned with the myofibril, but remaining in register between the A-bands. Within the bundles the normal hexagonal cross-section of thick and thin filaments is maintained. The unaligned Z-bodies, however, demonstrate attached thin filaments of very reduced length. Following washout of the drug, normal sarcomeric organization is restored in parallel -with resumption of spontaneous beating. The present data, therefore, are consistent with the hypothesis that one major effect of CB is an alteration in myofibril (myofilament) stability, and that this effect alone is sufficient to account for the observed inhibition of contractility.
Fine-structural identification and organization of the epidermal proliferative unit
Authors: Allen T. D. , Potten C. S.
Published: April 2021

Mouse dorsal interfollicular epidermis has a vertical organization consisting of approximately 1400 units/mm2. Each unit is identified by its uppermost 4 to 6 layers of roughly hexagonal flattened cornified cells or squames, which are stacked in a precise vertical column. Beneath each column of squames there are 3 differentiating cells and a group of 10 or 11 basal cells, which provide cells to replace those lost by desquamation at the top of the squame column. The whole unit is termed an epidermal proliferative unit or EPU. In the central region of the basal layer of each EPU is a single dendritic Langerhans cell, devoid of desmosomes, but held in position by the surrounding keratinocytes. The dendrites radiate outwards between the keratinocytes to the periphery of the unit. Keratinocyte migration into the spinous layer takes place from the edge of the unit. In the squame column itself, a modified cell-to-cell attachment (squamosome) runs around the edge of each cornified cell, and attaches it to the overlapping region of cells from adjacent squame columns.
The chloroplast nucleoid inOchromonas danica: II. evidence for an increase in plastid dna during greening
Authors: Gibbs Sarah P. , Mak R. , Ng R. , Slankis T.
Published: April 2021

During the first 24 h of light-induced chloroplast development in Ochromonas danica, the single plastid nucleoid increases 4-fold in volume. During this interval, the concentration of DNA within the nucleoid, as determined by eye and by counts of fibrils per /tm2 of nucleoid sectioned, remains constant. Thus, on morphological grounds, it appears that the amount of plastid DNA increases 4-fold during greening.

To determine whether the chloroplasts of light-grown cells contain more DNA than the proplastids of dark-grown cells, exponentially growing cultures of dark- and light-grown cells were each labelled for exactly one generation with [3H]thymidine. After fixation, the cells were embedded in Araldite, and serial 1μm sections through entire plastids and nuclei were prepared for autoradiography. In this study, the chloroplasts of light-grown cells incorporated almost 4 times as much label into DNA as the proplastids did, whereas the nuclei of the dark- and light-grown cells were equally labelled. Another study showed that light-grown cells have slightly more total cell DNA than dark-grown cells. These 2 studies provide prima facie evidence that chloroplasts contain more DNA than proplastids and support the hypothesis that an increase in plastid DNA accompanies chloroplast development in Ochromonas.
Light- and electron-microscope observations on certain leukocytes in a teleost fish and a comparison of the envelope-limited monolayers of chromatin structural units in different species
Authors: Davies H. G. , Haynes Μ. E.
Published: April 2021

Previously it was shown that the nuclear envelope-limited sheets of chromatin, monolayers of nucleoprotein structural units, are present in blood cells from 4 classes of vertebrates. Now we show that sheets of similar width are present in certain leukocytes of a fifth class, a teleost fish. We describe the fine structure of leukocytes in peripheral blood and in the main haematopoietic organ, kidney. We also examined the granulocytes of connective tissue in intestine. By May-Grunwald-Giemsa staining and electron microscopy heterophilic granulocytes, cosinophils but no basophils could be recognized in peripheral blood and kidney. Problems in classification of the cells are discussed. In one group (A) of 5 fish, sheets occurred at a frequency of roughly 1% in heterophilic (type 1) granulocytes and lymphocytes from peripheral blood. No sheets were found in a second group (B) of 5 fish. Kidney and intestine were examined in some fish from both groups and no sheets were present. In an atypical group (C) sheets were found in the eosinophilic (type 2) granulocytes from peripheral blood of one fish and in lymphocytes from connective tissue of intestine in another. Sheets were usually associated with nuclei of irregular shape and their width averaged 36 nm.

We tabulate data from other workers on occurence and width of sheets. They are found in all the main classes of tissue in mammals, namely blood and other connective tissues, in epithelial, nervous, germinal tissue and muscle, as well as in invertebrate and certain plants. Their nearly constant width, average value 35 nm, provides very convincing evidence for the hypothesis that the molecules of DNA and protein are organized into the same fundamental structural units, irrespective of species. We discuss the variable incidence of sheets among different cell types and the factors which might determine this.
Synthesis of ribosomal RNA in synkaryons and heterokaryons formed between human and rodent cells
Authors: Marshall C. J. , Handmaker S. D. , Bramwell Μ. E.
Published: April 2021

A study has been made of the ribosomal RNA and chromosome constitution of man-mouse hybrid cells. Previous work has shown that no human 28 s rRNA is detectable in man-mouse synkaryons. In general human chromosomes are lost from such hybrids.

With a recently developed method for distinguishing mouse from human chromosomes, an analysis of various man-mouse hybrid cell lines has been made. This indicates that not all the human chromosomes bearing nucleolar organizers are lost in the hybrid cells and such loss cannot alone explain the absence of human 28 s rRNA.

An examination of the 28 s rRNA synthesized by heterokaryons formed from several different parent cells has revealed that both parental types of 28 s rRNA are present in heterokaryons. The control of rRNA synthesis in hybrid cells is discussed.
Ultrastructural localization of phosphohydrolases in gametes, zygotes and zoospores of Ulva mutabilis føyn
Authors: Bråten T.
Published: April 2021

Gametes, zoospores, and zygotes of the multicellular, green alga Ulva mutabilis showed acid phosphatase reaction product in Golgi vesicles and on the membrane lining the vacuole. In addition gametes and zoospores showed enzyme reaction product on the entire surface membrane including the flagellar membrane. The surface membrane enzyme activity disappears from the zygote shortly after copulation and at the same time lysosome-like bodies start to appear in the cytoplasm. No alkaline phosphatase activity could be detected. The distribution of acid phosphatase is discussed in relation to the events taking place during and shortly after fertilization.
Intercellular adhesion and formation of aggregates in normal and Talpid3 Mutant chick limb mesenchyme
Authors: Ede D. A. , Flint O. P.
Published: April 2021

It is demonstrated, using the Couette viscometer method, that talpid3 mutant chick wing mesenchyme cells are more adhesive to one another than are normal cells. The relation of this to differences in the size and shape, and the internal architecture, of aggregates produced in rotation cultures of these cells was investigated. Sequences of sections through aggregates in all stages of formation, from 2-cell aggregates up to those with large cell numbers, were prepared. These confirm the theoretically predicted relationships among adhering cells which would produce the observed small, spherical talpid3 aggregates and the larger, unevenly shaped normal aggregates. The cell contacts are further analysed with electron micrographs.
Histone proteases of avian erythroid cells
Authors: Harlow R. , Wells J. R. E.
Published: April 2021

Protease activity associated with avian erythroid chromatin has been studied by gel electrophoresis of histones. Histone degradation is minimal at neutral pH, but is readily detected when chromatin is incubated at pH 3, and is evident to a lesser extent at pH 9.

As a result of the pH 3 activity, the f1 and f2 chistones are preferentially degraded when the histone complement is DNA-bound, but these histones are relatively resistant to attack when present as free histone.

The pH 3 activity reported here has properties similar to those of neutral histone proteases from other tissues, except that it is not inhibited by bisulphite. Added exogenous proteins are not degraded.

The activity of avian erythroid histone protease decreases as maturation of the cells proceeds. Since we have previously shown that turnover of DNA-bound f2c histone occurs in reticulocytes and histone synthesis is absent in erythrocytes, it is possible that the histone protease described here may be involved in f2c histone turnover.
A possible role for intercisternalelements in the formation of secretory vesicles in plant golgi apparatus
Authors: Mollenhauer H. H. , Morré D. J.
Published: April 2021

Oriented fibres in the intercisternal regions of plant dictyosomes are usually associated with flattened portions of cisternae. In outer cap cells of maize roots, however, the intercisternal fibres are associated mainly with unique secretory vesicles which are elongate or kidney-shaped during their formative stages. Fibres are oriented parallel with the long axes of the vesicles even at early stages of vesicle formation. Because of their early presence and orientation, the fibres may aid in organizing and/or shaping the secretory vesicles in this tissue.
Lipid staining for the electron microscope: a new method
Authors: Wigglesworth V. B.
Published: April 2021

Tissues fixed in osmium tetroxide or in combined osmium and glutaraldehyde (Hinde), embedded in Spurr’s medium, cut at 0 5–1 μm and mounted in Farrants’ gum medium containing ethyl gallate, show good staining of lipid-containing structures (droplets of triglyceride, membranes, mitochondria, etc.) in the light microscope.

Such preparations show moderate contrast in the electron microscope without further staining. But a specific increase in contrast in lipid-rich structures is obtained by partition of the tissues, before embedding, in 70 % ethanol saturated with the monoterpene hydrocarbon myrcene, with or without the addition of 0·1 % ethyl gallate, followed by osmium tetroxide.

This method will visualize both saturated and unsaturated lipids, including waxes.
Evidence for the presence of dna in the pellicle of Paramecium
Authors: Smith-Sonneborn Joan , Plaut W.
Published: April 2021

Two lines of evidence for the existence of DNA in the pellicle of Paramecium are presented : fluorescence staining and autoradiography. The latter shows deoxyribonuclease-sensitive incorporation of tritiated thymidine in or near the kineties. Fluorescence microscopy permits the localization of DNA at the site of kinetosomes. The possibility that the DNA is not native to the pellicle but introduced during preparative procedures is tested experimentally and shown to be unlikely.
Interaction between normal and transformed bovine fibroblasts in culture: I. cells transformed by rous sarcoma virus
Authors: Macintyre Elizabeth , Pontén J.
Published: April 2021

Base layers of untransformed normal embryonic lung fibroblasts in different stages of growth were challenged with RSV (Rous sarcoma virus)-transformed bovine fibroblasts. The effect of this admixture on the growth of the RSV-transformed cells was studied. In all cases, the transformed cells proliferated freely, and it is concluded that the normal cells exerted no inhibition on the transformed cells.
The fine structure of cytoplasmic inclusions in a mycoplasma-like infection in mice
Authors: Gay F. W. , Attridge J. T.
Published: April 2021

A mycoplasma-like agent, which resembled grey lung ‘virus ‘of Andrewes and Glover in its sensitivity to chemotherapeutic substances in vivo, in its failure to grow in culture media, and in its failure to elicit immunity in infected animals, was derived from rats with naturally acquired chronic pneumonia. In mice it produced a chronic pneumonia from which mycoplasmas could not be cultured. When sections of diseased mouse lung were examined by electron microscopy, completely novel intracytoplasmic inclusions were observed in mononuclear cells lying free in the alveoli and bronchioles. The inclusions, which were less numerous in mice being treated with chemotherapeutic substances which inhibit the growth of mycoplasmas, appeared to represent successive stages in a developmental process. The fine structure of the inclusions is described and their possible nature is discussed.
Control of cell size and cycle time in Schizosaccharomyces pombe
Authors: Fantes P. A.
Published: April 2021

Steady-state and perturbed cells of Schizosaccharomyces pombe have been observed through several division cycles by time-lapse photomicrography. Perturbed cells were produced by the use of a conditional cell division cycle mutant in which nuclear division is reversibly blocked at high temperature. These experiments show that in both populations cell length at division and cell cycle duration are homeostatically controlled, probably by a primary size-control mechanism. Cycle time is indirectly controlled, as cells which have an extended cycle are on average larger at division, so that daughters of such cells need to grow by a smaller amount and for a shorter period, before dividing again. In general, deviations from the mean are corrected within a single cycle, but in the case of very long cells the control breaks down because the cycle cannot be shortened by more than a quarter under the conditions used. These cells take more than one cycle to return to normal.
Differentiation of the tapetum in A Vena: I. the cell surface
Authors: Steer M. W.
Published: April 2021

The development of the tapetal cell surface and associated structures in Avena has been followed from cell formation to senescence. Plasmodesmata initially connect the tapetal cells to each other, the pollen mother cells, and the inner loculus wall cells. These connexions are subsequently severed, those to the sporogenous cells being broken first at the pollen mother cell surface during callose wall formation. Loss of cellulose from the tapetal walls was followed using the decline in the ability of the wall to bind the fluorescent brightener, Calcofluor White M2R New. Subplasma-membrane microtubules persist after loss of the cellulose wall. The tapetal plasma membrane facing the meiocytes then develops a series of depressions, or cups, over its surface, which are later the site of pro-orbicule formation. Sporopollenin is laid down over the pro-orbicules, to form orbicules, and over other tapetal cell surfaces. No morphological evidence was found for the intracytoplasmic formation of pro-orbicules or polymerized sporopollenin precursors.

These observations on Avena are compared with those on other plants. The changes in the cell wall and associated structures, plasmodesmata and microtubules, are considered in detail, while the general significance of cell wall loss to the water relations of the tissue are assessed. Proposals that pro-orbicule formation results from non-specific accumulation of lipid at a free cell surface are rejected, instead this formation is considered to be related to the presence of a specially modified plasmamembrane surface.
Growth In Vitro of tumour cell × fibroblast hybrids in which malignancy is suppressed
Authors: Straus D. S. , Jonasson J. , Harris H.
Published: April 2021

We have studied the growth in vitro of a lymphoma × fibroblast hybrid and several melanoma × fibroblast hybrids in which malignancy is suppressed. The parental cells, the hybrids, and malignant segregants derived from the hybrids were analysed for serum requirement, cloning efficiency in soft agarose, density-dependent inhibition of growth, and secretion of plasminogen-activating enzyme. One malignant segregant from the lymphoma × fibroblast cross was found by a number of criteria to have a more highly ‘transformed’ phenotype than the hybrid from which it was derived. However, in the case of the melanoma × fibroblast crosses, none of the parameters examined, could be correlated in a direct way with malignancy.
Synchrony in the rhythm of the contraction-relaxation cycle in two plasmodial strands of Physarum Polycephalum
Authors: Takeuchi Yuko , Yoneda Mitsuki
Published: April 2021

Rhythmicity of contraction of plasmodial strands of Physarum polycephalum was studied, by measuring the isometric tension exerted by isolated segments of the strands. When 2 strands were connected by way of a plasmodial mass, the contraction–relaxation cycle of the 2 strands synchronized. Such cyclic activity of the strand was found to be well coordinated with shuttle streaming in the plasmodial mass which had been in connexion with the strand. The presence of a control system which induces synchrony of periodic activity over the entire body of a plasmodium is discussed.
An analysis of transport, exchange, and binding of sodium and potassium in isolated amphibian follicles and denuded oocytes
Authors: Morrill Gene A. , Ziegler David , Zabrenetzky Vivian S.
Published: April 2021

The uptake and efflux of 22Na and 42,K were studied in fully grown, prophase-arrested Rana pipiens follicles and denuded oocytes. Follicles and denuded oocytes contained large stores of both cations, although only 15–30% of the total Na+ and 1–2% of the total K+ pools exchanged within the 12-h period studied. “Na uptake and efflux in follicles exhibited two-step kinetics with a smaller rapidly exchanging fraction (12–15%, t0·5 ∼ 15 min), and a larger slow fraction (t0·5. ∼ 0·5 day). Denuded oocytes displayed a single kinetic fraction with a rate constant similar to the slow fraction of follicles, suggesting that the fast fraction was associated with the follicular epithelium. Both follicles and denuded oocytes exhibited fast and slow 42K uptake kinetic fractions, although the follicular fast fraction was considerably larger. Conversely, whereas follicular 42K efflux also proceeded with two-step kinetics, 42K efflux from denuded oocytes appeared as a single slow fraction. Thus, a large portion of the fast K+ fraction taken up by the follicles is attributable to the somatic cells of the follicular envelopes. Na+ and K+ activities were measured in the cytoplasm of the in situ (follicular) oocyte using cation-selective microelectrodes. After correcting for Na+ and K+ associated with the follicular envelopes, only about 6% of the total ooplasmic Na+ and less than 1% of the K+ could be accounted for as bound or sequestered.
Ultrastructure of late oocyte nuclei in Rana temporaria
Authors: Gruzova M. N. , Parfenov V. N.
Published: April 2021

The ultrastructural organization of the nucleus during late oogenesis in Rana temporaria was examined in normal and in hormone-stimulated maturing oocytes in vitro. At this stage numerous nucleoli are assembled around a knot of highly contracted chromosomes (the karyosphere) making up a karyosphere capsule. The nucleoli are fibrillar. They bear no pro-ribosomal granules and do not synthesize RNA. This period is characterized by segregation of nucleolar material into core and cortex. The nucleoli are of irregular shape. The presence of micronucleoli and nuclear bodies indicates an intensive fragmentation of nucleolar material.

In the central fibrous zone of the capsule separating the chromosomes from the nucleoli, abundant accumulations of annuli lacking any membranous component occur. The annuli are connected by fibrous material and are regularly packed, forming peculiar pseudomembranes which are connected directly to the chromatin. Pseudomembranes, though less abundant and less regularly packed, are also found in the middle zone of the capsule. Along with annuli, membranous areas of various sizes and shapes are found in the pseudomembranes. Pseudomembranes are linked to micronuclei by granular filaments 20–30 nm thick.

A variety of membranous structures in the form of intranuclear annulate lamellae or membranous tubular formations was detected in the peripheral zone of the capsule and outside it. The conclusion is drawn that the fibrous component of the karyosphere capsule consists of different membranous and pseudomembranous structures. It is suggested that chromatin participates directly in the formation of pseudomembranes and intranuclear membranous structures.
Electron-microscope observations on the organization of hetero-chromatin in certain cells
Authors: Davies H. G.
Published: April 2021

Electron micrographs of sections through the heterochromatin (condensed chromosomes) of erythrocytes from chicken and lamprey reveal alternate equispaced electron-dense and relatively less dense bands lying adjacent and parallel to, and extending considerable distances along, the nuclear envelope. Frequently a triple-structured band (average half-width 183 Å), consisting of a less dense band, a dense band (width 130–170 Å), and a second less dense band is encountered; sometimes there are many (10–12) bands. The dense bands have a variable structure; they may appear continuous or consist of equispaced granules about 220 Å apart, which sometimes have a less dense centre. Similar but shorter dark bands and granules appear throughout the chromatin. Tilting the section in the microscope causes the micrographs to change, bands and granules disappearing and reappearing elsewhere, demonstrating that the images are produced by super position of structures small in dimensions compared with the thickness of the section. Tilting about an axis normal to the band may resolve it into granules. These data indicate that the heterochromatin contains a well-defined structural unit which can form ordered regions, namely layers in contact with the nuclear envelope. The possibility of errors in interpreting the substructure of the bands due to complexity of superposition effects is stressed. The simplest hypothesis to account for the images is that the units are microtubes of outside diameter 130–170 Å, perhaps microhelices formed by coiling DNA with protein, spaced apart equally, perhaps by spacing elements. Microtubes parallel to the optic axis would appear as hollow granules, several one above another in a plane parallel to the axis appearing as a dark band. A similar triple-structured band of average half-width 224 Å is found in cells from newt spleen, lymphocytes, polychromatophil erythroblasts, mature erythrocytes, basophilic granulocytes, reticular cells and macrophages. A survey of published micrographs shows a similar triple structured band of average half-width 212 Å to be a common feature of many cell types. A triple-structured band probably gives rise to the sheets of chromatin, now shown to have a similar triple-layered structure, limited on both sides by nuclear envelope, previously found attached to interphase nuclei and mitotic chromosomes in certain polychromatic erythroblasts from the newt. The effects of tilting the section were studied on objects of known geometry, membranes and cytoplasmic microtubules.
The fine structure of chloroplasts and pyrenoids in some marine dinoflagellates
Authors: Dodge J. D.
Published: April 2021

The chloroplasts of some members of the Dinophyceae are bounded by an envelope consisting of three membranes and having a mean thickness of 230 Å. Within the chloroplast are arranged, in a more or less parallel manner, many lamellae normally composed of three apposed thylakoids, although the number of thylakoids often varies and may reach 30 in a single stack. By study of disintegrated chloroplasts it was found that the thylakoids are circular in shape with a diameter of 0·15 –3·6μ and a mean thickness of 240 Å. Ribosomes, lipid droplets and DNA areas are present in the chloroplast stroma. No connexions were seen between the chloroplasts and any other organelles, nor did the chloroplasts contain girdle lamellae. Stalked pyrenoids, which are found in some dinoflagellates, are shown to arise from the inner face of the chloroplasts, to contain a finely granular material and to be frequently surrounded by an electron-transparent area. These findings are discussed in relation to the fine structure of the chloroplasts and pyrenoids of other algal classes.
Fine structure and radiation resistance in Acinetobacter: studies on a resistant strain
Authors: Thornley Margaret J. , Glauert Audrey M.
Published: April 2021

An electron-microscope study of thin sections and negatively stained preparations of intact cells and isolated cell walls of a bacterium which is moderately resistant to ionizing radiation, Acinetobacter strain 199 A, showed that it is similar to other Gram-negative bacteria except for its mode of division and for the fine structure of some of the surface layers. During division the cells form a fairly thick septum similar to those observed in Gram-positive bacteria. An examination of the appearance and chemical composition of isolated cell walls before and after treatment with enzymes, detergents and lipid solvents revealed that three layers, each with a characteristic fine structure, are present in the cell wall: (1) an outer membrane with an array of peg-like subunits; (2) a layer of wrinkled material which is digested by proteolytic enzymes; and (3) a smooth, rigid layer, which contains the mucopeptide components of the cell wall. These observations are compared with the results of other workers for various Gram-negative bacteria. From comparisons with the structure of more radiation-sensitive strains of Acinetobacter, it appears that layer (2) may be associated with the radiation resistance of the organism.
A radioautographic study of the time course of male meiosis in the newt Triturus vulgaris
Authors: Callan H. G. , Taylor J. H.
Published: April 2021

In male Triturus vulgaris at 16 °C the pre-meiotic synthesis of DNA (S-phase) takes 9–10 days. The S-phase starts 1–2 days after completion of the ultimate spermatogonial mitosis, and extends into leptotene. Heterochromatic regions, most of which lie close to the centromeres, start and finish replicating about 1 day later than other parts of the chromosomes. Synapsis starts 6 days after the end of pre-meiotic S and is completed 8 days later. Pachytene lasts for 4 or 5 days, diplotene for 1 or 2 days, and first metaphase occurs 20 or 21 days after the end of pre-meiotic S. Label distribution at first metaphase in spermatocytes stemming from spermatogonia which incorporated [3H]thymidine during the penultimate intennitotic S shows that random segregation and assortment of labelled and unlabelled chromatids took place at the ultimate spermatogonial mitosis.
Reaction of surface lamella of moth spermatozoa to vinblastine
Authors: Friedländer Michael , Gershon Janine
Published: April 2021

Previous ultrastructural studies appear to indicate that the lacinate appendages (highly elaborated laminar structures which cover the surface of moth spermatozoa) may be intra-cellular derivatives of transient microtubules found in the elongating spermatids of these insects. Additional support for this theory is supplied by the present study in which testes of the warehouse moth Ephestia cantella were treated in vivo with the antimitotic agent vinblastine sulphate. Solutions containing 10−5 M vinblastine caused the lacinate appendages to become poorly resolved, and at 10−3 M they disappeared. This concentration-dependent response of the appendages to vinblastine resembles that of tubulin-containing structures.