bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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 &lt; 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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.