bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of a Dictyostelium chemotaxis mutant with altered chemoattractant binding
Authors: Segall Jeffrey E. , Bominaar Anthony A. , Wallraff Eva , J. W. De Wit René 
Published: April 2021

ABSTRACT
A Dictyostelium discoideutn mutant defective in folate chemotaxis has been analysed using biochemical, behavioural, and genetic methods. A subset of the cell-surface folate binding sites appeared to be locked in a high-affinity state from which folate dissociated extremely slowly. Changes in cell area and motility induced by step increases in folate required 10-to 100-fold higher concentrations than in the wild type. Folate-stimulated cyclic GMP production was also altered. Chemotactic responses to cyclic AMP as well as cyclic AMP-stimulated cyclic GMP production were normal. The mutation responsible for the chemotaxis defect, termed folA1OOO, was localized to linkage group IV. The alterations in folate binding and sensitivity to folate co-localized with the folA1OOO mutation. We conclude that the folA1OOO mutation arrests the folate chemotaxis receptor in a high affinity state that can only poorly transduce folate binding into chemotactic responses.
Distinct controls of dna replication and of nuclear division in the cell cycles of the chlorococcal alga Scenedesmus quadricauda
Authors: Zachleder V. , Šetlík I. 
Published: April 2021

ABSTRACT
In the course of the cell cycle of Scenedesmus quadricauda, the syntheses of RNA and total protein occur in steps. Each step represents an approximate doubling of the preceding amount of RNA or protein per cell. The increase in protein content per cell runs parallel to, but with a constant delay behind, the corresponding RNA steps. When protein synthesis is suppressed (e.g. by maintaining the cells in the dark) after an RNA synthesis step has already occurred the cells double their DNA content, but no corresponding nuclear division occurs and uninuclear daughter cells with double the amount of DNA may be formed. Under conditions of phosphorus or nitrogen starvation RNA synthesis is stopped while protein synthesis continues. In this case, the number of DNA replication rounds corresponds to the reduced RNA content while the number of nuclear divisions tends to follow the number of protein synthesis steps until one genome per nucleus is attained. These results indicate that with each doubling of RNA content the cells become committed to DNA replication, while doubling of protein content is required for the commitment to the corresponding nuclear divisions.
Serum from partially hepatectomized rats induces primary hepatocytes to enter s phase: A role for prostaglandins?
Authors: Little Penelope , Skouteris George G. , Ord Margery G. , Stocken Lloyd A. 
Published: April 2021

ABSTRACT
Serum obtained from partially hepatectomized rats 1, 3 or 24 h after operation was more effective in stimulating DNA synthesis in primary adult rat hepatocytes than serum from sham-operated rats; exposure to the serum for 2h was sufficient to promote growth. Serum from the partially hepatectomized rats contained elevated levels of PGE2 and PGF2α; it promoted hepatocytes to release prostaglandins into their culture medium. Growthpromoting effects of the serum and its capacity to elicit prostaglandin release into the culture medium were inhibited by 0*1 mM-indomethacin or 1 mM-aspirin. 0–1 mM-indomethacin also prevented DNA synthesis if the inhibitor were added 4h after growth had been initiated by serum from partially hepatectomized rats, suggesting that prostaglandins continue to be important for the maintenance of hepatocyte growth for at least 6h.
Neuronal maintenance and neurite extension of adult mouse neurones in non-neuronal cell-reduced cultures is dependent on substratum coating
Authors: Orr Douglas J. , Smith Robert A. 
Published: April 2021

ABSTRACT
Adult mouse DRG neurones have been maintained for 14 days in cultures where non-neuronal cell proliferation was inhibited by the inclusion of 5xlO~6/iM-cytosine arabinoside (AraC) in the medium from the onset of culture. On uncoated plastic neurone numbers significantly declined in the absence of non-neuronal cell outgrowth compared with uninhibited co-cultures. However, when neurones were maintained in the presence of AraC on certain coated surfaces this decrease in neurone numbers was not observed. Combinations of fibronectin (FN) and laminin (LAM) proved most effective for 7 and 14 days in vitro, although either was beneficial if used separately. Microexudates produced by the fibroblast line, 3T6, also significantly improved neuronal counts for 14 days in vitro. However, a microexudate derived from primary cultures of mouse hepatocytes, although advantageous for 7 days in vitro, was not effective in maintaining neurones over the 14-day culture period, reminiscent of previous observations when synthetic cationic agents were used. Electrophoretic analysis of the fibroblast exudate indicated that fibronectin was present in the substrate-attached material generated by this cell line.
The reduction in non-neuronal cell growth facilitated the monitoring of neuronal structural detail by scanning electron microscopy. Examination of neurite extension, indicative of neurone differentiation, was particularly improved. FN/LAM and the fibroblast-derived exudate increased nerve fibre growth, whilst the hepatocyte exudate had little effect on neurite regeneration, and polylysine had a detrimental effect.
The data demonstrate that substrata can have a significant effect on maintenance and differentiation of adult neurones in primary culture. The use of cultured adult sensory neurones instead of only foetal ones in neurobiological research is therefore now a plausible alternative.
Cloning and sequencing of the cyclin-related Cdc13
+ gene and a cytological study of its role in fission yeast mitosis
Authors: Hagan Iain , Hayles Jacqueline , Nurse Paul 
Published: April 2021

ABSTRACT
We have cloned and sequenced the cdcl3+gene from fission yeast. When a major part of the cdc13+ gene is deleted from the chromosome, cells arrest in interphase, but partial loss of gene activity leads to cells containing condensed chromosomes, aberrant septa and a microtubular cytoskeleton with characteristics of both G2 and M. Expression of this phenotype is influenced by the nutritional status of the cell. Our results suggest that the cdc13+gene function is required for the control of the G2 to M transition. It appears to play a role in regulating the separate pathways of events involved in the physical process of mitosis, for example in the reorganization of the cytoskeleton on transition from G2 to mitosis. The cdc134- gene function interacts closely with both the yeast and human homologues of cdc2+ suggesting that mammalian cells may contain a cdc13+ homologue. The gene encodes a putative polypeptide of 482 amino acids, and a central region of 176 amino acids of this polypeptide is 50% identical with sea urchin cyclin. Therefore, the cdc13+ protein is cyclin related and could act as a regulator or substrate of the p34cdc2 protein kinase, which initiates mitosis.
Remodeling of mouse thymocyte nuclei depends on the time of their transfer into activated, homologous oocytes
Authors: Szöllösi Daniel , Łowska Renata , Szöllösi Maria S. , Tarkowski Andrzej K. 
Published: April 2021

ABSTRACT
The potential of parthenogenetically activated mouse oocytes to remodel somatic cell nuclei was studied by ultrastructural means using oocytethymocyte hybrids. Complete nuclear remodeling, initiated by nuclear envelope breakdown and chromosome condensation (which is followed by formation of pronucleus-like nucleus) is possible only during a short time gap between metaphase II and telophase of meiotic division. Maturationpromoting factor activity is high during this period. The thymocyte nucleus can follow the sequence of morphological changes only in concert with the development of the native nucleus and only after exposure of the chromatin to the ooplasm. If hybridization is effected with pronucleate oocytes, the thymocyte nucleus retains its interphase character but shows particular modifications in nucleolar morphology (identical to changes observed during reactivation of the nucleolus in stimulated lymphocyte) and in the activity of the nuclear envelope (blebbing). Thus the nucleus not exposed to maturation-promoting factor activity may be influenced by a ‘programme’ specific for oocyte (blebbing) and by a programme inherent in the introduced somatic cell nucleus.
Cytoplasmic to nuclear translocation of RNA polymerase I is required for lipopolysaccharide-induced nucleolar RNA synthesis and subsequent DNA synthesis in murine B lymphocytes
Authors: Halleck Margaret S. , Schlegel Robert A. , Rose Kathleen M. 
Published: April 2021

ABSTRACT
The synthesis of ribosomal RNA (rRNA) in murine B lymphocytes is markedly elevated in response to mitogens such as lipopolysaccharide (LPS). First, to investigate the mechanism involved, antibodies directed against RNA polymerase I, the enzyme responsible for transcription of ribosomal genes, were introduced into the cytoplasm of lymphocytes via red cell-mediated microinjection and the ability of cells to synthesize RNA was examined. Simultaneous immunofluorescence/autoradiography revealed that 7% or less of the cells injected with specific antibodies prior to stimulation were actively synthesizing rRNA 15 or 40 h following LPS addition. In contrast 19 % and 27 % of cells injected with control IgG were active at these times. Non-ribosomal RNA synthesis was unaffected by the presence of anti-RNA polymerase I antibodies. Since antibodies injected into the cytoplasm were limited to that compartment, these data suggest that rRNA synthesis induced by LPS requires translocation of cytoplasmic RNA polymerase I into the nucleus. Second, to test whether synthesis of rRNA is required for entry into S phase, the effect of anti-RNA polymerase I antibodies on DNA synthesis in response to LPS was evaluated. Only 7 % of cells containing anti-RNA polymerase I antibodies had initiated DNA synthesis 40 h after LPS addition whereas 25 % of cells containing control IgG were actively synthesizing DNA at that time. These results suggest that nuclear accumulation of RNA polymerase I and increased rRNA synthesis are required for LPS-induced DNA synthesis in B lymphocytes.
Characterization of the fission yeast cdc10
+ protein that is required for commitment to the cell cycle
Authors: Simanis Viesturs , Nurse Paul 
Published: April 2021

ABSTRACT
We have used antiserum raised against a β-galacto-sidase-cdcld4- fusion protein to identify the protein product of the cdcHT start gene of Schizosaccharo-myces pombe. This gene is required for progress through the Gi phase of the cell cycle and for activating processes such as the increase in histone mRNA level in preparation for S phase. The protein has an apparent molecular weight of 87 000 and is phosphorylated on multiple serine residues. The protein remains phosphorylated throughout the mitotic cell cycle and shows no significant steady-state changes in level. The antiserum has also detected a protein similar in size to pSTcdc10 in human cells.
Microtubules are acetylated in domains that turn over slowly
Authors: Webster Daniel R. , Borisy Gary G. 
Published: April 2021

ABSTRACT
Tubulin is subject to a post-translational acetylation reaction that is thought to be correlated with increased stability of the modified microtubules (MTs). We sought to test directly the stability of acetylated MTs by determining their specific rate of turnover. We used human fibroblasts, which contain a subset of MTs that display terminal and internal domains of acetylation. The turnover of acetylated domains was analysed by microinjecting cells with biotinylated brain tubulin and determining, by triple-label immunofluorescence, the progress of incorporation of biotinylated tubulin into acetylated and non-acetylated domains. Within two minutes after injection, biotinylated domains were contiguous with virtually all observed non-acetylated MT ends but were not contiguous with terminal acetylated domains, demonstrating that the former were growing while the latter were not. Ten minutes after injection, many MTs lacking acetylated domains had incorporated biotinylated subunits uniformly while most MTs containing acetylated domains remained unlabelled, indicating that non-acetylated MTs were turning over while most acetylated domains were not. One hour after injection, virtually all non-acetylated MTs were labelled with biotin whereas approximately half of the acetylated domains contained biotin, demonstrating that acetylated domains turned over much more slowly than the non-acetylated, bulk array. Nonacetylated MT regions flanking acetylated domains also lacked hapten, indicating that acetylation modified discrete regions along stable MTs. Sixteen hours after injection, cells that had not entered mitosis still retained acetylated domains that had not turned over (13% of all acetylated domains), indicating that acetylated domains can be extremely long-lived. Prophase cells displayed no acetylated tubulin staining, indicating that the maximum lifetime of cytoplasmic acetylated domains was one cell cycle. The results show that in this cell line only limited domains of stable MTs usually become acetylated, and that the turnover of these domains and the MTs that bear them is much slower than that of the bulk array.
Cells: Principles of Molecular Structure and Function
Authors: Downes C S. 
Published: April 2021

ABSTRACT
This textbook is intended to provide a manageable first course in cell biology, for students whose previous acquaintance with the subject and with several underlying disciplines may be rather slight. It succeeds in this aim, and is therefore a valuable addition to the range of texts available, shorter and conciser than the alternatives. There has been no equivalent introductory text since R. D.Dyson’s ‘Cell Biology: a Molecular Approach’, a useful contribution in its time, but now ten years out of date.
Functional recombination of outer dynein arms with outer arm-missing flagellar axonemes of a Chlamydomonas mutant
Authors: Sakakibara Hitoshi , Kamiya Ritsu 
Published: April 2021

ABSTRACT
A flagellar mutant of Chlamydomonas, oda, lacks the entire outer dynein arm but can swim at a speed of one third to half of that of the wild type. We found that the addition of a high-salt extract of wild-type axonemes to demembranated oda cell models restored up to 83 % of the outer arms normally present on the outer-doublet microtubules of wild-type axonemes. Furthermore, when reactivated in the presence of ATP after being mixed with the extract, the oda cell models gained a higher level of motility, close to that of the wild type. The increase in flagellar beat frequency parallelled the increase in the number of restored outer dynein arms. These observations indicate that the axoneme of the oda mutant retains the binding sites for the outer dynein arms, and that the outer arms solubilized with high salt are functionally active. This in vitro recombination system with the oda mutant should be useful as an assay system for various preparations of outer-arm dynein. Evidence is presented that the two axonemes on an oda cell model beat at the same frequency, whereas those on a wild-type model beat at different frequencies. The two oda axonemes beat at the same frequency even after the higher level of motility has been restored by addition of crude dynein extract. We propose that a heterogeneity in the outer dynein arms is responsible for the frequency imbalance between the two flagella of wild-type Chlamydomonas.
Differential partitioning of plasma membrane proteins into the Triton X-100-insoluble cytoskeleton fraction during concanavalin A-induced receptor redistribution
Authors: Patton Wayne F. , Dhanak Michelle R. , Jacobson Bruce S. 
Published: April 2021

ABSTRACT
The plasma membrane proteins of Dictyostelium discoideum were characterized with respect to their partitioning into the Triton-insoluble cytoskeleton fraction of the cell during concanavalin A-induced capping. Two fractions of plasma membrane-associated concanavalin A were identified; one that immediately associated with the cytoskeleton fraction via cell surface glycoproteins, and one that partitioned with the cytoskeleton only after extensive cell surface glycoprotein cross-linking. Three major classes of polypeptides were found in the plasma membrane that differed with respect to their partitioning properties into the cytoskeleton fraction. The temporal order of association of the polypeptides with the cytoskeleton during concanavalin A-induced capping corresponded to the strength of their association with the cytoskeleton fraction as determined by pH and ionic strength elution from unligated cytoskeletons.
Mitosis in Drosophila
Authors: Glover David M. 
Published: April 2021

ABSTRACT
Drosophila is an attractive organism in which to study both the rapid rounds of mitosis typical of embryonic development in many species, and the longer cell cycles of diploid tissues later in development. Mutations in genes essential for mitosis in Drosophila may result in lethality in late embryonic, larval or pupal stages of development. In addition, mutations in many genes required for the nuclear divisions of early embryogenesis have been found in screens for female sterility. The mitotic mutations have phenotypes indicative of lesions at a variety of mitotic stages. A combined molecular and genetic analysis of these genes has the potential to unravel the complex set of protein-protein interactions that occur in this dynamic process.
A gene for the suppression of anchorage independence is located in rat chromosome 5 bands q22-23, and the rat alpha-interferon locus maps at the same region
Authors: Islam M. Quamrul , Szpirer Josiane , Szpirer Claude , Islam Khaleda , Dasnoy Jean-Francois , Levan Göran 
Published: April 2021

ABSTRACT
Cell hybrids between malignant mouse hepatoma cells and normal rat fibroblasts with approximately one set of chromosomes from each parent exhibited remarkable karyotypic stability. Most chromosomes of both parents were retained even after prolonged culture in vitro. Normally, such hybrids showed suppression of the transformed phenotype and formed no colonies in soft agar. However, two hybrids, BS140 and BS181, formed a few colonies in soft agar when many cells were seeded, and also occasional foci of cells were detected piling up in monolayer cell cultures. We isolated soft agar colonies (a-subclones) and subclones from foci (h-subclones) of both hybrids, and, as a control, subclones of cells from random areas without foci of one hybrid (BS181 p-subclones). When tested for soft agar growth, cells from the a- and h-subclones of both BS140 and BS181 formed colonies at frequencies comparable to the malignant mouse hepatoma parent, whereas the control cells of the BS181 p-subclones (like the normal rat parental cells) yielded no soft agar colonies. All the cell lines were subjected to detailed karyotype analysis in G-banding, which resulted in the finding that cells from the original BS140 hybrid contained at least one copy of each rat chromosome, whereas BS140 a- and h-subclones had lost both copies of rat chromosome 5. Similarly, the original BS181 hybrid contained at least one copy of each rat chromosome, whereas BS181 a- and h-subclones displayed a deletion of the segment q22-23 of rat chromosome 5. In contrast, the control BS181 p-subclones contained one or two copies of non-deleted rat chromosome 5. The conclusion is that a gene for the suppression of anchorage independence is located in the segment 5q22-23. We propose to call this gene SAI1 (for suppression of anchorage independence).
Using Southern blotting, we tested whether any of several gene probes, known to correspond to DNA sequences in rat chromosome 5, were homologous to sequences in the deletion. Only one probe, corresponding to the active alphai-interferon gene, was shown to be located within the deletion. Hence, the SAI1 gene is closely linked to the alpha 1 -interferon gene, and might be identical to this locus.
Potassium depletion inhibits the intracellular transport of secretory proteins between the endoplasmic reticulum and the golgi complex
Authors: Judah Jacob D. , Howell Kathryn E. , Taylor Janet A. , Quinn Paul S. 
Published: April 2021

ABSTRACT
In this paper we show that hepatocytes that have been depleted of K+ secrete albumin, α-1-anti-trypsin and transferrin at a slower rate than cells to which K+ has been returned. K+ depletion has no effect on the intracellular nucleotide pools, and we provide evidence that the inhibitions of secretion caused by depletion of K+ and depletion of ATP are independent.
Studies of the processing of α-1-anti-trypsin show that K+ depletion inhibits the formation of the mature form of the protein, but that immature forms are never secreted. In cells to which K+ was returned, secretion of the mature form was restored. This implies that transport is blocked at a point before the proteins reach the processing enzymes. Proteins delayed by K+ depletion are not removed from the secretory pathway, but are free to mix with protein synthesized subsequently.
These data are supported by subcellular fractionation experiments, which show that the secretory proteins are delayed before reaching the Golgi complex, and by immunoelectron microscopic studies. These show that in K+-deficient cells the morphology of both the endoplasmic reticulum and the Golgi complex is normal. The secretory proteins are trapped in smooth vesicles that contain reaction product when incubated for glucose-6-phosphatase, a marker for the endoplasmic reticulum.
mrnas and a cloned histone gene are differentially expressed during anther and pollen development in rice (Oryza sativa L.)
Authors: Raghavan V. 
Published: April 2021

ABSTRACT
Spatial and temporal changes in the distribution of mRNA sequences during anther and pollen development in rice (Oryza sativa) were investigated by in situ hybridization with [3H] polyuridylic acid ([3H]poly(U)) and a cloned rice histone gene probe. Annealing of sections with [3H]poly(U) showed that poly(A)-containing RNA (poly(A)+RNA) was uniformly distributed in the cells of the anther primordium. During the formation of the archesporial initial, the primary parietal cell, the primary sporogenous cell and tapetum, there was no differential accumulation of poly(A)+RNA in their progenitor cells. Preparatory to meiosis, there was a sharp decrease in poly(A)+RNA concentration in the epidermis and middle layer of the anther wall, although the label persisted in the endothecium, tapetum and microsporocytes. Poly(A)+RNA concentration decreased in these cell types during meiosis and attained very low levels in the disintegrating tapetum and the persistent endothecium of the post-meiotic anther. Pollen development was characterized by the absence of [3H]poly(U) binding sites in the uninucleate microspores and by their presence in the vegetative and generative cells of the bicellular pollen grain. In anther sections hybridized with [3H]histone probe, gene expression was only detected in the endothecium of the premeiotic anther and in the bicellular pollen grains.