bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytokinesis in Aspergillus nidulans is controlled by cell size, nuclear positioning and mitosis
Authors: Wolkow Tom D. , Harris Steven D. , Hamer John E. 
Published: April 2021

ABSTRACT
The mycelium of Aspergillus nidulans is composed of multinucleate cellular compartments delimited by crosswalls called septa. Septum formation is dependent on mitosis and requires the recruitment of actin to the site of septum formation. Employing a collection of temperature sensitive nuclear distribution (nudA2, nudC3 and nudF7), nuclear division (nimA5, hfaB3), and septation (sepD5, sepGl) mutants, we have investigated the interdependency among nuclear positioning, mitosis, and cell growth in structuring the cellular compartments of A. nidulans. The cellular compartments of nud+ strains were highly uniform with regard to nuclear distribution and averaged 38 µm in length. Incubation of nud mutants at semi-restrictive temperature resulted in aberrant nuclear distribution that appeared to direct the formation of variable-sized cellular compart ments, ranging from 5 µm to greater than 81 µm. In germinating spores, the first septum forms at the basal end of the germ tube following the third round of nuclear division. Germlings must undergo mitosis in order to form a septum. Temperature-sensitive mitotic mutants were used to show that a single nuclear division is sufficient to activate septum formation, provided a critical cell size has been attained. In mitotic mutants and wild-type cells, delays in nuclear division resulted in the misplacement of the first septum. These results strongly support the role of mitotic nuclei in determining septal placement, and suggest that cell size control is post-mitotic in A. nidulans.
TGFβl promotes actin cytoskeleton reorganization and migratory phenotype in epithelial tracheal cells in primary culture
Authors: Boland Sonja , Boisvieux-Ulrich Emmanuelle , Houcine Odile , Baeza-Squiban Armelle , Pouchelet Marcel , Schoëvaërt Damien , Marano Francelyne 
Published: April 2021

ABSTRACT
In the present study we have investigated the effects of transforming growth factor β (TGFβ1) on rabbit tracheal epithelial cells in primary culture, with respect to cell proliferation and differentiation. Epithelial tracheal cells derived from an explant plated on an extracellular matrix, formed an outgrowth resulting from cell division and cell migration. TGFβ1 treatment produced a negative effect on cell proliferation, but in contrast, promoted a marked enhancement of cell migration and increase in outgrowth surface. TGFβ1 induced marked cell shape changes, including cell spreading and lack of stratification, associated with reduced cell-cell contacts and increased cell-substratum anchorage, as seen by electron microscopic observations. Immunocytological studies demonstrated major TGFβ1-induced actin cytoskeleton reorganization, corresponding to the development of a basal stress fiber network and decrease of the annular cell border, without affecting the tight junctions. The migratory phenotype was approached by microcinematography which clearly showed that TGFβ1 triggered a stimulatory effect on migration of epithelial cells, determined using an image analyzing system. Present findings suggest a beneficial role for TGFβ1 during wound healing in providing the acquisition of a migratory phenotype, with a higher capacity to migrate either on collagen or on different extracellular matrix components including laminin and fibronectin. Conversely, present data are not consistent with a squamous response to TGFβ1, since metaplastic differentiation did not occur, as characterized by cytokeratin expression and cross-linked envelopes formation.
Chromatin organization in the homogeneously staining regions of a methotrexate-resistant mouse cell line: Interspersion of inactive and active chromatin domains distinguished by acetylation of histone H4
Authors: Nicol Linda , Jeppesen Peter 
Published: April 2021

ABSTRACT
We have analyzed the organization of the homogeneously staining regions (HSRs) in chromosomes from a methotrexate-resistant mouse melanoma cell line. Fluorescence in situ hybridization techniques were used to localize satellite DNA sequences and the amplified copies of the dihydrofolate reductase (DHFR) gene that confer drug-resistance, in combination with immunofluorescence using antibody probes to differentiate chromatin structure. We show that the major DNA species contained in the HSRs is mouse major satellite, confirming previous reports, and that this is interspersed with DHFR DNA in an alternating tandem array that can be resolved at the cytological level. Mouse minor satellite DNA, which is normally located at centromeres, is also distributed along the HSRs, but does not appear to interfere with centromere function. The blocks of major satellite DNA are coincident with chromatin domains that are labelled by an autoantibody that recognizes a mammalian homologue of Drosophila heterochromatin-associated protein 1, shown previously to be confined to centric heterochromatin in mouse. An antiserum that specifically recognizes acetylated histone H4, a marker for active chromatin, fails to bind to the satellite DNA domains, but labels the intervening segments containing DHFR DNA. We can find no evidence for the spreading of the inactive chromatin domains into adjacent active chromatin, even after extended passaging of cells in the absence of methotrexate selection.
The spacer protein Spc110p targets calmodulin to the central plaque of the yeast spindle pole body
Authors: Spang Anne , Grein Katrin , Schiebel Elmar 
Published: April 2021

ABSTRACT
Yeast calmodulin (CaM) was found to be localized to the microtubule organizing centre, the spindle pole body. The spindle pole body is a multi-layered structure consisting of outer, central and inner plaques. In this paper, we report that a fraction of CaM is in association with the central plaque of the spindle pole body. This localization is dependent on the calmodulin-binding site of another spindle pole body component, Spc110p, which serves as a spacer connecting the inner plaque with the central plaque. Since the CaM-binding site of Spc110p is located near the carboxy terminus, Spc110p-dependent localization of calmodulin defines the orientation of Spc110p with the carboxy terminus towards the central plaque and the amino terminus towards the inner plaque. This orientation of Spc110p was confirmed using antibodies specific for the amino-terminal end of Spc110p, which predominantly labelled the inner plaque. In addition, synthetic peptides corresponding to the calmodulin-binding site of Spc110p bound to calmodulin with a Kd in the nanomolar range and nearly independent of Ca2+.
Location of the HIV-1 Rev protein during mitosis: Inactivation of the nuclear export signal alters the pathway for postmitotic reentry into nucleoli
Authors: Dundr Miroslav , Leno Gregory H. , Lewis Nancy , Rekosh David , Hammarskjöld Marie-Louise , Olson Mark O. J. 
Published: April 2021

ABSTRACT
The HIV-1 Rev protein localizes predominantly to the nucleolus of HIV-1-infected or Rev-expressing cells. The subcellular location of Rev during mitotic nucleolar disintegration was examined at various stages of mitosis in synchronized Rev-expressing CMT3 cells. During early prophase Rev was predominantly located in disintegrating nucleoli and began to accumulate at the peripheral regions of chromosomes in late prophase, eventually distributing uniformly on all chromosomes in prometaphase. In anaphase Rev remained associated with the perichromosomal regions, but significant amounts of Rev were also seen in numerous nucleolus-derived foci. The movement of Rev from disintegrating nucleoli to perichromosomal regions and foci was similar to that of nonribosomal nucleolar proteins, including fibrillarin, nucleolin, protein B23 and p52 of the granular component. During telophase Rev remained associated with perichromosomal regions and mitotic foci until the nuclear envelope started to reform.
When nuclear envelope formation was complete in late telophase, nonribosomal nucleolar proteins were present in prenucleolar bodies (PNBs) which were eventually incorporated into nucleoli; at the same time, Rev was excluded from nuclei. In contrast, a trans-dominant negative Rev protein containing an inactive nuclear export signal reentered nuclei by the nonribosomal nucleolar protein pathway in late telophase, associating with PNBs and reformed nucleoli. Rev protein reentry into postmitotic nuclei was delayed until early G1 phase, but before the arrival of ribosomal protein S6. Thus, Rev behaves like a nonribosomal nucleolar protein through mitosis until early telophase; however, its nuclear reentry seems to require reestablishment of both a nuclear import system and active nucleoli.
Molecular characterization of mitofilin (HMP), a mitochondria-associated protein with predicted coiled coil and intermembrane space targeting domains
Authors: Odgren Paul R. , Toukatly Gary , Bangs Peter L. , Gilmore Reid , Fey Edward G. 
Published: April 2021

ABSTRACT
We have identified and characterized a human protein of the mitochondria which we call mitofilin. Using monoclonal and polyclonal antibodies, we have isolated cDNA clones and characterized mitofilin biochemically. It appears as a 90 and 91 kDa doublet in western blots and is translated from a single 2.7 kb mRNA. Antibodies raised against cellular and bacterially-expressed protein give identical cytoplasmic immunofluorescence and immunoblot results. Mitofilin co-localizes with mitochondria in immunofluorescence experiments and co-purifies with mitochondria. Double label studies show co-localization only with mitochondria and not with Golgi or endoplasmic reticulum. Colocalization with mitochondria is retained when actin or tubulin are de-polymerized, and mitofilin is expressed in all human cell types tested. The cDNA encodes a polypeptide with a central α-helical region with predicted coiled coil domains flanked by globular amino and carboxy termini. Unlike coiled coil motor proteins, mitofilin is resistant to detergent extraction. The presence of mitochondrial targeting and stop-transfer sequences, along with the accessibility of mitofilin to limited proteolysis suggests that it resides predominantly in the intermembrane space, consistent with immuno-electron micrographs which show mitofilin mainly at the mitochondrial periphery. The cDNA sequence of mitofilin is identical to that recently reported by Icho et al. (1994; Gene 144, 301-306) for a mRNA preferentially expressed in heart muscle (HMP), consistent with the high levels of mitochondria in cardiac myocytes.
Expression, localization and functional role of small GTPases of the Rab3 family in insulin-secreting cells
Authors: Regazzi Romano , Ravazzola Mariella , Iezzi Mariella , Lang Jochen , Zahraoui Ahmed , Andereggen Elisabeth , Morel Philippe , Takai Yoshimi , Wollheim Claes B. 
Published: April 2021

ABSTRACT
We examined the presence of small molecular mass GTP-binding proteins of the Rab3 family in different insulinsecreting cells. Rab3B and Rab3C were identified by western blotting in rat and in human pancreatic islets, in two rat insulin-secreting cell lines, RINm5F and INS-1, as well as in the hamster cell line HIT-T15. In contrast, Rab3A was detected in rat pancreatic islets as well as in the two insulin-secreting rat cell lines but not in human pancreatic islets and was only barely discernible in HIT-T15 cells. These findings were confirmed by two-dimensional gel electrophoresis followed by GTP-overlay of homogenates of pancreatic islets and of the purified protein. Northern blotting analysis revealed that Rab3D is expressed in the same insulin-secreting cells as Rab3A. Separation of the cells of the rat islets by fluorescence-activated cell sorting demonstrated that Rab3A was exclusively expressed in β-cells. Rab3A was found to be associated with insulin-containing secretory granules both by immunoflu-orescence, immunoelectron microscopy and after sucrose density gradient. Overexpression in HIT-T15 cells of a Rab3A mutant deficient in GTP hydrolysis inhibited insulin secretion stimulated by a mixture of nutrients and bombesin. Insulin release triggered by these secretagogues was also slightly decresed by the overexpression of wildtype Rab3A but not by the overexpression of wild-type Rab5A and of a Rab5A mutant deficient in GTP hydrolysis. Finally, we studied the expression in insulin-secreting cells of rabphilin-3A, a putative effector protein that associates with the GTP-bound form of Rab3A. This Rab3A effector was not detectable in any of the cells investigated in the present study. Taken together these results indicate an involvement of Rab3A in the control of insulin release in rat and hamster. In human β-cells, a different Rab3 isoform but with homologous function may replace Rab3A.
Nuclear lamina and nuclear matrix organization in sperm pronuclei assembled in Xenopus egg extract
Authors: Zhang Chuanmao , Jenkins Hazel , Goldberg Martin W. , Allen Terry D. , Hutchison Christopher J. 
Published: April 2021

ABSTRACT
Nuclear lamina and matrices were prepared from sperm pronuclei assembled in Xenopus egg extracts using a fractionation and extraction procedure. Indirect immunofluorescence revealed that while chromatin was efficiently removed from nuclei during the extraction procedure, the distribution of lamins was unaffected. Consistent with this data, the ammount of lamin B3, determined by immunoblotting, was not affected through the extraction procedure. Nuclear matrices were visualised in DGD sections by TEM. Within these sections filaments were observed both at the boundary of the nucleus (the lamina) and within the body of the nucleus (internal nuclear matrix filaments). To improve resolution, nuclear matrices were also prepared as whole mounts and viewed using field emission in lens scanning electron microscopy (FEISEM). This technique revealed two distinct networks of filaments. Filaments lying at the surface of nuclear matrices interconnected nuclear pores. These filaments were readily labelled with monoclonal anti-lamin B3 antibodies. Filaments lying within the body of the nuclear matrix were highly branched but were not readily labelled with antilamin B3 antibodies. Nuclear matrices were also prepared from sperm pronuclei assembled in lamin B3 depleted extracts. Using FEISEM, filaments were also detected in these preparations. However, these filaments were poorly organised and often appeared to aggregate. To confirm these results nuclear matrices were also observed as whole mounts using TEM. Nuclear matrices prepared from control nuclei contained a dense array of interconnected filaments. Many (but not all) of these filaments were labelled with anti-lamin B3 antibodies. In contrast, nuclear matrices prepared from ‘lamin depleted nuclei’ contained poorly organised or aggregated filaments which were not specifically labelled with anti-lamin B3 antibodies.
Putative GTPase Gtr1p genetically interacts with the RanGTPase cycle in Saccharomyces cerevisiae
Authors: Nakashima Nobutaka , Hayashi Naoyuki , Noguchi Eishi , Nishimoto Takeharu 
Published: April 2021

ABSTRACT
In order to identify a protein interacting with RCC1, a guanine nucleotide-exchange factor for the nuclear GTPase Ran, we isolated a series of cold-sensitive suppressors of mtr1-2, a temperature-sensitive mutant of the Saccharomyces cerevisiae RCC1 homologue. One of the isolated suppressor mutants was mutated in the putative GTPase Gtr1p, being designated as gtr1-11. It also suppressed other alleles of mtr1-2, srm1-1 and prp20-1 in contrast to overexpression of the S. cerevisiae Ran/TC4 homologue Gsp1p, previously reported to suppress prp20-1, but not mtr1-2 or srm1-1. Furthermore, gtr1-11 suppressed the rna1-1, temperature-sensitive mutant of the Gsp1p GTPase-activating protein, but not the srp1-31, temperature-sensitive mutant of the S. cerevisiae importin α homologue. mtr1-2, srm1-1 and prp20-1 were also suppressed by overexpression of the mutated Gtr1p, Gtr1-11p. In summary, Gtr1p that was localized in the cytoplasm by immunofluoresence staining was suggested to function as a negative regulator for the Ran/TC4 GTPase cycle.
Engagement of L-selectin impairs the actin polymerizing capacity of β2 integrins on neutrophils
Authors: Ng-Sikorski Janet , Lindén Lotta , Eierman David , Franzen Lennart , Molony Leslie , Andersson Tommy 
Published: April 2021

ABSTRACT
A sequential activation of L-selectin and β2-integrins on neutrophils is crucial for the rolling, adherence and subsequent migration of these cells on the endothelium. However, little is known about a possible interplay between these adhesion receptors in the final regulation of cell motility. The results presented here show that sulfatides themselves (here used as tools to activate L-selectins), have no major effect on the cellular content of filamentous actin (F-actin), but cause a time-related decrease in the β2-integrin-induced formation of F-actin. This effect of sulfatides was abolished in cells lacking L-selectin as a result of pretreatment with chymotrypsin. A similar sulfatide-induced activation of Lselectin also caused a pronounced and time-related decrease of a subsequent chemotactic peptide-induced F-actin response. The effect of sulfatides on both β2-integrin- and chemotactic peptide-induced F-actin were abolished if Lselectin were blocked by preincubating the cells with specific antibodies to L-selectin. These effects of L-selectin engagement on cellular F-actin content were neither abolished by blocking the cytosolic free Ca2+ signal with bis(2-amino-5-methylphenoxy)ethane-N,N,N’,N’-tetraacetic-acid tetraacetoxymethyly ester (MAPT/AM) nor by blocking a cAMP-induced activation of protein kinase A by pretreating the cells with adenosine-3’,5’-cyclic monophosphorothioate (Rp-cAMPS). Instead we found that L-selectin engagement impaired an early β2-integrin-induced tyrosine kinase activation, an event shown to be necessary for a normal β2-integrin-mediated F-actin response. The present demonstration of a negative feed-back function of L-selectin on β2-integrin-induced modulations of the actin cytoskeleton, suggests that the relative distribution and/or density of the respective L-selectin and β2-integrin ligands on endothelial cells might be important factors in determining the final site of firm adhesion and extravasation of neutrophils.
Mitosis in heterobasidiomycetous yeasts: II. Rhodosporidium sp. (Rhodotorula glutinis) and Aessosporon salmonicolor (Sporobolomyces salmonicolor)
Authors: Mccully E. Kathleen , Robinow C. F. 
Published: April 2021

ABSTRACT
Mitotic events similar to those in Leucosporidium scottii also take place in 2 other hetero-basidiomycetous yeasts – Rhodosporidium sp. and Aessosporon salmonicolor, which were formerly known as Rhodotorula glutinis and Sporobolomyces salmonicolor. Therefore it is proposed that a mitosis which takes place within the bud may be a distinctive characteristic of heterobasidio-mycetous yeasts which can be used as a taxonomic indicator of basidiomycete relationships in asporogenous yeasts.
Mitosis in A. salmonicolor seems to be identical to that which we have previously described in L. scottii but a few differences have been found in Rhodosporidium sp. These are now described in detail.
Structures of physiological interest in the frog heart ventricle
Authors: Page Sally G. , Niedergerke R. 
Published: April 2021

ABSTRACT
Two structures of physiological interest in frog heart ventricles have been examined in detail: (a) the layer of endothelial cells which encloses each bundle of heart fibres, and (b) the sarcoplasmic reticulum (SR) inside the heart fibres. Some additional observations on fibre sizes and types have been made.
Movement across the endothelial cell layer of molecules (molecular or ionic size ≤ 12·5 nm) occurs through narrow clefts separating each endothelial cell from its neighbour. This conclusion results from experiments made with the extracellular markers ferritin and horseradish peroxidase.
A diffusion equation describing the movement of solutes into and out of the fibre bundle has been derived using several geometrical parameters, such as the length and width of the clefts and the size of the extracellular aqueous space inside the bundle, all of which were determined from electron micrographs of the tissue.
The theoretical solution for a stepwise change of external calcium concentration gives a half-time of 2·3 s (± 0·8 s, s.D. of 13 bundles) for diffusion equilibrium at the surface of the heart fibres; this value, however, is likely to be an overestimate, by some 20–30%, on account of several systematic errors which are described.
The sarcoplasmic reticulum in heart fibres consists of a network of thin tubules which partially encircle the myofibrils at Z-line level and also form occasional longitudinal connexions. Branches extend to peripheral regions of the cell and terminate in close apposition to the inner surface of the cell membrane. The volume of the SR is estimated to be approximately 0-5 % of the myofibrillar volume of the cells.
Cross-sectional areas of heart fibres (and also their shapes) vary considerably, from less than 2 to more than 100 μm2 (average 17·4 μm2). Fibres of large size and small surface/volume ratio contain many fewer myofibrils and more glycogen granules than fibres of the same size but larger surface/volume ratio.
Physiological implications of these results are discussed.
On the physical identity of scintillons: Bioluminescent particles in Gonyaulax polyedra
Authors: Fogel Margaret , Schmitter Ruth E. , Hastings J. W. 
Published: April 2021

ABSTRACT
The physical identity of the bioluminescent particles (‘scintillons’) extracted from the marine dinoflagellate Gonyaulax polyedra was investigated by electron microscopy and particle counts of the active fractions from sucrose density gradients. Membranous structures are abundantly present in purified fractions, while there is a decrease, relative to activity, in the numbers of guanine crystals, which had previously been implicated as bioluminescent structures. The significance of these findings with respect to the in vivo scinrillon is discussed.
Origin and structure of embryoids arising from epidermal cells of the stem of Ranunculus sceleratus l
Authors: Konar R. N. , Thomas E. , Street H. E. 
Published: April 2021

ABSTRACT
Embryoids are initiated from single highly cytoplasmic cells of the stem epidermis of plantlets of Ranunculus sceleratus L. derived from callus cultures. The embryoids show embryological development of the Crucifer type except that the suspensor is reduced or suppressed. The cells of the young embryoids have a large central nucleus surrounded by small vacuoles, a cytoplasm rich in free ribosomes or ribosomes in small polysomes, prominent amyloplastids and abundant spherosomes. These cells also frequently contain multivesicular and myelin bodies. The spherosomes are observed in various stages of development; they are typically arranged in a layer below the cell wall, the space between the spherosomes and the wall being rich in spherical vesicles and microtubules. As embryoid development proceeds the plastids show internal differentiation; globular centres and, surrounding them, electron-transparent droplets are associated with the origin of the thylakoid membranes. The walls of the embryogenic cells are initially rich in plasmodesmata but as the embryoid develops cytoplasmic continuity with the embedding tissue is severed and the embryoid is clearly delineated. The embryology and fine structure of the embryoid cells is compared with that of zygotic embryos of Capsella and Ranunculus.