bluuebunny/crossref_metadata_2025_split huggingface dataset:
Saccharomyces cerevisiae mutants lacking a functional vacuole are defective for aspects of the pheromone response
Authors: Dullo Vjekoslav , Riezman Howard 
Published: April 2021

ABSTRACT
The endl mutant belongs to a group of four vacuolar protein sorting mutants (class C vps) that lack a morphologically distinguishable and functional vacuole. These mutants share several other phenotypes, such as the inability to grow at 37 °C or on nonfermentable carbon sources. We show that, as in the case of the endl mutant, vpsl6, vpsl8 and vps33 mutants all internalize but do not degrade α. In addition, all four mutants are defective for α- factor-induced projection formation to the same extent. A more detailed investigation of pheromone response in the endl mutant reveals that one aspect of the early response (induction of FUS1) is as defective as late responses (cell cycle arrest and projection formation). In contrast, another measure of the early response (induction of STE2) is normal. These data suggest that the biogenesis of a functional vacuole is necessary for optimal response to pheromone.
Microtubule distribution and function in early Pelvetia development
Authors: Kropf Darryl L. , Maddock Anna , Gard David L. 
Published: April 2021

ABSTRACT
We have used immunofluorescence microscopy to examine the distribution of microtubules (Mts) during the first two cell cycles in embryos of the brown alga, Pelvetia. Prior to germination of the zygote at 12 h post-fertilization, Mts radiated from the circumnuclear region into the peripheral cytoplasm. After rhizoid emergence, Mts resolved into two perinuclear microtubule organizing centers (MTOCs). The axis defined by the pair of MTOCs was oriented transverse to the growth axis, with Mts extending from each MTOC into the rhizoid. The axis defined by the MTOCs then reoriented by 90 degrees, and aligned with the growth axis. The first mitotic spindle formed between these MTOCs. The division plane bisected the spindle, giving rise to rhizoid and thallus cells with distinct developmental potentials. During the second cell cycle, the axis defined by MTOCs in the rhizoid cell again reoriented from an orthogonal to an axial alignment with respect to the growth axis. MTOC reorientation did not occur in the thallus cell, and the division planes in the rhizoid and thallus cells were orthogonal to one another.
Zygotes treated with amiprophos methyl (APM) or taxol established an axis and initiated rhizoid outgrowth. However, treated zygotes ceased growing soon after germination and failed to divide. Cytochalasin D, which prevents establishment of the developmental axis, interfered with the proper orientation of the spindle. From these results we conclude that(1)Mts are not required for establishment of the rhizoid-thallus axis or rhizoid germination;(2)an F-actin-dependent process, probably establishment of a developmental axis, is required for rotation of the axis defined by MTOCs; and (3) the alignment of perinuclear MTOCs dictates the orientation of spindle and subsequent division planes, and thereby controls cell lineage.
Selective digestion of nuclear envelopes from Xenopus oocyte germinal vesicles: possible structural role for the nuclear lamina
Authors: Whytock Sue , Moir Robert D. , Stewart Murray 
Published: April 2021

ABSTRACT
We have used enzymic digestion as a structural probe to investigate components of the nuclear envelope of germinal vesicles from Xenopus oocytes. Previous studies have shown that these envelopes are composed of a double membrane in which nuclear pore complexes are embedded. The nuclear pore complexes are linked to a fibrous lamina that underlies the nucleoplasmic face of the envelope. The pores are also linked by pore-connecting fibrils that attach near their cytoplasmic face. Xenopus oocyte nuclear envelopes were remarkably resistant to extraction with salt solutions and, even after treatment with 1M NaCl or 3 M MgCl2, pores, lamina and pore-connecting fibrils remained intact. However, mild proteolysis with trypsin selectively removed the lamina fibres from Triton-extracted nuclear envelopes to leave only the pore complexes and connecting fibrils. This observation confirmed that the pore connecting fibrils were different from the lamina fibres and were probably constructed from different proteins. Trypsin digestion followed by Triton treatment resulted in the complete disintegration of the nuclear envelope, providing direct evidence for a structural role for the lamina in maintaining envelope integrity. Digestion with ribonuclease did not produce any marked change in the structure of Triton-extracted nuclear envelopes, indicating that probably neither the pore-connecting fibrils nor the cytoplasmic granules on the pore complexes contained a substantial proportion of RNA that was vital for their structural integrity.
p34cdc2 homologue level, cell division, phytohormone responsiveness and cell differentiation in wheat leaves
Authors: John P. C. L. , Sek F. J. , Carmichael J. P. , Mccurdy D. W. 
Published: April 2021

ABSTRACT
Formation of a plant involves generation of new cells by the division cycle and development in these of specialised structure and metabolism. Specialisation is accompanied by a decreasing capacity for division, which declines with particular rapidity in cells of monocotyledonous plants such as the cereals. Here we report that in wheat leaves a homologue of the cell cycle control protein p34cdca participates in the control of these developmental programmes. Accumulation of p34cdc2 to a maximum level in dividing cells and the cessation of its accumulation during subsequent cell growth and expansion indicate that it contributes specifically to division. There is a decline in p34cdc2 level as cell differentiation pro ceeds, in close parallel with the previously established decline of cell division in response to auxin hormones. A basal level of p34cdc2 in fully differentiated cells that is one-sixteenth of that in dividing cells correlates with their loss of capacity to divide. We conclude that p34cdc2 level is controlled in diverse multicellular eukaryotes and suggest that it is an important element in the switch from cell division to differentiation.
Development of desmosomal adhesion between MDCK cells following calcium switching
Authors: Mattey D. L. , Burdge G. , Garrod D. R. 
Published: April 2021

ABSTRACT
The development or maturation of intercellular adhesions following their initiation has received very little attention even though this is an area of significance for a variety of in vivo processes. Using Ca2+-induced desmosome formation in MDCK cells as a study system it is shown that, following its initiation, desmosome formation continues for many hours. Following Ca2+ switching the major desmosomal glycoproteins, dg2/3a,b (desmocollins), accumulate progressively at the cell surface. Accumulation is first detectable within 45 min, but continues linearly for ∼16h, reaching a plateau at 24–32 h at 15 times the amount present in low-Ca2+ medium (LCM). Desmosomes do not increase in size during this time, but appear to become more numerous. These results suggest that cells progressively increase their desmosome-mediated adhesion over this period of time.
Cycloheximide treatment shows that ∼93% of the total dg2/3a,b accumulation is dependent upon protein synthesis after Ca2+ switching and only ∼7% on assembly of pre-synthesised material. Thus, although triggering of desmosome formation is rapid, protein synthesis makes a major contribution to the gradual development of desmosomal adhesion in these cells.
The initial assembly phase itself can be inhibited by treating cells in LCM with chloroquine, which reduces the cell surface concentration of dg2/3a,b by 40–50%. However, slow dg2/3a,b accumulation does take place in chloroquine and, if protein synthesis is permitted, desmosome formation occurs.
It is suggested that when cell contacts are formed in vivo, maximisation of intercellular adhesiveness may take many hours and is dependent on the synthesis and accumulation of adhesive components.
Polarization of pseudopodial activities: cytoskeletal mechanisms
Authors: Vasiliev J. M. 
Published: April 2021

ABSTRACT
The reorganization of the cytoskeleton resulting in a stabilized polarization in cells of two types, Dictyo-stelium amoebae and cultured mammalian fibroblasts, is compared. It is suggested that there are two levels of reorganization: basal level reorganization of actin-myosin cortex and a higher level of reorganization of microtubules and intermediate filaments.
Non-neuronal 210×103Mr microtubule-associated protein (MAP4) contains a domain homologous to the microtubule-binding domains of neuronal MAP2 and tau
Authors: Chapin Steven J. , Chloë Bulinski Jeannette 
Published: April 2021

ABSTRACT
A polyclonal antiserum raised against a HeLa cell microtubule-associated protein of Mr210000 (210 kD MAP or MAP4), an abundant non-neuronal MAP, was used to isolate cDNA clones encoding MAP4 from a human fetal brain λ gtll cDNA expression library. The largest of these clones, pMAP4.245, contains an insert of 4.1 kb and encodes a 245 kD β-galactosidase fusion protein. Evidence that pMAP4.245 encodes MAP4 sequences includes immunoabsorption of MAP4 antibodies with the pMAP4.245 fusion protein, as well as identity of protein sequences obtained from HeLa 210 kD MAP4 with amino acid sequences encoded by pMAP4.245. The MAP4.245 cDNA hybridizes to several large (∼6–9 kb) transcripts on Northern blots of HeLa cell RNA. DNA sequencing of overlapping MAP4 cDNA clones revealed a long open reading frame containing a C-terminal region with three imperfect 18-amino acid repeats; this region is homologous to a motif present in the microtubule (MT)-binding domain of two prominent neuronal MAPs, MAP2 and tau. The pMAP4.245 sequence also encoded a series of unrelated repeats, located in the MAP’s projection domain, N-terminal to the MT-binding domain. MAP4.245 fusion proteins bound to MTs in vitro, while fusion proteins that contained only the projection domain repeats failed to bind specifically to MTs. Thus, the major human non-neuronal MAP resembles two neuronal MAPs in its MT-binding domain, while most of the molecule has sequences, and presumably functions, distinct from those of the neuronal MAPs.
Murine cDNAs coding for the centrosomal antigen centrosomin A*
Authors: Joswig Gaby , Petzelt Christian , Werner Dieter 
Published: April 2021

ABSTRACT
Screening of an induced Ehrlich ascites cell-derived λgtll cDNA library with an antibody (GP1), immunoreacting specifically with centrosomal antigen(s) of interphase and mitotic cells of different species, released a partial cDNA clone (λP10A) encoding the carboxy-terminal section of a centrosome-specific antigen. This specificity of the clone λP10 A could be verified by 7acZ-directed antigen expression from Escherichia coli Y1089 lysogenized with the recombinant phage λP10 A and subsequent production of centrosome-specific antibodies by means of the recombinant antigen. Using the λP10A insert as a probe, two types of cDNA clones were identified in a λgt10 cDNA library by plaque-hybridization. The inserts of PN1 type clones were 1.2 kb (kilobases) and those of PN5 type clones were 2.2 kb in length. The DNA sequence of a PN1 type clone revealed its fulllength cDNA nature. The open reading frame of PN1 encodes a rather hydrophilic and highly charged 34.5 × 103 Mr polypeptide comprising short but apparently significant strings of 100% sequence identity with the major nuclear lamina polypeptides lamins A/C and lamin B. Restriction enzyme mapping of PN1 and PN5 inserts, cross-hybridization experiments and comparison of overlapping DNA sequences indicate that the 1.2 kb and 2.2 kb cDNAs code for the same 34.5×103Mr polypeptide, termed centrosomin A. Western blots of Ehrlich ascites cell proteins show a second, larger GP1 antigen (centrosomin B) whose cDNA has not been cloned. It remains to be investigated whether centrosomin B is encoded by a second mRNA or whether it reflects an oligomeric or a postranslationally modified form of centrosomin A.
Expression and compartmentalization of integral plasma membrane proteins by hepatocytes and their progenitors in the rat pancreas
Authors: Bartles James R. , Rao M. Sambasiva , Zhang Liqin , Fayos Barbara E. , Nehme Cheryl L. , Reddy Janardan K. 
Published: April 2021

ABSTRACT
A combination of Western blotting, Northern blotting and immunofluorescence was used to examine the expression and compartmentalization of plasma membrane proteins by those hepatocyte-like cells that arise in the pancreases of rats subjected to sequential dietary copper depletion and repletion. The pancreatic hepatocytes were found to: (1) express several integral membrane proteins known to be concentrated within the apical, lateral or basolat-eral domains of the plasma membranes of hepatocytes in liver; and (2) compartmentalize the membrane proteins to equivalent plasma membrane domains, despite the organization of these cells into clusters instead of highly vascularized plates. The apical plasma membrane proteins dipeptidylpepti-dase IV and HA 4 were found to line bile canaliculus-like openings between adjacent pancreatic hepato-cytes; these openings were shown to be continuous with the pancreatic exocrine duct by India ink infusion. In contrast, the basolateral plasma membrane protein rat hepatic lectin-1 and lateral plasma membrane protein HA 321 were detected elsewhere about the surfaces of the pancreatic hepatocytes: by analogy to their respective localizations on hepatocytes in liver, rat hepatic lectin-1 was concentrated on those surfaces exposed to the pancreatic matrix at the periphery of the hepatocyte clusters (the basal surface equivalent), whereas HA 321 was concentrated on those surfaces exposed to adjacent hepatocytes within the clusters. The hepatocyte plasma membrane proteins were found to be expressed in the pancreas at different times during the copper depletion/repletion protocol: for example, rat hepatic lectin-1 and the bulk of the HA 4 were expressed relatively late in the protocol, only after large numbers of pancreatic hepatocytes had appeared; whereas dipeptidylpeptidase IV was induced &gt; 10-fold early in the protocol and proved to be an apical-specific marker for those ductular epithelial cells that are believed to be the progenitors of the pancreatic hepatocytes.
Evidence that estramustine binds MAP-1A to inhibit type IV collagenase secretion
Authors: Stearns Mark E. , Wang Min , Sousa Odete 
Published: April 2021

ABSTRACT
Estramustine is a novel anti-microtubule drug shown to bind MAP-1 and MAP-2 (microtubule-associated proteins) in vitro. In this paper we have shown that estramustine specifically binds MAP-1A in Du 145a cells, resulting in disruption of MAP-1A microtubules and inhibition of type IV collagenase secretion. Immunofluorescence studies revealed that at 30μM levels estramustine blocked type IV collagenase secretion by partial disruption of the MAP-1A microtubule networks. Immunoprecipitation studies with polyclonal antibodies provided quantitative evidence that 30–60 μM estramustine blocked secretion of a 105 ×103Mr type IV collagenase. Pulse labeling experiments confirmed that the effect was not a result of inhibition of either protein synthesis or altered rates of type IV collagenase turnover. Finally, drug uptake studies with [3H]estramustine, scintillation counting and fluorography demonstrated that the principal target of the drug was MAP-1A. For the first time we have shown that the drug blocks secretion by binding MAP-1A and causing incomplete disruption of the microtubule networks.
Isolation and characterisation of clones from the Caco-2 cell line displaying increased taurocholic acid transport
Authors: Woodcock Sian , Williamson Ian , Hassan Ian , Mackay Martin 
Published: April 2021

ABSTRACT
The Caco-2 cell line has been cloned by the limiting dilution technique. Clones and reclones have been tested for growth characteristics, transepithelial electrical resistance, ability to transport taurocholic acid specifically and morphological homogeneity. Although clones have similar growth patterns to the parental population they display a variety of electrophysiological, biochemical and morphological characteristics. One clone, clone 40, has been characterised in detail and shown to transport significantly higher amounts of taurocholic acid. Moreover, this clone displays morphological homogeneity and is stable with respect to this parameter over an extended time period.
Influence of basement membrane molecules on directional migration of human breast cell lines in vitro
Authors: Coopman P. J. , Bracke M. E. , Lissitzky J. C. , Bruyne G. K. De , Roy F. M. Van , Foidart J. M. , Mareel* M. M. 
Published: April 2021

ABSTRACT
Spheroidal cell aggregates were prepared from four tumorigenic human breast cell lines (HBL-100 and three MCF-7 variants). Cells from these aggregates were allowed to migrate towards lanes of basement membrane components coated on a glass substratum. Matrigel™ (reconstituted basement membrane) lanes permanently arrested the migration of one MCF-7 cell line, while migration of the others was permitted. Amongst several purified basement membrane constituents only laminin, not collagen type IV or fibronectin, was found to cause the same arrest of migration. Within the laminin molecule only the pepsin Pl, not the elastase E8 fragment, efficiently arrested migration of that cell line. Although migration was inhibited by these components, timelapse video recordings revealed that arrested cells still proliferated and actively ruffled on top of the coatings.
These data suggest that, amongst several basement membrane components, laminin can function as a stop signal for cell migration. Within laminin, this activity seems to be mainly associated with the Pl fragment We conclude that laminin is the major determinant of the barrier-function of the basement membrane, to which some cell types have become insensitive.
Embryonic cell invasiveness: an in vitro study of chick gastrulation
Authors: Sanders E. J. 
Published: April 2021

ABSTRACT
An investigation has been made into some of the possible mechanisms underlying the invasionary activity of gastrulating cells at the primitive streak of the early chick embryo. At gastrulation, epithelial cells in the upper epiblast layer of the embryo undergo a transformation into fibroblastic mesenchyme cells by passage through the primitive streak and penetration of a basement membrane. The resulting cells constitute the first embryonic mesoderm, which then invades the underlying tissue space. This phenomenon has been studied in vitro using the invasion of Matrigel, a reconstituted basement membrane, as a model. Mesoderm cells explanted into this matrix were subjected to treatments aimed at perturbing a number of putative mechanisms for cellular invasion. Application of inhibitors of glycosylation (tunicamycin) and oligosaccharide processing (castanospermine, deoxyman- nojirimycin, swainsonine) resulted in various degrees of inhibition of invasion. By contrast, cell binding fragments from fibronectin and laminin did not impede invasion, and neither did a panel of enzyme inhibitors, including serine protease and metalloprotease inhibitors. It is concluded that the primary determinant of the invasionary behaviour of these cells at gastrulation is a change in cell surface carbohydrate determinants, and that there is no evidence for the participation of localized enzymic activity. The medial disruption of the basement membrane seen at the primitive streak is therefore most likely to be due to local failure of synthesis, rather than local degradation.
Interpreting nucleolar structure: where are the transcribing genes?
Authors: Jordan E. Gwyn 
Published: April 2021

ABSTRACT
The nucleolus, the site of ribosomal RNA synthesis, provides us with one of the best opportunities for unravelling the relationships between transcription and the spatial organization of chromatin. Some of the best visualizations of the transcription process have come from nucleolar spread preparations (Miller, 1981) but this procedure introduces major structural reorganizations that deny us a molecular interpretation of the intact nucleolus.
Evidence that cyclic GMP may regulate the association of myosin II heavy chain with the cytoskeleton by inhibiting its phosphorylation
Authors: Liu Gang , Newell Peter C. 
Published: April 2021

ABSTRACT
Previous studies have implicated cyclic GMP in the regulation of myosin II heavy chain (MHC) association with the cytoskeleton in Dictyostelium discoideum. Here we provide evidence that cyclic GMP may regulate MHC association with the cytoskeleton through MHC phosphorylation. Comparative data are presented of MHC phosphorylation in the wildtype strain NC4, the parental strain XP55 and streamer mutants NP368 and NP377.
Using an anti-MHC monoclonal antibody to immunoprecipitate MHC from [32P]phosphate-labelled developing cells, we found that cyclic AMP stimulation of the wild-type strain NC4 and parental strain XP55 induced MHC phosphorylation in vivo. A peak of phosphorylation was observed at 30–40 s, followed by a gradual decrease to basal level at 160 s. In contrast, in both of the streamer mutants NP368 and NP377 (which have prolonged cyclic GMP accumulation and prolonged MHC association with the cytoskeleton), the phosphorylation of MHC was delayed and did not form a peak until 60–80s after cyclic AMP stimulation. We also found that cyto-skeletal MHC showed only minor phosphorylation, the majority of the phosphorylated MHC being found in the cytosol.
We present a model to account for these results in which cyclic GMP regulates MHC association with the cytoskeleton by regulating the phosphorylation/ dephosphorylation cycle of MHC in these cells.
Overproduction and secretion of β2-microglobulin by a rat thymic epithelial cell line that expresses MHC class I heavy chain
Authors: Dargemont Catherine , Dunon Dominique , Salamero Jean , Deugnter Marie-Ange , Davoust Jean , Thiery Jean Paul 
Published: April 2021

ABSTRACT
Major histocompatibility complex (MHC) class I antigens are constituted of dimers consisting of a peripheral light chain, β2-microglobulin (β2m) and a transmembrane heavy chain whose cell surface expression depends on its assembly with β2m. In contrast, soluble β2m can be secreted in the absence of heavy chain expression. The presence of β2m in medium conditioned by a rat thymic epithelial cell line, IT45-R1 (IT45) prompted us to investigate whether β2m could be secreted by cells that express MHC class I antigens. IT45 cells produce three to five times more β2m in the culture supernatant than another rat thymic epithelial cell line, IT26-R21 (IT26). The IT45 cell line exported β2m through a constitutive pathway of secretion, as indicated by the kinetics of production and localization of intracellular β2m. Although cells from the IT45 cell line expressed a much higher amount of β2m as compared to IT26 and NBT II cells (a rat bladder epithelial cell line), all three of these cell lines expressed the same amount of membrane and intracellular MHC class I heavy chain. These data are thus consistent with a constitutive secretion of 02m dependent upon an overexpression of MHC class I light chain as compared to the heavy chain. The amount of β2m mRNA and the ratio of β2m versus MHC class I heavy chain transcripts were higher in IT45 than in IT26 cells, indicating that overexpression of 02m in IT45 cells could be due to an enhanced level of β2m mRNA. These results demonstrate that β2m can be oversynthezised and consequently secreted by cells that express MHC class I heavy chains. It may thus suggest that β2m could be secreted differentialy at specific body sites, which remain to be determined.