bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytoskeletal involvement in the sequential capping of rat thymocyte surface glycoproteins
Authors: Turner Christopher E. , Newton Mary R. , Shotton David M. 
Published: April 2021

ABSTRACT
The independent capping of the three major rat thymocyte glycoproteins, the leucocyte-common (L-C) antigen, the leucocyte sialoglycoprotein (LSGP) and Thy-1, was investigated using specific monoclonal antibodies. The capping of each antigen did not require redistribution of the other major surface glycoproteins, and was acΛcompanied by a partial co-capping of the cytoΛskeletal proteins fodrin and actin, but not of tubulin. A study of the ability of a cell that already possesses one glycoprotein cap to cap a second different glycoprotein showed that this was possΛible in all cases to varying degrees, the second cap always forming at the same position on the cell surface as the first. Colchicine failed to perturb this observed sequential capping polarity, indiΛcating that microtubules did not direct this second capping event.
Tubulin gene expression in the Chlamydomonas reinhardtii cell cycle: Elimination of environmentally induced artifacts and the measurement of tubulin mrna levels
Authors: Nicholl Desmond S. T. , Schloss Jeffery A. , John Peter C. L. 
Published: April 2021

ABSTRACT
To investigate the involvement of tubulin gene expression in controlling cell division events in Chlamydomonas reinhardtii we have measured tubulin mRNA levels during the cell cycle under different environmental conditions. In C. reinhardtii cells grown under the synchronizing conditions of 14 h of light followed by 10 h of darkness, mRNAs for tubulin and associated flagellar proteins were found to accumulate periodically with a peak just prior to cell division. This was not seen when previously synchronized cells were transferred to constant environmental conditions in a turbidostat, suggesting that dramatic changes in tubulin mRNA levels are not required for successful completion of the cell cycle. A hypothesis to explain the patterns of tubulin mRNA accumulation found under different environmental conditions is presented.
Exocytosis, endocytosis and membrane recycling in Tetrahymena thermophila
Authors: Tiedtke Arno , Hünseler Peter , Florin-Christensen Jorge , Florin-Christensen Monica 
Published: April 2021

ABSTRACT
Mutant and wild-type cell lines of Tetrahymena thermophila were used to investigate a possible connection between acid hydrolase secretion and the major processes through which membranes are recycled in this ciliated protozoon. These processes consist of food vacuole formation (endocytosis), and food vacuole egestion and muco-cyst release (both exocytosis). We have found that a mutant (MS-1, sec−) blocked in hydrolase secretion is not blocked in either food vacuole formation or egestion and that it has normal mucocyst exocytosis. Another line of experiments with wild-type cells showed also that hydrolase secretion and endocytosis are independent of each other. Thus, sucrose (0·1 M) did not interfere with hydrolase secretion, but blocked food vacuole formation. Furthermore, release of acid hydrolases was selectively stimulated by dibucaine without any effect on food vacuole egestion. Finally, exocytosis of mucocysts could occur without simultaneous release of acid hydrolases, as when cells were exposed to 0’15M-NaCl, which evokes a massive secretory response of mucocysts. Our results demonstrate that formation and egestion of food vacuoles and exocytosis of mucocysts are unrelated to secretion of acid hydrolases. Furthermore, they suggest that secretion of acid hydrolases is not a secondary effect of membrane recycling through these processes.
Insemination of the archegonium and fertilization in Taxus baccata L
Authors: Pennell Roger I. , Bell Peter R. 
Published: April 2021

ABSTRACT
A study of fertilization in Taxus baccata in the electron microscope has revealed novel features. Insemination of the archegonium is facilitated by local perforation of the wall of the young pollen tube. Digestion of the wall begins before the pollen tube pierces the megaspore membrane but is not completed until its tip makes contact with the neck cells of the archegonium. As soon as a pore is formed a single sperm nucleus and some cytoplasm of the male gametophyte enter the archegonium. Which of the paired sperm nuclei move from the pollen tube into the archegonium appears to be a matter of chance. Close apposition of sperm nucleus and egg nucleus is followed by the formation of numerous points of contact between the two. The membranes fuse at these points and pores are rapidly formed. The progressive enlargement of these pores ultimately eliminates any partitions and yields the zygotic nucleus. There is a possibility that, as in some other gymnosperms, the plastids and mitochondria of the zygote come in part from the male gametophyte, but whether from the remains of the spermatogenous cell cytoplasm or from the pollen tube lumen is not clear.
Freeze-etched pollen walls of Artemisia pycnocephala and Lilium humboldtii
Authors: Southworth D. , Branton D. 
Published: April 2021

ABSTRACT
Mature pollen was examined by freeze-etching. The fracture and etch faces of Artemisia ektexine are unstructured and homogeneous. The endexine fracture face contains particles in paired rows which correspond to the endexine lamellae with a central white line seen in osmium stained thin sections. The intine fracture face in Artemisia is coarsely pitted and has very long fibrils. Small vesicles are observed on both sides of the plasmalemma. The fracture face of Lilium ektexine has radiating fibrils which end in a regular array near the surface; the etch face on the surface is smooth. In thin sections the staining of the Lilium ektexine differs from that of the core, giving evidence that the smooth ektexine surface is chemically distinct from the fibrillar core. The intine in Lilium shows no fibrils. Vesicles near the plasmalemma appear to be fusing with the plasmalemma creating smooth depressions in the particulate plasmalemma fracture face. The plasmalemma in both species is beset with particles in regular arrays.
Silver staining of ribosomal proteins
Authors: Smith J. W. , Stuart R.J. 
Published: April 2021

ABSTRACT
The effects of staining several tissues with silver nitrate were studied in the electron microscope. Tissues were fixed in 2 % glutaraldehyde buffered to pH 7·3 and containing 0·22 M sucrose, some being post-osmicated. Staining was effected by immersion of Araldite sections in unbuffered 5 % silver nitrate for 30 min.
Increase in electron density was restricted to all nucleic acid-containing structures except mitochondrial DNA which is probably not associated with histones. Treatment of fixed tissues with cold 10% perchloric acid for 24 h, which extracts 85 % of the total cell RNA, abolished silver staining within the nucleolus but did not affect that of cytoplasmic or mitochondrial ribo8omes. Incubation of isolated, formalin-fixed liver cells with DNase I did not abolish nuclear staining. This evidence suggests that silver nitrate stains selectively the proteins associated with nucleic acids: the abolition of nucleolar staining by perchloric acid is not at present understood but may be due to some difference in relationship of protein to RNA in this, compared with other situations.
Silver staining indicates that the loci occupied by RNA-associated proteins differ in size and number in different types of ribosomes. Cytoplasmic ribosomes probably contain 5 loci of 4-6 nm diameter, 2 being situated in the 60-s subunit and 3 in the 40-s subunit. Mitochondrial ribosomes appear to contain 2 smaller loci. In the nucleolus the majority of the ribosomes constituting the granulosa contain 2 unequal loci of about 4 and 6 nm respectively, while the appear ance of the pars fibrosa is compatible with the view that it consists of a network of long, extended RNA molecules with which small 2’5-nm protein loci are associated.
Ultrastructure of the fungal nucleus: II. the kinetochore equivalent (kce)*
Authors: Girbardt M. 
Published: April 2021

ABSTRACT
The electron-dense material which regularly occurs at the poles of the nuclei of certain fungi during division has been studied in hyphal interphase nuclei of 4 basidio- and 3 ascomycetes. The shape of this material varies with the species and the nuclear age and may be that of a sphere or a dumbbell. In some instances paired diskoidal structures are found in the place of the globular elements of the dumbbell configuration. The organelle in question lies in an invagination of the nuclear envelope preferentially at the forward pointing pole of the nucleus. Its size (0·1–o·5 /&lt;m) is correlated with the size of the nucleus. In Polystictus versicolor the diameter of both globular elements of the polar organelle increases during initiation of the division process.
The structure is identical with the fungal ‘centriole’ of light-microscopical studies but lacks the characteristic organization of a true centriole. It is suggested that the polar organelle is the equivalent of a kinetochore because it maintains continuous and direct contact with the nuclear envelope (on its cytoplasmic aspect), seems to be connected with the karyoplasm, exhibits oscillating movements, is continuous with microtubules during division and resembles in its fine structure the kinetochores of the chromosomes of higher plants and animals. In addition to its function as an organelle of nuclear motility it also seems to play a part in the initiation of DNA synthesis and nuclear division. If this is correct one would expect to find the genome of the fungal nucleus having the form of a unitary, coherent compound structure (chain) extending from or incorporating a single, solitary kinetochore.
The glucose, insulin and glutamine requirements of suspension cultures of hela cells in a defined culture medium
Authors: Blaker G. J. , Birch J. R. , Pirt S. J. 
Published: April 2021

ABSTRACT
The serum supplement in a defined medium for the growth of HeLa cells could be replaced by protamine-zinc-insulin (0·2 u./ml). Insulin (0·4 u./ml) replaced the growth-stimulatory properties of protamine-zinc-insulin, whilst protamine sulphate (5 μg/ml) was found to be toxic to the cells. The addition of insulin to cultures depleted of insulin increased both cell growth rates and maximum cell populations. In the defined medium, HeLa cells could only utilize glutamate when a small amount of glutamine was included. Glucose, at a level of 2 mg/ml, was shown to limit maximum cell populations. The growth yield from glucose was 295 μg cell dry weight/mg glucose. When the medium glucose concentration was increased to 4 mg/ml, HeLa cell populations in excess of 16×105 cells (i.e. 640 μg dry weight)/ml were routinely achieved in the defined medium supplemented with insulin. Growth is then limited by the amino acid supply. Increasing the amino acid concentration of the medium by 50% raised the maximum cell population to 23·5 × 105 cells (i.e. 940 μg dry weight)/ml.
Fine structure of swarmers of Cladophora and Chaetomorpha: I. the plasmalemma and golgi apparatus in naked swarmers
Authors: Robinson D. G. , Preston R. D. 
Published: April 2021

ABSTRACT
Naked swarmers of both Cladophora rupestris and Chaetomorpha melagonium have been examined by the freeze-etching technique. The swarmers of Cladophora, collected just after settling, reveal several layers of granules external to the plasmalemma and internal to the so-called ‘fibrous-layer’. Chaetomorpha swarmers collected just before settling show extrusion of vesicles through the plasmalemma. The structures associated with the membranes are discussed in relation to known features of these swarmers already observed by sectioning. The role of granules in the synthesis of cell wall microfibrils is strengthened though the spatial arrangement of the granules seen in this investigation does not completely fulfil the ‘ordered granule’ hypothesis.
Description of, and comments on, features related to cell wall synthesis, particularly the Golgi and vacuolar systems, are given.
Synaptic structures in the nuclei of sporulating yeast, Saccharomyces cerevisiae (hansen)
Authors: Moens P. B. , Rapport E. 
Published: April 2021

ABSTRACT
After 4 h on sporulation medium the larger cells have formed, within the nucleolus, a spherical body of amorphous substance which stains less densely than the nucleolus. At 8 h most of these bodies contain synaptonemal complex-like structures. There is usually only one such body per nucleus. Only rarely are normal synaptonemal complexes detectable in the nucleus. At the first meiotic division these bodies are still present but they no longer have polycomplexes associated with them. At this time they become sequestered in a nuclear evagination and they are no longer detectable after the second meiotic division. It is argued that the polycomplex body may elaborate synaptic elements which function in meiotic chromosome pairing but that the resulting complexes are difficult to detect because of the lack of chromosome condensation, a characteristic of several fungi.
Growth and changes in pool and macromolecular components of Schizosaccharomyces pombe during the cell cycle
Authors: Stebbing Nowell 
Published: April 2021

ABSTRACT
Amino acids, nucleotide and carbohydrate material were found to account for 46 % of the total dry weight of pool material in Schizosaccharomyces pombe growing in minimal medium. The composition of the amino acid pool was also determined by autoanalysis and was found to be unaltered during growth in 2 M sorbitol, indicating that pool amino acids are not important in the osmoregulation of the cell. Kinetic analysis of the amino acid pool using 14C-labelled amino acids showed that amino acids accumulated from the medium enter an ‘expandable’ pool distinct from the ‘internal ‘pool which is maintained during growth on minimal medium.
Total RNA, protein, pool amino acid and pool ‘nucleotide’ material were estimated in synchronous cultures grown in minimal medium. All these components appeared to accumulate in an exponential manner during the cell cycle. Direct estimation of total cellular dry weight and the total pool in synchronous cultures showed that total cell dry weight increased exponentially and the pool did not fluctuate during growth in minimal medium. This contrasts with previous work on single cells of S. pombe grown in complex medium which showed that the dry weight of the pool fluctuates during the cell cycle and total cell dry weight increased linearly. Linear growth of S. pombe in malt extract broth can be accounted for by the presence of the second (‘expandable ‘) pool of amino acids formed during growth in complex medium.
The phenomenon of linear growth during the cell cycle is shown to occur generally only in cells growing in complex medium. The phenomenon is considered in relation to mechanisms for controlling the size of the pool during growth in complex media.
Identification of a set of calcium-binding proteins in reticuloplasm, the luminal content of the endoplasmic reticulum
Authors: Macer Darryl R. J. , Koch Gordon L. E. 
Published: April 2021

ABSTRACT
A procedure was developed for the isolation of reticuloplasm, the luminal material of the endoplasmic reticulum (ER). A reticuloplasm-rich extract was prepared from a murine plasmacytoma cell line that contains large amounts of ER, by first extracting the cytoplasmic contents using hypotonic lysis to yield ER-rich ‘shells’ followed by mechanical lysis to release the ER contents. The extract contains five major proteins with apparent molecular weights of 100, 75, 60, 58 and 55 (×103)Mr by SDS-polyacrylamide gel electrophoresis. The 100, 75 and 58 (×103)Mr species were identified as the known ER proteins endoplasmin, BiP and PD1, respectively. The ER association of the 60 and 55 (×103) Mr proteins was confirmed by confocal fluorescence microscopy with affinity-purified antibodies.
Equilibrium dialysis with isolated reticuloplasm gave a calcium-binding capacity of 300 nmoles calcium per mg protein with half-maximal binding at 3 mM-Ca2+. Purified endoplasmin bound 280 nmoles calcium per mg protein at a calcium concentration of 5 mM-Ca2+.
A calcium overlay test revealed that, in addition to endoplasmin, reticuloplasm contained at least three other calcium-binding proteins: i.e. BiP, PDI and the 55×103Mr protein, respectively, with endoplasmin and the 55×103Mr protein (CRP55) accounting for the major proportion of the calcium-binding activity.
Treatment of cells with calcium ionophore led to the specific over-expression of the major calcium-binding reticuloplasmins endoplasmin, BiP and CRP55.
These studies show that the lumen of the ER contains a family of proteins with the capacity to bind significant amounts of calcium in the millimolar range and thereby to confer upon the ER the ability to perform a calcium storage function analogous to that of the sarcoplasmic reticulum in muscle cells.
Spontaneous changes in intermediate filament protein expression patterns in lung cancer cell lines
Authors: Broers Jos L. V. , Rot Mirjam Klein , Oostendorp Tineke , Bepler Gerold , Leij Lou De , Carney Desmond N. , Vooijs G. Peter , Ramaekers Frans C. S. 
Published: April 2021

ABSTRACT
The usefulness of cell lines in the study and prediction of the clinical behaviour of lung cancer is still a matter of debate. However, lung tumour cell cultures have been of value in investigations concerning molecular and cell biological aspects of these neoplasms. Especially in the examination of characteristics specific for the main types of differentiation (squamous cell carcinoma, adenocarcinoma, small cell carcinoma), in vitro studies have been most important.
Twenty eight lung cancer cell lines were cultured for up to four years, and were examined at regular intervals for their intermediate filament protein (IFP) expression patterns using a panel of cytokeratin (CK) and neurofilament (NF) antibodies. These studies showed that the classic type of small cell lung cancer (SCLC) cell lines contain CKs 8,18, and occasionally CK 19, while the variant-type SCLC cell lines generally express no CKs but can contain NFs. Non-SCLC cell lines, such as squamous cell carcinoma and adenocarcinoma cell lines, contain CKs 7 (in most cases), 8, 18 and 19. In one variant SCLC cell line and in one adenocarcinoma cell line CKs 4, 10 and 13, characteristic of squamous cell differentiation, were found. Although most cell lines have remained stable with respect to growth characteristics and IFP expression patterns, five lung cancer cultures exhibited a transition from one cell type to another, paralleled by changes in IFP expression. Progressions from classic to variant SCLC cell lines have been observed, next to conversions from variant SCLC to cell lines re-expressing cytokeratins. In some cases this resulted in a coexpression of CKs and NFs within a cell line and even within individual tumour cells. These results strongly support the earlier finding that CK expression in SCLC cell lines is a reliable marker for the classic type of differentiation, while the absence of CKs and the presence of NFs marks the variant type of differentiation. Our results are discussed in view of previous histological findings.
Characterization of monoclonal antibodies to trichocyst antigens in Paramecium
Authors: Fok Agnes K. , Olegario Rhodora P. , Ueno Marilynn S. , Allen Richard D. 
Published: April 2021

ABSTRACT
Ten mouse monoclonal antibodies (mAbs) were raised against trichocyst contaminants present in crude or enriched lysosome fractions of Paramecium multimicronucleatum. Using an indirect immunofluorescence assay (IFA) and immunogold labelling on frozen thin sections, epitopes were located on the outer edge, cortex and the core of the trichocyst body, as well as the sheath covering the tip. Except for the two on the tip, epitopes were reactive after SDS-PAGE under non-reducing conditions. Four mAbs (131C1E8, Al–3, A16–2, D7) were directed to a trio of bands of 37, 34 and 29 (× 103) Mr from the beaded or meshlike trichocyst body sheath. A fifth mAb (135B9E7), directed to epitopes on the cortex inside the beaded body sheath, reacted strongly with the 37 and 34 bands, but weakly with the 29×103Mr band. The last three mAbs (270D5, 22C7F2, D8) were reactive with one or more of three families of antigens found on the trichocyst core. mAb 270D5 reacted mainly with the 34 and 29(×103)Mr bands of the family containing the above trio, while mAb 22C7F2 reacted consistently with the 47×103 band of the higher Mr family but variably with both the trio of bands and the 17×103 band of the lower Mr family. mAb D8, which was directed to epitopes on the trichocyst core and small vesicles in the endoplasm, reacted only with the 29×103Mt band. The mAbs were cross-reactive with the trichocysts of P. primaurelia, P. tetraurelia, P. caudatum and P. calkinsi with some small variation in blotting patterns. Except for the reactivity of mAbs 22C7F2 and 270D5 with a 64×103Mr band, Tetrahymena thermophila was unreactive with these mAbs either by IF A or after SDS–PAGE and blotting. These results show that: (1) the mAbs obtained are specific for selected polypeptides in four trichocyst locations; (2) antigenic differences exist within the core, cortex and the beaded sheath of the trichocyst body; and (3) the antigenic determinants were conserved in all paramecia species tested.
Chicken histone h5 inhibits transcription and replication when introduced into proliferating cells by microinjection
Authors: Bergman Mathias G. , Wawra Edgar , Winge MÅrten 
Published: April 2021

ABSTRACT
Chicken erythrocyte histone H5 has been suggested repeatedly to be a general suppressor of transcription and replication. Therefore, the biological functions of H5 were investigated and compared with those of Hl (Hla + Hlb) by microinjection of the purified proteins into proliferating L6 rat myoblasts. By pulse-labelling of the injected cells with [3H] uridine and [3H] thymidine it was shown that H5 blocked both transcription and replication substantially, and that the chromatin of the injected cells became densely compacted. Hl also suppressed these functions, but to a much lesser degree. The effects were specific and not caused by change in intracellular pH caused by introduction of the very basic H5, or its non-specific interaction with nucleic acid, since injection of protamine or lysozyme did not affect the cells. The migration and localization of injected H5 was monitored at different times after injection by immunofluorescence, which revealed that H5 was efficiently and stably concentrated in the nucleus.
The results indicate that H5 indeed might function as an inactivator of the erythroid genome in its natural environment, probably by keeping the chromatin in a very condensed state.