bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intermediate cells of the pancreas: II. the effects of dietary soybean trypsin inhibitor on acinar-β cell structure and function in the rat
Authors: Melmed R. N. , Turner R. C. , Holt S. J. 
Published: April 2021

ABSTRACT
The well known hypertrophy of the rat exocrine pancreas caused by dietary soybean trypsin inhibitor (STI) has now been shown to be accompanied by an increased prominence of acinar-β intermediate cells and a reduction in the size of the islets of Langerhans. The acinar-β cells are situated in the exocrine tissue surrounding the islets where the acinar cells in STI-fed rats show a greater number of zymogen granules than in acinar cells elsewhere in the pancreas or in peri-islet acinar cells of control rats.
Consistent with the reduction in islet size in STI-fed rats is a lowered insulin content of the pancreas and a lowered insulin secretion following the intravenous administration of glucose. However, the release of insulin into the blood and pancreatic juice after intravenous administration of the hormone secretin is similar in both STI-fed and control rats.
The results of these morphological and functional studies are discussed in relation to the possible contribution of the acinar-β cell to the functional insulin pool.
Origin and development of kineto somes in Oxytricha fallax
Authors: Grimes G.W. 
Published: April 2021

ABSTRACT
Two significant features of the origin and development of kinetosomes in the ciliate, Oxytricha fallax, are indicated by electron micrography of serial sections. (1) Some kinetosomes arise in varied orientations to adjacent kinetosomes instead of in the single orientation regularly found in other material; and some kinetosomes arise in positions that are not adjacent to any kineto some. Hence, even in ciliates, some kinetosomes arise without using existing kinetosomes or their micromilieu as nucleation sites. (2) Growth of kinetosomal microtubules appears to occur at their proximal as well as distal ends. This is indicated by proximal cross-sections with only one or two microtubules of a triplet, while more distal sections of the same incompletely grown kinetosome show the complete triplet pattern.
Ultrastructure of meiosis and centriole behaviour in Ulva mutabilis fØyn
Authors: Bråten T. , Nordby Ø. 
Published: April 2021

ABSTRACT
The present work deals with the ultrastructure of the meiotic processes leading to the formation of zoospores. The formation of an exit pore on the outer surface of the sporangium is the first visible sign that the cell will undergo meiosis and not just a somatic division. Prophase I nuclei differ from nuclei in mitotic prophase by having one or several invaginations of the nuclear membrane. Electron-dense lines probably representing the lateral elements of the synaptinemal complex are observed during prophase I. The central element of the complex has, however, never been observed.
The fate of the centrioles during meiosis is described in detail. The number of duplications of the centrioles is found to be the same at meiotic and mitotic zooid formation. The number of cell divisions is, however, different in the 2 cases.
The synaptonemal complex and the achiasmatic condition
Authors: Stack S. 
Published: April 2021

ABSTRACT
The onion species AUium amplectans includes both a triploid and a tetraploid variety. By light microscopy both varieties appear to have normal synapsis during pachytene of meiosis. However, the triploid does not form chiasmata and exhibits almost total asynapsis following pachytene. The tetraploid forms at least one chiasma per homologue and retains pairing through metaphase I. Electron-microscopic examination of pachytene nuclei in these 2 varieties reveals apparently identical synaptonemal complexes. Three-dimensional reconstructions of chromosome arrangements in triploid pachytene nuclei confirm that synapsis is as complete as could be expected in an autotriploid. These observations give firm support to the hypothesis that the presence of apparently structurally normal synaptonemal complexes is not a sufficient prerequisite to ensure chiasma formation. It is suggested that a faulty or missing endonuclease which is normally involved in crossing over is responsible for the achiasmatic condition in triploid A. amplectans.
An ultrastructural and radio autographic study of the effect of ethidium bromide on the interphase nucleus of meristematic plant cells
Authors: Lord A. , Lafontaine J. G. 
Published: April 2021

ABSTRACT
In the present work the effects of an intermediate dose (20 μg/ml) of ethidium bromide on nuclear structures of meristematic plant cells (Raphanus sativtis) have been studied under both light and electron microscopy. Radioautography was also exploited to assess the action of this drug on the incorporation activity of nucleic acid precursors.
After a 30-min treatment with ethidium bromide, no noticeable ultrastructural modifications are detected but the incorporation of both thymidine and uridine is already markedly impaired. As treatment is extended to 1 h, the numerous light lacunae characterizing the fibrillar nucleolar zones in normal cells transform into elongated areas which are often found to extend to the surface of this organelle and are continuous with perinucleolar chromatin masses. After 2 h, many small bodies consisting of granular material appear in the nucleoplasm. The nucleolus gradually loses most of its granular component and, eventually, becomes predominantly fibrillar in texture; in many cells it breaks up into a number of irregular masses. Throughout various stages of the experiment, certain cells show small spherical nucleoli characterized by the presence on their surface of one or two conspicuous reticulate masses which are heavily labelled with thymidine and, consequently, consist mostly of chromatin. In view of the fact that ethidium bromide has been observed in this study to induce a certain degree of condensation of chromatin within the nuclear cavity, it is surmised that this drug also brings about migration of intranucleolar DNA to the surface of this organelle.
The spermatozoon of arthropoda. XXII. the 12 + 0’, ‘14 + 0’ or aflagellate sperm of protura
Authors: Baccetti B. , Dallai R. , Fratello B. 
Published: April 2021

ABSTRACT
The spermatozoa of three genera of Protura are unconventional. Two of them, Acerentulus and Acerentomon, display hitherto undescribed axoneme patterns: ‘12 + 0 ‘in the former, ‘14 + 0’ in the latter. All the doublets are devoid of arms. The third genus, Eosentomon has a disk-shaped spermatozoon, devoid of tail. The presence of such unusual patterns is related to the non-motility of the spermatozoa.
The effect of partial extraction of dynein arms on the movement of reactivated sea-urchin sperm
Authors: Gibbons Barbara H. , Gibbons I. R. 
Published: April 2021

ABSTRACT
Sea-urchin sperm were extracted with 0 · 5 M KC1 for 45 s at room temperature in the presence of Triton X-100, and then transferred to reactivating solution containing 1 mM ATP. The flagellar beat frequency of these KCl-extracted sperm (16 beats/s) was only about half that of control Triton-extracted sperm that had not been exposed to 0 · 5 M KC1 (31 beats/salthoughthe form of their bending waves was not significantly altered. Examination by electron microscopy showed that the extraction with 0 · 5 M KC1 removed the majority of the outer arms from the doublet tubules, leaving the inner arms apparently intact. By varying the duration of the KCl-extraction, it was shown that the rate of decrease in beat frequency paralleled the rate of disappearance of the arms. Prolonging the extraction time beyond 45 3 at room temperature, or 4 min at o°C, had little further effect on beat frequency. ATPase measurements suggested that 60—65 % of the dynein in the original axonemes had been solubilized when the extraction with KC1 was permitted to go to completion. These results indicate that the generation and propagation of flagellar bending waves of essentially typical form are not prevented by the removal of the outer row of dynein arms from the doublet tubules. In terms of the sliding filament model of flagellar bending, the results suggest that the rate of sliding between tubules under these conditions is proportional to the number of dynein arms present. The lack of significant change in wave form implies that the total amount of sliding that occurs during each bending cycle is not affected by the reduced number of dynein arms, but is regulated independently in some manner by the elastic forces generated by other structures in the bent axoneme.
Plasma membrane fluidity and surface motility of mouse C-1300 neuroblastoma cells
Authors: Comoglio P. M. , Filogamo G. 
Published: April 2021

ABSTRACT
Under suitable conditions, topographical redistribution of plasma membrane molecules with oligosaccharide residues specifically bound by Concanavalin-A can be induced on neuroblastoma C-1300 cells. This shows that transformed nerve cell membrane is fluid at 37 °C and provides further support for the suggestion that such fluidity may be a common property of all animal cells. As previously reported for mesenchymal cells (lymphocytes and fibroblasts), clustering of Concanavalin-A binding sites on the cell surface is dependent on temperature and on reagent concentration. The formation of larger aggregates, known as patches or polar caps, requires metabolic energy provided by the cellIn fibroblasts caps are formed in as little as 15–30 min. C-1300 neuroblastoma cells, however, need several hours of incubation before patches or, more rarely, single caps appear. The mechanism of formation of patches and caps is discussed with reference to cell membrane fluidity and the possibility that there exists a membrane motility characteristic of each cell type.
Lethality of adenosine for cultured mammalian cells by interference with pyrimidine biosynthesis
Authors: Ishii K. , Green H. 
Published: April 2021

ABSTRACT
Adenosine at low concentration is toxic to mammalian cells in culture. This may escape notice because some sera (such as calf or human) commonly used in culture media, contain adenosine deaminase. In the absence of serum deaminase, adenosine produced inhibition of growth of a number of established cell lines at concentrations as low as 5 × 10 − 6 M, and killed at 2 × 10 −5 M. This effect required the presence of cellular adenosine kinase, since a mutant line deficient in this enzyme was 70-fold less sensitive to adenosine. The toxic substance is therefore derived from adenosine by phosphorylation, and is probably one of the adenosine nucleotides.
The toxic effect of adenosine in concentrations up to 2 × 10 −4 M was completely prevented by the addition of uridine or of pyrimidines potentially convertible to uridine, suggesting that the adenosine was interfering with endogenous synthesis of uridylate. In the presence of adenosine, the conversion of labelled aspartate to uridine nucleotides was reduced by 80–85 % and labelled orotate accumulated in both the cells and in the culture medium. The lethality of adenosine results from inhibition by one of its nucleotide products of the synthesis of uridylate at the stage of phosphoribosylation of orotate.
Pollen-wall proteins: release of the allergen antigen e from intine and exine sites in pollen grains of ragweed and Cosmos
Authors: Howlett B. J. , Knox R. B. , Heslop-Harrison J. 
Published: April 2021

ABSTRACT
Cytochemical staining methods and immunofluorescence techniques have been used to follow the release of proteins, including the allergen Antigen E, from whole pollen of ragweeds (Ambrosia spp.) and Cosmos bipinnatus (Compositae). These proteins have been detected in 2 sites in the wall: in the inner cellulosic intine layer especially at the germinal apertures, and in the cavea and the cavities of the outer exine layer, the sexine. It was found that the release of exine-associated proteins, including the allergenic fraction, begins within 2 8 of contact with aqueous media, the loss being mainly through the micropores of the tectum at the bases of the sexine spines. The intine proteins were emitted more slowly, discharge beginning at the colpi after 1 min of moistening. So far as can be judged from the methods used, most of the mobile protein lost from the pollen of Cosmos on hydration comes from the exine and is therefore sporophvtic in origin, while in the ragweeds the bulk comes from the intine in the neighbour-hood of the germinal apertures, and so is gametophytic.
Axonal microtubules and associated filaments stained by alcian blue
Authors: Hinkley R. E. 
Published: April 2021

ABSTRACT
Delicate filamentous projections 3–8 nm in thickness radiate laterally from the surface of microtubules in crayfish ventral axons and anastomose with similar filaments projecting from neighbouring microtubules and with unattached filaments in the axoplasmic matrix. Following Alcian blue treatment, a layer of alcianophilic material 5–30 nm thick was revealed on the axoplasmic surface of all intra-axonal structures, including microtubules, and the filamentous projections possessed significantly enhanced contrast. In Alcian blue-penetrated axons these prominent filamentous projections were organized into a conspicuous axoplasmic network connecting microtubules up to 350 nm apart. Intra-axonal alcianophilia was nearly abolished when connectives were stained in the presence of 0·1–0·2 M MgCl2 or when pretreated with hyaluronidase. The filamentous elements and the exterior surface of microtubules retained some degree of alcianophilia when stained at pH 5·5 and 4·1 but few deposits were associated with intra-axonal membrane systems. These observations are consistent with the hypothesis that the projecting filamentous elements and perhaps the exterior surface of the microtubule walls have, at least in part, a carboxylated polyanionic character.
Further observations on the fine structure of freeze-cleaved tight junctions
Authors: Staehelin L. A. 
Published: April 2021

ABSTRACT
The fine structure of freeze-cleaved tight junctions has been examined in high-resolution replicas of rat small intestine. By carefully comparing the changes in the surface topography of the cleavage faces of specimens, which, before freezing, were either prefixed with glutaraldehyde and then infiltrated with glycerol, infiltrated with glycerol alone, or infiltrated with glycerol and then fixed with glutaraldehyde, a more precise definition of the tight-junction architecture at the supramolecular level has become possible. The results of this analysis suggest that the bilayer membranes contributing to a tight junction are held together along interconnected fines of attachment that are arranged in the form of a continuous band-like meshwork. Each line consists of 2 parallel rows, one in each membrane, of closely spaced adhesion particles. The sensitivity of these particles to glutaraldehyde and their cleaving behaviour under different experimental conditions indicate that they represent globular proteins which bridge the width of the adjoining membranes and are linked together in the plane of the intercellular space. Thus, the morphology of a tight-junction seal resembles a modified zipper with the locking units making head to head contact. Similarly, the presence of many open-ended sealing elements between crypt cells has been interpreted as suggesting that the formation of tight-junction seals could resemble a ‘zippering-up’ process.
At the juncture of 3 cells the tight-junction meshwork is both modified and extended basally to produce a characteristic pattern. In the central area of such a triple junction, 3 parallel and very closely spaced vertical seals have been resolved, each joining a pair of adjacent plasma membranes. Small, regularly spaced, cross-bridging elements interlink pairs of central seals within the plane of each membrane. At different levels each individual central seal may further give rise to horizontal sealing elements which connect in a ladder-like fashion either to the major network or to vertical elements positioned at greater distances from the central axis.
Evidence is presented suggesting that fragments of tight junctions can be internalized and broken down in lysosome-like vesicles.
An ultrastructural autoradiographic study of the incorporation of [35S]cystine in the wool fibre cortex
Authors: Chapman R. E. , Gemmell R. T. 
Published: April 2021

ABSTRACTPrevious autoradiographic and chemical studies gave incompatible results as regards the incorporation of cystine into and cystine content of the 2 cortical segments of the wool fibre. In this study the incorporation of [35S]cystine into the wool fibre cortex was therefore re-examined by electron-microscope autoradiography. Skin samples were taken from a Merino sheep 1 h and 5 h after intradermal injections of L-[35 S]cystine. At both times there was very little incorporation of 35S in the follicle bulbs. By 5 h incorporation occurred distally from the suprabulbar region throughout the zone of macrofibril (filament bundle) formation. More 35S was incorporated per unit area in the paracortex than in the orthocortex, and at the level of maximal uptake near the middle of this zone there was about a 2-fold difference per unit area. However, when the relative cross-sectional areas of the cortical segments were also considered, the actual amount of 35S incorporated at this level was slightly greater in the orthocortex than in the paracortex. These differences in the incorporation of [35S]cystine by the cortical segments agreed with previous results from chemical studies on cortical fractions separated from wool.
Studies of the effect of temperature shocks on preparation for cell division in mouse fibroblast cells (l cells)
Authors: Miyamoto Hiroshi , Rasmussen L. , Zeuthen E. 
Published: April 2021

ABSTRACT
As L cells go through their growth-division cycle they acquire the capacity to respond progressively more strongly to certain standard changes in the temperature of the environment. Using techniques described earlier, we found that chilling to 1, 6 or 10 °C for 1 h had little effect on the timing of the forthcoming division. Conversely, heating for 1 h to temperatures between 41 and 42 °C had a strong effect. Generally, the older the cell when heated, the more extended is its generation time; in other words, the longer is the forthcoming division postponed. We found evidence that late in the cycle the cells undergo transition from a state in which they are maximally delayed with respect to the performance of a division to one in which they are less delayed.
We attempted to synchronize cell divisions with single and with series of heat shocks (41·6 °C for 1 h). Like our predecessors in the field, we obtained only partial synchrony. However, because L cells appear to prepare for division between shocks, and because heat shocks tend to reverse such preparations for division, we find reason to continue these experiments, using previous experience with Tetrahymena and Schizosaccharomyces as a guide. Both the latter cells respond to proper temperature treatment with synchronous cell division.
Transcription and translation of the sex message in the smut fungus, Ustilago violacea: I. the effect of ultraviolet light
Authors: Day A. W. , Cummins J. E. 
Published: April 2021

ABSTRACT
Cells of opposite mating type, a1 and a2, of the anther smut, Ustilago violácea assemble a conjugation tube after about 3–4 h of mating on nutrient-free media. Low doses of ultraviolet light (u.v.) delay but do not prevent conjugation in wild-type strains if given in the first 2–3 h of mating. However, irradiation later than this period has little effect and conjugation proceeds normally. The u.v. effect is photoreactivable and we conclude that u.v. induces dimers which affect transcription of specific messenger RNA molecules needed for conjugation (‘sex message ‘). Our evidence suggests that the dimers may cause mistranscription rather than the complete prevention of transcription. The effect of u.v. on conjugation in reciprocal crosses of u.v.-sensitive and wild-type strains indicates clearly that both partners must complete transcription of sex messages in order to conjugate. Inactivation of either partner before transcription prevents conjugation, but conjugation proceeds when either cell is inactivated after transcription of the sex messages has occurred. These results suggest that a mutual and reciprocal exchange of information between the 2 mating-types occurs prior to the assembly of the conjugation tube.
The process of selection of erythromycin-resistant mitochondria by erythromycin in Paramecium
Authors: Perasso R. , Adoutte A. 
Published: April 2021

ABSTRACT
Mitochondrial mutations conferring erythromycin resistance (ER) are available in Paramecium and it is possible to obtain (by conjugation and cytoplasmic exchange) exconjugant cells containing a majority of wild-type erythromycin-sensitive (ES) mitochondria and a minority of E? ones. In the presence of erythromycin, such ‘mixed’ cells progressively become resistant.
This process of acquisition of resistance has been studied cytologically (on thin sections of single cells) and genetically (by evaluating, on the basis of previous data, the proportion of ER/ES mitochondrial genomes at various times).
While at early stages of the process of transformation the whole mitochondrial population appears rather homogeneous, at later stages, (i.e. when the cell has resumed growth in the antibiotic-containing medium) one finds, side by side, both resistant-looking mitochondria (structurally normal) and sensitive-looking ones, showing the typical alterations induced in ES cells by erythromycin. Conversely, a progressive decrease in the number of Es genomes can be demonstrated.
The complete genetical and cytological transformation from erythromycin sensitivity to erythromycin resistance can occur after less than three fissions in erythromycin-containing medium.
The results indicate that intensive selective multiplication of ER mitochondria occurs, under the pressure of erythromycin, virtually in the absence of cellular division. The possibility of dissociating mitochondrial division from cell division emphasizes the extent of mitochondrial autonomy.
Different kinds of heterochromatin in higher plant chromosomes
Authors: Stack S. M. , Clarke C. R. , Cary W. E. , Muffly J. T. 
Published: April 2021

ABSTRACT
After the use of different Giemsa staining techniques, variations in chromosome banding patterns have often been observed in animal chromosomes. Such staining differences are usually interpreted to indicate that there is more than one type of heterochromatin in many animal chromosomes. Using two differential Giemsa staining techniques we have found different staining patterns in the chromosomes of two higher plants, Allium cepa and Ornithogalum virens. Furthermore, pericentric heterochromatin that occurs so commonly in animal chromosomes was specifically Giemsa stained in O. virens. These results suggest the basic similarity of higher plant and animal chromosomes.