bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mechanism of watery vacuolation in the acinar cells of the submandibular gland
Authors: Tapp R. L. 
Published: April 2021

ABSTRACTWatery vacuolation was induced in the acinar cells of the rat submandibular gland by allowing small pieces of tissue (2 mm 3) to stand in suitable unoxygenated fluids at 20 °C, and cells in various stages of vacuolation were examined by light and electron microscopy. No structural evidence for pinocytosis was found.Using basic solution (NaCl, 8·0 g/1.; CaCl2, 0·2 g/1.; NaHCO3, 1·0 g/1.) it was confirmed that vacuolation does not occur at 0 °C, and that it is greatly reduced if Ca2+ is omitted. Vacuoles develop in pieces of tissue which have been separated from the animal for up to 2 h, provided that the pieces are then immersed in a suitable fluid.Vacuolation can occur in the absence of external Na+ or Cl−: cations substituted for Na+ allowed vacuolation in the order: Li+, full; Cs+, slight; K+ and Rb+, none. It can be prevented, however, if sufficient sucrose (&gt; 210 m-osmoles) or glucose is added to the external fluid, but not by the same quantities of urea, glycerol, or propylene glycol. Metabolic poisons which block oxidative phosphorylation or glycolysis do not prevent vacuolation.It is concluded that vacuolation does not involve pinocytosis but represents the secondary segregation of fluid from an oedematous cytoplasm. The mechanism of secondary segregation and its possible relationship to secretion are discussed.
The expression of genetic information: A study with hybrid animal cells
Authors: Harris H. , Sidebottom E. , Grace D. M. , Bramwell M. E. 
Published: April 2021

ABSTRACT
When the nucleus of a hen erythrocyte is introduced into the cytoplasm of a human or mouse cell in culture, it resumes the synthesis of RNA. The reactivated erythrocyte nucleus undergoes great enlargement, but it does not, for at least 2 or 3 days, develop nucleoli which can be discerned under the light microscope. During this period, the heterokaryon, although it may contain several active erythrocyte nuclei, does not synthesize any hen-specific surface antigens; and the hen-specific antigens introduced into the surface of the heterokaryon by the process of cell fusion are eliminated. But when, later, the erythrocyte nuclei do develop nucleoli, hen-specific antigens reappear on the surface of the heterokaryon and progressively accumulate.
Before developing nucleoli, the erythrocyte nuclei synthesize little, if any, normal 28 s or 16 s RNA; but they do synthesize large amounts of the RNA which shows polydisperse sedimentation in conventional sucrose density gradients. Autoradiographic studies involving the use of a microbeam of ultraviolet light show, however, that this ‘polydisperse ‘RNA is not transferred to the cytoplasm of the cell in detectable amounts so long as the erythrocyte nucleus lacks a definitive nucleolus. The inability of the erythrocyte nucleus at this stage to determine the synthesis of hen-specific surface antigens is thus attributable to the fact that it fails to transfer the RNA made on its chromosomes to the cytoplasm of the cell. When the erythrocyte nuclei develop nucleoli, however, the RNA which they make is transferred to the cytoplasm of the cell, and the synthesis of hen-specific surface antigens then begins. These experiments suggest that the nucleolus may play a decisive role in the transfer of information from nucleus to cytoplasm. The possible nature of this role is discussed.
The energetics of mammalian cell growth
Authors: Kilburn D. G. , Lilly M. D. , Webb F. C. 
Published: April 2021

ABSTRACT
Data from batch growth curves of mouse LS cells cultivated at controlled dissolved oxygen partial pressures were used to calculate the weight of cells produced per mole of adenosine triphosphate generated (YATP). These values agree well with those reported for bacteria. A theoretical relationship was developed which allowed the biosynthetic and maintenance energy requirements to be estimated. The biosynthesis of LS cells required 1 · 6 × 10 −11 moles of ATP/cell. The maintenance energy, which is a function of growth rate, was 2 · 9 × 10 −11 moles ATP/new cell when the mean generation time was 1 · 15 days. The proportion of the total energy used for maintenance under these conditions was 65 %. This corresponds to a value of less than 10% for bacterial maintenance when the organisms are grown at near their maximum rate. A comparison of biosynthetic energy requirements indicates that bacteria and moulds require about 4 times as much energy as animal cells to generate the same weight of cell material. Possible explanations of this difference are discussed.
The uptake of tritiated uridine and phenylalanine by the ovaries of rats and monkeys
Authors: Baker T. G. , Beaumont Heather M. , Franchi L. L. 
Published: April 2021

ABSTRACT
Rats and monkeys (Macaca mulatto, M. irus) were injected with tritiated uridine or phenylalanine and ovarian tissue was recovered at intervals from 15 min to 24 h later. Autoradiographs were prepared and studied by light microscopy; in addition some specimens which received uridine were examined using the electron microscope.
The two isotopes are taken up by the ovaries of both species. The trace obtained with phenylalanine shows a very general distribution, whereas uridine seems to be more selectively in corporated by the various components of the ovary. The nuclei of primordial and growing oocytes are labelled with uridine, and so are the granulosa cells in follicles at all stages of development. The theca surrounding multilayered and vesicular follicles also shows a trace which appears heavier than that over the ovarian stroma.
In the neonatal rat, the nuclei of oocytes at the pachytene and diplotene stages take up uridine. Autoradiographs prepared from ovaries fixed from 30 min to 4 h after injection and examined under the electron microscope show silver grains associated with the nucleoli and electron-dense chromosomal cores which are characteristic of these stages in meiotic prophase. Oocytes in primordial follicles, in immature and mature rats, are also labelled, showing that nuclear uptake continues as oocytes enter the ‘resting’ or dictyate stage. Since the chromosomes lose their morphological identity at this time, however, silver grains appear to be randomly distributed over the nuclear matrix. Primordial oocytes in the monkey also have a heavy nuclear label, seen under the light microscope to be associated with chromosomes and nucleoli. At the ultra structural level, most of the extra-nucleolar silver grains are associated with condensed fibrillar material thought to represent part of the lateral component of chromosomes which are of the ‘lampbrush’ type.
The synthetic activity of germinal and somatic elements in the ovary is discussed, and possible differences in the structure and metabolic activity, of oocyte chromosomes are considered in relation to intra- and inter-specific variations in radiosensitivity.
The development of intracellular membranes concomitant with the appearance of hcl secretion in oxyntic cells of the metamorphosing bullfrog tadpole
Authors: Forte Gertrude M. , Limlomwongse L. , Forte J. G. 
Published: April 2021

ABSTRACT
Bullfrog tadpole stomachs of various metamorphic stages were examined to determine the fine-structural development of oxyntic cells and to correlate observed morphological development with the capacity to secrete HCL It was found that in vitro tadpole stomachs can consistently be stimulated to secrete acid by stage XXIV of metamorphosis, when tail reabsorption is nearly complete. Concomitant with the appearance of HC1 secretion, identifiable oxyntic cells were found in the gastric glands.
Prior to stage XXIV (stages XXI and XXII) the majority of cells present in the developing gastric glands exhibit features of cytological organization characteristic of undifferentiated cells: large nuclei, relatively scanty cytoplasm, and numerous ribosomal particles within the cytoplasmic matrix. The newly differentiated oxyntic cells of stage XXIV tadpole stomachs are recognizable by the accumulation of tubular members of the smooth-surfaced endoplasmic reticulum in the apical portion of the cells. These membranous structures appear to be formed by the Golgi complex which is extremely elaborate at this stage of development. As the animals complete metamorphosis (stage XXV) further development of the oxyntic cells occurs, especially the elaboration of the tubular components of the smooth-surfaced endoplasmic reticulum. The abundance of these membranous tubules within the apical cell regions and the pattern of their packing is similar to that observed in oxyntic cells of adult frogs.
Also consistent with studies on adult frogs, structural alterations associated with HC1 secretion were seen in the later stages of metamorphosis. In stages XXIV and XXV tadpole stomachs, which had been stimulated to secrete acid by addition of histamine, the apical surfaces of oxyntic cells were invested with long filamentous microvilli which projected into the glandular lumen. These observations support the hypothesis that membrane transformations play an integral role in the mechanism of HC1 secretion and they implicate the morphogenesis of the smooth-surfaced endoplasmic reticulum as a basic prerequisite in the development of gastric secretory function.
A quantitative electron-microscope analysis of chromatin from Xenopus laevis lampbrush chromosomes
Authors: Hill R. S. 
Published: April 2021

ABSTRACT
The morphology of the DNP axis and RNP transcripts from Xenopus laevis lampbrush chromosomes has been analysed using a modified Miller spreading technique. Two basic types of chromatin have been distinguished. (1) Discrete portions of DNP exhibiting high levels of transcriptive activity, with clear initiation and termination points (transcription units). Interspersed with the units are sequences with little or no transcriptive activity (spacer DNP). The combination of transcription unit plus spacer DNP is normally repeated to form a transcriptive array. (2) Large aggregates of loosely packed, mainly transcriptively inactive regions (chromomeric DNP). Where the DNP axis is not obscured by tightly packed polymerases it has a regular beaded appearance, both in the transcriptive arrays and in chromomeric DNP. The beads are 17–20 nm in diameter and have packing densities of about 40 beads per μm of chromatin in preparations from young females not stimulated by human chorionic gonadotrophin. Most transcription units have polymerase packing densities of 13–20 polymerases per μm, but in some cases the density is much lower (&lt; 10 polymerases/μm). The lateral RNP transcripts in most units have a complex, bushlike appearance, the axis being beaded and folded to form circles and branches.
Cell adhesion and proteoglycans: I. the effect of exogenous proteoglycans on the attachment of chick embryo fibroblasts to tissue culture plastic and collagen
Authors: Knox P. , Wells p. 
Published: April 2021

ABSTRACT
Proteoglycan, was isolated from cartilage and freed from contaminating glycoproteins and hyaluronic acid. The macromolecule consists of a protein core covalently linked to a number of glycosaminoglycan side chains, namely chondroitin sulphate and keratan sulphate. This proteoglycan retards the attachment of a variety of cell types to tissue culture plastic and to collagen. Glycosaminoglycans alone, have no significant effect on rates of attachment. Similarly, trypsinized proteoglycan is without effect. It is concluded that the structural integrity of the proteoglycan macromolecule is essential for its effect on cell adhesion.
The ultrastructure of mitosis inPlasmodiophora brassicae(plasmodiophorales)
Authors: Garber Robert C. , Aist James R. 
Published: April 2021

ABSTRACTMitosis was examined in plasmodia of Plasmodiophora brassicae within artificially inoculated cabbage roots, using light- and electron microscopy. Mitotic nuclear divisions are characterized by a persistent nucleolus, bipolar centrioles paired end-to-end, densely staining chromatin, and a complex array of membranes that surround and ramify through the spindle. Chromatin begins to condense in prophase, and is aligned at metaphase in a reticulate plate on the nuclear equator. The chromatin is not resolvable into distinct chromosomes at metaphase, and a chromosome count is not possible. Large amounts of membrane cistemae within the spindle are most clearly visible at metaphase, and apparently represent the remains of the nuclear envelope. The nuclear envelope is disrupted during prometaphase and may become entangled in the spindle when centriolar microtubules enter the nucleus. Several concentric sheets of perinuclear endoplasmic reticulum surround the spindle and give the mitotic nucleus the superficial appearance of having an intact nuclear envelope. This interpretation of the identity of nucleus-associated membranes differs from those previously reported for other protists, including members of the Plasmodiophorales.
Paracrystalline arrays in atypical cristae and mitochondrial division
Authors: Nathaniel Doris R. 
Published: April 2021

ABSTRACT
Paracrystalline arrays in atypical cristae were observed in a few large mitochondria in the process of replication, in the follicular cell of the normal and gonadectomized rabbit thyroid gland. They were about 30 nm in diameter and spaced approximately 35–40 nm apart, and oblique sections showed parallel arrays which had a pitch of 25 nm. The number of inclusions varied in number and were similar to those reported in the normal follicular cell. The site of replication was often at the base of the mitochondrion and in some instances the continuity of the outer membrane was present. The helical nature of the inclusions suggests that they may be associated with the complex proteins of the inner mitochondrial membrane and space which have the capacity of helix formation. The cristae with the paracrystalline arrays appear to be in the orthodox configuration, a non-energized stage of the energy cycle. The mitochondria probably utilizes its unique ability to control respiration according to its functional requirement during replication.
The effects of applied electric fields onMicrasterias: II. the distributions of cytoplasmic and plasma membrane components
Authors: Brower Danny L. , Giddings Thomas H. 
Published: April 2021

ABSTRACTThe accompanying paper describes the effects of applied electric fields on the morphogenesis and patterns of wall deposition of growing cells of Micrasterias denticulata. This paper details the effects of electric fields (∼ 14 V cm−1) on the subcellular components of Micrasterias, including a description of the plasma membrane of growing semi-cells as visualized by freezefracturing.There are no gross cytoplasmic abnormalities or asymmetries in the distributions of cytoplasmic organelles caused by the fields. In particular, neither the Large Vesicles nor Dark Vesicles are concentrated in the cathode-facing (CF) halves of lobes oriented perpendicular to the fields, where extra deposition of wall material has been shown to occur.In freeze-fracture replicas, there are about twice as many plasma membrane particles near the tips of growing lobes as there are in proximal regions of the lobes. Additionally, rosettes, consisting of 6 membrane particles, are seen predominantly in the distal parts of the lobes, and these rosettes are believed to be important in the synthesis of cell wall microfibrils. The applied fields cause a large asymmetry in the distributions of membrane particles, with larger numbers being found on the CF sides of lobes oriented perpendicular to the fields. We were not able to detect a specific effect on any class of particles.Taken all together, the data support the hypothesis that some of the factors responsible for growth localization in Micrasterias reside in the plasma membrane.
Secretion of newly synthesized proteins by isolated liver cells
Authors: Kooij R. J. Van , Poort C. 
Published: April 2021

ABSTRACT
Suspensions of isolated liver cells were incubated with [3H]leucine as a precursor. The appearance of radioactive albumin and α1-acid glycoprotein in the incubation medium was determined. After about 20 min both albumin and α1-acid glycoprotein were secreted in a linear way. When fucose and galactose were used as radioactive precursors, time lags of about 10 min could be observed.
Food capture and ingestion in the large heliozoan, Echinosphaerium nucleofilum*
Authors: Suzaki T. , Shigenaka Y. , Watanabe S. , Toyohara A. 
Published: April 2021

ABSTRACT
Using its microtubule-containing axopodia, a heliozoan Echinosphaerium nucleofilum feeds on various kinds of protozoans and small metazoans. The present study revealed that food capture and ingestion were carried out in 2 different ways or by a combination of them. The first one was by the rapid contraction of axopodia, by which the food organism was conveyed directly toward the body surface. After such a contraction, many of the microtubules which had been present inside the axopodia degraded and were replaced by C-shaped microtubules. Bundles of tubular bodies were also detected alongside the axonemal microtubules, especially following the use of glutaraldehyde fixative containing ruthenium red. The second method was by means of axopodial flow, by which a food organism attached to an axopodium was conveyed to the body surface along the axopodial surface without accompanying axopodial degradation or contraction. Subsequently the food organism was surrounded by several small pseudopodia to form a food vacuole; many filamentous structures (5–10 nm in diameter) were observed inside the pseudopodia. During the ingestion process many cytoplasmic extensions, including rosary-like filaments, were observed to protrude from the contracted axopodia and the cell body. Mottled dense granules were observed to be discharged from the axopodial surface just when the prey was captured.
Evidence for a polarized movement of the lateral loops of newt lampbrush chromosomes during oogenesis
Authors: Snow M. H. L. , Callan H. G. 
Published: April 2021

ABSTRACT
Actinomycin D inhibits RNA synthesis on the lateral loops of newt lampbrush chromsomes. Partial inhibition does not provoke marked morphological alteration of ordinary lateral loops, most of which recover to the full their capacity for RNA synthesis within 2 days of treatment. However, occasional ordinary loops do not recover completely within the first few days after treatment, and in such loops RNA-synthesizing capacity is restricted to a region adjoining the thinner insertion in the parent chromomere. A greater degree of inhibition of RNA synthesis is accompanied by loss of matrix from ordinary lateral loops, and in the extreme case the loop axes retract to their parent chromomeres and neighbouring chromomeres coalesce; for the ordinary loops, full recovery from this stripped condition is nevertheless possible. Some 20 μ per loop extends during the first day following exposure to actinomycin, and normal morphology and RNA-synthesizing capacity are regained within 2–4 days. The giant granular loop of Triturus cristatus cristatus chromosome XII responds to extreme actinomycin D poisoning in different fashion. Matrix does not at once slough off its loop axis, but the loop present at the time of treatment is progressively replaced by a new granular loop which develops between the parent chromomere and the original loop’s dense tip. These observations support the theory that the DNA-containing axes of all lateral loops of lampbrush chromosomes continually extend from their parent chromomeres, engage in RNA synthesis while extended, and carry the associated RNP matrix along as they move towards the return insertions in the parent chromomeres, where loop axis retraction occurs.
External factors limiting the multiplication potential ofTetrahymena
Authors: Hofmann Elke , Cleffmann Günter 
Published: April 2021

ABSTRACTBy variation of nutritional and other external conditions we have determined the factors that limit the multiplication rate and the culture growth in Tetrahymena thermophila. The enriched synthetic medium of Kidder & Dewey (1951), a culture temperature of 29 °C, and aeration by agitation were chosen as reference conditions. The final cell density is increased by and proportional to the amount of the complete set of nutrients. Testing single nutritional factors or groups of them revealed that only nitrogen sources yield higher cell densities. But none of them or any combination is as capable of increasing the cell density as the complete medium. Therefore, the medium has to be considered as well balanced. Ammonia, cell density, Oa supply, and pH have been excluded as factors limiting the capacity for multiplication There are no known factors promoting or inhibiting culture growth.
Expression of chronic myeloid leukaemia-associated changes in membrane glycopeptides in somatic cell hybrids
Authors: van Kessel A. H. M. Geurts , Smets L. A. , van Rooy H. , Hagemeijer A. 
Published: April 2021

ABSTRACT
Hybrid cell lines, derived from fusion of rodent cells with peripheral leukocytes from patients with chronic myeloid leukaemia (CML) and from normal donors, were assayed for the presence of CML-associated changes in the carbohydrate moieties of membrane glycoproteins. Expression of this characteristic phenotype did occur in several hybrid clones derived from fusions both with leukaemic and normal human leukocytes. But, expression was only observed when tumourigenic rodent cells were used as fusion partners, and was not observed after fusion with non-tumourigenic rodent cells. Chromosome analysis of the hybrid cells did not reveal a single human chromosome- or chromosomal aberration (e.g. the Philadelphia chromosome)-bearing factor(s) responsible for this expression. The phenotypic expression observed could be due to dissociation of certain human genes from their regulator′s), as a result of chromosome loss in interspecific cell hybrids.
Some effects of treatment of hen erythrocytes in vitro with N-methyl-N-nitrosourea
Authors: Ward T. H. , Itzhaki Ruth F. 
Published: April 2021

ABSTRACT
Studies have been made of the effect of AT-methyl-N-nitrosourea on hen erythrocytes in vitro. These were done to find whether the highly condensed state of the chromatin and the very low metabolic activity of these cells would affect the extent of methylation of the DNA and chromatin proteins and the persistence of any methylation sites in these macromolecules with time after treatment. Also, the effect of methylnitrosourea on incorporation of [3H]uridine into RNA has been examined.
It has been found that the DNA, histones and non-histone proteins are methylated. The main methylation site in DNA is 7-methylguanine and its level is higher than that found by others in the DNA of other cell types after treatment with methylnitrosourea; however, methylation of the two types of protein (especially the histones) is relatively very low. The level of methylation decreases in the DNA and the chromatin proteins with time after treatment. The amount of [3H] uridine in RNA was found to decrease after the treatment.