bluuebunny/crossref_metadata_2025 huggingface dataset:
Oocyte maturation: aberrant post-fusion responses of the rabbit primary oocyte to penetrating spermatozoa
Authors: Berrios M. , Bedford J. M.
Published: April 2021

Primary oocytes cannot be fertilized normally; they begin to develop this capacity as meiosis resumes. To elucidate the changes involved in acquisition of their fertilizability, rabbit primary oocytes displaying a germinal vesicle (GV oocytes) were placed in Fallopian tubes inseminated previously with spermatozoa, recovered 2–5 h later and examined by light and electron microscopy. At least 4 aspects of GV oocyte/sperm interaction were abnormal. Although the vestments and oolemma seem normally receptive to spermatozoa, fusion with the oolemma of the primary oocyte did not elicit exocytosis of cortical granules, and consequently multiple entry of spermatozoa into the ooplasm was common. Secondly, the GV oocyte cortex failed to achieve a normal engulfment of the anterior part of the sperm head. It sank into the ooplasm capped by only a small rostral vesicle or left the stable inner acrosomal membrane as a patch in the oolemma. Only rarely then was there significant dispersion of the sperm chromatin, and this remained surrounded by nuclear envelope. The persistence of this envelope constitutes a further aberrant feature, for it disappears immediately in secondary oocytes and was absent in primary oocytes in which germinal vesicle breakdown had occurred. The results are discussed with particular reference to current ideas about male pronucleus formation.
Lymphocyte surface and cytoplasmic changes associated with translational motility and spontaneous capping of Ig
Authors: Bhalla D. K. , Braun J. , Karnovsky M. J.
Published: April 2021

Murine B-lymphocytes during translatory motion undergo a series of changes with respect to their morphology and distribution of surface immunoglobulins (Ig). The sequence of events comprising these changes was followed by fluorescence microscopy and a correlated detection of surface features by scanning microscopy on exactly the same cell. A round, presumably non-motile lymphocyte exhibited a random distribution of Ig and its surface displayed evenly distributed microvilli. Formation of a ruffled edge at one pole, accompanied by a decreased fluorescence at this pole marked the initial events of lymphocyte motility. In the subsequent stages, the ruffled edge became progressively prominent and displayed a constriction at its base, while the microvilli were displaced to the opposite pole. Ig in such lymphocytes was localized at the trailing, microvilli-rich pole. Thin sections of motile lymphocytes revealed Ig, microtubules, microfilaments and coated vesicles as the characteristic features of the trailing end. These observations may have bearing on the mechanism of lymphocyte motility and spontaneous capping of Ig.
Scanning electron-microscopic study of the uptake of Leishmania parasites by macrophages
Authors: Zenian Asadour , Rowles Peter , Gingell David
Published: April 2021

The interaction of promastigotes of the protozoan parasite Leishmania tropica with mouse peritoneal macrophages in vitro was studied by scanning electron microscopy. Motile promastigotes attached to host cells by their flagellar tips to which the macrophages responded by producing rather closely fitting lamellar sheaths and progressively enveloping first the flagellum and then the body of the parasite. Lamellar advance during engulfment was rapid in the first 10 min but much slower later on. Fully engulfed parasites could be seen after i h but most parasites associated with host cells remained extracellular even after 4 h. On the other hand, parasites immobilized by fixation adhered by either their flagellar or somatic ends. Engulfment proceeded at a steady rate, and by 4 h most of them were completely engulfed. Both the attachment and engulfment stages of parasite uptake were inhibited by low temperature, cytochalasin D and mild fixation of macrophages. The rheological features of the host cells’ response to parasite adherence indicate that invasion by parasites is through phagocytosis rather than penetration.
Temperature effects on anaphase chromosome movement in the spermatocytes of two species of crane flies (Nephrotoma suturalis loew and Nephrotoma ferruginea fabricius)
Authors: Schaap Catherine J. , Forer Arthur
Published: April 2021

Using phase-contrast cinemicrography on living crane fly (Nephrotoma suturalis Loew and Nephrotoma ferruginea Fabricius) spermatocytes, we have studied the effects of a range of temperatures (6–30 °C) on the anaphase I chromosome-to-pole movements of both autosomes and sex chromosomes. In contrast to previous work we have been able to study chromosome-to-pole velocities of autosomes without concurrent pole-to-pole elongation. In these cells we found that the higher the temperature, the faster was the autosomal chromosome movement. From reviewing the literature we find that the general pattern of the effects of temperature on chromosome movement is similar whether or not pole-to-pole elongation occurs simultaneously with the chromosome-to-pole movement. Changes in cellular viscosities calculated from measurements of particulate Brownian movement do not seem to be able to account for the observed velocity differences due to temperature.

Temperature effects on muscle contraction speed, flagellar beat frequency, ciliary beat frequency, granule flow in nerves, and chromosome movement have been compared, as have the activation energies for the rate-limiting steps in these motile systems: no distinction between possible mechanisms of force production is possible using these comparisons. The data show that even the different autosomes within single spermatocytes usually move at different speeds. These velocity differences cannot simply be related to chromosome size as the autosomes are visually indistinguishable.

The sex chromosomes start their anaphase poleward movement after that of the autosomes, and move more slowly (by a factor of about 4), but their velocities appear to be affected by temperature in the same fashion as those of the autosomes. The interval between the onset of autosome anaphase and sex chromosome anaphase is also affected by temperature: the higher the temperature, the shorter the interval between the 2 stages. We have observed abnormalities in sex chromosome segregation, which may be due to temperature, but have not determined what the exact temperature shift conditions are that cause these abnormalities.
Mitochondrial associations with specific microtubular components of the cortex of Tetrahymena thermophile: I. Cortical patterning of mitochondria
Authors: Aufderheide Karl
Published: April 2021

Many of the mitochondria of Tetrahymena thermophila are localized in the cell cortex in regular, identifiable patterns. Two different mitochondrial patterns are seen; whether a cell expresses one or the other type apparently depends upon nutrient conditions in the culture and not upon other factors tested. Consistent associations between cortical mitochondria and certain of the cortical microtubular bands are seen at the light-microscopic level. Electron-microscopic observations confirm this and, furthermore, identify ultrastructural associations between cortical microtubules and the cortically located mitochondria. It appears that the cortical microtubular arrays serve as a guide for the localization (and thus patterning) of the cortical mitochondria.
Intracellular distribution of lead in Tetrahymena during continuous exposure to the metal
Authors: Nilsson Jytte R.
Published: April 2021

Lead acetate (0·1–0·2%) forms a precipitate with the organic growth medium. The Tetrahymena cells ingest this lead-containing precipitate and cell growth is resumed after a variable lag period. Ingested lead is observed as electron-dense material in food vacuoles. Soon after exposure, cytoplasmic lead (preserved with certain fixation only) is revealed as electron-dense particles in cilia and in a halo around digestive vacuoles. Later the lead particles pervade the entire cell but after the lag period they are confined to membrane-bound spaces. In dilute growth medium, high concentrations of lead inhibit food-vacuole formation and cell growth. Under these conditions lead is deposited in alveoli of the pellicle and is also found in autophagic vacuoles and other membrane-limited structures. The study has revealed that lead enters Tetrahymena through the membrane of digestive vacuoles and through the cell surface. The change in distribution of lead during the lag period indicates that a mechanism is activated for removal of lead into membrane-bound spaces. The final storage of lead seems to be in lysosomes.
Some observations on the nucleolus inSpirogyra
Authors: Jordan E. G. , Godward M. B. E.
Published: April 2021

Several species of Spirogyra have been collected and fixed for electron microscopy in either 2 % osmium tetroxide or 5 % glutaraldehyde. Mitotic cells were selected with the light microscope from filaments of Spirogyra embedded in Epon.

Evidence is given for an interphase cycle in the nucleolus of Spirogyra. A clear association between nucleolar material and chromosomes occurs at mitosis. The breakdown of the nucleolus is shown to occur in two stages, one as a consequence of the withdrawal of the nucleolar chromosomes, and the other after telophase in the new nucleus. The significance of these findings is discussed.
The mechanism of watery vacuolation in the acinar cells of the submandibular gland
Authors: Tapp R. L.
Published: April 2021

Watery 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 (> 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

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

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

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

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

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 (< 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

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

Mitosis 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.
Isolation and characterization of glycosaminoglycans secreted by human foetal lung type ii pneumocytes in culture
Authors: Sahu Saura C. , Tanswell A. Keith , Lynn William S.
Published: April 2021

Hyaluronic acid, but not other glycosaminoglycans are secreted by human foetal Type II pneumocytes in culture.
Paracrystalline arrays in atypical cristae and mitochondrial division
Authors: Nathaniel Doris R.
Published: April 2021

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

The 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

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

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

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

By 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

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

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.
An autoradiographical study of amino acid and nucleoside incorporation during the cell cycle of Amoeba proteus
Authors: Mills K. I. , Bell L. G. E.
Published: April 2021

The incorporation of tritiated thymidine, uridine and leucine, into the acid-precipitable material of DNA, RNA and proteins, respectively, was studied by autoradiography throughout the cell cycle of Amoeba proteus. DNA synthesis occupied the first 17 h of the cycle (57 h long) and 2 peaks between 0·5–7 and 9–13 h accounted for the majority of the thymidine incorporation. RNA synthesis was represented by a series of peak uridine grain counts, the 3 major peaks occurring at to, 26–27 and 47–48 h. The incorporation of leucine also followed a pattern of peaks and dips, the main peaks occurring 1-2 h after the major increases in uridine incorporation. The fraction of label present over the nucleus decreased during the cell cycle, and this was probably due to a lowered incorporation of the leucine label by proteins synthesized in the cytoplasm and destined to become nuclear proteins. The incorporation patterns of 6 amino acids (arginine, aspartic acid, leucine, lysine, serine and valine) were studied individually during 3 periods of the cell cycle: 0–10 h (S phase); 20–30 h (early G 2); and 40-50 h (mid-late G 2). Variations in the intensity and timings of the incorporation maxima of the amino acids were observed, although the timings of increased grain counts of some of the amino acids frequently coincided. ‘Unique’ incorporation peaks (i.e. only observed in one of the amino acids studied) possibly indicate the synthesis of phase-specific proteins. The amino acid and nucleoside incorporation profiles presented in this paper will enable the results obtained from future studies on amoebae to be related to the macromolecular synthesis patterns.
Electron microscopic studies of silver-stained proteins in nucleolar organizer regions: location in nucleoli of rat sympathetic neurons during light and dark periods
Authors: Pébusque Marie-Joséphe , Seïte Raymond
Published: April 2021

Ag-AS staining of nucleolar organizer regions was carried out on interphasic superior cervical ganglia neurons of rats sacrificed during light and dark periods. While the Ag-AS technique has mostly been used on monolayer cell lines or cell suspensions, the present study showed that in electron microscopy this technique is also applicable to small pieces of tissues. The finest pictures are obtained when (1) all solutions used for the staining procedure are at pH 4·5–4·7 and (2) the second step of the reaction involving ammoniacal silver and formalin developing solutions does not exceed 3 min. The results indicate that in the 2 time periods studied, a positive reaction took place exclusively in nucleolar fibrillar centres and in the fibrillar ribonucleoprotein (RNP) component (dense fibrillar component). The other nucleolar components, i.e. granular and vacuolar, were devoid of silver deposits. As previously shown in sympathetic neurons, the fibrillar centres of the nucleoli show a 10-fold increase in volume during the dark period. In this period, silver grains were located on both ‘giant’ and smallsized fibrillar centres. The fibrillar RNP component seen either at the periphery of fibrillar centres or in the form of a well-delimited network showed the strongest reaction. The same distribution of silver grains was observed in the sympathetic neurons of rats sacrificed during the light period. Here again, silver accumulation occurred exclusively in the fibrillar centres and the fibrillar RNP component. The same difference in reactivity was observed as for the dark period, the fibrillar RNP component being the main site of the reaction.
Structural heterogeneity of endocytic membranes in macrophages as revealed by the cholesterol probe, filipin
Authors: Montesano Roberto , Vassalli Pierre , Orci Lelio
Published: April 2021

The polyene antibiotic, filipin, by specifically interacting with cholesterol, produces ∼ 25-nm protuberances (filipin-sterol complexes) in freeze-fractured membranes, and the addition of filipin to aldehyde fixatives has been recently introduced as a cytochemical technique for the localization of cholesterol in cell membranes. In a previous study we showed that, in fibroblasts, filipin-sterol complexes are absent from endocytic coated pits. To establish whether the absence of filipin-sterol complexes is a phenomenon restricted to coated pits or is correlated with endo-cytosis in general, we applied the filipin probe to cultured mouse peritoneal macrophages, in which different forms of endocytosis take place. The macrophages were incubated with bovine albumin or concanavalin A (Con A) to induce pinocytosis, and with heat-killed staphylococci or opsonized erythrocytes to induce phagocytosis, then fixed in glutaraldehyde/filipin and freeze-fractured. Filipin-sterol complexes were plentiful on the plasma membrane, on the smooth-membrane invaginations and vesicles induced by albumin, on the large endocytic vacuoles induced by Con A, and on the membrane of phagosomes but, in contrast, they were absent from coated pits and vesicles, as well as from coated segments of invaginations or vesicles. These results indicate that the membranes involved in different types of endocytosis do not react in the same way with filipin and may, therefore, have a different cholesterol content. This could reflect different mechanisms of formation for the various types of endocytic vesicles.
Acetylcholinesterase in mammalian erythroid cells
Authors: Keyhani Ezzatollah , Maigne JoËlle
Published: April 2021

The biosynthesis of acetylcholinesterase in mammalian erythroid cells during differentiation and maturation was studied using a cytochemical method. Acetylcholinesterase was actively synthesized in basophilic erythroblasts I and II, and polychromatophilic erythroblasts, where it was present in the nuclear membrane, endoplasmic reticulum and Golgi apparatus. In orthochromatophilic erythroblasts the enzyme was present only in the Golgi apparatus, thus suggesting the end of the biosynthesis of acetylcholinesterase at this stage of maturation. In mouse and human marrow, evidence was also found suggesting the secretion of acetylcholinesterase into the extracellular compartment. No acetylcholinesterase reaction product was found in cat erythroblasts.
Polygonal networks in living chick embryonic cells
Authors: Ireland Grenham W. , Voon Frank C. T.
Published: April 2021

Regular polygonal networks have been found in explants and dissociated cells of early chick embryos. These networks are readily observable in live cells with phase-contrast optics thus allowing time-lapse cinemicroscopy. They consisted of a regular pattern of nodes and radiating struts found predominantly in the lamelliplasm of the free edges of the cells bordering expiants. At the outer edge, the network was terminated by radial struts associated with substrate-attached retraction processes whilst toward the centre of the cells it faded out.

The network was also associated with stress fibres running across the cell and with microextensions on the dorsal surface. Even within one cell the network varied in size. Time-lapse films showed that microvilli were protruded from the dorsal surface over the nodes. Although the cells containing the networks were poorly motile the network itself was a mobile structure.

Many explants from regions differing in prospective fates developed these networks after 2–4 days in culture. They appeared earlier in the smaller less yolky cells of definitive endoblast and epiblast. Experiments with dissociated and reaggregated cells confirmed their occurrence mainly in free edges of cells. The relationship between these networks seen in living chick embryo cells and those seen in other cell types using immunofluorescent techniques is discussed and a mechanism is proposed for their formation.
Nuclear crystalloids in sieve elements of species ofEchium(Boraginaceae)
Authors: Esau Katherine , Thorsch Jennifer
Published: April 2021

Ultrastructural studies of differentiating phloem of the midvein in 15 species of Echium (Boraginaceae) have shown that in every species one or more crystalloids develop in sieve-element nuclei. These inclusions appear as soon as the cell begins to differentiate from a procambial derivative. Small at first, they enlarge later, particularly in length. The crystalloid may extend end-to-end in the correspondingly elongated nucleus. When the nucleus disin-tegrates in the maturing cell the crystalloid is released into the cell lumen where it remains intact or becomes fractured into large pieces. No dissociation into. subunits was observed. The crystalloids are composed of tightly packed narrow rods (tubules) forming a two-dimensional lattice of squares in transections and a system of parallel striations in longitudinal sections. The similarities of these inclusions to the crystalline form of P-protein in Fabaceae raises the question of terminological delimitation of P-protein, a common component of angiospermous sieve-element protoplasts. The occurrence of nuclear crystalloids in another previously investigated genus in the Boraginaceae, Amsinckia, suggests that this inclusion should be explored in boraginaceous representatives for its possible value as a systematic character.
Localization of mitotic factors on metaphase chromosomes
Authors: Adlakha Ramesh C. , Sahasrabuddhe Chintaman G. , Wright David A. , Lindsey William F. , Rao Potu N.
Published: April 2021

The objective of this study was to determine whether the mitotic factors of HeLa cells, which induce meiotic maturation, i.e. germinal vesicle breakdown (GVBD) and chromosome condensation, when injected into fully grown Xenopus laevis oocytes, were localized in the cytoplasm or associated with the metaphase chromosomes. Cytoplasmic extracts Were prepared by lysing mitotic HeLa cells in low-salt hypotonic buffer and separating the chromosomes by centrifugation. The mitotic factors bound to chromosomes were extracted with high-salt (0·2 M-NaCl) buffer. Both the cytoplasmic and chromosomal protein fractions were evaluated for their maturation-promoting activity (MPA) in the Xenopus oocytes. The results of this study indicate that both the cytoplasmic and chromosomal fractions are identical in many respects, including their ability to induce GVBD, but the specific activity of the chromosomal fraction was at least threefold greater than that of the cytoplasmic fraction. These data suggest that a major portion of the mitotic factors is localized on the metaphase chromosomes. This association does not appear to be due to adventitious binding of mitotic proteins to chromosomes during the extraction procedures. Furthermore, when extracts were prepared in a similar way from early- and mid-G2-phase HeLa cells, only the nuclear extracts had MPA and no activity was found in the cytoplasmic fraction. Both the cytoplasmic and nuclear extracts of late-G2 cells exhibited MPA. These data support the conclusion that the mitotic factors become preferentially bound to chromatin as soon as they are synthesized, and as the cell synthesizes more of these factors in preparation for mitosis, increasing amounts of them are retained in the cytoplasm.
Dna repair synthesis in subpopulations of human lymphocytes
Authors: Lewensohn R. , Ringborg U. , Baral E. , Lambert B.
Published: April 2021

Human peripheral blood lymphocytes enriched in T or B cells were exposed to ultraviolet irradiation, nitrogen mustard or methylmethane sulphonate and investigated regarding their capacity for DNA repair synthesis. The DNA repair synthesis, measured as [3H]thymidine incorporated, was determined by autoradiography as unscheduled DNA synthesis (LIDS). No systematic difference could be found in the capacity for UDS between the T- and B-cell-enriched fractions. A larger individual variation in UDS was found in the B-cell-compared to the T-cell-enriched lymphocytes.
Changes in the fine structure of the apical plasma membrane of endometrial epithelial cells during implantation in the rat
Authors: Murphy C. R. , Swift J. G. , Mukherjee T. M. , Rogers A. W.
Published: April 2021

In previous work we have shown that ovarian hormones, when injected into ovariectomized rats, alter the fine structure of the plasma membrane of endometrial epithelial cells. In this paper freeze-fracture techniques have been used to study the apical plasma membrane of endometrial epithelial cells of rats during the period of blastocyst implantation of normal pregnancy. On day 1 of pregnancy there were 2354 ±114 intramembranous particles (IMPs) per μm2 of membrane. The particles were spherical and randomly distributed. On day 5 of pregnancy IMP density rose to 2899 ± 289 per μm2 and some rod-shaped particles were also visible. By day 6 of pregnancy IMP density had risen to 4014 ±206 per μm2 and there were more rod-shaped IMPs than before. In addition, on day 6 IMPs were also present as rows of particles and some gap-junction-like arrays of particles were also seen.

Our findings indicate that there are fine-structural alterations in the apical plasma membrane of endometrial epithelial cells, the site of first contact between maternal and embryonic cells, during the period of early pregnancy. The findings are discussed in the light of suggested mechanisms of blastocyst attachment to the uterine epithelium at implantation.
Macrocyst development in Dictyostelium discoideum: I. Induction of synchronous development by giant cells and biochemical analysis
Authors: Saga Y. , Yanagisawa K.
Published: April 2021

In Dictyostelium discoideum, cytological and physiological studies on macrocyst formation revealed that this process consists of at least two steps: the production of giant cells, which are believed to be formed from the fusion of cells of two opposite mating types, and the subsequent induction of macrocyst development by the giant cells. The conditions that had been considered formerly to be required for macrocyst formation, such as darkness and the presence of two cells of complementary mating types in heterothallic strains, were actually required only for the production of the giant cells. Once giant cells are produced, the surrounding cells can aggregate and form macrocysts even in the light. Furthermore, it was demonstrated that giant cells can switch the developmental mode of the surrounding cells to macrocyst formation. That is, if a critical number of the isolated giant cells are introduced into a cell population of a single strain of NC4, which normally would produce only fruiting-bodies, macrocysts are formed instead. When in the presence of giant cells, the development of macrocysts may be initiated by starvation. Therefore, if all cells are made to starve simultaneously development begins and proceeds synchronously. Using this technique of synchronous development, the developmental kinetics of enzyme activities were assayed during macrocyst and fruiting-body formation. Considerable differences in the patterns of those enzyme activities were demonstrated between the two developmental modes of D. discoideum.