Showing papers by "University College London published in 1975"

Fate of teratocarcinoma cells injected into early mouse embryos

Abstract: ANALYSIS of early mammalian development is complicated by technical difficulties. The initial processes of cellular determination and differentiation in the mouse embryo take place in small populations of cells1,2, and major embryogenic events occur after uterine implantation when the embryo is largely inaccessible. Recent work, however, suggests that murine teratocarcinomas may provide a convenient model for studying mammalian development3–6. These are transplantable tumours of germ cell or embryonic cell origin3–6, typically consisting of a variety of differentiated tissues and undifferentiated stem cells. The stem cells, called embryonal carcinoma, resemble cells of early embryos in morphological, biochemical and cell surface properties, and in developmental potential3–6. They can be propagated in tissue culture to provide sufficient material for biochemical analysis. After inoculation into histocompatible adult hosts they form differentiated teratocarcinomas. They also differentiate in vitro7,8 where the first stages of their differentiation seem to parallel normal embryonic development. We show here that embryonal carcinoma cells can participate in normal embryogenesis, thus providing further evidence for the validity of the use of these cultures as a model of normal embryonic development.

Mammalian plasma membranes.

Abstract: 1975 is the fiftieth anniversary of the proposal, by Gorter and Grendel, that biological membranes are based on a lipid bilayer. Now well established, this proposal, like the DNA double helix, was a major breakthrough in molecular cell biology. Here we discuss current concepts about the molecular composition, organisation and behaviour of the plasma membranes of mammalian erythrocytes and nucleated cells.

Effect of electric fields on the daytime high-latitude E and F regions

Abstract: We have obtained solutions of the coupled continuity, momentum, and energy equations for NO(+), O(+), and O2(+) ions for conditions appropriate to the daytime high-latitude E and F regions. Owing to the rapid increase of the reaction O(+) + N2 yielding NO(+) + N with ion energy, high-latitude electric fields and consequent perpendicular-E x B drifts deplete O(+) in favor of NO(+). For electric field strengths less than about 10 mV/m the depletion of O(+) is small, and the altitude profiles of ion density are similar to those found at mid-latitudes. However, for moderate electric field strengths (50 mV/m), NO(+) is substantially increased in relation to O(+) and becomes an important ion throughout the F region. For large electric fields (200 mV/m), NO(+) completely dominates the ion composition to at least 600 km, decreasing at high altitudes with a diffusive equilibrium scale height. Since the overall F region electron density decreases markedly with increasing electric field strength, it appears that high-latitude, daytime electron density troughs are directly related to the presence of ionospheric electric fields.

Induction of increased calcium uptake in mouse T lymphocytes by concanavalin A and its modulation by cyclic nucleotides.

Abstract: The binding of concanavalin A to T but not B mouse spleen lymphocytes increases Ca2+ uptake in these cells which is measurable by 45 s and complete by 1 min. Dibutyryl cyclic AMP, but not sodium azide inhibits induced Ca2+ uptake, whereas dibutyryl cyclic GMP enhances it. B cell mitogens do not cause a similar Ca2+ uptake in mouse B lymphocytes. The induction of increased Ca2+ uptake by T cells is discussed in terms of gated membrane channels for Ca2+.

Immunohistochemical localisation of S-100 protein in brain.

Abstract: IT is accepted that the brain-specific protein S–100 is associated predominantly with glial cells1–5. More equivocal evidence exists to suggest a possible relationship of S–100 to neurones3,6,7. Although well characterised antisera against S–100 have long been available8, few immunohistochemical studies of the location of S–100 antigen in brain have appeared. Two such studies have reported that S–100 is associated with neuronal elements9,10 but in both cases the major glial fraction of S–100 does not appear to have been localised by the immunohistochemical techniques used. The recent study by Haglid et al.10 claimed to demonstrate that S–100 antigen is associated with the junctional membranes of brain synapses, and on this basis an ambitious theory of chemical events underlying “learning” has been proposed11 in which S–100 is assigned a key role. We have now reinvestigated the distribution of S–100 in brain tissue using a specific antiserum against S–100 ( a generous gift from Dr L. Levine) which gave a positive response against rat brain extract at 1 : 1,400 dilution in complement fixation assay. The immunological properties of this antiserum have been described in detail by Kessler et al.12.

Non-linear angle-sum relations for polyhedral cones and polytopes

Abstract: It is shown that the internal and external angles at the faces of a polyhedral cone satisfy various bilinear relations. The first two of these are related to the Gauss–Bonnet and Steiner parallel formulae for spherical polytopes, while the third is completely new. However, the proofs are basically combinatorial in nature, rather than differential geometric, as in the more classical treatments. These relations lead to inversion formulae, analogous to Euler-type relations, for certain functions defined on polytopes and polyhedral cones. As a result, various new relations involving quermassintegrals and Grassmann angles are found; there is also an application to lattice polytopes.

Stochastic properties of binocular rivalry alternations

Abstract: Previous researches have demonstrated that the successive phase durations in binocular rivalry are independent. These findings are confirmed and extended to chromatic stimuli. The nature of the function that is shown to describe the distribution of the dominance phase durations is consistent with the independence of successive phases and suggests that a parallel may exist between binocular rivalry and the perceptual reversal of ambiguous figures.

Ly antigens as markers for functionally distinct subpopulations of thymus-derived lymphocytes of the mouse.

Abstract: THYMUS-DERIVED lymphocytes (T cells) have several functions1–3, and in some instances it appears that two sub-populations of T cells interact to amplify their response4,5. But recognition of the diverse functions and interactions of T cells has not been matched by the development of techniques for identifying and separating the different T-cell subpopulations involved. The ability to do so would greatly aid study of the many roles of T cells. We report here experiments with mice that show that antisera to different Ly alloantigens can identify functionally-distinct subpopulations of T cells.

Relation between the shape of population distribution and the robustness of four simple test statistics

Abstract: SUMMARY The underlying theory upon which a great number of statistical procedures are based assumes that the variable or variables sampled are normally distributed. While there has been a good deal of theoretical research on the robustness of these procedures, the results seem not to have been set out in terms which the unsophisticated user of statistical methods can easily assimilate. The present paper, based on extensive computer simulation, aims at relating diagrammatically the shape of population to the robustness of the distribution of

Tubulin in postsynaptic junctional lattice

Abstract: TUBULIN, the primary protein of microtubules1,2, has been identified as a major soluble protein in isolated synaptosomes3,4. Indirect evidence for the presence of tubulin in the synaptosomal plasma membranes themselves has been accumulating for some time. Colchicine-binding activity, used as an assay for the presence of tubulin1,2, has been found in synaptosomal plasma membranes5–7. These membranes, prepared by several different techniques, all show a prominent protein band of apparent molecular weight 52,000–53,000 when solubilised and electrophoresed in sodium dodecyl sulphate–polyacrylamide gel systems8–12; such gel techniques applied to well characterised microtubule preparations yield molecular weights for tubulin which have been reported to range from 52,000 to 56,000 (refs 1 and 2), the precise value depending on the particular electrophoretic system used. Sequential solubilisation of synaptosomal plasma membranes with Triton X-1000 and N-lauroyl sarcosinate yields isolated postsynaptic densities13 whose major protein has a molecular weight of 53,000 (ref. 14), and similarly digestion of the synaptosomal lipid unit membrane by sodium deoxycholate results in isolated postsynaptic junctional lattices15 with a major protein of approximate molecular weight 53,000 (ref. 12). We report here the identification of tubulin in the postsynaptic junctional lattices of rat forebrain both by two-dimensional electrophoresis of 125I-labelled tryptic peptides and by electron microscope immunohistochemistry.

Stimulation of mouse lymphocytes by insoluble anti-mouse immunoglobulin.

Abstract: IT is generally agreed that B-cell surface immunoglobulin (Ig) functions as the receptor for antigen, and so accounts for the specificity of the immune response by clonal selection. It is not known, however, how the combination of surface Ig with antigen stimulates the cell to proliferation and/or differentiation to secrete antibody at a high rate1. A signal could be delivered directly through the receptors, either by an allosteric transition in the receptor itself or by cross-linkage or aggregation of receptor Ig in the fluid cell membrane, analogous to antigen-induced or anti-IgE-induced histamine release from mast cells2. Alternatively, the receptor may act passively as an antigen-specific ‘address’ for the delivery of an antigen-associated nonspecific (that is, potentially polyclonal) signal to some other site on the cell surface3.

Ligand-induced redistribution of lymphocyte membrane ganglioside GM1.

Abstract: Dynamic aspects of the binding of cholera toxin to lymphocyte membranes have been studied. We have shown that the receptor for this ligand—the GM1 ganglioside—can be laterally redistributed into aggregates and caps. Exogenous purified GM1 inserted into GM1-deficient human leukaemic cells can undergo a similar pattern of ligand-induced mobilisation. These observations may have important implications for both the general behaviour of cell surface glycolipids and the mode of action of cholera toxin on adenyl cyclase.

Chromosome assignment of some human enzyme loci: mitochondrial malate dehydrogenase to 7, mannosephosphate isomerase and pyruvate kinase to 15 and probably, esterase D to 13.

Abstract: Eleven independent man-mouse hybrids and 40 subclones from four to them were analysed for up to 42 enzyme markers. Nine subclones from three hybrid lines were fully karyotyped. The data presented suggest that the gene for the human enzyme MOR-M can be assigned to chromosome 7, whilst those for MPI and PK-3 are on chromosome 15. The use of a small number of well-characterized hybrids for gene assigments is discussed as well as the significance of some known human linkage relationships.

Complex tight junctions of epithelial and of endothelial cells in early foetal brain.

Abstract: ?The morphology of epithelial and of endothelial intercellular junctions in human foetal (9-15 weeks gestation) and sheep foetal (50, 60 and 125 days gestation, term 147 days) brain has been studied using the freeze-fracture technique and thin section transmission electronmicroscopy. Freeze-fracture replicas of the choroid plexus of both early human and sheep foetuses showed that the choroidal ependymal cells are linked at the ventricular surface by tight junctions. Freeze-fracture replicas of foetal cortical endothelial cell junctions showed that they are still more complex than those of choroidal epithelial cells, in all specimens so far examined. In some 60 day sheep foetuses the dye Alcian blue, which binds to plasma albumin and which iselectrondense when treated with osmium tetroxide, was injected intravenously a few minutes prior to fixation. The dye penetrated from blood into brain extracellular space and c.s.f. but apparently not by an intercellular route. The dye was found in a tubular system (endoplasmic reticulum) in both choroidal epithelial and cortical endothelial cells. The possibility that protein penetrates into the foetal brain and c.s.f. by a transcellular route is discussed. The possible significance of these findings in relation to previous ideas and studies of the development of blood-brain barrier mechanisms is also considered.

Presynaptic Microtubules and their Association with Synaptic Vesicles

Abstract: When fragments of rat or frog brain are teased in albumin solution before fixation, the synapses show microtubules focused on the presynaptic membrane and in close association with synaptic vesicles.

Hypertrophy of intestinal smooth muscle.

Abstract: Proximal to an experimental stenosis of the small intestine of rats and guinea-pigs a remarkable hypertrophy of the muscle coat develops 3–5 weeks after the operation. There is no increase in the length of the intestine but an overall increase in volume of the muscularis externa up to 10 times. This increase is accounted for by an increase in size and in number (by mitosis) of smooth muscle cells of both the longitudinal and circular layers. Bundles of newly-formed smooth cells appear in the serosa and are circularly arranged. In the hypertrophic smooth muscle cells of the circular layer the ratio of surface to volume is 0.80 (0.80 μm2 of cell surface for every μm3 of cell volume) as against 1.4 in the control muscle. The hypertrophic muscle cells have a highly developed sarcoplasmic reticulum and show a large number of nexuses. The density of innervation (number of axons per given number of smooth muscle cells) is smaller than in controls. Few collagen fibrils are visible in the extracellular space.

The role of macrophages in the generation of T helper cells. III. Influence of macrophage-derived factors in helper cell induction.

Abstract: Helper cell induction to soluble or particulate antigens in vitro requires the cooperation of T cells and macrophages. A direct contact between macrophages and T cells is not obligatory for this cooperation and factors released from macrophages are as effective in activating T cells as the cells themselves. Two different types of macrophage-derived factors where found. The supernatant obtained from purified macrophages incubated with antigen for several days generates helper cells in absence of macrophages or additional antigen, but only if obtained from macrophages which were identical at the I-A subregion of the H-2 complex as the T cells. This factor was called genetically related macrophages factor (GRF). The other factor(s), which is present in the supernatant obtained from macrophages incubated for several days without antigen, replaces macrophages only if the antigen is particulate. This factor(s), called nonspecific macrophage factor (NMF) is not restricted genetically and is also obtained from allogeneic macrophages. The importance of both these factors in helper cell induction is discussed.

Comparative studies of purinergic nerves.

Abstract: Purinergic nerves supply the gastrointestinal tract of vertebrates, including fish, amphibians, reptiles and birds, as well as mammals. Their cell bodies are located in Auerbach's plexus and their axons extend in an anal direction before innervating mainly the circular muscle coat. In the stomach they are controlled by preganglionic cholinergic fibres of parasympathetic origin. They are involved in “receptive relaxation” of the stomach, “descending inhibition” in peristalsis and reflex relaxation of oesophageal and internal anal sphincters. The terminal varicosities of purinergic nerves are characterised by a predominance of “large opaque vesicles,” which can be distinguished from the “large granular vesicles” found in small numbers in both adrenergic and cholinergic nerves. Stimulation of purinergic nerves with single pulses produces hyperpolarisations of up to 25 mV (inhibitory junction potentials) in smooth muscle cells. These potentials are unaffected by atropine, adrenergic neuron blocking agents or sympathetic denervation, but are abolished by tetrodotoxin. The “rebound contraction” which characteristically follows cessation of purinergic nerve stimulation is probably due to prostaglandin. Evidence that ATP is the transmitter released from purinergic nerves includes: (1) synthesis and storage of ATP in nerves; (2) release of ATP from the nerves when they are stimulated; (3) exogenously applied ATP mimicking the action of nerve-released transmitter, both producing a specific increase in K+ conductance; (4) the presence of Mg-activated ATPase, 5′-nucleotidase and adenosine deaminase, enzymes which inactivate ATP; (5) drugs (including quinidine, some 2-substituted imidazolines, 2-2′pyridylisatogen and dipyridamole) which produce similar blocking or potentiating effects on the response to exogenously applied ATP and nerve stimulation. Speculations are made about the evolution and development of the nervous system, including the possibility that purinergic nerves are a primitive nerve type.

Observations of a transient X-ray source with a period of 104 s

Abstract: DURING routine observations of the Crab Nebula by Ariel V, experiment A, the rotation modulation collimator (RMC), discovered a new X-ray source A0535+26. The source was just detectable during the first observation on April 13, and during the 16 d of observation was seen to brighten to nearly twice the Crab's intensity (in the 3–7 keV range). The source varies periodically, with a period of 104 s, and has a very flat spectrum in the 3–7 keV range.

Differentiation of the neural plate and neural tube in the young chick embryo. A study by scanning and transmission electron microscopy.

Abstract: The differentiation of the presumptive neural plate, the neural plate and the neural tube have been investigated in the chick embryo by SEM, TEM and histochemical techniques. The relationship of these tissues to neighbouring structures, including extracellular materials, has also been studied. When SEM micrographs of primitive streak stage embryos were examined in stereo, it was found that cells which had been invaginating at the time of fixation were similar in shape to fibroblasts migrating in vitro. It was concluded that SEM stereo pairs could provide evidence about the mode and direction of cell migration. Many more mid-bodies have been found associated with the developing neural tissue than with the lateral ectoderm. It was found possible to recognise mid-bodies not only by TEM but also by SEM. It is therefore proposed that SEM montages may be used for assessing which regions of a tissue have recently undergone extensive mitosis. The beads on the specialised threads seen in the early stages of development are now considered to be formed from mid-bodies. Similar, but unbeaded threads have been described which span the gap between the neural folds just prior to the dorsal closure of the neural tube and it seems probably that these threads help to close the neural tube. It is suggested that the beaded threads arise by incomplete separation of two daughter cells at mitosis, whereas the unbeaded threads form by outgrowth of cell processes.

Role of macrophages in in vitro induction of T-helper cells.

Abstract: MACROPHAGES are of importance in the initiation of immune responses, both in vitro1 and in vivo1,2. Both immune responses involving B cells, such as antibody production3–6, and those involving T cells, such as the lymphocyte transformation7, the mixed lymphocyte reaction (MLR) (refs 8 and 9), and the induction of cytotoxic responses10 require macrophages. Various concepts of macrophage function in immune induction have been suggested. The simplest concept proposed is that macrophages augment lymphocyte survival in vitro11. Although this is one of their functions in vitro, it does not explain fully their role in vitro and especially in vivo. In the induction of antibody responses, two functions were defined, the breakdown of antigens to the appropriate size5 and the presentation of antigen to B cells in an optimally immunogenic manner12. Because the T-cell reactions already studied, such as the MLR, involve ill-defined antigens, the surfaces of living cells, even less is known about the mechanisms of macrophage function in the stimulation of T cells than of B cells.

Functional analysis of murine and human B lymphocyte subsets.

Abstract: The cellular population structure of the immune system appears to reveal increasing heterogeneity and complexity as new methods for analysis become available. Recent studies illustrate the division of T and B lymphocyte populations into physically and functionally defined subsets and the existence of multiple direct and indirect interactions between lymphocytes and other immunologically relevant cells. Lymphocytes provide a unique model system for analysing the signals and sequential steps involved in the elieitation and regulation of physiological response. Clearly, however, both the rational design of experiments and the interpretation of results rest heavily on an appreciation of special characteristics of individual cellular components and the integrated nature of their responses. The performance of individual cells at any given time under the experimental conditions depends largely on past programming experiences, or 'life history'. TTiis will include non-antigen driven maturation (Cooper et al. 1972, Toivanen et al. 1974, Ivanyi 1973, Lafleur et al. 1973), and antigen driven development of memory cells (McMichael & Williamson 1974, Strober & Dilley 1973) and effector cells (Gudat et al. 1970, Leduc et al. 1968). These processes are likely to be complex, involving multiple regulatory controls, and the inter-relationships between these different parameters of response are at present uncertain.