Showing papers in "Nature in 1992"
TL;DR: In this paper, the synthesis of mesoporous inorganic solids from calcination of aluminosilicate gels in the presence of surfactants is described, in which the silicate material forms inorganic walls between ordered surfactant micelles.
Abstract: MICROPOROUS and mesoporous inorganic solids (with pore diameters of ≤20 A and ∼20–500 A respectively)1 have found great utility as catalysts and sorption media because of their large internal surface area. Typical microporous materials are the crystalline framework solids, such as zeolites2, but the largest pore dimensions found so far are ∼10–12 A for some metallophosphates3–5 and ∼14 A for the mineral cacoxenite6. Examples of mesoporous solids include silicas7 and modified layered materials8–11, but these are invariably amorphous or paracrystalline, with pores that are irregularly spaced and broadly distributed in size8,12. Pore size can be controlled by intercalation of layered silicates with a surfactant species9,13, but the final product retains, in part, the layered nature of the precursor material. Here we report the synthesis of mesoporous solids from the calcination of aluminosilicate gels in the presence of surfactants. The material14,15 possesses regular arrays of uniform channels, the dimensions of which can be tailored (in the range 16 A to 100 A or more) through the choice of surfactant, auxiliary chemicals and reaction conditions. We propose that the formation of these materials takes place by means of a liquid-crystal 'templating' mechanism, in which the silicate material forms inorganic walls between ordered surfactant micelles.
15,125 citations
4,800 citations
TL;DR: Observations indicate that a normal p53 gene is dispensable for embryonic development, that its absence predisposes the animal to neoplastic disease, and that an oncogenic mutant form of p53 is not obligatory for the genesis of many types of tumours.
Abstract: Mutations in the p53 tumour-suppressor gene are the most frequently observed genetic lesions in human cancers. To investigate the role of the p53 gene in mammalian development and tumorigenesis, a null mutation was introduced into the gene by homologous recombination in murine embryonic stem cells. Mice homozygous for the null allele appear normal but are prone to the spontaneous development of a variety of neoplasms by 6 months of age. These observations indicate that a normal p53 gene is dispensable for embryonic development, that its absence predisposes the animal to neoplastic disease, and that an oncogenic mutant form of p53 is not obligatory for the genesis of many types of tumours.
4,710 citations
TL;DR: It is shown that vascular endothelial growth factor (VEGF) probably functions as a hypoxia-inducible angiogenic factor and is specifically induced in a subset of glioblastoma cells distinguished by their immediate proximity to necrotic foci and the clustering of capillaries alongside VEGF-producing cells.
Abstract: Inefficient vascular supply and the resultant reduction in tissue oxygen tension often lead to neovascularization in order to satisfy the needs of the tissue. Examples include the compensatory development of collateral blood vessels in ischaemic tissues that are otherwise quiescent for angiogenesis and angiogenesis associated with the healing of hypoxic wounds. But the presumptive hypoxia-induced angiogenic factors that mediate this feedback response have not been identified. Here we show that vascular endothelial growth factor (VEGF; also known as vascular permeability factor) probably functions as a hypoxia-inducible angiogenic factor. VEGF messenger RNA levels are dramatically increased within a few hours of exposing different cell cultures to hypoxia and return to background when normal oxygen supply is resumed. In situ analysis of tumour specimens undergoing neovascularization show that the production of VEGF is specifically induced in a subset of glioblastoma cells distinguished by their immediate proximity to necrotic foci (presumably hypoxic regions) and the clustering of capillaries alongside VEGF-producing cells.
4,627 citations
TL;DR: Folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.
Abstract: In the cell, as in vitro, the final conformation of a protein is determined by its amino-acid sequence. But whereas some isolated proteins can be denatured and refolded in vitro in the absence of other macromolecular cellular components, folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.
4,181 citations
TL;DR: In this article, the authors explore the consequences of placing players in a two-dimensional spatial array: in each round, every individual 'plays the game' with the immediate neighbours; after this, each site is occupied either by its original owner or by one of the neighbours, depending on who scores the highest total in that round; and so to the next round of the game.
Abstract: MUCH attention has been given to the Prisoners' Dilemma as a metaphor for the problems surrounding the evolution of coopera-tive behaviour1–6. This work has dealt with the relative merits of various strategies (such as tit-for-tat) when players who recognize each other meet repeatedly, and more recently with ensembles of strategies and with the effects of occasional errors. Here we neglect all strategical niceties or memories of past encounters, considering only two simple kinds of players: those who always cooperate and those who always defect. We explore the consequences of placing these players in a two-dimensional spatial array: in each round, every individual 'plays the game' with the immediate neighbours; after this, each site is occupied either by its original owner or by one of the neighbours, depending on who scores the highest total in that round; and so to the next round of the game. This simple, and purely deterministic, spatial version of the Prisoners' Dilemma, with no memories among players and no strategical elaboration, can generate chaotically changing spatial patterns, in which cooperators and defectors both persist indefinitely (in fluctuating proportions about predictable long-term averages). If the starting configurations are sufficiently symmetrical, these ever-changing sequences of spatial patterns—dynamic fractals—can be extraordinarily beautiful, and have interesting mathematical properties. There are potential implications for the dynamics of a wide variety of spatially extended systems in physics and biology.
3,822 citations
TL;DR: In this article, a statistical quantity (RfreeT) is defined to measure the agreement between observed and computed structure factor amplitudes for a 'test' set of reflections that is omitted in the modelling and refinement process.
Abstract: THE determination of macromolecular structure by crystallography involves fitting atomic models to the observed diffraction data1. The traditional measure of the quality of this fit, and presumably the accuracy of the model, is theR value. Despite stereochemical restraints2, it is possible to overfit or 'misfit' the diffraction data: an incorrect model can be refined to fairly good R values as several recent examples have shown3. Here I propose a reliable and unbiased indicator of the accuracy of such models. By analogy with the cross-validation method4,5 of testing statistical models I define a statistical quantity (RfreeT) that measures the agreement between observed and computed structure factor amplitudes for a 'test' set of reflections that is omitted in the modelling and refinement process. As examples show, there is a high correlation between RfreeT and the accuracy of the atomic model phases. This is useful because experimental phase information is usually inaccurate, incomplete or unavailable. I expect that RfreeT will provide a measure of the information content of recently proposed models of thermal motion and disorder6–8, time-averaging9 and bulk solvent10.
3,714 citations
TL;DR: The three-dimensional structure of human serum albumin has been determined crystallographically to a resolution of 2.8 Å and should provide insight into future pharmacokinetic and genetically engineered therapeutic applications of serumalbumin.
Abstract: The three-dimensional structure of human serum albumin has been determined crystallographically to a resolution of 2.8 A. It comprises three homologous domains that assemble to form a heart-shaped molecule. Each domain is a product of two subdomains that possess common structural motifs. The principal regions of ligand binding to human serum albumin are located in hydrophobic cavities in subdomains IIA and IIIA, which exhibit similar chemistry. The structure explains numerous physical phenomena and should provide insight into future pharmacokinetic and genetically engineered therapeutic applications of serum albumin.
3,482 citations
TL;DR: It is shown that an effective test of the accuracy of a 3D protein model is a comparison of the model to its own amino-acid sequence, using a3D profile, computed from the atomic coordinates of the structure 3D profiles of correct protein structures match their own sequences with high scores, in contrast,3D profiles for protein models known to be wrong score poorly.
Abstract: As methods for determining protein three-dimensional (3D) structure develop, a continuing problem is how to verify that the final protein model is correct. The revision of several protein models to correct errors has prompted the development of new criteria for judging the validity of X-ray and NMR structures, as well as the formation of energetic and empirical methods to evaluate the correctness of protein models. The challenge is to distinguish between a mistraced or wrongly folded model, and one that is basically correct, but not adequately refined. We show that an effective test of the accuracy of a 3D protein model is a comparison of the model to its own amino-acid sequence, using a 3D profile, computed from the atomic coordinates of the structure 3D profiles of correct protein structures match their own sequences with high scores. In contrast, 3D profiles for protein models known to be wrong score poorly. An incorrectly modelled segment in an otherwise correct structure can be identified by examining the profile score in a moving-window scan. The accuracy of a protein model can be assessed by its 3D profile, regardless of whether the model has been derived by X-ray, NMR or computational procedures.
3,213 citations
TL;DR: TGF-β1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.
Abstract: Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.
3,010 citations
TL;DR: The Ipr mice develop lymphadenopathy and suffer from a systemic lupus erythematosus-like autoimmune disease, indicating an important role for Fas antigen in the negative selection of autoreactive T cells in the thymus.
Abstract: Fas antigen is a cell-surface protein that mediates apoptosis. It is expressed in various tissues including the thymus and has structural homology with a number of cell-surface receptors, including tumour necrosis factor receptor and nerve growth factor receptor. Mice carrying the lymphoproliferation (lpr) mutation have defects in the Fas antigen gene. The lpr mice develop lymphadenopathy and suffer from a systemic lupus erythematosus-like autoimmune disease, indicating an important role for Fas antigen in the negative selection of autoreactive T cells in the thymus.
NEC1
TL;DR: In this article, the authors used a variant of the standard arc-discharge technique for fullerene synthesis under a helium atmosphere, where a carbonaceous deposit formed on one of the graphite rods, consisting of a macroscopic (diameter of about 5 mm) cylinder.
Abstract: INTEREST in carbon fibres1,2 has been stimulated greatly by the recent discovery of hollow graphitic tubules of nanometre dimensions3. There has been much speculation about the properties and potential application of these nanotubes4–8. Theoretical studies predict that their electronic properties will depend on their diameter and degree of helicity4,5. Experimental tests of these ideas has been hampered, however, by the lack of macroscopic quantities of the material. Here we report the synthesis of graphitic nanotubes in gram quantities. We use a variant of the standard arc-discharge technique for fullerene synthesis under a helium atmosphere. Under certain conditions, a carbonaceous deposit forms on one of the graphite rods, consisting of a macroscopic (diameter of about 5 mm) cylinder in which the core comprises pure nanotubes and nanoscale particles in high yield. The purity and yield depend sensitively on the gas pressure in the reaction vessel. Preliminary measurements of the conductivity of the bulk nanotube material indicate a conductivity of about 100 S cm–11.
TL;DR: For some mammalian cells, programmed death seems to occur by default unless suppressed by signals from other cells, so dependence on specific survival signals provides a simple way to eliminate misplaced cells, for regulating cell numbers and, perhaps, for selecting the fittest cells.
Abstract: Programmed cell death occurs in most animal tissues at some stage of their development, but the molecular mechanism by which it is executed is unknown. For some mammalian cells, programmed death seems to occur by default unless suppressed by signals from other cells. Such dependence on specific survival signals provides a simple way to eliminate misplaced cells, for regulating cell numbers and, perhaps, for selecting the fittest cells. But how general is this dependence on survival signals?
TL;DR: Purification and cloning of the complementary DNA indicates that IL-lβ-converting enzyme is composed of two nonidentical subunits that are derived from a single proenzyme, possibly by autoproteolysis.
Abstract: Interleukin-1 beta (IL-1 beta)-converting enzyme cleaves the IL-1 beta precursor to mature IL-1 beta, an important mediator of inflammation. The identification of the enzyme as a unique cysteine protease and the design of potent peptide aldehyde inhibitors are described. Purification and cloning of the complementary DNA indicates that IL-1 beta-converting enzyme is composed of two nonidentical subunits that are derived from a single proenzyme, possibly by autoproteolysis. Selective inhibition of the enzyme in human blood monocytes blocks production of mature IL-1 beta, indicating that it is a potential therapeutic target.
TL;DR: In this paper, a flexible polyethylene terephthalate (PET) based light-emitting diodes (LEDs) were constructed from conjugated polymers, using poly(ethylene-terephthalates) as the substrate, soluble poly-aniline as the hole-injecting electrode, substituted poly(1,4-phenylene-vinylene) as electroluminescent layer and calcium as the electron-injection top contract.
Abstract: THE recent fabrication of light-emitting diodes (LEDs) from conjugated polymers1,2demonstrates the technological potential of this class of electronic materials. A variety of colours are possible, because the wavelength of luminescence emission can be chemically tuned during synthesis1–4. In addition, the mechanical properties of polymers suggest that light-emitting structures can be made that are more flexible than their inorganic counterparts, provided appropriate materials can be found for the substrate and electrodes. Here we report the fabrication of a fully flexible LED using poly(ethylene terephthalate) as the substrate, soluble poly-aniline as the hole-injecting electrode, a substituted poly(1,4-phenylene-vinylene) as the electroluminescent layer and calcium as the electron-injecting top contract. The structure is mechanically robust and may be sharply bent without failure. The LED is easily visible under room lighting and has an external quantum efficiency of about 1%. With a turn-on voltage for light emission of 2–3 V, the 'plastic' LED demonstrates that this unique combination of optical, electrical and mechanical properties can be used to make novel structures that are compatible with conventional devices.
TL;DR: In this paper, the authors report results of electronic-structure calculations on two classic examples of ferroelectric perovskites, BaTiO3 and PbTiO2, and demonstrate that hybridization between the titanium 3d states and the oxygen 2p states is essential for ferroelectivity.
Abstract: FERROELECTRIC materials are characterized by a switchable macroscopic polarization. Most technologically important ferroelectrics are oxides with a perovskite structure. The origin of their ferroelectric behaviour is unclear, however, and there is incomplete understanding of why similar, but chemically different, perovskites should display very different ferroelectric behaviour. The great sensitivity of ferroelectrics to chemistry, defects, electrical boundary conditions and pressure arises from a delicate balance between long-range Coulomb forces (which favour the ferroelectric state) and short-range repulsions (which favour the nonpolar cubic structure). To model the transition accurately, total-energy techniques are required which incorporate the effects of charge distortion and covalency. Here I report results of electronic-structure calculations on two classic examples of ferroelectric perovskites, BaTiO3 and PbTiO3, and demonstrate that hybridization between the titanium 3d states and the oxygen 2p states is essential for ferroelectricity. The different ferroelectric phase behaviour of the two materials is also clear: in PbTiO3, the lead and oxygen states hybridize, leading to a large strain that stabilizes the tetragonal phase, whereas in BaTiO3 the interaction between barium and oxygen is completely ionic, favouring a rhombohedral structure.
TL;DR: The isolation of single-stranded DNA aptamers to the protease thrombin of the blood coagulation cascade is described and binding affinities in the range 25–200 nM are reported.
Abstract: Aptamers are double-stranded DNA or single-stranded RNA molecules that bind specific molecular targets. Large randomly generated populations can be enriched in aptamers by in vitro selection and polymerase chain reaction. But so far single-stranded DNA has not been investigated for aptamer properties, nor has a target protein been considered that does not interact physiologically with nucleic acid. Here we describe the isolation of single-stranded DNA aptamers to the protease thrombin of the blood coagulation cascade and report binding affinities in the range 25-200 nM. Sequence data from 32 thrombin aptamers, selected from a pool of DNA containing 60 nucleotides of random sequence, displayed a highly conserved 14-17-base region. Several of these aptamers at nanomolar concentrations inhibited thrombin-catalysed fibrin-clot formation in vitro using either purified fibrinogen or human plasma.
TL;DR: It is shown that expression of an endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), is induced in astrocytoma cells but is dramatically upregulated in two apparently different subsets of glioblastoma cells, which strongly support the concept that tumour angiogenesis is regulated by paracrine mechanisms and identify VEGF as a potential tumourAngiogenesis factor in vivo.
Abstract: Clinical and experimental studies suggest that angiogenesis is a prerequisite for solid tumour growth. Several growth factors with mitogenic or chemotactic activity for endothelial cells in vitro have been described, but it is not known whether these mediate tumour vascularization in vivo. Glioblastoma, the most common and most malignant brain tumour in humans, is distinguished from astrocytoma by the presence of necroses and vascular proliferations. Here we show that expression of an endothelial cell-specific mitogen, vascular endothelial growth factor (VEGF), is induced in astrocytoma cells but is dramatically upregulated in two apparently different subsets of glioblastoma cells. The high-affinity tyrosine kinase receptor for VEGF, flt, although not expressed in normal brain endothelium, is upregulated in tumour endothelial cells in vivo. These observations strongly support the concept that tumour angiogenesis is regulated by paracrine mechanisms and identify VEGF as a potential tumour angiogenesis factor in vivo.
TL;DR: The simple methodology greatly enhances the production and rapid evaluation of random libraries of millions of peptides so that acceptor-binding ligands of high affinity can be rapidly identified and sequenced, on the basis of a "one-bead, one-peptide9 approach.
Abstract: OUR aim was to improve techniques for drug development by facilitating the identification of small molecules that bind with high affinity to acceptor molecules (for example, cell-surface receptors, enzymes, antibodies) and so to mimic or block their interaction with the natural ligand1,2. Previously such small molecules have been characterized individually on a serial basis. The systematic synthesis and screening of peptide libraries of defined structure represents a new approach. For relatively small libraries, predetermined sequence variations on solid-phase supports have been used3,4, and large libraries have been produced using a bacteriophage vector into which random oligodeoxynucleotide sequences have been introduced5–8, but these techniques have severe limitations. Here we investigate an alternative approach to synthesis and screening of peptide libraries. Our simple methodology greatly enhances the production and rapid evaluation of random libraries of millions of peptides so that acceptor-binding ligands of high affinity can be rapidly identified and sequenced, on the basis of a "one-bead, one-peptide9 approach.
TL;DR: It is reported that transient expression of LIF in mice is essential for implantation, and females lacking a functional LIF gene are fertile, but their blastocysts fail to implant and do not develop.
Abstract: A critical point during mammalian pregnancy is the implantation of the blastocyst when the embryo attaches to the wall of the uterus. The autonomously developing preimplantation embryo then becomes dependent on the maternal environment for its continued development. Little is known about the regulation of implantation, except that a complex interaction between peptide and steroid hormones synchronizes the preparation of the uterus for implantation with the development of the embryo. Whether the implantation event is under maternal or embryonic control is also unclear (reviewed in refs 1, 2). We have previously shown that a cytokine, leukaemia inhibitory factor (LIF), is expressed in the uterine endometrial glands specifically on the fourth day of pregnancy. This burst of expression is under maternal control and always precedes implantation of the blastocyst. Here we report that transient expression of LIF in mice is essential for implantation. Females lacking a functional LIF gene are fertile, but their blastocysts fail to implant and do not develop. The blastocysts, however, are viable and, when transferred to wild-type pseudopregnant recipients, they can implant and develop to term.
TL;DR: Results are consistent with the hypothesis thatMDM2 binds to p53, and that amplification of MDM2 in sarcomas leads to escape from p53-regulated growth control, and this mechanism of tumorigenesis parallels that for virally-induced tumours.
Abstract: Despite extensive data linking mutations in the p53 gene to human tumorigenesis, little is known about the cellular regulators and mediators of p53 function. MDM2 is a strong candidate for one such cellular protein; the MDM2 gene was originally identified by virtue of its amplification in a spontaneously transformed derivative of mouse BALB/c cells and the MDM2 protein subsequently shown to bind to p53 in rat cells transfected with p53 genes. To determine whether MDM2 plays a role in human cancer, we have cloned the human MDM2 gene. Here we show that recombinant-derived human MDM2 protein binds human p53 in vitro, and we use MDM2 clones to localize the human MDM2 gene to chromosome 12q13-14. Because this chromosomal position appears to be altered in many sarcomas, we looked for changes in human MDM2 in such cancers. The gene was amplified in over a third of 47 sarcomas, including common bone and soft tissue forms. These results are consistent with the hypothesis that MDM2 binds to p53, and that amplification of MDM2 in sarcomas leads to escape from p53-regulated growth control. This mechanism of tumorigenesis parallels that for virally-induced tumours, in which viral oncogene products bind to and functionally inactivate p53.
TL;DR: It is reported that the DD genotype, which is associated with higher levels of circulating ACE than the ID and II genotypes, is significantly more frequent in patients with myocardial infarction than in controls, especially among subjects with low body-mass index and low plasma levels of ApoB.
Abstract: Factors involved in the pathogenesis of atherosclerosis, thrombosis and vasoconstriction contribute to the development of coronary heart disease. In a study comparing patients after myocardial infarction with controls, we have explored a possible association between coronary heart disease and a variation found in the gene encoding angiotensin-converting enzyme (ACE). The polymorphism ACE/ID is strongly associated with the level of circulating enzyme. This enzyme plays a key role in the production of angiotensin II and in the catabolism of bradykinin, two peptides involved in the modulation of vascular tone and in the proliferation of smooth muscle cells. Here we report that the DD genotype, which is associated with higher levels of circulating ACE than the ID and II genotypes, is significantly more frequent in patients with myocardial infarction (n = 610) than in controls (n = 733) (P = 0.007), especially among subjects with low body-mass index and low plasma levels of ApoB (P < 0.0001). The ACE/ID polymorphism seems to be a potent risk factor of coronary heart disease in subjects formerly considered to be at low risk according to common criteria.
TL;DR: Evidence is provided that mutations of the APC gene play a major role in the early development of colorectal neoplasms, and the frequency of such mutations remained constant as tumours progressed from benign to malignant stages.
Abstract: HUMAN tumorigenesis is associated with the accumulation of mutations both in oncogenes and in tumour suppressor genes1–3 But in no common adult cancer have the mutations that are critical in the early stages of the tumorigenic process been defined We have attempted to determine if mutations of the APC gene play such a role in human colorectal tumours, which evolve from small benign tumours (adenomas) to larger malignant tumours (carcinomas) over the course of several decades Here we report that sequence analysis of 41 colorectal tumours revealed that the majority of colorectal carcinomas (60%) and adenomas (63%) contained a mutated APC gene Furthermore, the APC gene met two criteria of importance for tumour initiation First, mutations of this gene were found in the earliest tumours that could be analysed, including adenomas as small as 05 cm in diameter Second, the frequency of such mutations remained constant as tumours progressed from benign to malignant stages These data provide strong evidence that mutations of the APC gene play a major role in the early development of colorectal neoplasms
TL;DR: The unexpected identification of the 4K (Mr 4,000) Aβ and a truncated form of Aβ in media from cultures of primary cells and untransfected and β-APP-transfected cell lines grown under normal conditions provide the basis for using simple cell culture systems to identify drugs that block the formation or release of A β, the primary protein constituent of the senile plaques of Alzheimer's disease.
Abstract: Alzheimer's disease is characterized by the extracellular deposition in the brain and its blood vessels of insoluble aggregates of the amyloid beta-peptide (A beta), a fragment, of about 40 amino acids in length, of the integral membrane protein beta-amyloid precursor protein (beta-APP). The mechanism of extracellular accumulation of A beta in brain is unknown and no simple in vitro or in vivo model systems that produce extracellular A beta have been described. We report here the unexpected identification of the 4K (M(r) 4,000) A beta and a truncated form of A beta (approximately 3K) in media from cultures of primary cells and untransfected and beta-APP-transfected cell lines grown under normal conditions. These peptides were immunoprecipitated readily from culture medium by A beta-specific antibodies and their identities confirmed by sequencing. The concept that pathological processes are responsible for the production of A beta must not be reassessed in light of the observation that A beta is produced in soluble form in vitro and in vivo during normal cellular metabolism. Further, these findings provide the basis for using simple cell culture systems to identify drugs that block the formation or release of A beta, the primary protein constituent of the senile plaques of Alzheimer's disease.
TL;DR: In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr as discussed by the authors. But this was not shown to be the case for the uplift of the Tibetan plateau and positive feedbacks initiated by this event.
Abstract: Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.
TL;DR: It is demonstrated that Aβ is produced and released both in vivo and in vitro, and new opportunities for developing diagnostic tests for Alzheimer's disease and therapeutic strategies aimed at reducing the cerebral deposition of Aβ are offered.
Abstract: CEREBRAL deposition of the β-amyloid peptide (Aβ) is an invariant feature of Alzheimer's disease. Since the original isola-tion and characterization of αβ (ref. 1) and the subsequent cloning of its precursor protein2–5, no direct evidence for the actual production of discrete Aβ has been reported6–11. Here we investigate whether Aβ is present in human biological fluids using antibodies specific for an epitope within Aβ that spans the site of normal constitutive cleavage12,13. These antibodies were used to construct a sandwich type enzyme-linked immunosorbent assay that detects Aβ in cerebrospinal fluid, plasma and conditioned medium of human mixed-brain cells grown in vitro (see also ref. 14). By affinity chromatography, we have purified and sequenced Aβ and a novel Aβ fragment from human cerebrospinal fluid and conditioned medium of human mixed-brain cell cultures. These findings demonstrate that Aβ is produced and released both in vivo and in vitro. These observations offer new opportunities for developing diagnostic tests for Alzheimer's disease and therapeutic strategies aimed at reducing the cerebral deposition of Aβ.
TL;DR: A mouse strain has been constructed in which one allele of Rb is disrupted, and heterozygous animals are not predisposed to retinoblastoma, but some display pituitary tumours arising from cells in which the wild-type Rb allele is absent.
Abstract: The retinoblastoma gene is mutated in several types of human cancer and is the best characterized of the tumour-suppressor genes. A mouse strain has been constructed in which one allele of Rb is disrupted. These heterozygous animals are not predisposed to retinoblastoma, but some display pituitary tumours arising from cells in which the wild-type Rb allele is absent. Embryos homozygous for the mutation die between days 14 and 15 of gestation, exhibiting neuronal cell death and defective erythropoiesis.
TL;DR: In this article, the formation of equivalent stable structures in the layered semiconductor tungsten disulphide was reported, and the closed nature of the structures was verified by electron diffraction and lattice imaging.
Abstract: FOLLOWING the discovery of C60(ref. 1) and the advent of fullerene chemistry, considerable attention has been directed towards the associated cylindrical2,3 and polyhedral4,5 forms of graphite. To date, however, observations of such closed structures have been limited to the carbon system. Here we report the formation of equivalent stable structures in the layered semiconductor tungsten disulphide. After the heating of thin tungsten films in an atmosphere of hydrogen sulphide, transmission electron microscopy reveals a variety of concentric polyhedral and cylindrical structures (ranging in size from 100 nm) growing from the amorphous tungsten matrix. The closed nature of the structures is verified by electron diffraction and lattice imaging. As with the carbon system, complete closure of the tungsten disulphide layers requires the presence of structural defects (for example, edge dislocations), or the arrangement of atoms in polyhedra other than a planar hexagonal geometry.
TL;DR: C cultured cells which express a β-APP complementary DNA bearing a double mutation found in a Swedish FAD family produce ∼6–8-fold more Aβ than cells expressing normalβ-APP, and this increase is confirmed for elucidating the fundamental mechanism of Alzheimer's disease.
Abstract: PROGRESSIVE cerebral deposition of the 39–43-amino-acid amy-loid β-protein (Aβ) is an invariant feature of Alzheimer's disease which precedes symptoms of dementia by years or decades. The only specific molecular defects that cause Alzheimer's disease which have been identified so far are missense mutations in the gene encoding the β-amyloid precursor protein (β3-APP) in certain families with an autosomal dominant form of the disease (familial Alzheimer's disease, or FAD)1–5. These mutations are located within or immediately flanking the Aβ region of β-APP, but the mechanism by which they cause the pathological phenotype of early and accelerated Aβ deposition is unknown. Here we report that cultured cells which express a β-APP complementary DNA bearing a double mutation (Lys to Asn at residue 595 plus Met to Leu at position 596) found in a Swedish FAD family5 produce ∼6–8-fold more Aβ than cells expressing normal β-APP. The Met 596 to Leu mutation is principally responsible for the increase. These data establish a direct link between a FAD genotype and the clinicopathological phenotype. Further, they confirm the relev-ance of the continuous Aβ production by cultured cells6–8 for elucidating the fundamental mechanism of Alzheimer's disease.