Increasing evidence indicates that extracellular vesicles (EVs) secreted from tumor cells play a key role in the overall progression of the disease state. EVs such as exosomes are secreted by a wide variety of cells and transport a varied population of proteins, lipids, DNA, and RNA species within the body. Gliomas constitute a significant proportion of all primary brain tumors and majority of brain malignancies. Glioblastoma multiforme (GBM) represents grade IV glioma and is associated with very poor prognosis despite the (...) cumulative advances in diagnostic procedures and treatment strategies. Here, the authors describe the progress in understanding the role of EVs, especially exosomes, in overall glioma progression, and how new research is unraveling the utilities of exosomes in glioma diagnostics and development of next‐generation therapeutic systems. Finally, based on an understanding of the latest scientific literature, a model for the possible working of therapeutic exosomes in glioma treatment is proposed. (shrink)

Once regarded as cellular ‘debris’ extracellular vesicles (EVs) emerge as one of the most intriguing entities in cancer pathogenesis. Intercellular trafficking of EVs challenges the notion of cancer cell autonomy, and highlights the multicellular nature of such fundamental processes as stem cell niche formation, tumour stroma generation, angiogenesis, inflammation or immunity. Recent studies reveal that intercellular exchange mediated by EVs runs deeper than expected, and includes molecules causative for cancer progression, such as oncogenes (epidermal growth factor receptor, Ras), and tumour (...) suppressors (PTEN). The uptake of oncogenic EVs (oncosomes) by various cells may profoundly change their biology, signalling patterns and gene expression, and in some cases cause their overt tumorigenic conversion. Moreover, EVs circulating in blood and present in body fluids provide an unprecedented access to the molecular circuitry driving cancer cells, and new technologies are being developed to exploit this property as a source of unique cancer biomarkers. (shrink)

No cure yet exists for devastating Alzheimer's disease (AD), despite many years and humongous efforts to find efficacious pharmacological treatments. So far, neither designing drugs to disaggregate amyloid plaques nor tackling solely inflammation turned out to be decisive. Mesenchymal stem cells (MSCs) and, in particular, extracellular vesicles (EVs) originating from them could be proposed as an alternative, strategic approach to attack the pathology. Indeed, MSC‐EVs—owing to their ability to deliver lipids/proteins/enzymes/microRNAs endowed with anti‐inflammatory, amyloid‐β degrading, and neurotrophic activities—may be exploited (...) as therapeutic tools to restore synaptic function, prevent neuronal death, and slow down memory impairment in AD. Herein the results presented in the most recently published studies on this topic are critically evaluated, providing a strong rationale for possible employment of MSC‐EVs in AD. (shrink)

Neurotransmitter release takes place by the exocytosis of loaded synaptic vesicles. The vesicles then fuse to the presynaptic membrane and are recycled by an endocytotic mechanism. A quantitative optical assay that detects uptake and release of a fluorescent dye during presynaptic activity was recently developed and used on the frog neauromuscular junction. I discuss a report(1) that demonstrates the effective application of this method to a Drosophila preparation. The authors use the shibire mutation and a spider venom to identify two (...) intermediates in vesicle recycling. Their report, along with other recent studies, demonstrates the power and promise of the genetic approach for the understanding of mechanisms of synapse function and development. (shrink)

Lipid vesicles are often used as compartment structures for preparing cell‐like systems and models of protocells, the hypothetical precursor structures of the first cells at the origin of life. Although the various artificially made vesicle systems are already remarkably complex, they are still very different from and much simpler than any known living cell. Nevertheless, the preparation and study of the structure and the dynamics of functionalized vesicle systems may contribute to a better understanding of biological cells, in (...) particular of the essential features of a living cell that are not found in the non‐living form of matter. The study of protocell models may possibly lead to a better understanding of the origin of the first cells. To avoid misunderstanding in this field of research, it would be useful if generally accepted definitions of terms like “artificial cells,” “synthetic cells,” “minimal cells,” “protocells,” and “primitive cells” exist. Editor's suggested further reading in BioEssaysSynthetic cells and organelles: compartmentalization strategies Abstract. (shrink)

Thinkers from a variety of fields analyze the roles of imaging technologies in science and consider their implications for many issues, from our conception of selfhood to the authority of science. In what follows, I encourage scholars to develop an applied philosophy of imaging, that is, to collect these analyses of scientific imaging and to reflect on how they can be made useful for ongoing scientific work. As an example of this effort, I review concepts developed in Don Ihde’s phenomenology (...) of technology and refigure them for use in the analysis of scientific practice. These concepts are useful for drawing out the details of the interpretive frameworks scientists bring to laboratory images. Next, I apply these ideas to a contemporary debate in neurobiology over the interpretation of images of neurons which have been frozen at the moment of transmitter release. This reveals directions for further thought for the study of neurotransmission. (shrink)

Microfluidic technology – the manipulation of fluids at micrometer scales – has revolutionized many areas of synthetic biology. The bottom‐up synthesis of “minimal” cell models has traditionally suffered from poor control of assembly conditions. Giant unilamellar vesicles (GUVs) are good models of living cells on account of their size and unilamellar membrane structure. In recent years, a number of microfluidic approaches for constructing GUVs has emerged. These provide control over traditionally elusive parameters of vesicular structure, such as size, lamellarity, membrane (...) composition, and internal contents. They also address sophisticated cellular functions such as division and protein synthesis. Microfluidic techniques for GUV synthesis can broadly be categorized as continuous‐flow based approaches and droplet‐based approaches. This review presents the state‐of‐the‐art of microfluidic technology, a robust platform for recapitulating complex cellular structure and function in synthetic models of biological cells. (shrink)

Recently, Gao et al. and Chappie et al. elucidated the crystal structures of the polytetrameric stalk domain of the dynamin‐like virus resistance protein, MxA, and of the G‐domain dimer of the large, membrane‐deforming GTPase, dynamin, respectively. Combined, they provide a hypothetical oligomeric structure for the complete dynamin protein. Here, it is discussed how the oligomers are expected to form and how they participate in dynamin mediated vesicle fission during the process of endocytosis. The proposed oligomeric structure is compared with (...) the novel mechanochemical model of dynamin function recently proposed by Bashkirov et al. and Pucadyil and Schmid. In conclusion, the new model of the dynamin oligomer has the potential to explain how short self‐limiting fissogenic dynamin assemblies are formed and how concerted GTP hydrolysis is achieved. The oligomerisation of two other dynamin superfamily proteins, the guanylate binding proteins (GBPs) and the immunity‐related GTPases (IRGs), is addressed briefly. (shrink)

Trafficking and persistence of fetal microchimeric cells (fMCs) and circulating extracellular vesicles (EVs) have been observed in animals and humans, but their consequences in the maternal body and their mechanistic contributions to maternal physiology and pathophysiology are not yet fully defined. Fetal cells and EVs may help remodel maternal organs after pregnancy‐associated changes, but the cell types and EV cargos reaching the mother in preterm pregnancies after exposure to various risk factors can be distinct from term pregnancies. As preterm delivery‐associated (...) maternal complications are rising, revisiting this topic and formulating scientific questions for future research to reduce the risk of maternal morbidities are timely. Epidemiological studies report maternal cardiovascular risk as one of the major complications after preterm delivery. This paper suggests a potential link between fMCs and circulating EVs and adverse maternal cardiovascular outcomes post‐pregnancies, the underlying mechanisms, consequences, and methods for and how this link might be assessed. (shrink)

The cilium/flagellum is a sensory-motile organelle ancestrally present in eukaryotic cells. For assembly cilia universally rely on intraflagellar transport (IFT), a specialised bidirectional transport process mediated by the ancestral and conserved IFT complex. Based on the homology of IFT complex proteins to components of coat protein I (COPI) and clathrin-coated vesicles, we propose that the non- vesicular, membrane-bound IFT evolved as a specialised form of coated vesicle transport from a protocoatomer complex. IFT thus shares common ancestry with all protocoatomer (...) derivatives, including all vesicle coats and the nuclear pore complex (NPC). This has major implications for the evolutionary origin of the cilium. First, it reinforces the tenet that duplication and divergence of pre-existing structures, rather than symbiosis, were the major themes during cilium evolution. Second, it suggests that the initial step in the autogenous origin of the cilium was the establishment of a membrane patch with transmembrane proteins transported by the ancestral vesicle-coating IFT complex. We propose a scenario for how the initial membrane patch gradually protruded to enhance exposure to the environment, then started to move, and finally compartmentalised to render receptor signalling and ciliary beating more efficient. BioEssays 28: 191–198, 2006. © 2006 Wiley periodicals, Inc. (shrink)

Joining an antagonistic phosphoinositide (PtdInsP) kinase and phosphatase into a single protein complex may regulate rapid and local PtdInsP changes. This may be important for processes such as membrane fission that require a specific PtdInsP and that are innately local and rapid. Such a complex could couple vesicle formation, with erasing of the identity of the donor organelle from the vesicle prior to its fusion with target organelles, thus preventing organelle identity intermixing. Coordinating signals are postulated to switch (...) the relative activities of the kinase and phosphatase in a spatio‐temporal manner that matches membrane fission events. The discovery of two such complexes supports this hypothesis. One regulates the interconversion of phosphatidylinositol and PtdIns(3)P by joining the Vps34 PtdIns 3‐kinase and the myotubularin 3‐phosphatases. The other regulates the interconversion between PtdIns(3)P and PtdIns(3,5)P2 through the Fab1/PIKfyve kinase and the Fig4/mFig4 phosphatase. These lipids are essential components of the endosomal identity code. (shrink)

The Arf family proteins are best known for their roles in the vesicle biogenesis. However, they also play fundamental roles in a wide range of cellular regulation besides vesicular trafficking, such as modulation of lipid metabolic enzymes, cytoskeleton remodeling, ciliogenesis, lysosomal, and mitochondrial morphology and functions. Growing studies continue to expand the downstream effector landscape of Arf proteins, especially for the less‐studied members, revealing new biological functions, such as amino acid sensing. Experiments with cutting‐edge technologies and in vivo functional (...) studies in the last decade help to provide a more comprehensive view of Arf family functions. In this review, we summarize the cellular functions that are regulated by at least two different Arf members with an emphasis on those beyond vesicle biogenesis. (shrink)

In possible scenarios on the origin of life, protocells represent the precursors of the first living cells. To study such hypothetical protocells, giant vesicles are being widely used as a simple model. Lipid vesicles can undergo complex morphological changes enabling self‐reproduction such as growth, fission, and extra‐ and intravesicular budding. These properties of vesicular systems may in some way reflect the mechanism of reproduction used by protocells. Moreover, remarkable similarities exist between the morphological changes observed in giant vesicles and bacterial (...) L‐form cells, which represent bacteria that have lost their rigid cell wall, but retain the ability to reproduce. L‐forms feature a dismantled cellular structure and are unable to carry out classical binary fission. We propose that the striking similarities in morphological transitions of L‐forms and giant lipid vesicles may provide insights into primitive reproductive mechanisms and contribute to a better understanding of the origin and evolution of mechanisms of cell reproduction.Editor's suggested further reading in BioEssays Synthesizing artificial cells from giant unilamellar vesicles: State‐of‐the art in the development of microfluidic technology Abstract. (shrink)

Information transmission from tumor cells to non‐tumor cells in the surrounding microenvironment via microvesicles is a more recently studied form of intercellular signaling that can have a marked impact on the tumor microenvironment. Tumor‐derived microvesicles (TMVs) are packed with information including signaling proteins and nucleic acids, and can be taken up by target cells, enabling paracrine signaling. While previous research has focused on how vesicles released from pathologic cells differ from normal cells, the heterogeneity that exists within the TMV population (...) itself is not fully characterized, and only beginning to be appreciated. In this review, we summarize current understanding of the biogenesis and roles of shed TMVs in the tumor microenvironment, and speculate on the consequences for tumor cell signaling in light of the hypothesis that there exists variance within the TMV population. The analysis of differential signaling upon cell‐TMV interactions provides insights into potential mechanisms of intercellular communication. (shrink)

Despite its biological importance, the mechanism of formation of cutin, the polymeric matrix of plant cuticles, has not yet been fully clarified. Here, for the first time, we show the participation in the process of lipid vesicles formed by the self‐assembly of endogenous polyhydroxy fatty acids. The accumulation and fusion of these vesicles (cutinsomes) at the outer part of epidermal cell wall is proposed as the mechanism for early cuticle formation. BioEssays 30:273–277, 2008. © 2008 Wiley Periodicals, Inc.

The Endosomal Sorting Complexes Required for Transport (ESCRTs) drive membrane remodeling in a variety of cellular processes that include the formation of endosomal intralumenal vesicles (ILVs) during multivesicular body (MVB) biogenesis. During MVB sorting, ESCRTs recognize ubiquitin (Ub) attached to membrane protein cargo and execute ILV formation by controlling the activities of ESCRT‐III polymers regulated by the AAA‐ATPase Vps4. Exactly how these events are coordinated to ensure proper cargo loading into ILVs remains unclear. Here we discuss recent work documenting the (...) ability of Bro1, an ESCRT‐associated Ub‐binding protein, to coordinate ESCRT‐III and Vps4‐dependent ILV biogenesis with upstream events such as cargo recognition. (shrink)

Synaptophysin (Syp) was the first synaptic vesicle (SV) protein to be cloned. Since its discovery in 1985, it has been used by us and by many laboratories around the world as an invaluable marker to study the distribution of synapses in the brain and to uncover the basic features of the life cycle of SVs. Although single gene ablation of Syp does not lead to an overt phenotype, a large body of experimental data both in vitro and in vivo (...) indicate that Syp (alone or in association with homologous proteins) is involved in multiple, important aspects of SV exo‐endocytosis, including regulation of SNARE assembly into the fusion core complex, formation of the fusion pore initiating neurotransmitter release, activation of SV endocytosis and SV biogenesis. In this article, we summarise the main results of the studies on Syp carried out by our and other laboratories, and explain why we believe that Syp plays a major role in SV trafficking. BioEssays 26:445–453, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

The self-avoiding walk is a classical model in statistical mechanics, probability theory and mathematical physics. It is also a simple model of polymer entropy which is useful in modelling phase behaviour in polymers. This monograph provides an authoritative examination of interacting self-avoiding walks, presenting aspects of the thermodynamic limit, phase behaviour, scaling and critical exponents for lattice polygons, lattice animals and surfaces. It also includes a comprehensive account of constructive methods in models of adsorbing, collapsing, and pulled walks, animals and (...) networks, and for models of walks in confined geometries. Additional topics include scaling, knotting in lattice polygons, generating function methods for directed models of walks and polygons, and an introduction to the Edwards model.This essential second edition includes recent breakthroughs in the field, as well as maintaining the older but still relevant topics. New chapters include an expanded presentation of directed models, an exploration of methods and results for the hexagonal lattice, and a chapter devoted to the Monte Carlo methods. (shrink)

An entirely different mechanism and localization were recently proposed for the COPII coat complex, challenging its well‐accepted function to select and concentrate cargo into small COPII‐coated spherical transport vesicles. Instead, the COPII complex is suggested to form a dynamic yet stationary collar that forms a boundary between the ER and the ER export membrane domain. This membrane domain, the ER exit site (ERES), is the site of COPII‐mediated sorting and concentration of transport competent proteins. Subsequently, the ERES is implicated to (...) mature and bud to form a sizeable pleiomorphic transport carrier that translocate on microtubules to fuse with the Golgi apparatus. Despite this drastic mechanistic dogma shift, most of the underlying protein‐protein and protein‐membrane interactions remain unchanged. Here, we attempt to provide a detailed description of the newly proposed model of how ER to Golgi transport works by describing the role of several essential proteins of the transport machinery. (shrink)

Fission of cellular membranes is ubiquitous and essential for life. Complex protein machineries, such as the dynamin and ESCRT spirals, have evolved to mediate membrane fission during diverse cellular processes, for example, vesicle budding. A new study suggests that non-specialized membrane-bound proteins can induce membrane fission through mass action due to protein crowding. Because up to 2/3 of the mass of cellular membranes is contributed by proteins, membrane protein crowding is an important physiological parameter. Considering the complexity of membrane (...) shape transitions during a fission reaction, spatial and temporal variability in protein distribution, and the abundance of intrinsically disordered regions in proteins on an invaginating membrane, protein crowding can have diverse consequences for fission in the cell. The question is, how and to what extent this mechanism combines with the action of dedicated fission machineries. Membrane fission, which is required for formation of vesicles or cytokinesis, can be carried out by specialized proteins like dynamin and the ESCRT complex. Recent work suggests that fission of cellular membranes, which are densely packed with proteins, can also be induced by protein crowding due to high entropic tension. (shrink)

The exocyst is a conserved octameric complex that physically tethers a vesicle to the plasma membrane, prior to membrane fusion. It is important not only for secretion and membrane delivery but also, in mammalian cells, for cytokinesis, ciliogenesis, autophagy, tumorigenesis, and host defense. The combination of genome editing and advanced light microscopy of exocyst subunits in living cells has recently shown the complex to be much more dynamic than previously appreciated, and exposed how little we still know about its (...) function and regulation. (shrink)

Ras homolog enriched in the striatum (Rhes) is a striatal enriched protein that promotes the formation of thin membranous tubes resembling tunneling nanotubes (TNT)—“Rhes tunnels”—that connect neighboring cell and transport cargoes: vesicles and proteins between the neuronal cells. Here the literature on TNT‐like structures is reviewed, and the implications of Rhes‐mediated TNT, the mechanisms of its formation, and its potential in novel cell‐to‐cell communication in regulating striatal biology and disease are emphasized. Thought‐provoking ideas regarding how Rhes‐mediated TNT, if it exists, (...) in vivo, would radically change the way neurons communicate in the brain are discussed. (shrink)

COPII coated vesicles bud from an ER domain termed the transitional ER (tER), but the mechanism that clusters COPII vesicles at tER sites is unknown. tER sites are closely associated with early Golgi or pre‐Golgi structures, suggesting that the clustering of nascent COPII vesicles could be achieved by tethering to adjacent membranes. This model challenges the prevailing view that COPII vesicles are clustered by a scaffolding protein at the ER surface. Although Sec16 was proposed to serve as such a scaffolding (...) protein, recent data suggest that rather than organizing COPII into higher‐order structures, Sec16 acts at the level of individual COPII vesicles to regulate COPII turnover. A plausible synthesis is that tER sites are created by tethering to Golgi membranes and are regulated by Sec16. Meanwhile, the COPII vesicles that bud from tER sites are thought to nucleate new Golgi cisternae. Thus, an integrated self‐organization process may generate tER‐Golgi units. (shrink)

During the last two decades, a new understanding of life emerged at the forefront of science.The development of complexity theory, technically known as nonlinear dynamics, has allowed scientists and mathematicians to model the complexities of living systems in new ways that have yielded many important discoveries. In this article, the author reviews the basic concepts, current achievements and status of complexity theory from the perspective of the new understanding of biological life. Models and theories discussed include the theory of dissipative (...) structures for nonlinear chemical systems, the application of bifurcation theory to genetic networks and cell differentiation, the study of the origin of biological form, a new approach to the understanding of developmental stability in embryology, and a model of the ‘origin of life’ and prebiotic evolution in tiny, membrane-bounded vesicles in the primeval oceans. (shrink)

Fertilization triggers cytoplasmic movements in the frog egg that lead in mysterious ways to the stabilization of β‐catenin on the dorsal side of the embryo. The novel Huluwa (Hwa) transmembrane protein, identified in China, is translated specifically in the dorsal side, acting as an egg cytoplasmic determinant essential for β‐catenin stabilization. The Wnt signaling pathway requires macropinocytosis and the sequestration inside multivesicular bodies (MVBs, the precursors of endolysosomes) of Axin1 and Glycogen Synthase Kinase 3 (GSK3) that normally destroy β‐catenin. In (...) Xenopus, the Wnt‐like activity of GSK3 inhibitors and of Hwa mRNA can be blocked by brief treatment with inhibitors of membrane trafficking or lysosomes at the 32‐cell stage. In dorsal blastomeres, lysosomal cathepsin is activated and intriguing MVBs surrounded by electron dense vesicles are formed at the 64‐cell stage. We conclude that membrane trafficking and lysosomal activity are critically important for the earliest asymmetries in vertebrate embryonic development. (shrink)

Capacity of conscious agents to perform genuine choices among future alternatives is a prerequisite for moral responsibility. Determinism that pervades classical physics, however, forbids free will, undermines the foundations of ethics, and precludes meaningful quantification of personal biases. To resolve that impasse, we utilize the characteristic indeterminism of quantum physics and derive a quantitative measure for the amount of free will manifested by the brain cortical network. The interaction between the central nervous system and the surrounding environment is shown to (...) perform a quantum measurement upon the neural constituents, which actualize a single measurement outcome selected from the resulting quantum probability distribution. Inherent biases in the quantum propensities for alternative physical outcomes provide varying amounts of free will, which can be quantified with the expected information gain from learning the actual course of action chosen by the nervous system. For example, neuronal electric spikes evoke deterministic synaptic vesicle release in the synapses of sensory or somatomotor pathways, with no free will manifested. In cortical synapses, however, vesicle release is triggered indeterministically with probability of 0.35 per spike. This grants the brain cortex, with its over 100 trillion synapses, an amount of free will exceeding 96 terabytes per second. Although reliable deterministic transmission of sensory or somatomotor information ensures robust adaptation of animals to their physical environment, unpredictability of behavioral responses initiated by decisions made by the brain cortex is evolutionary advantageous for avoiding predators. Thus, free will may have a survival value and could be optimized through natural selection. (shrink)

In a companion review1 we discussed the data supporting the conclusion that at least two subtypes of spectrin exist in mammalian brain. One form is found in the cell bodies, dendrites, and post‐synaptic terminals of neurons (brain spectrin(240/235E)) and the other subtype is located in the axons and presynaptic terminals (brain spectrin(240/235)). Our recent understanding of brain spectrin subtype localization suggests a possible explanation for a conundrum concerning brain 4.1 localization. Amelin, an immunoreactive analogue of red blood cell (rbc) cytoskeletal (...) protein 4.1, is localized in neuronal cell bodies and dendrites when brain sections are stained with antibody against rbc protein 4.1. However, it has recently been suggested that synapsin I, a neuron‐specific phosphoprotein associated with the cytoplasmic surface of small synaptic vesicles, is related to erythrocyte 4.1. In this review we hypothesize that there are at least two forms of brain 4.1: a cell body/dendritic form (amelin) which is detected with rbc protein 4.1 antibody, and a unique form found exclusively in the presynaptic terminal (synapsin I). The binding of synapsin I to brain spectrin(240/235), and its ability to stimulate the spectrin/F‐actin interaction in a phosphorylation‐dependent manner suggests a model for the regulation of synaptic transmission mediated by the neuronal cytoskeleton. (shrink)

The origins and evolution of the Archaea, Bacteria, and Eukarya remain controversial. Phylogenomic‐wide studies of molecular features that are evolutionarily conserved, such as protein structural domains, suggest Archaea is the first domain of life to diversify from a stem line of descent. This line embodies the last universal common ancestor of cellular life. Here, we propose that ancestors of Euryarchaeota co‐evolved with those of Bacteria prior to the diversification of Eukarya. This co‐evolutionary scenario is supported by comparative genomic and phylogenomic (...) analyses of the distributions of fold families of domains in the proteomes of free‐living organisms, which show horizontal gene recruitments and informational process homologies. It also benefits from the molecular study of cell physiologies responsible for membrane phospholipids, methanogenesis, methane oxidation, cell division, gas vesicles, and the cell wall. Our theory however challenges popular cell fusion and two‐domain of life scenarios derived from sequence analysis, demanding phylogenetic reconciliation. (shrink)

Twenty five years ago, Sir John Carew Eccles together with Friedrich Beck proposed a quantum mechanical model of neurotransmitter release at synapses in the human cerebral cortex. The model endorsed causal influence of human consciousness upon the functioning of synapses in the brain through quantum tunneling of unidentified quasiparticles that trigger the exocytosis of synaptic vesicles, thereby initiating the transmission of information from the presynaptic towards the postsynaptic neuron. Here, we provide a molecular upgrade of the Beck and Eccles model (...) by identifying the quantum quasiparticles as Davydov solitons that twist the protein α-helices and trigger exocytosis of synaptic vesicles through helical zipping of the SNARE protein complex. We also calculate the observable probabilities for exocytosis based on the mass of this quasiparticle, along with the characteristics of the potential energy barrier through which tunneling is necessary. We further review the current experimental evidence in support of this novel bio-molecular model as presented. (shrink)

The autophagy initiation complex is brought about via a highly ordered and stepwise assembly process. Two crucial signaling molecules, mTORC1 and AMPK, orchestrate this assembly by phosphorylating/dephosphorylating autophagy‐related proteins. Activation of Atg1 followed by recruitment of both Atg9 vesicles and the PI3K complex I to the PAS (phagophore assembly site) are particularly crucial steps in its formation. Ypt1, a small Rab GTPase in yeast cells, also plays an essential role in the formation of the autophagy initiation complex through multiple regulatory (...) pathways. In this review, our primary focus is to discuss how signaling molecules initiate the assembly of the autophagy initiation complex, and highlight the significant roles of Ypt1 in this process. We end by addressing issues that need future clarification. (shrink)

Many enveloped viruses are released from infected cells by maturing and budding at the plasma membrane. During this process, viral core components are incorporated into membrane vesicles that contain viral transmembrane proteins, termed ‘spike’ proteins. For many years these spike proteins, which are required for infectivity, were believed to be incorporated into virions via a direct interaction between their cytoplasmic domains and viral core components. More recent evidence shows that, while such direct interactions drive budding of alphaviruses, this may not (...) be the case for negative strand RNA viruses and retroviruses. These viruses can bud particles in the absence of spike proteins, using only viral core components to drive the process. In some cases the spike proteins, without the viral core, can be released as virus‐like particles. Optimal budding and release may, therefore, depend on a ‘push‐and‐pull’ concerted action of core and spike, where oligomerization of both components plays a crucial role. (shrink)

The goal of constructing artificial photosynthetic assemblies is to use sunlight for the generation of hydrogen from water; the hydrogen obtained should be an ideal energy source. The use of surfactant vesicle entrapped‐catalyst coated colloidal semiconductors and sacrificial electron donors for photosensitized water reduction illustrates how chemists mimic photosynthesis.

SNAREs (soluble N‐ethylmaleimide‐sensitive factor attachment protein receptors) are a large family of proteins that are present on all organelles involved in intracellular vesicle trafficking and secretion. The interaction of complementary SNAREs found on opposing membranes presents an attractive lock‐and‐key mechanism, which may underlie the specificity of vesicle trafficking. Moreover, formation of the tight complex between a vesicle membrane SNARE and corresponding target membrane SNAREs could drive membrane fusion. In synapses, this tight complex, also referred to as the (...) synaptic core complex, is essential for neurotransmitter release. However, recent observations in knockout mice lacking major synaptic SNAREs challenge the prevailing notion on the executive role of these proteins in fusion and open up several questions about their exact role(s) in neurotransmitter release. Persistence of a form of regulated neurotransmitter release in these mutant mice also raises the possibility that other cognate or non‐cognate SNAREs may partially compensate for the loss of a particular SNARE. Future analysis of SNARE function in central synapses will also have implications for the role of these molecules in other vesicle trafficking events such as endocytosis and vesicle replenishment. Such analysis can provide a molecular basis for synaptic processes including certain forms of short‐term synaptic plasticity. BioEssays 24:926–936, 2002. © 2002 Wiley Periodicals, Inc. (shrink)

The cellular processes of transport, division and, possibly, early development all involve microtubule‐based motors. Recent work shows that, unexpectedly, many of these cellular functions are carried out by different types of kinesin and kinesin‐related motor proteins. The kinesin proteins are a large and rapidly growing family of microtubule‐motor proteins that share a 340‐amino‐acid motor domain. Phylogenetic analysis of the conserved motor domains groups the kinesin proteins into a number of subfamilies, the members of which exhibit a common molecular organization and (...) related functions. The kinesin proteins that belong to different subfamilies differ in their rates and polarity of movement along microtubules, and probably in the particles/organelles that they transport. The kinesins arose early in eukaryotic evolution and gene duplication has allowed functional specialization to occur, resulting in a surprisingly large number of different classes of these proteins adapted for intracellular transport of vesicles and organelles, and for assembly and force generation in the meiotic and mitotic spindles. (shrink)

Secretion is a fundamental cellular process involving the regulated release of intracellular products from cells. Physiological functions such as neurotransmission, or the release of hormones and digestive enzymes, are all governed by cell secretion. Anomalies in the processes involved in secretion contribute to the development and progression of diseases such as diabetes and other hormonal disorders. To unravel the mechanisms that govern such diseases, it is essential to understand how hormones, growth factors and neurotransmitters are synthesized and processed, and how (...) their signals are recognized, amplified and transmitted by intracellular signaling pathways in the target cells. Here, we discuss diverse aspects of the detailed mechanisms involved in secretion based on mathematical models. The models range from stochastic ones describing the trafficking of secretory vesicles to deterministic ones investigating the regulation of cellular processes that underlie hormonal secretion. In all cases, the models are closely related to experimental results and suggest theoretical predictions for the secretion mechanisms. (shrink)

The generation of asymmetric cell shapes is a recurring theme in biology. In budding yeast, one form of cell asymmetry occurs for division and is generated by anisotropic growth of the mother cell to form a daughter cell bud. Previous genetic studies uncovered key roles for the small GTPase Cdc42 in organizing the actin cytoskeleton and vesicle delivery to the site of bud growth,1,2 but a recent paper has also raised questions about how control of Cdc42 activity is integrated (...) into a proposed hierarchical regulatory pathway that specifies a unique site of bud formation.3 BioEssays 25:833–836, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Clathrin and the endocytosis machinery has recently been described as being required in mammalian cells for the internalization of large particles including pathogenic bacteria, fungi, and large viruses. These apparently unexpected observations, within the framework of the classical mechanisms for the formation of clathrin‐coated vesicles, are now considered as examples of a new non‐classical function of clathrin, which can promote the internalization of membrane domains associated to planar clathrin lattices. The role of actin downstream of clathrin seems to be critical (...) for this still poorly characterized process. The historical frontier between endocytosis and phagocytosis is vanishing in the light of this new role for clathrin. (shrink)

A Paramecium cell has a stereotypically patterned surface, with regularly arranged cilia, dense‐core secretory vesicles and subplasmalemmal calcium stores. Less strikingly, there is also a patterning of molecules; for instance, some ion channels are restricted to certain regions of the cell surface. This design may explain very effective and selective responses, such as that to Ca2+ upon stimulation. It enables the cell to respond to a Ca2+ signal precisely secretion (exocytosis) or by changing its ciliary activity. These responses depend on (...) the location and/or type of signal, even though these two target structures co‐exist side‐by‐side, and normally only limited overlap occurs between the different functions. Furthermore, the patterning of exocytotic sites and the possibility of synchronous exocytosis induction in the sub‐second time range have considerably facilitated analyses, and thus led to new concepts of exocytotic membrane fusion. It has been possible to dissect complicated events like overlapping Ca2+ fluxes produced from external sources and from internal stores. Since molecular genetic approaches have become available for Paramecium, many different gene products have been identified only some of which are known from “higher” eukaryotes. Although a variety of basic cellular functions are briefly addressed to demonstrate the uniqueness of this unicellular organism, this article focuses on exocytosis regulation. BioEssays 24:649–658, 2002. © 2002 Wiley Periodicals, Inc. (shrink)

Endosomes shuttle select cargoes between cellular compartments and, in doing so, maintain intracellular homeostasis and enable interactions with the extracellular space. Directionality of endosomal transport critically impinges on cargo fate, as retrograde (microtubule minus‐end directed) traffic delivers vesicle contents to the lysosome for proteolysis, while the opposing anterograde (plus‐end directed) movement promotes recycling and secretion. Intriguingly, the endoplasmic reticulum (ER) is emerging as a key player in spatiotemporal control of late endosome and lysosome transport, through the establishment of physical (...) contacts with these organelles. Earlier studies have described how minus‐end‐directed motor proteins become discharged from vesicles engaged at such contact sites. Now, Raiborg et al. implicate ER‐mediated interactions, induced by protrudin, in loading plus‐end‐directed motor kinesin‐1 onto endosomes, thereby stimulating their transport toward the cell's periphery. In this review, we recast the prevailing concepts on bidirectional late endosome transport and discuss the emerging paradigm of inter‐compartmental regulation from the ER‐endosome interface viewpoint. (shrink)

Lysosomes are the site of degradation of obsolete intracellular material during autophagy and of extracellular macromolecules following endocytosis and phagocytosis. The membrane of lysosomes and late endosomes is enriched in highly glycosylated transmembrane proteins of largely unknown function. Significant progress has been made in recent years towards elucidating the pathways by which these lysosomal membrane proteins are delivered to late endosomes and lysosomes. While some lysosomal membrane proteins follow the constitutive secretory pathway and reach lysosomes indirectly via the cell surface (...) and endocytosis, others exit the trans‐Golgi network in clathrin‐coated vesicles for direct delivery to endosomes and lysosomes. Sorting from the Golgi or the plasma membrane into the endosomal system is mediated by signals encoded by the short cytosolic domain of these proteins. This review will discuss the role of lysosomal membrane proteins in the biogenesis of the late endosomal and lysosomal membranes, with particular emphasis on the structural features and molecular mechanisms underlying the intracellular trafficking of these proteins. (shrink)

Cell communication plays a key role in multicellular organisms. In developing embryos as in adult organisms, cells communicate by coordinating their differentiation through the establishment and/or renewal of a variety of cell communication channels. Under both these conditions, cells interact by either receptor signalling, surface recognition of specific cell adhesion molecules or transfer of cytoplasmic components through junctional coupling. In recent years, it has become apparent that cells may also communicate through the extracellular release of microvesicles. They may originate as (...) either exosomes from the endosomal compartment upon fusion of multivesicular bodies with the plasma membrane or be shed directly from the plasma membrane via extensions of the cell surface. Microvesicles may disperse over long distances through body fluids and deliver their molecular cargo onto a variety of target cells. As a general rule, the metabolic fate of these cells is determined by the molecular nature of the vesicular cargo, while targeting itself depends on the affinity of the molecules expressed on the enclosing membrane. In this paper, we will be arguing that intercellular vesicular transfer is substantially different from other types of cell communication, allowing cells and molecules to interact on varying levels. Cells interacting via ligand signalling owe their specificity to the steric coupling with cognate receptor molecules. As such, it is a pure molecular process that affects target cells only upon integration into their responding repertoire. In this relationship, coupled cells are reciprocally adapted to each other through the selection of their respective signalling capacities, following exploration of their receptor specificity. Interaction by intercellular vesicles realizes a substantially different type of cell communication. Vesicular traffic allows donor cells to carry out a horizontal type of gene transfer and target this information over long distances via independently controlled mechanisms. Because of this independence, cells interacting via vesicular traffic are not expected to adapt their signalling correspondences, but to control instead the efficiency of their cargo delivery irrespective of the receptor repertoire expressed by the target tissue. In this paper, the multifaceted functions of the intercellular vesicular traffic will be discussed in a multilevel biosemiotic perspective with the aim of unravelling the cellular mechanisms devised by nature to accomplish communication. (shrink)

In circulation, T cells are spherical with selectin enriched dynamic microvilli protruding from the surface. Following extravasation, these microvilli serve another role, continuously surveying their environment for antigen in the form of peptide‐MHC (pMHC) expressed on the surface of antigen presenting cells (APCs). Upon recognition of their cognate pMHC, the microvilli are initially stabilized and then flatten into F‐actin dependent microclusters as the T cell spreads over the APC. Within 1–5 min, clathrin is recruited by the ESCRT‐0 component Hrs to (...) mediate release of T cell receptor (TCR) loaded vesicles directly from the plasma membrane by clathrin and ESCRT‐mediated ectocytosis (CEME). After 5‐10 min, Hrs is displaced by the endocytic clathrin adaptor epsin‐1 to induce clathrin‐mediated trans‐endocytosis (CMTE) of TCR‐pMHC conjugates. Here we discuss some of the functional properties of the clathrin machinery which enables it to control these topologically opposite modes of membrane transfer at the immunological synapse, and how this might be regulated during T cell activation. (shrink)

The chromosomes undergo a condensation‐decondensation cycle within the life cycle of mammalian cells. Chromosome condensation is a complex and critical event that is necessary for the equal distribution of genetic material between the two daughter cells. Although chromosome condensation‐decondensation and segregation is mechanistically complex, it proceeds with high fidelity during the eukaryotic cell division cycle. Cell fusion studies have indicated the presence of chromosome condensation factors in mammalian cells during mitosis. If extracts from mitotic cells are injected into immature oocytes (...) of Xenopus laevis, they induce meiotic maturation (i.e. germinal vesicle breakdown and chromosome condensation) within 2–3 hours. Recently, we showed that the maturation‐promoting activity of the mitotic cell extracts is inactivated by certain protein factors present in cells during the G1 period. The activity of the G1 factors coincides with the process of chromosome decondensation that begins at telophase and continues throughout the G1 period. These studies have revealed that the mitotic factors and the G1 factors play a pivotal role in the regulation of condensation and decondensation of chromosomes. Furthermore, our studies strongly suggest that nonhistone protein phosphorylation and dephosphorylation may mediate chromosome condensation and decondensation, respectively. (shrink)

In this article we present a new kind of computing device that uses biochemical reactions networks as building blocks to implement logic gates. The architecture of a computing machine relies on these generic and composable building blocks, computation units, that can be used in multiple instances to perform complex boolean functions. Standard logical operations are implemented by biochemical networks, encapsulated and insulated within synthetic vesicles called protocells. These protocells are capable of exchanging energy and information with each other through transmembrane (...) electron transfer. In the paradigm of computation we propose, protoputing, a machine can solve only one problem and therefore has to be built specifically. Thus, the programming phase in the standard computing paradigm is represented in our approach by the set of assembly instructions that directs the wiring of the protocells that constitute the machine itself. To demonstrate the computing power of protocellular machines, we apply it to solve a NP-complete problem, known to be very demanding in computing power, the 3-SAT problem. We show how to program the assembly of a machine that can verify the satisfiability of a given boolean formula. Then we show how to use the massive parallelism of these machines to verify in less than 20 min all the valuations of the input variables and output a fluorescent signal when the formula is satisfiable or no signal at all otherwise. (shrink)

Cytoplasmic dynein is the major minus‐end‐directed motor protein in eukaryotes, and has functions ranging from organelle and vesicle transport to spindle positioning and orientation. The mode of regulation of dynein in the cell remains elusive, but a tantalising possibility is that dynein is maintained in an inhibited, non‐motile state until bound to cargo. In vivo, stable attachment of dynein to the cell membrane via anchor proteins enables dynein to produce force by pulling on microtubules and serves to organise the (...) nuclear material. Anchor proteins of dynein assume diverse structures and functions and differ in their interaction with the membrane. In yeast, the anchor protein has come to the fore as one of the key mediators of dynein activity. In other systems, much is yet to be discovered about the anchors, but future work in this area will prove invaluable in understanding dynein regulation in the cell. (shrink)

Synapsins I and II are a family of synaptic vesicle‐associated phosphoproteins involved in the short‐term regulation of neurotransmitter release. In this review, we discuss a working model for the molecular mechanisms by which the synapsins act. We propose that synapsin I links synaptic vesicles to actin filaments in the presynaptic nerve terminal and that these interactions are modulated by the reversible phosphorylation of synapsin I through various signal transduction pathways. The high degree of homology between the synapsins suggests that (...) some of the functional properties of synapsin I are also shared by synapsin II. (shrink)