DOCSLIB.ORG

'Generic' Physical Mechanisms of Morphogenesis and Pattern Formation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
'Generic' Physical Mechanisms of Morphogenesis and Pattern Formation Development 110, 1-18 (1990) Review Article Printed in Great Britain © The Company of Biologists Limited 1990 'Generic' physical mechanisms of morphogenesis and pattern formation STUART A. NEWMAN1 and WAYNE D. COMPER2 ^Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595, USA 2Department of Biochemistry, Monash University, Clayton, Victoria 3168, Australia Summary The role of 'generic' physical mechanisms in morpho- phogenetic and patterning effects are the inevitable genesis and pattern formation of tissues is considered. outcome of recognized physical properties of tissues, and Generic mechanisms are defined as those physical pro- that generic physical mechanisms that act on these cesses that are broadly applicable to living and non- properties are complementary to, and interdependent living systems, such as adhesion, surface tension and with genetic mechanisms. We also suggest that major gravitational effects, viscosity, phase separation, con- morphological reorganizations in phylogenetic lineages vection and reaction-diffusion coupling. They are con- may arise by the action of generic physical mechanisms trasted with 'genetic' mechanisms, a term reserved for on developing embryos. Subsequent evolution of genetic highly evolved, machine-like, biomolecular processes. mechanisms could stabilize and refine developmental Generic mechanisms acting upon living tissues are outcomes originally guided by generic effects. capable of giving rise to morphogenetic rearrangements of cytoplasmic, tissue and extracellular matrix com- ponents, sometimes leading to 'microfingers', and to Key words: pattern formation, morphogenesis, genetic chemical waves or stripes. We suggest that many mor- mechanism, generic physical mechanism. Introduction diffusion (Crick, 1970) and interfacial tension (Stein- berg, 1978; Heintzelman et al. 1978), participate in Developing, regenerating, healing and neoplastic tis- important ways in morphogenesis and pattern forma- sues undergo changes in form and cellular composition tion. In contrast to molecular machines, which are by mechanisms that are poorly understood. While all mainly suited to bringing about precise outcomes in contemporary approaches assume that tissue morpho- spatially localized tissue regions, some of these general genesis and position-dependent cell differentiation physical effects may act globally, so as to influence (pattern formation) are caused ultimately by the inter- tissue shape and composition over relatively long dis- play of physicochemical behaviors of macromolecules, tances. such behaviors fall into at least two distinguishable Because both highly evolved biomolecular processes categories. Certain developmental processes depend on (conveniently referred to as 'genetic') and more broadly highly organized interactions between specific macro- applicable ('generic') physical processes can each con- molecules, and can be appropriately characterized as tribute to any given developmental episode, investi- 'molecular machines'. The existence of each such gators need to take both categories of phenomenon into machine presupposes the coevolution of several biologi- account. But research on generic morphogenetic and cal macromolecules, leading to the coordination of their patterning processes is a rapidly expanding area of physicochemical properties in the service of a particular physical chemistry that is unfamiliar to most develop- function. Examples include cytoplasmic 'motors' that mental biologists. This has restricted the influx of a affect the shape and motility of individual cells (Vale, number of fruitful concepts into developmental biology 1987), and gene promoter elements sensitive to com- and impeded the use of several informative cell-free plexes of spatially distributed DNA-binding proteins experimental models of morphogenesis. (Stanojevid et al 1989; Goto et al. 1989). In what follows we will attempt to redress this But there is also evidence that physical forces and deficiency by presenting a typology of generic physical dynamical processes that are not the products of the mechanisms relevant to animal tissue behavior. These evolved coordination of macromolecular properties, mechanisms include familiar physical effects such as but are organizing principles of nonliving as well as gravity, viscous flow, phase separation and adhesion. living systems, such as gravity (Ancel and Vintem- But they also include such exotic processes as Maran- berger, 1948; Malacinski, 1984), adhesion (Steinberg, goni effects, convective fingering and chemical concen- 1978; McClay and Ettensohn, 1987; Armstrong, 1989), tration waves. Previous applications of some of these S. A. Newman and W. D. Comper mechanisms to development will be reviewed, and cellular matrices, under this assumption, would have additional examples will be given of developmental less of the character of 'molecular machines' than most processes that may profitably be analyzed in terms of intracellular macromolecular assemblages, and would such mechanisms. therefore be more typical loci for the physical processes In our discussion, the morphogenetic properties of we have termed 'generic'. individual cells - e.g. their extensibility, contractility and motility - are treated as given; they are assumed to arise from the physical chemistry of highly evolved Examples of Generic Processes intracellular proteins such as tubulin, actin, myosin and kinesin, in the presence of sources of metabolic energy The mechanical properties of materials are con- and appropriate cofactors. In this sense they are 'gen- veniently described in terms of their responses to etic'. Similarly, the ability of cells to undergo differen- stresses, which are forces applied to bodies of matter. A tiation in response to microenvironmental signals, and change in the dimensions of a body produced by a stress to produce and secrete specific macromolecules, is is called a strain. Shear stresses act tangentially to planes assumed. Secreted macromolecules will be considered within the material and cause continguous parts of the here only insofar as they can potentially play the role of body to slide past one another. In solids, shear stresses dynamical components in some of the generic physical are opposed by bonds between adjacent subunits and by processes that we will describe. And whereas eggs and elastic restoring forces, whereas liquids begin to flow as multicellular embryos have the ability to produce trans- soon as a shear stress is applied. The capacity of a liquid cellular ion currents and endogenous electrical fields to flow is due to the ability of the liquid's molecules or that reflect morphogenetic polarity, growth and regen- other subunits to readily changetheir relative positions. eration (Jaffe, 1981; Nucitelli, 1984), it is not clear that The physical state of a living tissue, can span the range bioelectricity as a generic phenomenon has a role in from liquid (blood) to solid (bone). But it is only in developing systems, apart from its association with intermediate state, semisolid tissues tljat developmen- transport and utilization of specific ions. We will there- tally significant, short-term morphogenetic effects can fore tentatively group these phenomena with other take place. Typical tissues exhibit both-elastic proper- active chemical processes, and refer the reader to the ties, which permit them to resume their shape when a reviews cited above for further details. shear stress is removed, and viscous properties, in Our main purpose is to familiarize developmental which rearrangement of internal components (cells or biologists with the range of generic physical mechan- extracellular matrix materials) permits shape change in isms that can participate in biological morphogenesis response to shear stress. (Phillips and Steinberg, 1978; and pattern formation, and to indicate possible re- Steinberg and Poole, 1982).- lationships between these processes and the highly Viscoelastic fluids can be compressible or noncom- specific molecular interactions that also mediate devel- pressible; that is, their volume will decrease or remain opmental events and are responsible for the precision of unchanged under compressive stresses, which are forces their outcomes. In particular, we suggest that many directed normal to planes within the material. How- morphogenetic processes may have first arisen in evol- ever, tissues are generally noncompressible because of ution by the action of generic physical mechanisms on their high water content. Even when local reductions of cells and tissues, and that particularly favorable results extracellular space occur, as in mesenchymal tissues were later stabilized and made more dependable by the undergoing condensation (Thorogood and Hinchliffe, superimposition of more evolved genetically deter- 1975), retention of water will ensure that the overall mined mechanisms. In this perspective, the de novo tissue volume is conserved. origin of developmental mechanisms becomes less Like other fluid systems, tissues are subject to the problematic: contemporary molecular mechanisms ubiquitous effects of gravity and adhesion. Either of could have evolved as reinforcements for less precise these forces can effect shape change, but the degree of generic physical determinants, the conditions for which deformation will depend on the mechanical properties may or may not currently prevail. And while the of the particular tissue (its relative elasticity and vis- possible generic origins of certain morphogenetic
Load more

Recommended publications
  • Self-Organization Principles of Intracellular Pattern Formation
    Self-organization principles of intracellular pattern formation J. Halatek. F. Brauns, and E. Frey∗ Arnold{Sommerfeld{Center for Theoretical Physics and Center for NanoScience, Department of Physics, Ludwig-Maximilians-Universit¨atM¨unchen, Theresienstraße 37, D-80333 M¨unchen,Germany (Dated: February 21, 2018) Abstract Dynamic patterning of specific proteins is essential for the spatiotemporal regulation of many important intracellular processes in procaryotes, eucaryotes, and multicellular organisms. The emergence of patterns generated by interactions of diffusing proteins is a paradigmatic example for self-organization. In this article we review quantitative models for intracellular Min protein patterns in E. coli, Cdc42 polarization in S. cerevisiae, and the bipolar PAR protein patterns found in C. elegans. By analyzing the molecular processes driving these systems we derive a theoretical perspective on general principles underlying self-organized pattern formation. We argue that intracellular pattern formation is not captured by concepts such as \activators", \inhibitors", or \substrate-depletion". Instead, intracellular pattern formation is based on the redistribution of proteins by cytosolic diffusion, and the cycling of proteins between distinct conformational states. Therefore, mass-conserving reaction-diffusion equations provide the most appropriate framework to study intracellular pattern formation. We conclude that directed transport, e.g. cytosolic diffusion along an actively maintained cytosolic gradient, is the key process underlying pattern formation. Thus the basic principle of self-organization is the establishment and maintenance of directed transport by intracellular protein dynamics. Keywords: self-organization; pattern formation; intracellular patterns; reaction-diffusion; cell polarity; arXiv:1802.07169v1 [physics.bio-ph] 20 Feb 2018 NTPases 1 INTRODUCTION In biological systems self-organization refers to the emergence of spatial and temporal structure.
    [Show full text]
  • Visualizing Morphogenesis with the Processing Programming Language 15
    Visualizing Morphogenesis with the Processing Programming Language 15 Visualizing Morphogenesis with the Processing Programming Language Avik Patel, Amar Bains, Richard Millet, and Tamira Elul changing tissue shapes. A powerful technique for elucidating the We used Processing, a visual artists’ programming dynamic cellular mechanisms of morphogenesis is time-lapse video- language developed at MIT Media Lab, to simulate microscopic imaging of cells in embryonic tissues undergoing cellular mechanisms of morphogenesis – the generation morphogenesis (Elul and Keller 2000; Elul et al., 1997; Harris et al., of form and shape in embryonic tissues. Based on 1987). The mechanisms underlying morphogenetic processes can be clarified by observation of cell dynamics from these time-lapse video observations of in vivo time-lapse image sequences, we sequences. Morphometric measurement further defines the created animations of neural cell motility responsible for quantitative and statistical relationships between the cell dynamics that elongating the spinal cord, and of optic axon branching underlie morphogenesis (Kim and Davidson 2011; Marshak et al., dynamics that establish primary visual connectivity. 2007; Elul et al., 1997; Witte et al., 1996). Mathematical These visual models underscore the significance of the decomposition of cell dynamics additionally facilitates the computational decomposition of cellular dynamics computational modeling of cellular mechanisms that drive underlying morphogenesis. morphogenesis (Satulovsky et al., 2008). Methods In this paper, we use the Processing programming language to visualize dynamic cell behaviors driving morphogenesis in the Introduction developing nervous system. Based on in vivo time-lapse image sequences, we created models of cell dynamics underlying two Processing is a Java based software language and environment morphogenetic processes in the developing nervous system.
    [Show full text]
  • Transformations of Lamarckism Vienna Series in Theoretical Biology Gerd B
    Transformations of Lamarckism Vienna Series in Theoretical Biology Gerd B. M ü ller, G ü nter P. Wagner, and Werner Callebaut, editors The Evolution of Cognition , edited by Cecilia Heyes and Ludwig Huber, 2000 Origination of Organismal Form: Beyond the Gene in Development and Evolutionary Biology , edited by Gerd B. M ü ller and Stuart A. Newman, 2003 Environment, Development, and Evolution: Toward a Synthesis , edited by Brian K. Hall, Roy D. Pearson, and Gerd B. M ü ller, 2004 Evolution of Communication Systems: A Comparative Approach , edited by D. Kimbrough Oller and Ulrike Griebel, 2004 Modularity: Understanding the Development and Evolution of Natural Complex Systems , edited by Werner Callebaut and Diego Rasskin-Gutman, 2005 Compositional Evolution: The Impact of Sex, Symbiosis, and Modularity on the Gradualist Framework of Evolution , by Richard A. Watson, 2006 Biological Emergences: Evolution by Natural Experiment , by Robert G. B. Reid, 2007 Modeling Biology: Structure, Behaviors, Evolution , edited by Manfred D. Laubichler and Gerd B. M ü ller, 2007 Evolution of Communicative Flexibility: Complexity, Creativity, and Adaptability in Human and Animal Communication , edited by Kimbrough D. Oller and Ulrike Griebel, 2008 Functions in Biological and Artifi cial Worlds: Comparative Philosophical Perspectives , edited by Ulrich Krohs and Peter Kroes, 2009 Cognitive Biology: Evolutionary and Developmental Perspectives on Mind, Brain, and Behavior , edited by Luca Tommasi, Mary A. Peterson, and Lynn Nadel, 2009 Innovation in Cultural Systems: Contributions from Evolutionary Anthropology , edited by Michael J. O ’ Brien and Stephen J. Shennan, 2010 The Major Transitions in Evolution Revisited , edited by Brett Calcott and Kim Sterelny, 2011 Transformations of Lamarckism: From Subtle Fluids to Molecular Biology , edited by Snait B.
    [Show full text]
  • Guiding Self-Organized Pattern Formation in Cell Polarity Establishment
    ARTICLES https://doi.org/10.1038/s41567-018-0358-7 Guiding self-organized pattern formation in cell polarity establishment Peter Gross1,2,3,8, K. Vijay Kumar" "3,4,8, Nathan W. Goehring" "5,6, Justin S. Bois" "7, Carsten Hoege2, Frank Jülicher3 and Stephan W. Grill" "1,2,3* Spontaneous pattern formation in Turing systems relies on feedback. But patterns in cells and tissues seldom form spontane- ously—instead they are controlled by regulatory biochemical interactions that provide molecular guiding cues. The relationship between these guiding cues and feedback in controlled biological pattern formation remains unclear. Here, we explore this relationship during cell-polarity establishment in the one-cell-stage Caenorhabditis elegans embryo. We quantify the strength of two feedback systems that operate during polarity establishment: feedback between polarity proteins and the actomyosin cortex, and mutual antagonism among polarity proteins. We characterize how these feedback systems are modulated by guid- ing cues from the centrosome, an organelle regulating cell cycle progression. By coupling a mass-conserved Turing-like reac- tion–diffusion system for polarity proteins to an active-gel description of the actomyosin cortex, we reveal a transition point beyond which feedback ensures self-organized polarization, even when cues are removed. Notably, the system switches from a guide-dominated to a feedback-dominated regime well beyond this transition point, which ensures robustness. Together, these results reveal a general criterion for controlling biological pattern-forming systems: feedback remains subcritical to avoid unstable behaviour, and molecular guiding cues drive the system beyond a transition point for pattern formation. ell polarity establishment in Caenorhabditis elegans zygotes phase where myosin appears to reach a steady state (Supplementary is a prototypical example for cellular pattern formation that Fig.
    [Show full text]
  • Nicotinic Receptor Alpha7 Expression During Tooth Morphogenesis Reveals Functional Pleiotropy
    Nicotinic Receptor Alpha7 Expression during Tooth Morphogenesis Reveals Functional Pleiotropy Scott W. Rogers1,2*, Lorise C. Gahring1,3 1 Geriatric Research, Education and Clinical Center, Veteran’s Administration, Salt Lake City, Utah, United States of America, 2 Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, Utah, United States of America, 3 Division of Geriatrics, Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City, Utah, United States of America Abstract The expression of nicotinic acetylcholine receptor (nAChR) subtype, alpha7, was investigated in the developing teeth of mice that were modified through homologous recombination to express a bi-cistronic IRES-driven tau-enhanced green fluorescent protein (GFP); alpha7GFP) or IRES-Cre (alpha7Cre). The expression of alpha7GFP was detected first in cells of the condensing mesenchyme at embryonic (E) day E13.5 where it intensifies through E14.5. This expression ends abruptly at E15.5, but was again observed in ameloblasts of incisors at E16.5 or molar ameloblasts by E17.5–E18.5. This expression remains detectable until molar enamel deposition is completed or throughout life as in the constantly erupting mouse incisors. The expression of alpha7GFP also identifies all stages of innervation of the tooth organ. Ablation of the alpha7-cell lineage using a conditional alpha7Cre6ROSA26-LoxP(diphtheria toxin A) strategy substantially reduced the mesenchyme and this corresponded with excessive epithelium overgrowth consistent with an instructive role by these cells during ectoderm patterning. However, alpha7knock-out (KO) mice exhibited normal tooth size and shape indicating that under normal conditions alpha7 expression is dispensable to this process.
    [Show full text]
  • Delta-Notch Signaling: the Long and the Short of a Neuron’S Influence on Progenitor Fates
    Journal of Developmental Biology Review Delta-Notch Signaling: The Long and the Short of a Neuron’s Influence on Progenitor Fates Rachel Moore 1,* and Paula Alexandre 2,* 1 Centre for Developmental Neurobiology, King’s College London, London SE1 1UL, UK 2 Developmental Biology and Cancer, University College London Great Ormond Street Institute of Child Health, London WC1N 1EH, UK * Correspondence: [email protected] (R.M.); [email protected] (P.A.) Received: 18 February 2020; Accepted: 24 March 2020; Published: 26 March 2020 Abstract: Maintenance of the neural progenitor pool during embryonic development is essential to promote growth of the central nervous system (CNS). The CNS is initially formed by tightly compacted proliferative neuroepithelial cells that later acquire radial glial characteristics and continue to divide at the ventricular (apical) and pial (basal) surface of the neuroepithelium to generate neurons. While neural progenitors such as neuroepithelial cells and apical radial glia form strong connections with their neighbours at the apical and basal surfaces of the neuroepithelium, neurons usually form the mantle layer at the basal surface. This review will discuss the existing evidence that supports a role for neurons, from early stages of differentiation, in promoting progenitor cell fates in the vertebrates CNS, maintaining tissue homeostasis and regulating spatiotemporal patterning of neuronal differentiation through Delta-Notch signalling. Keywords: neuron; neurogenesis; neuronal apical detachment; asymmetric division; notch; delta; long and short range lateral inhibition 1. Introduction During the development of the central nervous system (CNS), neurons derive from neural progenitors and the Delta-Notch signaling pathway plays a major role in these cell fate decisions [1–4].
    [Show full text]
  • Development and Evolution
    AccessScience from McGraw-Hill Education Page 1 of 4 www.accessscience.com Development and evolution Contributed by: Brian K. Hall Publication year: 2010 The disciplines of developmental biology (or embryology) and evolutionary biology have come together twice—once as evolutionary embryology in the late nineteenth century and again as evolutionary developmental biology (evo-devo, as it is typically known) in the late twentieth century. The current intersections of development and evolution are proving to be of paramount importance for creating a fully integrated theory of biology. History Prior to and into the nineteenth century, the word “evolution” had a completely different meaning from its usage today. Then, it was used to describe a particular type of embryonic or larval development—the preformation and unfolding of a more or less fully formed organism from an embryonic or larval stage (for example, a butterfly from a caterpillar, or aphids from the body of an adult female). In fact, Charles Darwin did not use the word “evolution” per se in On the Origin of Species , which was published in 1859, although “evolved” was the final word of his book. To reach its present-day definition, the term “evolution” had to undergo a slow transformation from development within a single generation to transformation (transmutation) between generations. As for the field of developmental biology, in the nineteenth century, embryology (referring to the study of embryonic development) was a progressive field in biology, with researchers describing normal development and then manipulating animal embryos [ experimental or physiological embryology (also known as developmental mechanics)] in search of altered outcomes that would help explain how development occurred.
    [Show full text]
  • Synthetic Morphogenesis
    Downloaded from http://cshperspectives.cshlp.org/ on September 24, 2021 - Published by Cold Spring Harbor Laboratory Press Synthetic Morphogenesis Brian P. Teague, Patrick Guye, and Ron Weiss Synthetic Biology Center, Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Correspondence: [email protected] Throughout biology, function is intimately linked with form. Across scales ranging from subcellular to multiorganismal, the identity and organization of a biological structure’s subunits dictate its properties. The field of molecular morphogenesis has traditionally been concerned with describing these links, decoding the molecular mechanisms that give rise to the shape and structure of cells, tissues, organs, and organisms. Recent advances in synthetic biology promise unprecedented control over these molecular mechanisms; this opens the path to not just probing morphogenesis but directing it. This review explores several frontiers in the nascent field of synthetic morphogenesis, including programmable tissues and organs, synthetic biomaterials and programmable matter, and engineering complex morphogenic systems de novo. We will discuss each frontier’s objectives, current approaches, constraints and challenges, and future potential. hat is the underlying basis of biological 2014). As the mechanistic underpinnings of Wstructure? Speculations were based on these processes are elucidated, opportunities macroscopic observation until the 17th century, arise to use this knowledge to direct mor- when Antonie van Leeuwenhoek and Robert phogenesis toward novel, useful ends. We call Hooke discovered that organisms were com- this emerging field of endeavor “synthetic mor- posed of microscopic cells (Harris 1999), and phogenesis.” Inspired by and based on natural that the size and shape of the cells affected the morphogenic systems, synthetic morphogenesis properties of the structures they formed.
    [Show full text]
  • Pattern Formation, Social Forces, and Diffusion Instability in Games
    EPJ manuscript No. (will be inserted by the editor) Pattern Formation, Social Forces, and Diffusion Instability in Games with Success-Driven Motion Dirk Helbing ETH Zurich, UNO D11, Universit¨atstr.41, 8092 Zurich, Switzerland Received: date / Revised version: date Abstract. A local agglomeration of cooperators can support the survival or spreading of cooperation, even when cooperation is predicted to die out according to the replicator equation, which is often used in evolutionary game theory to study the spreading and disappearance of strategies. In this paper, it is shown that success-driven motion can trigger such local agglomeration and may, therefore, be used to supplement other mechanisms supporting cooperation, like reputation or punishment. Success-driven motion is formulated here as a function of the game-theoretical payoffs. It can change the outcome and dynamics of spatial games dramatically, in particular as it causes attractive or repulsive interaction forces. These forces act when the spatial distributions of strategies are inhomogeneous. However, even when starting with homogeneous initial conditions, small perturbations can trigger large inhomogeneities by a pattern-formation instability, when certain conditions are fulfilled. Here, these instability conditions are studied for the prisoner's dilemma and the snowdrift game. Furthermore, it is demonstrated that asymmetrical diffusion can drive social, economic, and biological systems into the unstable regime, if these would be stable without diffusion. PACS. 02.50.Le Decision theory and game theory { 87.23.Ge Dynamics of social systems { 82.40.Ck Pattern formation in reactions with diffusion, flow and heat transfer { 87.23.Cc Population dynamics and ecological pattern formation 1 Introduction tions [17,18], which agree with replicator equations for the fitness-dependent reproduction of individuals in biology Game theory is a well-established theory of individual [19,20,21].
    [Show full text]
  • Principles of Differentiation and Morphogenesis
    Swarthmore College Works Biology Faculty Works Biology 2016 Principles Of Differentiation And Morphogenesis Scott F. Gilbert Swarthmore College, [email protected] R. Rice Follow this and additional works at: https://works.swarthmore.edu/fac-biology Part of the Biology Commons Let us know how access to these works benefits ouy Recommended Citation Scott F. Gilbert and R. Rice. (2016). 3rd. "Principles Of Differentiation And Morphogenesis". Epstein's Inborn Errors Of Development: The Molecular Basis Of Clinical Disorders On Morphogenesis. 9-21. https://works.swarthmore.edu/fac-biology/436 This work is brought to you for free by Swarthmore College Libraries' Works. It has been accepted for inclusion in Biology Faculty Works by an authorized administrator of Works. For more information, please contact [email protected]. 2 Principles of Differentiation and Morphogenesis SCOTT F. GILBERT AND RITVA RICE evelopmental biology is the science connecting genetics with transcription factors, such as TFHA and TFIIH, help stabilize the poly­ anatomy, making sense out of both. The body builds itself from merase once it is there (Kostrewa et al. 2009). Dthe instructions of the inherited DNA and the cytoplasmic system that Where and when a gene is expressed depends on another regula­ interprets the DNA into genes and creates intracellular and cellular tory unit of the gene, the enhancer. An enhancer is a DNA sequence networks to generate the observable phenotype. Even ecological fac­ that can activate or repress the utilization of a promoter, controlling tors such as diet and stress may modify the DNA such that different the efficiency and rate of transcription from that particular promoter.
    [Show full text]
  • Using Neural Networks for Pattern Association for the Online Purchase
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by AIS Electronic Library (AISeL) Association for Information Systems AIS Electronic Library (AISeL) All Sprouts Content Sprouts 7-26-2009 Using Neural Networks for Pattern Association for the Online Purchase of Products Arpan Kumar Kar XLRI School of Business & Human Resources, [email protected] Supriyo Kumar De XLRI School of Business & Human Resources, [email protected] Follow this and additional works at: http://aisel.aisnet.org/sprouts_all Recommended Citation Kar, Arpan Kumar and De, Supriyo Kumar, " Using Neural Networks for Pattern Association for the Online Purchase of Products" (2009). All Sprouts Content. 281. http://aisel.aisnet.org/sprouts_all/281 This material is brought to you by the Sprouts at AIS Electronic Library (AISeL). It has been accepted for inclusion in All Sprouts Content by an authorized administrator of AIS Electronic Library (AISeL). For more information, please contact [email protected]. Working Papers on Information Systems ISSN 1535-6078 Using Neural Networks for Pattern Association for the Online Purchase of Products Arpan Kumar Kar XLRI School of Business & Human Resources, India Supriyo Kumar De XLRI School of Business & Human Resources, India Abstract Abstract: Today, a huge percentage of all the business transactions that take place in the domain of e-commerce are dominated by online shopping after the "virtual market" conceptualization of the business. This paper focuses on how pattern association rules may be obtained from the dynamic databases generated during purchases in an e-Store to maximize the profit of the marketer.
    [Show full text]
  • Notch Signaling in Vascular Morphogenesis Jackelyn A
    Notch signaling in vascular morphogenesis Jackelyn A. Alva and M. Luisa Iruela-Arispe Purpose of review © 2004 Lippincott Williams & Wilkins 1065–6251 This review highlights recent developments in the role of the Notch signaling pathway during vascular morphogenesis, angiogenesis, and vessel homeostasis. Introduction Recent findings Notch encodes a 300-kDa transmembrane receptor pro- Studies conducted over the past 4 years have significantly tein characterized by extracellular epidermal growth fac- advanced the understanding of the effect of Notch signaling tor repeats and an intracellular domain that consists of a on vascular development. Major breakthroughs have RAM motif,six ankyrin repeats,and a transactivation elucidated the role of Notch in arterial versus venular domain. Four mammalian Notch receptors (Notch 1–4) specification and have placed this pathway downstream of have been cloned and characterized in mammals. These vascular endothelial growth factor. bind to five ligands (Jagged 1 and 2 and Delta-like (Dll) Summary 1,3,and 4). Because both Notch receptors and ligands An emerging hallmark of the Notch signaling pathway is its contain transmembrane domains,signaling occurs be- nearly ubiquitous participation in cell fate decisions that affect tween closely associated cells. The interaction between several tissues, including epithelial, neuronal, hematopoietic, ligand and receptor leads to proteolytic cleavage and and muscle. The vascular compartment has been the latest shedding of the extracellular portion of the Notch recep- addition to the list of tissues known to be regulated by Notch. tor. This is followed by a second cleavage event via a Unraveling the contribution of Notch signaling to blood vessel regulated membrane proteolysis that releases the intra- formation has resulted principally from gain-of-function and cellular Notch from the cell membrane.
    [Show full text]