DOCSLIB.ORG

Forebrain Development: Prosomere Model 315

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Forebrain Development: Prosomere Model 315 Forebrain Development: Prosomere Model 315 Forebrain Development: Prosomere Model L Puelles, University of Murcia, Murcia, Spain model in which all sorts of detailed data on form and ã 2009 Elsevier Ltd. All rights reserved. structure down to cellular aspects can be systematically accumulated, organized, compared, and differentiated one from another in their mutual relationships. The basic model of the vertebrate brain is the concept of Definition the closed neural tube, from which adult brains emerge via differential morpho- and histogenesis. Since we The prosomeric model is a segmental structural model cannot know all from the beginning, morphological of the brain of vertebrates that explicitly holds that models essentially are reasonable and useful conjec- the brain is formed by an uninterrupted series of trans- tures about how many parts there are and how they verse subunits of the neural tube, generally called are patched together. Such models are periodically neuromeres. Among such subunits is a large rostral perfected over time, becoming in the case of brains forebrain unit – the secondary prosencephalon – that increasingly complex operational scaffolds based on encompasses hypothalamus, eyes, and telencephalon, accumulated data and a number of assumptions. There followed by three caudal forebrain or diencephalic is always the possibility of constructing better (or neuromeres (i.e., prosomeres), which are regarded as worse) models. being serially homologous with more-caudal neuro- A good model in essence should be parsimonious; meres, namely, a single midbrain mesomere, 11 hind- that is, it should identify a minimal set of characteris- brain rhombomeres, and the spinal myelomeres. It is tic parts or landmarks in the modeled system, which important to note that for descriptive purposes, the can be generally recognized and seem to encompass, model postulates in all vertebrates a morphogenetic or be able to explain, most if not all available struc- bending of the longitudinal axis of the tubular neural tural data. A good model also may delimit various primordium, most marked at the cephalic flexure, ‘unfilled’ conceptual domains, where new data should whose incurvation causes wedge-shaped deformation fit in (as the periodic table of chemical elements did of the topologically transverse cylindrical neuromeric when it was first formulated). Such predictive aspects sectors of the neural tube. These units share a set of of models are highly useful because they implicitly fundamental longitudinal zones (due to common dor- indicate which new questions might be meaningful soventral (DV) patterning processes) and therefore or how best to pose and answer them in practice. represent segments, that is, metameric developmental Simultaneously, models are instrumental in providing units (anteroposterior (AP) patterning). The common possible significance to any new, unexpected observa- causal background of the longitudinal zones establishes tion. Scientists in principle believe in and use a par- the property of metamery (i.e., serial homology) across ticular model as long as it seems to accommodate all neuromeres, irrespective of their differential molec- established knowledge, inspire significant research, ular identities and individual prospective adult fates and allow satisfactory incorporation of emerging and of the variable border properties of the cells sets of new data. Historical periods in which techno- found at the interneuromeric boundaries. Therefore, logical improvements produce radically novel sorts the prosomeric model visualizes all vertebrate brains of data are particularly critical for the survival of as segmented structures constructed along the same a model. Bauplan (same set of DV and AP developmental units). Models widely shared among a scientific commu- Orthogonal intersection of DV and AP boundaries in nity represent a scientific paradigm. In contrast to the neural tube wall defines a checkerboard pattern hypotheses and theories, paradigms are not meant of domains (histogenetic areas) in which specific prop- to be tested, since one must believe in one of them erties and finer regionalization phenomena appear and use it as if it represented the truth, in the very (shared or not among vertebrates). This makes the process of testing a hypothesis experimentally. A par- model useful for systematic descriptive neuroembryo- adigm comes dangerously close to becoming a dogma, logy, comparative neuroanatomy, and causal analysis a belief that wholly escapes criticism or doubt and is of conserved or variant brain morphogenesis. considered ascientific. Several models may coexist historically, sometimes because each one is perceived Characteristics to have different advantages, but usually due to lack of awareness that one of them is distinctly better than Why We Use Models the others, compounded with the human tendency to Structural neurobiology studies the form and func- persist irrationally in long-held beliefs. Nevertheless, tional inner structure of brains. This needs a conceptual models and paradigms eventually may be perceived as 316 Forebrain Development: Prosomere Model obsolete and be discarded by newer, less committed writings by von Kupffer, Hill, His, Neal, Palmgren, generations of scientists, particularly when they are Rendahl, Tello, and Vaage, among others, contain less manifestly unable to account for some data and explicit antecedents. A large-scale review of shared efforts to apply them lead to highly unparsimonious, neuromeric structural data collected for all vertebrate complicated lines of thought. Continued use of an lineages from agnatha to mammals was published by obsolete model, or mixed-up joint use of elements of von Kupffer at the turn of the twentieth century. different models, tends to obstruct the progress of Wilhelm His produced an alternative very influential science. neural model, though he certainly must have known Some neuroscientists wrongly think that they do the neuromeric views of von Kupffer and other con- not use a neural model. This means they simply are temporaries well. His defined the floor, basal, alar, and unaware of the model they are using. Frequently, roof plates, the alar-basal boundary (sulcus limitans some aspects they mistakenly regard as facts actually of His), the concept of isthmus, and the idea of neural are conjectures. Dogmatic conscious or unconscious tube morphogenetic deformation due to axial bend- belief in models is a condition that is prone to poor ing. This model was very influential because it under- thinking and poor science. Due to the great complex- pinned the first Nomina Anatomica in 1895, whose ity of the studied organ, brain science is a field where committee was presided over by His. The model was such interpretive malfunctioning is not uncommon. not explicitly neuromeric, though His’ concepts of axial bending and longitudinal zonation and most of Neuromeric Models his transverse boundaries, including those of the isth- The earliest morphological models of the brain were mus, clearly were consistent with neuromeric models based on the adult form of the human and animal (Figure 2). brains. This approach provided over time a rich set of neuroanatomical terms and conjectural meanings, Columnar Models many of which are now obsolete, although some old At the height of the prestige of neuromeric brain terms and concepts still persist in textbooks. During models, an important unrelated breakthrough resulted the late nineteenth century, and as a result of various from the analysis of functional components in the important advances such as microscopy, evolutionary cranial and spinal nerves. It was discovered that each theory, and cell theory, comparative anatomical and nerve component (motor or sensory fibers) either embryological knowledge of brains advanced enough originates from or projects on a distinct columnar to allow the initial formulation of developmental domain of the hindbrain or spinal cord. Separate brain models generally valid for all vertebrates. Devel- columns could be assigned to visceral and somatic opmental models also appeared for the entire body. nerve components. Afferent fibers usually bifurcate The first generally accepted developmental structural into ascending and descending branches that distrib- paradigm for brains was a segmental model of the ute widely within the corresponding column. In so neural tube, which appeared hand in hand with a doing, they do not respect the neuromeric bound- segmental model of the body and head of vertebrates. aries. These data were widely perceived as important, The axial skeleton was conceived as being segmented and they threw doubt on the neuromeric models, at into metameric vertebrae (with a number of units least for application to advanced embryos and adults, fused together in the sacrum and in the cranial basis). since the basic functional organization of the hind- The branchial apparatus also seemed segmented into brain and spinal cord seemed to be columnar and not serial branchial arches and slits. The brain and the set segmental, irrespective of the separate, more or less of spinal and cranial nerves were postulated to consist periodic nerve roots, and the peripheral dermatomes of a number of segmental units correlated one to one and myotomes. It was increasingly thought that with the vertebrae and/or branchial arches. maybe neuromeres were transient early embryonic The term ‘neuromere’ that was soon applied to these phenomena without impact in the mature brain, in transverse neural
Load more

Recommended publications
  • Works Neuroembryology
    Swarthmore College Works Biology Faculty Works Biology 1-1-2017 Neuroembryology D. Darnell Scott F. Gilbert Swarthmore College, [email protected] 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 D. Darnell and Scott F. Gilbert. (2017). "Neuroembryology". Wiley Interdisciplinary Reviews: Developmental Biology. Volume 6, Issue 1. DOI: 10.1002/wdev.215 https://works.swarthmore.edu/fac-biology/493 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]. HHS Public Access Author manuscript Author ManuscriptAuthor Manuscript Author Wiley Interdiscip Manuscript Author Rev Dev Manuscript Author Biol. Author manuscript; available in PMC 2018 January 01. Published in final edited form as: Wiley Interdiscip Rev Dev Biol. 2017 January ; 6(1): . doi:10.1002/wdev.215. Neuroembryology Diana Darnell1 and Scott F. Gilbert2 1University of Arizona College of Medicine 2Swarthmore College and University of Helsinki Abstract How is it that some cells become neurons? And how is it that neurons become organized in the spinal cord and brain to allow us to walk and talk, to see, recall events in our lives, feel pain, keep our balance, and think? The cells that are specified to form the brain and spinal cord are originally located on the outside surface of the embryo. They loop inward to form the neural tube in a process called neurulation.
    [Show full text]
  • The Genetic Basis of Mammalian Neurulation
    REVIEWS THE GENETIC BASIS OF MAMMALIAN NEURULATION Andrew J. Copp*, Nicholas D. E. Greene* and Jennifer N. Murdoch‡ More than 80 mutant mouse genes disrupt neurulation and allow an in-depth analysis of the underlying developmental mechanisms. Although many of the genetic mutants have been studied in only rudimentary detail, several molecular pathways can already be identified as crucial for normal neurulation. These include the planar cell-polarity pathway, which is required for the initiation of neural tube closure, and the sonic hedgehog signalling pathway that regulates neural plate bending. Mutant mice also offer an opportunity to unravel the mechanisms by which folic acid prevents neural tube defects, and to develop new therapies for folate-resistant defects. 6 ECTODERM Neurulation is a fundamental event of embryogenesis distinct locations in the brain and spinal cord .By The outer of the three that culminates in the formation of the neural tube, contrast, the mechanisms that underlie the forma- embryonic (germ) layers that which is the precursor of the brain and spinal cord. A tion, elevation and fusion of the neural folds have gives rise to the entire central region of specialized dorsal ECTODERM, the neural plate, remained elusive. nervous system, plus other organs and embryonic develops bilateral neural folds at its junction with sur- An opportunity has now arisen for an incisive analy- structures. face (non-neural) ectoderm. These folds elevate, come sis of neurulation mechanisms using the growing battery into contact (appose) in the midline and fuse to create of genetically targeted and other mutant mouse strains NEURAL CREST the neural tube, which, thereafter, becomes covered by in which NTDs form part of the mutant phenotype7.At A migratory cell population that future epidermal ectoderm.
    [Show full text]
  • Subject Index
    979 Subject Index Acellularity Asymmetry of embryonic starfish mesenchyme cells: KANEKO AND development of left/right asymmetry: BROWN AND OTHERS 129 WOLPERT 1 Acetylcholinesterase Avian tropomyosin/cholinesterase expression in ascidian embryo zygotes: CROWTHER AND OTHERS 953 localization of bFGF: KALCHEIM AND NEUFELD 203 Acrosome Axis reaction anterior-posterior zona receptors on guinea-pig spermatozoa: JONES AND organizer amount and axial pattern in Xenopus: WILLIAMS 41 STEWART AND GERHART 363 Actin Axogenesis effect of stretch on muscle gene expression: LOUGHNA AND Thy-1 expression in murine olfactory bulb: XUE AND OTHERS 217 OTHERS 851 Adult Axolotl rat embryo perinatnl ndu coexistence of O-2A and O-2A " progenitors: extracellular matrix in neural crest pathways: PERRIS WOLSWIJK AND OTHERS 691 AND OTHERS 533 Aggregation Axon pattern guidance of Dictyostelium discoideum: FOERSTER AND OTHERS 11 axon patterning at rat floor plate: BOVOLENTA AND Aging DODD 435 NGF receptor in rat dental tissue: BYERS AND OTHERS 461 outgrowth Agouti growth associated protein in chick visual system: cellular action of the mouse lethal yellow mutation: BARSH SCHLOSSHAUER AND OTHERS 395 AND OTHERS 683 rat Ammonia prenatal Schwann cell development: MIRSKY AND promotes cAMP accumulation in Dictyostelium: RILEY AND OTHERS 105 BARCLAY 715 regeneration AMP effects of protease inhibitors: FAWCETT AND HOUSDEN cyclic 59 ammonia promotes cAMP accumulation in Dictyostelium: RILEY AND BARCLAY 715 prenatal Schwann cell development: MIRSKY AND Back-transplantation OTHERS
    [Show full text]
  • Clonal Dispersion During Neural Tube Formation 4097 of Neuromeres
    Development 126, 4095-4106 (1999) 4095 Printed in Great Britain © The Company of Biologists Limited 1999 DEV2458 Successive patterns of clonal cell dispersion in relation to neuromeric subdivision in the mouse neuroepithelium Luc Mathis1,*, Johan Sieur1, Octavian Voiculescu2, Patrick Charnay2 and Jean-François Nicolas1,‡ 1Unité de Biologie moléculaire du Développement, Institut Pasteur, 25, rue du Docteur Roux, 75724 Paris Cedex 15, France 2Unité INSERM 368, Ecole Normale Supérieure, 46 rue d’Ulm, 75230 Paris Cedex 05, France *Present address: Beckman Institute (139-74), California Institute of Technology, Pasadena, CA, 91125, USA ‡Author for correspondence (e-mail: [email protected]) Accepted 5 July; published on WWW 23 August 1999 SUMMARY We made use of the laacz procedure of single-cell labelling the AP and DV axis of the neural tube. A similar sequence to visualize clones labelled before neuromere formation, in of AP cell dispersion followed by an arrest of AP cell 12.5-day mouse embryos. This allowed us to deduce two dispersion, a preferential DV cell dispersion and then by a successive phases of cell dispersion in the formation of the coherent neuroepithelial growth, is also observed in the rhombencephalon: an initial anterior-posterior (AP) cell spinal cord and mesencephalon. This demonstrates that a dispersion, followed by an asymmetrical dorsoventral (DV) similar cascade of cell events occurs in these different cell distribution during which AP cell dispersion occurs in domains of the CNS. In the prosencephalon, differences in territories smaller than one rhombomere. We conclude that spatial constraints may explain the variability in the the general arrest of AP cell dispersion precedes the onset orientation of cell clusters.
    [Show full text]
  • Fate of the Mammalian Cardiac Neural Crest
    Development 127, 1607-1616 (2000) 1607 Printed in Great Britain © The Company of Biologists Limited 2000 DEV4300 Fate of the mammalian cardiac neural crest Xiaobing Jiang1,3, David H. Rowitch4,*, Philippe Soriano5, Andrew P. McMahon4 and Henry M. Sucov2,3,‡ Departments of 1Biological Sciences and 2Cell & Neurobiology, 3Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, 2250 Alcazar St., IGM 240, Los Angeles, CA 90033, USA 4Department of Molecular and Cell Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA 5Program in Developmental Biology, Division of Basic Sciences, A2-025, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, PO Box 19024, Seattle, WA 98109, USA *Present address: Department of Pediatric Oncology, Dana Farber Cancer Institute, 44 Binney St., Boston, MA 02115, USA ‡Author for correspondence (e-mail: [email protected]) Accepted 26 January; published on WWW 21 March 2000 SUMMARY A subpopulation of neural crest termed the cardiac neural of these vessels. Labeled cells populate the crest is required in avian embryos to initiate reorganization aorticopulmonary septum and conotruncal cushions prior of the outflow tract of the developing cardiovascular to and during overt septation of the outflow tract, and system. In mammalian embryos, it has not been previously surround the thymus and thyroid as these organs form. experimentally possible to study the long-term fate of this Neural-crest-derived mesenchymal cells are abundantly population, although there is strong inference that a similar distributed in midgestation (E9.5-12.5), and adult population exists and is perturbed in a number of genetic derivatives of the third, fourth and sixth pharyngeal arch and teratogenic contexts.
    [Show full text]
  • Stages of Embryonic Development of the Zebrafish
    DEVELOPMENTAL DYNAMICS 2032553’10 (1995) Stages of Embryonic Development of the Zebrafish CHARLES B. KIMMEL, WILLIAM W. BALLARD, SETH R. KIMMEL, BONNIE ULLMANN, AND THOMAS F. SCHILLING Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403-1254 (C.B.K., S.R.K., B.U., T.F.S.); Department of Biology, Dartmouth College, Hanover, NH 03755 (W.W.B.) ABSTRACT We describe a series of stages for Segmentation Period (10-24 h) 274 development of the embryo of the zebrafish, Danio (Brachydanio) rerio. We define seven broad peri- Pharyngula Period (24-48 h) 285 ods of embryogenesis-the zygote, cleavage, blas- Hatching Period (48-72 h) 298 tula, gastrula, segmentation, pharyngula, and hatching periods. These divisions highlight the Early Larval Period 303 changing spectrum of major developmental pro- Acknowledgments 303 cesses that occur during the first 3 days after fer- tilization, and we review some of what is known Glossary 303 about morphogenesis and other significant events that occur during each of the periods. Stages sub- References 309 divide the periods. Stages are named, not num- INTRODUCTION bered as in most other series, providing for flexi- A staging series is a tool that provides accuracy in bility and continued evolution of the staging series developmental studies. This is because different em- as we learn more about development in this spe- bryos, even together within a single clutch, develop at cies. The stages, and their names, are based on slightly different rates. We have seen asynchrony ap- morphological features, generally readily identi- pearing in the development of zebrafish, Danio fied by examination of the live embryo with the (Brachydanio) rerio, embryos fertilized simultaneously dissecting stereomicroscope.
    [Show full text]
  • NERVOUS SYSTEM هذا الملف لالستزادة واثراء المعلومات Neuropsychiatry Block
    NERVOUS SYSTEM هذا الملف لﻻستزادة واثراء المعلومات Neuropsychiatry block. قال تعالى: ) َو َل َق د َخ َل قنَا ا ِْلن َسا َن ِمن ُس ََل َل ة ِ من ِطي ن }12{ ثُ م َجعَ لنَاه ُ نُ ط َفة فِي َق َرا ر م ِكي ن }13{ ثُ م َخ َل قنَا ال ُّن ط َفة َ َع َل َقة َف َخ َل قنَا ا لعَ َل َقة َ ُم ضغَة َف َخ َل قنَا ا ل ُم ضغَة َ ِع َظا ما َف َك َس ونَا ا ل ِع َظا َم َل ح ما ثُ م أَن َشأنَاه ُ َخ ل قا آ َخ َر َفتَبَا َر َك ّللا ُ أَ ح َس ُن ا ل َخا ِل ِقي َن }14{( Resources BRS Embryology Book. Pathoma Book ( IN DEVELOPMENTAL ANOMALIES PART ). [email protected] 1 OVERVIEW A- Central nervous system (CNS) is formed in week 3 of development, during which time the neural plate develops. The neural plate, consisting of neuroectoderm, becomes the neural tube, which gives rise to the brain and spinal cord. B- Peripheral nervous system (PNS) is derived from three sources: 1. Neural crest cells 2. Neural tube, which gives rise to all preganglionic autonomic nerves (sympathetic and parasympathetic) and all nerves (-motoneurons and -motoneurons) that innervate skeletal muscles 3. Mesoderm, which gives rise to the dura mater and to connective tissue investments of peripheral nerve fibers (endoneurium, perineurium, and epineurium) DEVELOPMENT OF THE NEURAL TUBE Neurulation refers to the formation and closure of the neural tube. BMP-4 (bone morphogenetic protein), noggin (an inductor protein), chordin (an inductor protein), FGF-8 (fibroblast growth factor), and N-CAM (neural cell adhesion molecule) appear to play a role in neurulation.
    [Show full text]
  • And Krox-20 and on Morphological Segmentation in the Hindbrain of Mouse Embryos
    The EMBO Journal vol.10 no.10 pp.2985-2995, 1991 Effects of retinoic acid excess on expression of Hox-2.9 and Krox-20 and on morphological segmentation in the hindbrain of mouse embryos G.M.Morriss-Kay, P.Murphy1,2, R.E.Hill1 and in embryos are unknown, but in human embryonal D.R.Davidson' carcinoma cells they include the nine genes of the Hox-2 cluster (Simeone et al., 1990). Department of Human Anatomy, South Parks Road, Oxford OXI 3QX The hindbrain and the neural crest cells derived from it and 'MRC Human Genetics Unit, Western General Hospital, Crewe are of particular interest in relation to the developmental Road, Edinburgh EH4 2XU, UK functions of RA because they are abnormal in rodent 2Present address: Istituto di Istologia ed Embriologia Generale, embryos exposed to a retinoid excess during or shortly before Universita di Roma 'la Sapienza', Via A.Scarpa 14, 00161 Roma, early neurulation stages of development (Morriss, 1972; Italy Morriss and Thorogood, 1978; Webster et al., 1986). Communicated by P.Chambon Human infants exposed to a retinoid excess in utero at early developmental stages likewise show abnormalities of the Mouse embryos were exposed to maternally administered brain and of structures to which cranial neural crest cells RA on day 8.0 or day 73/4 of development, i.e. at or just contribute (Lammer et al., 1985). Retinoid-induced before the differentiation of the cranial neural plate, and abnormalities of hindbrain morphology in rodent embryos before the start of segmentation. On day 9.0, the RA- include shortening of the preotic region in relation to other treated embryos had a shorter preotic hindbrain than the head structures, so that the otocyst lies level with the first controls and clear rhombomeric segmentation was pharyngeal arch instead of the second (Morriss, 1972; absent.
    [Show full text]
  • Expression Patterns of Neural Genes in Euperipatoides Kanangrensis Suggest Divergent Evolution of Onychophoran and Euarthropod Neurogenesis
    Expression patterns of neural genes in Euperipatoides kanangrensis suggest divergent evolution of onychophoran and euarthropod neurogenesis Bo Joakim Eriksson and Angelika Stollewerk1 School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, United Kingdom Edited by Thomas C. Kaufman, Indiana University, Bloomington, IN, and approved November 10, 2010 (received for review June 28, 2010) One of the controversial debates on euarthropod relationships pattern of neurogenesis that has been retained in these groups centers on the question as to whether insects, crustaceans, and and thus cannot be used to resolve euarthropod phylogeny? myriapods (Mandibulata) share a common ancestor or whether Analysis of neurogenesis in a closely related group, the Ony- myriapods group with the chelicerates (Myriochelata). The debate chophora, might shed light on this problem. Although the phy- was stimulated recently by studies in chelicerates and myriapods logenetic position of onychophorans is still debated, many that show that neural precursor groups (NPGs) segregate from the phylogenies group them with euarthropods and possibly tardi- neuroectoderm generating the nervous system, whereas in insects grades in the phylum Arthropoda; thus onychophorans share and crustaceans the nervous tissue is produced by stem cells. Do a common ancestor with euarthropods (8, 19–23). Analyses of the shared neural characters of myriapods and chelicerates repre- neurogenesis in onychophorans suggests that, similar to insects sent derived characters that support the Myriochelata grouping? and crustaceans, single neural precursors are formed in the neu- Or do they rather reflect the ancestral pattern? Analyses of neuro- roectoderm, rather than groups of cells as seen in chelicerates and genesis in a group closely related to euarthropods, the onycho- myriapods (24–26).
    [Show full text]
  • Hox Genes Make the Connection
    Downloaded from genesdev.cshlp.org on September 26, 2021 - Published by Cold Spring Harbor Laboratory Press PERSPECTIVE Establishing neuronal circuitry: Hox genes make the connection James Briscoe1 and David G. Wilkinson2 Developmental Neurobiology, National Institute for Medical Research, Mill Hill, London, NW7 1AA, UK The vertebrate nervous system is composed of a vast meres maintain these partitions. Each rhombomere array of neuronal circuits that perceive, process, and con- adopts unique cellular and molecular properties that ap- trol responses to external and internal cues. Many of pear to underlie the spatial organization of the genera- these circuits are established during embryonic develop- tion of cranial motor nerves and neural crest cells. More- ment when axon trajectories are initially elaborated and over, the coordination of positional identity between the functional connections established between neurons and central and peripheral derivatives of the hindbrain may their targets. The assembly of these circuits requires ap- underlie the anatomical and functional registration be- propriate matching between neurons and the targets tween MNs, cranial ganglia, and the routes of neural they innervate. This is particularly apparent in the case crest migration. Cranial neural crest cells derived from of the innervation of peripheral targets by central ner- the dorsal hindbrain migrate ventral-laterally as discrete vous system neurons where the development of the two streams adjacent to r2, r4, and r6 to populate the first tissues must be coordinated to establish and maintain three branchial arches (BA1–BA3), respectively, where circuits. A striking example of this occurs during the they generate distinct skeletal and connective tissue formation of the vertebrate head.
    [Show full text]
  • Cephalic Neurulation in the Mouse Embryo Analyzed by SEM and Morphometry
    THE ANATOMICAL RECORD 203:375-396 (1982) Cephalic Neurulation in the Mouse Embryo Analyzed by SEM and Morphometry ANTONE G. JACOBSON AND PATRICK P.L. TAM Department of Zoology. Uniuersity of Texas, Austin, TX 78712 (A.G.J.) and Department of Anatomy, (‘hinese University of Hong Kong, Shatin, N.T., Hong Kong IP.PL.T) ABSTRACT A detailed account of mouse neurulation is given based mostly on SEM analysis over 20 hr of development. Many observations and measure- ments were made on staged living embryos and on embryos prepared for scanning and light microscopy to help deduce what mechanisms may contribute to neural tube formation. Each lateral half of the early cephalic neural plate makes a convex bulge, opposite to the way it must fold to form a tube. Underlying mesenchyme and matrix are reported to have a role in forming these bulges. Processes that form the tube must overcome this opposed folding and the forces that produce it. Crani- al flexure begins long before tube formation. The flexure commences at the rostra1 tip of the cephalic neural plate, then the apex of the flexure migrates caudally to the mesencephalic region. Early appearance of this flexure imposes a mechanical impediment to tube closure in forebrain and midbrain regions. Tube closure begins in the cervical region exactly where the neural plate is reflected dorsally by a bend in the embryo. This bend may mechanically assist closure in this region. Cells of the mouse neural plate are reported to contain organized microfilaments and mi- crotubules, and the plate cells appear to change shape (reduce apical area and in- crease cell height) in the same manner as that suggested in embryos of some other species to contribute to neural tube formation.
    [Show full text]
  • R-Cadherin Expression During Nucleus Formation in Chicken Forebrain Neuromeres
    The Journal of Neuroscience, June 1995, 15(6): 4157-4172 R-Cadherin Expression during Nucleus Formation in Chicken Forebrain Neuromeres Susanne I. I. GBnzler and Christoph Redies Department of Biochemistry, Max Planck Institute for Developmental Biology, D-72072 Tiibingen, Germany The primordial neuroepithelium of the vertebrate forebrait dahl, 1924; Vaage, 1969; Kuhlenbeck, 1973; Puelleset al., 1987; consists of transverse and longitudinal morphogenetic Puelles and Rubenstein, 1993) that represent independentmor- compartments (“neuromeres”). During development, neu- phogenetic fields (Bergquist and KallCn, 1953a,b, 1954; Keyser, rons born in the ventricular zone of each neuromere mi- 1972; Puelleset al., 1987). The boundariesbetween neuromeres grate outward to the mantle zone. Here, neuroblasts grad- often coincide with primordial fiber tracts and restrict cell lin- ually accumulate and aggregate either into sheets (“lami- eage and migration. Generally, they coincide with the borders nae”) or into roundish structures (“nuclei”). As brain ar- of expressionof generegulatory proteins (reviewed in Lumsden, chitecture matures, sets of nuclei and laminae derived from 1990, 1993; Figdor and Stern, 1993; Krumlauf et al., 1993; Puel- several neuromeres become connected by fiber tracts to les and Rubenstein, 1993; Wilson et al., 1993). form functional circuits. We show by immunostaining and During development, a percentageof cells born in the prolif- in situ hybridization techniques that, in the E3-E5 chicken erative (ventricular) zone of each neuromerebecome postmitotic embryo, the cell adhesion molecule R-cadherin is ex- and migrate as neuroblastsoutward into the mantle zone (Sauer, pressed in several stripes and patches in the forebrain neu- 1935; Fujita, 1964; Morest, 1970) in two or three sustained roepithelium.
    [Show full text]