Table Of ContentAtlas of Early Zebrafish
Brain Development
A Tool for Molecular Neurogenetics
Atlas of Early Zebrafish
Brain Development
A Tool for Molecular Neurogenetics
Thomas Mueller
Kansas State University
Manhattan, KS, United States of America
Mario F. Wullimann
Ludwig-Maximilians-Universität Munich
Munich, Germany
AMSTERDAM (cid:127) BOSTON (cid:127) HEIDELBERG (cid:127) LONDON
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ISBN: 978-0-12-418669-9
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Preface 2015
So, here we are again 10 years down the road. Meanwhile, the zebraf-
ish field has remarkably progressed. The first edition of our atlas promoted new
and effective ways of identifying expression patterns in the early zebrafish brain.
Clearly, standards for neuroanatomical studies in zebrafish have increased. For
example, there is a marked increase in zebrafish-related papers in the Journal of
Comparative Neurology if we compare the years prior to the publication of our atlas
(1994-2004) to the decade after its publication (2004-2014). A quick PubMed search
in these two decades reveals a doubling of hits, that is, 54 versus 118 papers. In
similar ways, we find a significant increase in the application of large-scale and
3D confocal imaging technique often using transgenic lines. Still, only precise
identification of zebrafish brain structures in a comparative context will allow
integration of data from the fields of molecular neuroanatomy, transcriptome, and
connectome studies.
To provide maximal consistency with the first edition, we kept the struc-
ture of Chapter 1 (historical account) and Chapter 2 (atlas). Notably, we added
a number of new plates of immunofluorescence microphotographs to illustrate
GABA cell development. In contrast, we greatly modified design and content of
Chapters 3 and 4. Chapter 3 now offers a more comprehensive analysis of the
development of all major transmitter phenotypes, and in particular glutamatergic
and GABAergic neurons. In addition, we describe critical modulatory transmitter
systems, such as the dopaminergic, noradrenergic, serotoninergic, histaminergic,
and cholinergic neurons. We also comment on glycinergic neurons, and we fo-
cus on the two regions with unusual nonperiventricular proliferation in the dien-
cephalon and the cerebellum. Finally, we compare various BrdU approaches and
discuss their usefulness for developmental fate studies.
Chapter 4 provides a broad comparative overview. It explains how
zebrafish data on neurogenesis are embedded in the vertebrate evo-devo context,
in particular in relation to data from the mouse and frog (Xenopus). This chapter
also contrasts conserved developmental processes in various vertebrate model
systems with ontogenetic peculiarities of zebrafish.
ix
Preface 2015
The second edition of the Atlas, thus, offers a more complete and balanced
view of neurogenetic events in the zebrafish brain. We also advance a comparative
evaluation of these events in the context of key model animals. We hope that this
second edition will again be well received in the zebrafish community.
Thomas Mueller
Mario F. Wullimann
Manhattan (Kansas, United States of America)
and Martinsried (Germany)—Spring 2015
x
Preface 2005
No one doubts that methodological revolutions shape the direction of
science. For instance, the invention of the microscope led almost directly to the
recognition of the cell as the basic module of all organisms. Equally decisive for the
scientific progress are ideas and concepts, which sometimes predate their confir-
mation by adequate methodology. These two closely intertwined processes shape
past and present scientific endeavors and are part of human culture created by the
efforts of people interconnected by a common interest in similar questions over
many decades. The admiration for methodological innovations and the respect for
scientific ideas or concepts both represent important foundations of science.
Therefore, the first chapter of this book puts into perspective historically
important contributions to the field of early vertebrate central nervous system
development. With this, we wish to clarify how the cellular–molecular data de-
livered in the second, main chapter relate to the larger neurobiological context of
neurogenesis in early brain development. The second chapter delivers the actual
atlas pages that the readership may use pragmatically to identify certain early
zebrafish brain areas. The third chapter takes up the dynamic aspects of how the
atlas may be used, be it to elucidate locally differing dynamics of proliferation,
determination, and differentiation of neural cells or to implement additional gene
expression data. Finally, the fourth chapter delivers a comparative perspective
of gene expression patterns between major model animals, especially between
mouse and zebrafish.
In addition to delivering a refined early neuroanatomy of the zebrafish
brain, the cellular and molecular genetic nature of the data presented in this book
allows a starting point for understanding the local differences in the distribution
of proliferative, early neuronally determined and differentiating cells and their
underlying neurogenetic pathways. The book also is intended to facilitate the use
of the zebrafish model animal in many future neurobiologically oriented investi-
gations in basic as well as biomedically relevant research projects.
xi
Acknowledgments
One of the pleasures of finishing a book is to acknowledge the colleagues
and friends who gave important feedback, supplied us with probes, and s upported
the project in various ways. Thanks go to Patrick Blader (Toulouse, France);
Uwe Strähle (Karlsruhe, Germany); Michael Lardelli (Adelaide, Australia); Eric
Weinberg (Philadelphia, PA, USA); and Rachel McDonald, Ingvild Mikkola, and
Steve Wilson (London, UK) for providing probes and antibodies. A big merci
goes to Philippe Vernier (Gif-sur-Yvette, France) for enabling us to embark on
this project in the first place. Thomas Mueller also thanks Wolfgang Driever
(University of Freiburg, Germany) for his support above and beyond what can
be expected. In addition, Thomas Mueller is grateful for the generous support
of Brian Spooner, Susan Brown, and Gary Conrad from the Division of Biology
at Kansas State University. Mario Wullimann thanks Benedikt Grothe (Ludwig-
Maximilians-Universität Munich, Germany) for continuing support. Last but not
least, this second edition would not have been possible without support and un-
derstanding of our families and friends. Thomas Mueller thanks Steffi Dippold;
without her presence, work on this book would not have been half as enjoyable.
xiii
Vertebrate Central Nervous System
Development
Chapter 1
Introduction
Atlas of Early Zebrafish Brain Development. http://dx.doi.org/10.1016/B978-0-12-418669-9.00001-5
© 2016 Elsevier B.V. All rights reserved.
1. Vertebrate Central Nervous System Development
1. Vertebrate Central Nervous System Development
1.1 Introductory Remarks: The Order of the Universe
The individual universe each human being mentally carries around is a
product of our brain, which most likely represents the most complex object in the
world. How does the brain come into existence during development? The ontog-
eny of the vertebrate central nervous system (CNS: brain and spinal cord) itself is
a highly complex yet strongly conserved morphogenetic process. The early ver-
tebrate embryo exhibits three embryonic cellular sheets called germ layers, the
most peripheral one being the ectoderm. Its dorsal portion represents the neuro-
ectoderm that develops into the prospective nervous system. The neuroectoderm
segregates early from the ventrolaterally lying general ectoderm, which forms the
future epidermal skin and its derivatives. Subsequently, the central main portion
of the neuroectoderm, the neural plate, is “swallowed” by the general ectoderm
through the process of neurulation. As a result, the neural plate separates from
the general ectoderm and descends into the deep of the embryo, where it devel-
ops into a hollow neural tube surrounding a cerebrospinal fluid- (liquor-) filled
ventricle. Meanwhile, the general ectoderm closes the temporarily opened dorsal
backside of the embryo. The apparent formation along the anteroposterior axis of
initially three brain vesicles (forebrain, midbrain, hindbrain) that transform sub-
sequently into five brain vesicles (telencephalon, diencephalon, mesencephalon,
metencephalon, myelencephalon) somewhat hides the parallel establishment of
finer transverse subdivisions called neuromeres (rhombomeres in the hindbrain,
prosomeres in the forebrain, see later). What follows is the differentiation of func-
tional subdivisions of the brain and spinal cord (for example, the optic tectum/
superior colliculus, a midbrain sensorimotor integration center, or the hypothala-
mus, the major control center of visceral processes).
These events of vertebrate CNS formation are accompanied by the em-
igration of the most lateral portions of the neuroectoderm, the neural folds
(Neuralwülste) and some directly adjacent neuroectodermal regions, which are
not incorporated into the neural tube during neurulation. These neuroectodermal
components comprise the neural crest of the head and trunk and the placodes that
are located in the head only. Eventually neural crest and placodes give rise to cells
that migrate to their final destination in the adult body, where they form almost all
sensory organs and the sensory neurons in dorsal root and cranial nerve ganglia,
3
1. Vertebrate Central Nervous System Development
which innervate them, and the visceral ganglia of the autonomic nervous system.
These somatic and visceral ganglia and their associated nerves represent the pe-
ripheral nervous system (PNS).
For many decades, scientists have investigated these complex develop-
mental events leading to the formation of a nervous system in various vertebrates,
especially in model animals, such as in the African clawed frog Xenopus, the chick,
rodents like the mouse and rat, and most recently, the zebrafish, at molecular, cel-
lular, histological, or morphological levels. Thus, a wealth of scientific literature is
available, ready to satisfy almost any hunger for information.
Why then the present book? First of all, it integrates knowledge on CNS
development coming from classical developmental studies with recent molec-
ular data related to neuro- and gliogenesis. In particular, we will demonstrate
the detailed spatiotemporal order of early postembryonic zebrafish brain de-
velopment using molecular and cellular markers of neuro- and gliogenesis to
visualize local differences, embedded in a holistic morphogenetic context. By
combining old and new knowledge, we provide a neuroanatomically based mo-
lecular atlas of neural development in the zebrafish brain. We hope that such
information—beyond delivering a refined molecular neuroanatomy—will prove
to be enlightening in the future elucidation of neurogenetic pathways and their
mechanisms.
1.2 Major Developmental Stages of the Vertebrate Neural Tube
Historically, scientists have always aimed to identify the fundamental
building blocks of the vertebrate brain. In other words, they have tried to de-
termine the basic developmental brain units and to answer the question of how
these transform into functional structures of the mature brain. Before going into
a more detailed discourse of the development of finer brain subdivisions (see
Section 1.3), we will shortly examine the early events of brain morphogenesis
relating to the emergence of vesicles and neuromeres, as well as of longitudinal
zones, followed by an account on the neuromeric (prosomeric) model and on
central nervous neurogenesis. An excellent in-depth historical account on the un-
derstanding of vertebrate brain morphogenesis has been given by Nieuwenhuys
(1998a,b,c).
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