Table Of ContentHorst Grunz (Ed.)
The Vertebrate Organizer
Springer-Verlag Berlin Heidelberg GmbH
Horst Grunz (Ed.)
The Vertebrate
Organizer
With 97 Figures, 23 in Color, and 20 Tables
Springer
Professor Dr. HORST GRUNZ
FB9 Department of Zoophysiology
University Duisburg-Essen
UniversWitsstraBe 5
45117 Essen
Germany
ISBN 978-3-642-05732-8
Library of Congress Cataloging-in-Publication Data
The vertebrate organizer I Horst Grunz (ed.).
p. cm.
Includes bibliographical references.
ISBN 978-3-642-05732-8 ISBN 978-3-662-10416-3 (eBook)
DOI 10.1007/978-3-662-10416-3
1. Vertebrates--Embryology. 2. Organizer (Embryology) I. Grunz, Horst, 1983-
QL959.V46 2003
571.8'616--dc22
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Originally published by Springer-Verlag Berlin Heidelberg New York in 2004
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Cover design: Design & Production, Heidelberg
Cover photographs: Whole mount in situ preparations of Xenopus embryos. Original data with
photos in color see contribution of Abraham Fainsod and Vered Levy (page 102)
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Preface
Springer-Verlag approached me about editing a book about the Spemann
Mangold Organizer, to be published as an issue of a series concerning phy
siology. I already had some experience as an editor together with Michael
Trendelenburg from the special issue, "Developmental Biology in Germany"
[Int. J. Dev. Biol. 40(1), 1996]. Primarily, I wondered if it was reasonable to
publish another book about the Spemann organizer so shortly after the
appearance of the special issue "Spemann-Mangold Organizer [Eds. Eddy
De Robertis and Juan Arechaga; Int. J. Dev. Biol. 40(1), 2000]. It could, how
ever, be argued that knowledge in this field is growing exponentially and that
a lot of new data are available.
Since homologous zones of the Spemann-Mangold Organizer have mean
while been identified in zebrafish, chicken and mice, we decided that the "Ver
tebrate Organizer" would be a better title for the book. I invited many col
leagues to participate as contributors. Since the response was very positive,
Springer has decided to publish the book as a separate volume.
Since the 1970s, a large increase in knowledge about the early development
of the vertebrate embryo has been observed, which has accelerated dra
matically in the last decade. The first embryonic-inducing factor isolated,
the vegetalizing factor, whose concentration dependently induces not only
mesodermal but also endodermal tissues, was shown to be a homologue of
activin A in 1990 (Grunz 1983; Green and Smith 1991). The mesoderm-induc
ing activity of the erythroid differentiation factor (identical to activin A) was
discovered in 1989. In 1987, after the vegetalizing factor was shown to bind to
heparin, the preferentially ventral-mesoderm-inducing activity of the hepar
in-binding growth factors (identical to fibroblast growth factors) was de
tected. The ventralizing activity of the bone morphogenetic proteins was dis
covered in amphibian embryos in 1991 and, in 1993, the nodal factor, belong
ing to the activin family, was discovered in chicken embryos. Nodal induces
also mesoderm and endoderm. All these factors belong to the TGF-~ super
family. Since then, a large number of secreted factors (Chordin, Noggin, Xlim,
Xvent, Cerberus, ADMP, DKK and others) as well as transcription factors
(VegT, Smad's, Fox's and others) have been detected; (see also De Robertis
and Wessely, this Vol.). Other approaches have used the isolation of tissues
as well as the transplantation of cells to elucidate the mechanism of embryonic
differentiation. The four animal cells isolated as a quartet from Xenopus eight
cell embryos, which include the future ectoderm and part of the mesoderm
but no endoderm, have the ability to develop into muscle and notochord but
not to endodermal tissues. After cortical rotation differentiation factors are
VI Preface
localized in the presumptive mesodermal (the so-called marginal zone) and
endodermal regions of amphibian embryos. This shows that the mesoderm is
determined very early and not induced by the endoderm. In early gastrulae
after midblastula transition an exchange of factors between endoderm and
mesoderm can occur. The same gene(s) can be expressed in adjacent parts
of the mesoderm and endoderm (different germ layers). During gastrulation
the definitive borders between endoderm and mesoderm are formed.
Dissociation of amphibian ectoderm followed by reaggregation leads to
neural differentiation (Grunz and Tacke 1989, 1990). Obviously, neural differ
entiation is inhibited in the intact ectoderm and occurs only when this inhibi
tion is released. BMP and Wnt proteins, which inhibit neuralization of the
ectoderm, can be bound by Cerberus, Dickkopf and probably other proteins
(reviews: Dev. Growth Differ. 43:469-502, 2001; Int. J. Dev. Biol. 45(1), 2001;
Int. J. Dev. Biol. 40(1), 1996; Naturwissenschaften 82:123-134, 1995; Blut
59:207-213, 1989).
Since the many genes and signaling pathways identified in vertebrates, in
cluding amphibians (mainly Xenopus), chicken and mice, show a high degree
of identity with corresponding human genes, these discoveries are of general
interest for both (molecular) biology and medicine. Since pluripotent cells
(i.e. ectodermal cells) are easily available in the amphibian embryo and
can be experimentally shifted into multiple pathways of differentiation,
they are well suited for the study of basic molecular processes of differentia
tion.
In the last 5 years (molecular) developmental biology has been established
as a core discipline of modern biology and medicine. From the 1950s until the
1970s, developmental biology (especially amphibian developmental biology
correlated with the organizer phenomena) was considered a dead-end science.
Nowadays, this research field has been restored to the main stream (see also
review Grunz: Developmental Biology of amphibians in Germany Int. J. Dev.
Biol. special issue: Spemann-Mangold organizer, 45:39-50).
Three main fields should mentioned:
1. Evolutionary developmental biology (EvoDevo)
2. Ecological developmental biology (EcoDevo)
3. Stem cell research and organ engineering
Using molecular genetic techniques, developmental biology could extend
our knowledge to research fields formerly studied by traditional techniques.
Comparative molecular studies of different species and even phyla have re
sulted in new insights into evolutionary conserved genes and mechanisms
of differentiation. Excellent examples are the urbilateralia concept and the
role of PAX genes in eye development in different species and phyla. Mean
while, the term evolutionary developmental biology (EvoDevo) is well estab
lished. There are many contributions in this volume which directly or indir
ectly address these topics.
Preface VII
Of central interest even in the popular media are the effects of chemical
substances including pesticides on human health. Since the recent German
Nitrofen scandal, this topic has been discussed among the general public
as if it were a new topic. It might be that many people have forgotten the
developmental human malformations caused by Contergan (Thalidomide)
in the 1960s, or they did not imagine that harmful drugs could be a part
of their daily food. Many people are discussing the possible risks of genetically
manipulated plants and animals, although the acceptance of molecular genet
ics in forensic medicine is meanwhile very broad. Although Nitrofen was also
found in chicken eggs, public knowledge about the correlation between sub
stances dispersed in the environment and negative influences on early em
bryonic development of most organisms is rather low. For a long time,
even ecologists ignored the crucial influence of natural and anthropogenic
environmental factors on early embryonic development of non-human spe
cies. In the meantime, this research field is defined as Ecological Developmen
tal Biology, even in textbooks (EcoDevo, first coined by Scott Gilbert), and
research activities in this area are likely to increase exponentially in impor
tance in the coming years. Contaminations of the environment by hormones
or hormone-like substances, factors interacting with receptors of the signaling
pathways or reagents directly interacting with the DNA and RNA, especially
during embryogenesis, are not only relevant for human fetal development, but
also for invertebrates and non-human vertebrates as an important link in the
food chain. Conversions of sex determination during embryonic and larval
stages have already been observed in alligator and polar bear populations.
For a better understanding of the risk of environmental factors on embryonic
development, we need basic information about gene regulation and the com
plex signaling pathways during normogenesis. The data presented in this
volume are fundamental to understanding environmental factors and pro
cesses involved in carcinogenesis and teratology.
Several chapters in this volume discuss the experimental programming of
pluripotent cells to initiate different pathways of differentiation. Our group
reported about organ (heart) rescue in amphibians 4 years ago (Grunz
1999), and Asashima's laboratory reported about culture and rescue experi
ments with kidney (see Chap. 15). Heart muscle with its typical honeycomb
like appearance, surrounded by an endothelial-lined pericardial cavity, can
also be induced by recombinant bFGF at high concentrations in Xenopus
ectoderm. Pluripotent cells from amphibians can be converted into derivatives
of all three germ layers using appropriate inducing factors (activin, FGF,
retinoic acid, etc.). These reports show that animal model systems can
give substantial answers to basic mechanistic questions concerning the deter
mination and differentiation of pluripotent cells from all species including
humans. Experimental model systems such as amphibians have the advantage
that they can deliver pluripotent cells in nearly unlimited amounts. The use of
human-derived stem cells only grown for basic research or human cloning
issues is highly debatable and creates many ethical concerns. Other procedures
VIII Preface
for the production of human stem cells for clinical use are available (reviewed
in Tiedemann, Asashima, Grunz, Knochel, Dev. Growth. Differ. 43:469-502,
2001).
Since Spemann and Hilde Mangold's famous organizer experiment in 1924,
enormous progress has been made in this research field, especially following
the introduction of molecular genetic techniques.
Totally new insights into mechanisms of evolution, analogy and homology
relationships, and in molecular ecological studies, stem cell research and
tissue/organ engineering restore developmental biology as a core discipline
of modern biology and medicine.
We are optimistic that this volume will stimulate further activities of new
young groups in this flourishing research field allover the world. We thank
Anette Lindqvist, Editorial Assistant, for her hard work and patience turning
24 manuscripts into a book.
Essen, September 2003 HORST GRUNZ
Contents
EARLY STEPS LEADING TO THE FORMATION OF THE ORGANIZER
1 Maternal VegT and ~-Catenin: Patterning the Xenopus Blastula.
Matthew Kofron, Jennifer Xanthos, and Janet Heasman
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1
1.2 Cell Fate Specification in the Animal-Vegetal Axis ......... " 1
1.2.1 Endodermal Transcription Factors Downstream of
VegT Have General and Specific Roles in Fate Specification . . .. 4
1.2.2 The Importance of Inductive Interactions in Mesoderm
and Endoderm Specification . . . . . . . . . . . . . . . . . . . . . . . . . .. 4
1.3 Patterning in the Dorso-Ventral Axis ................... " 5
1.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8
References ...................................... " 9
2 Short-Versus Long-Range Effects of Spemann's Organizer. . . .. 11
Ira 1. Blitz and Ken W. Y. Cho
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11
2.2 What Are the Organizer-Derived Dorsalizing Signal(s)? . . . . . .. 13
2.3 Are the Long-Range Effects of the Organizer Really Long Range? 15
2.3.1 The Heart Primordia and Anterior Somites Are Specified
by Short-Range Signaling During Gastrulation. . . . . . . . . . . . .. 16
2.3.2 Specification of the Pronephros Provides an Example
of a Secondary Induction Occurring During Late Gastrulation .. 17
2.3.3 Specification of Posterior Somites Provides an Example
of Late Short-Range Induction by Organizer-Derived Structures. 18
2.4 Concluding Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20
3 Formation of the Endoderm in Xenopus. . . . . . . . . . . . . . . . .. 25
Hugh R. Woodland and Debbie Clements
3.1 Intro duction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25
3.1.1 Concepts and Views of Patterning of the Embryo. . . . . . . . . . .. 25
3.2 Early Endoderm Formation in Xenopus. . . . . . . . . . . . . . . . . .. 27
3.2.1 Phases of Endoderm Formation. . . . . . . . . . . . . . . . . . . . . . . .. 27
3.2.2 The Initiation/Maternal Phase of VegT Action .. . . . . . . . . . . .. 29
3.2.3 The Establishment of the Endoderm . . . . . . . . . . . . . . . . . . . .. 29
3.2.4 Why Are There So Many Signalling Molecules Involved
in the Endoderm Community Effect? . . . . . . . . . . . . . . . . . . . .. 31
X Contents
3.2.5 The Role of VegT Targets in Endoderm Formation. . . . . . . . . .. 32
3.2.6 Delimitation of the Endodermal Domain. . . . . . . . . . . . . . . . .. 35
3.3 Patterning of the Endoderm . . . . . . . . . . . . . . . . . . . . . . . . . .. 35
3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 37
4 Role of Fox Genes During Xenopus Embryogenesis .......... 41
Hsiu-Ting Tseng, Isaac Brownell, Ryuju Hashimoto,
Heithem El-Hodiri, Olga Medina-Martinez, Rina Shah,
Carolyn Zilinski, and Milan Jamrich
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41
4.2 Expression of Fox Genes in the Mesoderm. . . . . . . . . . . . . . . .. 42
4.2.1 FoxA4 (XFKHl) .................................... 44
4.2.2 FoxC2 (XFKH7) ..................................... 44
4.2.3 FoxFl (XFD-13) .................................... 45
4.3 Expression of Fox Genes in the Ectoderm . . . . . . . . . . . . . . . .. 46
4.3.1 Neuroectoderm ..................................... 46
4.3.1.1 FoxGl (XFKH4/ XBF-l) ............................... 47
4.3.1.2 FoxB2 (XFD-S) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48
4.3.1.3 FoxD3 (XFD6/ XFKH6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48
4.3.2 Placodal Ectoderm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 49
4.3.2.1 FoxE4 (Xlensl) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 49
4.3.3 Epidermis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50
4.3.3.1 Fox!l (XFKHS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51
THE ROLE OF THE ORGANIZER
5 The Molecular Nature of Spemann's Organizer. . . . . . . . . . . .. 55
E. M. De Robertis and Oliver Wessely
5.1 Historical Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 55
5.2 The Spemann Organizer Transcription Factors. . . . . . . . . . . . .. 55
5.3 The Organizer Secreted Factors. . . . . . . . . . . . . . . . . . . . . . . .. 57
5.3.1 TGFp Superfamily Antagonists. . . . . . . . . . . . . . . . . . . . . . . . .. 58
5.3.1.1 The Chordin and Noggin BMP Antagonists ................. 58
5.3.1.2 Gremlin and Sclerostin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 58
5.3.1.3 Follistatin......................................... 59
5.3.1.4 Xnr-3............................................ 59
5.3.1.5 Lefty and Antivin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59
5.3.1.6 Cerberus......................................... 60
5.3.1.7 Secreted Wnt Inhibitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 61
5.4 Chordin and the Organizer . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63
5.5 The Chordin Co-factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 65
5.6 Neural Induction and the Spemann Organizer. . . . . . . . . . . . .. 66
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 68
