The Neural Crest and Neural Crest Cellsin Vertebrate Development and Evolution

Brian K. Hall

The Neural Crest and NeuralCrest Cells in VertebrateDevelopment and Evolution

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Brian K. HallDepartment of BiologyDalhousie UniversityHalifax, Nova ScotiaCanada B3H4J1bkh@dal.ca

and

Centre for Science and SocietySchool of Life SciencesArizona State UniversityTempe, Arizona85287-3301

ISBN 978-0-387-09845-6 e-ISBN 978-0-387-09846-3DOI 10.1007/978-0-387-09846-3

Library of Congress Control Number: 2008941099

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Preface

Knowledge of the development and evolution of the neural crest sheds light on manyof the oldest questions in developmental and evolutionary biology. What is the roleof germ layers in early embryogenesis? How does the nervous system develop? Howdoes the vertebrate head arise developmentally, and how did it arise evolutionarily?How did the vertebrate dorsal nervous system, heart, skeleton, teeth (and the neuralcrest itself) originate? How do growth factors and Hox genes direct cell differentia-tion and embryonic patterning? What goes wrong if development is misdirected bymutations, or if embryos are exposed to exogenous agents such as drugs, alcohol, orexcess vitamin A (retinoic acid)?

Twenty years ago, I was instrumental in organizing the publication of a facsimilereprint of the classic monograph by Sven Horstadius, The Neural Crest: Its prop-erties and derivatives in the light of experimental research, originally published in1950. Included with the reprint was an analysis of subsequent studies on the neuralcrest and its derivatives. A decade later, the first edition of this book was published(Hall, 1999a). The explosion of interest in and knowledge of the neural crest overthe past decade prompted me to write this second edition.

As in my 1988 overview of the reprinting of ‘Horstadius’—as his book is knownto many—and as in the first edition of this book, I take a broad approach in deal-ing with the discovery, embryological and evolutionary origins, migration, differ-entiation and cellular derivatives of the neural crest. Cells from the neural crestare associated with many developmental abnormalities, many of which have theirorigins in a defective neural crest (NC) or in defective neural crest cells (NCCs).The book would be incomplete without discussing neurocristopathies—those tu-mors and syndromes involving NCCs or those birth defects in which NCCs playa role.

The book is organized into three parts.Part I (Discovery and Origins) begins with a chapter devoted to the discovery

of the neural crest and the impact of that discovery on entrenched notions of germ-layer specificity and the germ-layer theory, a theory that placed a straitjacket aroundembryology and evolution for almost a century. Primary and secondary neurulationand the neural crest as the fourth germ layer are introduced in this chapter.

In Chapter 2, I discuss the embryological origins of the neural crest, includingthe identification of future NCCs in gastrula-stage embryos; molecular and cellular

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markers of future NCCs; neural and neural crest induction; and rostrocaudal pat-terning of the developing neural tube and neural crest.

Chapter 3 takes NCCs out of the neural tube with discussions of:

• the delamination of NCCs from the neural tube as mesenchymal cells (a processrequiring the transformation of epithelial to mesenchymal cells, usually writtenin the text as EMT or epithelial —> mesenchymal transformation),

• NCC migration and the nature of the extracellular matrices (ECM) throughwhich or along which they migrate, and

• the differentiative potential of NCCs.

Chapter 4 is devoted to the evolutionary origins of the neural crest through ananalysis of fossils and of cell types, genes, and gene networks in extant cephalo-chordates (amphioxus) and in urochordates (chiefly ascidians) in an effort to answerthe question ‘Is there any evidence of precursors of the neural crest in urochordatesor in cephalochordates?’ The second aim of Chapter 4 is to examine the origin ofneural and skeletal tissues of neural crest origin in the first vertebrates (i.e., chor-dates with a head), and the origin of the jaws in the transition from jawless to jawedvertebrates.

Part II (Neural-Crest Derivatives) presents an analysis of our knowledge of thecell types into which NCCs differentiate. The organization of this part differs fromthe first edition in which the chapters were organized by major groups of vertebrates,each of which included a discussion of similar cell types—neural, pigment, andskeletal cells. In this edition, I have organized each of the four chapters around majorclass of cells and the tissues and organs they form or to which they contribute:

• pigment cells and color patterns (Chapter 5);• neurons and the nervous system (Chapter 6);• cartilage, bone, and skeletal systems (Chapter 7); and• dentine-forming cells and teeth, and the smooth muscle, septa and valves of the

heart (Chapter 8).

These chapters cover:

• trunk neural crest cells (TNCCs)—Chapter 5;• the vagal and sacral neural crest (VNC, SNC), peripheral nervous system

(spinal and cranial ganglia), autonomic and parasympathetic nervous systems(sympathetic and parasympathetic ganglia, enteric ganglia, adrenal chromaffincells), Schwann and glial cells, and Rohon–Beard neurons—Chapter 6;

• cranial neural crest cells (CNCC), chondroblasts and osteoblasts, mesenchyme,the skeletogenic (chondrogenic) neural crest, and epithelial–mesenchymalinteractions—Chapter 7;

• the odontogenic neural crest, odontoblasts (dentine-forming cells), tooth for-mation, and the cardiac neural crest (CarNC), the heart, and development ofvalves, septa and the aortic arches—Chapter 8.

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Part III consists of two chapters, Chapter 9 devoted to tumors of neural-crestorigin (neurocristopathies), Chapter 10 to a reconsideration of NCC development inthe context of birth defects.

Chapter 9 includes discussions of neuroblastomas, neoplasia, and examples ofsyndromes based in defective NC or NCCs, the two major examples being APUDo-mas and DiGeorge syndrome.

Chapter 10 broadens the scope to birth defects (often but not always involvingthe neural tube to which NCCs contribute) or which are induced by a teratogen—vitamin A and craniofacial defects in this case. Mutations affecting NCCs are dis-cussed as is the ability of NCCs to compensate for lost cells, a developmental prop-erty known as regulation and a discussion that brings us full circle to the differingpotentials of subpopulations of NCCs and whether any NCCs persist as stem cellsin embryos or adults.

To avoid interrupting the flow of the text, I have placed most references andsome supporting statements in numbered notes, which are gathered at the end ofeach chapter, and which serve as an annotated bibliography through which accessto the literature may be obtained. I have not included all of the literature publishedbefore 1999, much of which is in the first edition (Hall, 1999a∗). Otherwise, I havesurveyed the literature to early 2008. References marked with an ∗ are significantreviews or analyses. Occasionally, I use footnotes (⊗) for general points that applythroughout. Similarly, boxes are used for items of general interest, biographies, orinteresting case studies. *signifies an extinct taxon. Gene names are italicized andcapitalized (Shh), proteins are in plain text and capitalized (Shh). Human genes andproteins are capitalized (SHH, SHH). As a shorthand expression for a transformationor interaction I use the symbol —>. The text is extensively illustrated and there is adetailed index. A list of abbreviations is provided. From that list, the following areabbreviations for regions of the neural crest (NC) or for populations of neural crestcells (NCCs).

NC NCCsCarNC — cardiac neural crest CarNCCs — cardiac neural crest cellsCNC — cranial neural crest CNCCs — cranial neural crest cellsNC — neural crest NCCs — neural crest cellsSNC — sacral neural crest SNCCs — sacral neural crest cellsTNC — trunk neural crest TNCCs — trunk neural crest cellsVN — vagal neural crest VNCCs — vagal neural crest cells

I am grateful to the following experts who provided invaluable comment on in-dividual chapters—chapter reviewed are shown in parenthesis—Marianne Bronner-Fraser (2), Carol Erickson (3), Daniel Meulemans (4), Lennart Olsson (5), RyanKerney (7), and Gerhard Schlosser (6, Part). Ryan Kerney and Jennifer Quinn pro-vided helpful comments on stem cells, Cory Bishop comments on ascidians. TimFedak prepared 20 of the new figures. Many thanks, Tim. June Hall edited the

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manuscript for style and comprehensibility in her inimitable way. Many thanks,June. Individuals who provided figures are acknowledged in the appropriate figurelegend. Figure 7.10 is modified from Del Pino and Medina (1998), published byUBC Press, Leioa, Vizcaya, Spain. Financial support for my research program onthe neural crest and its derivatives from the Natural Sciences and Engineering Re-search Council (NSERC) of Canada is gratefully acknowledged.

Halifax and Tempe Brian K. Hall

Contents

Part I Discovery and Origins

1 Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Zwischenstrang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5A Brief Overview of the Past 120 Years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1890–1950s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61960s–1970s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91980s to the 21st Century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Neural Crest and Germ-Layer Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Germ-Layer Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Multiple Tissues from Single Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Heads and Tails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Secondary Neurulation and Tail Buds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Induction of Tail Buds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Neural Crest as the Fourth Germ Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Neural Crest as Inhibitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2 Embryological Origins and the Identification of Neural Crest Cells . . 23Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Before Neurulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Establishing the Epidermal–Neural Border . . . . . . . . . . . . . . . . . . . . . . . . . . 25NCC Markers and Specification of the NC . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

HNK-1 and Pax7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Snail-2, Bmp4, and Cadherins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Sox Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Wnt genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Specification of Ectoderm as Neural or Epidermal . . . . . . . . . . . . . . . . . . . . 38NC Induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Bmps, Wnts, and Fgfs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Xenopus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

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Chicken Embryos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42A Role for Notch in NCC Induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42A Role for Bmps in NCC Induction and Beyond . . . . . . . . . . . . . . . . . . . 46Zic3 and Zic5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Msx Genes and Specification of NCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Establishing Cranial and Trunk Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . 51Chicken Embryos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Mouse Embryos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Ectoderm from the Most Rostral Neural Tube . . . . . . . . . . . . . . . . . . . . . . . . 53Rostrocaudal Patterning of CNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Hox Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54A Role for Mesoderm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56The Midbrain–Hindbrain Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Dlx Genes and Dorsoventral Patterning of CNC . . . . . . . . . . . . . . . . . . . 58

Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3 Delamination, Migration, and Potential . . . . . . . . . . . . . . . . . . . . . . . . . . 63Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Cellular Changes Driving Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . 66Cadherins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Extracellular Spaces and Delamination . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71Pathways of CNCC Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71Pathways of TNCC Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Migration into Dorsal Fins and Tails . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Molecular Control of NCC Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78Extracellular Matrices, Cell Surface Ligands, and Receptors . . . . . . . . 78

Permitting Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Fibronectin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Proteoglycan Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81Neural Crest Cells Contribute to Extracellular Matrices

to Permit Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Thrombospondins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Tyrosine Kinases Receptors (Trk) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Ephrins and Eph Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Inhibiting Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Components of ECMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Guiding Migrating NCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Barriers and Components of ECMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85The Environment at the Final Destination . . . . . . . . . . . . . . . . . . . . . . . . 86Endothelins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Semaphorins, Delamination, and Migration . . . . . . . . . . . . . . . . . . . . . . . 90

Subpopulations of NCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92Restricted Premigratory and Early Migrating Populations

of TNCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

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Restriction During Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97Restriction Along the Neural Axis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Differentiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99Differentiation of Bipotential Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

A Role for Growth Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110Dedifferentiate and Redifferentiate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

4 Evolutionary Origins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Precursors of the Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118Cephalochordates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122Genes and Gene Networks in Cephalochordates . . . . . . . . . . . . . . . . . . . . . . 125AmphiSnail1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Hox genes: AmphiHox1–AmphiHox12 . . . . . . . . . . . . . . . . . . . . . . . . . . . 127AmphiDll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128AmphiOtx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129AmphiBmp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130AmphiPax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

Retinoic Acid and Retinoic Acid Receptors . . . . . . . . . . . . . . . . . . . . . . . 131Urochordates–Ascidians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Nervous System and Notochord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135Pigment Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Calcitonin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Bipotentiality and Conditional Specification . . . . . . . . . . . . . . . . . . . . . . . . . 137Genetic Control of Ascidian Neural Development . . . . . . . . . . . . . . . . . . . . . 137

Bmps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Snail and Hnf3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Pax Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Fossil Chordates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

Burgess Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139Chengjiang Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

The First Vertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141The Pharyngeal Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141The Origin of Cartilage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

Comparative Genomics and Bioinformatics . . . . . . . . . . . . . . . . . . . . . . . . . . 146Molecular Fingerprinting: Genetic Labeling/Selection and GeneChip

Microarray Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149Jawless Vertebrates and the Origin of Jaws . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Jaws from Gill Arches? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Part II Neural-Crest Derivatives

5 Pigment Cells (Chromatophores) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Types of Chromatophores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

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Melanosomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162Lampreys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Urodele and Anuran Amphibians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Patterns of Pigmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164Larval-to-Adult Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Teleost Fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167Migration and Cell Fate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Larval Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169Genes and Cell Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

Birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172Patterning Feather Tracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Non-Avian Reptiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Mammals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Pattern Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Neurocristopathies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

6 Neuronal Cells and Nervous Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179The Neural Crest, Neurons, and Nervous Systems . . . . . . . . . . . . . . . . . . . . 180The Peripheral Nervous System–Spinal and Cranial Ganglia . . . . . . . . . . . . 181Placodal Ectoderm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Placodal Markers and Specification of Placodal Ectoderm . . . . . . . . . . 189The Panplacodal Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191Induction of Individual Placodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

The Autonomic Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193Schwann Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Glial Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Vagal and Sacral Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197Rohon–Beard Neurons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Apoptosis Removes R–B Neurons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198Neural Crest Origin and Relationships to Other Neurons . . . . . . . . . . . . 198Genetic Control of R–B Neurons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

7 Cartilage Cells and Skeletal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203Pharyngeal Skeletons of Hagfish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205Pharyngeal Skeletons of Lamprey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

Cartilages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208Vitamin A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

Amphibian Craniofacial Skeletons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213Extirpating and Transplanting Amphibian Neural Crest . . . . . . . . . . . . . 214Epithelial–Mesenchymal Interaction Required to Initiate

Chondrogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217Cascades of Interactions in Amphibian Craniofacial Development . . . . 218Labeling Amphibian CNCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221Timing of Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

Contents xiii

Mapping CNCCs in Fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227Elasmobranchs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227Teleosts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

Zebrafish Mutants and Pharyngeal Arch Development . . . . . . . . . . . . . . . . . 228Distalless (Dlx) and the First and Second Pharyngeal Arches . . . . . . . . 228Chameleon (Con) and the Caudal Pharyngeal Arches . . . . . . . . . . . . . . 229Chinless (Chn) and the Absence of NCC from all Pharyngeal Arches . 229Ninja and the Growth of Pharyngeal Arch Cartilages . . . . . . . . . . . . . . . 229

Skeletogenic NCCs in Reptiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230CNCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230TNCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

Avian CNCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2313H-thymidine Labeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231Quail/Chicken Chimeras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232The Chondrogenic CNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Cell Lineages in CNCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233CNCCs and Muscle Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

Mapping the Mouse CNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

8 Teeth and Hearts: The Odontogenic and Cardiac Neural Crests . . . . 247Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

The Odontogenic Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Teeth but not Cartilage from Trunk NCCs . . . . . . . . . . . . . . . . . . . . . . . . 250Cartilage from TNCCs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252Origination of Dentine and Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

Hearts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Indirect Effects of Cranial NCCs on Heart Function . . . . . . . . . . . . . . . . 256Direct Effects of Cranial NCCs on Heart Function . . . . . . . . . . . . . . . . . 256The Avian Cardiac Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257Cardiac Cartilages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Cardiac Neural Crest in Fish and Amphibians . . . . . . . . . . . . . . . . . . . . . 261Cardiac Neural Crest in Mammals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261Cardiac Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

Part III Abnormal Development and the Neural Crest

9 Neurocristopathies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269Antiquity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269Syndromology and Neural Tube Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269The Utility of the Germ-Layer Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271Types of Neurocristopathies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273CHARGE Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276

xiv Contents

PAX6 and CHD7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276Neuroblastomas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

The Neoplastic State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279RaLP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279Model Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

von Recklinghausen Neurofibromatosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280Involvement of Non-Neural-Crest Cells . . . . . . . . . . . . . . . . . . . . . . . . . . 282John Merrick–the ‘Elephant Man’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282Animal Models and Mutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

APUDomas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284Hirschsprung Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286DiGeorge Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289Genes Involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

10 NCC Development Revisited in the Context of Birth Defects . . . . . . . . 295Susceptible Stages of Neural Crest Development . . . . . . . . . . . . . . . . . . . . . 298

Defective Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299Defective Proliferation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300Enhanced Cell Death . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300Defective Induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

Vitamin A, Craniofacial Defects, and the Neural Crest . . . . . . . . . . . . . . . . . 302Direct Action In Vivo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302Craniofacial Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305Mechanisms of Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308Indirect Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309Evolutionary Origins of Sensitivity to Retinoic Acid . . . . . . . . . . . . . . . 309

Defects Following Disruption of the Hox Code . . . . . . . . . . . . . . . . . . . . . . . 310Hoxa1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310Hoxa2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311Hoxa1, Hoxa2, and Hoxb1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311Mutations and Birth Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312Looptail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312Splotch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

Sources of Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316Completeness of Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316Pharyngeal-Arch Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Dorsal Root Ganglion Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Regulation of Cardiac Neural Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319Placodal Regulation from the Cardiac Neural Crest? . . . . . . . . . . . . . . . 320

Neural Crest Cells as Stem Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321Bi-, Tri-, and Multipotential NCCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

Contents xv

What is a Stem Cell? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322NCCs as Stem Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

Common Names of Species Discussed . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

Species (with Common Names) Arranged by Major Groups . . . . . . . . 333

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

Abbreviations

AAdam13 a member of the Adam family of membrane-anchoring

metalloprotease (named from a disintegrin andmetalloprotease domain)

Amphi prefix for genes in amphioxus (Branchiostoma spp.), forexample, AmphiOtx

APUDomas tumors that share amine precursor uptake and decarboxylation

BBALB/c an inbred strain of mice that develops numerous tumors in later

lifeBdnf brain-derived neurotrophic factorbHLH basic helix–loop–helix transcription factorsBmp bone morphogenetic protein family of genes and their productBmpR bone morphogenetic protein receptor, for example, BmpR1

CCarNC cardiac neural crestCarNCCs cardiac neural crest cellsCbfa1 Core binding factor alpha 1; see Runx2Cdh Cadherin, a family of 20 Ca++-binding transmembrane

proteins that function in cell adhesionch congenital hydrocephalus mutant miceCHD7 chromodomain helicase DNA binding protein 7Chn Chinless mutant zebrafishCi prefix for genes in the sea vase, Ciona intestinalis (an ascidian)cls colorless mutant in zebrafishCNC cranial neural crestCNCCs cranial neural crest cellsCNS central nervous system of vertebratesCol2α1 the gene for the procollagen type II alpha 1 chain.Con Chameleon mutant zebrafishCraBP cellular retinoic acid binding proteinCRKL v-crk sarcoma virus CT10 oncogene homolog [avian]-like

xvii

xviii Abbreviations

DDiI 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl indocarbocyanine

perchlorateDil the dilute (dil) allele in the budgerigar, a mutation in

melanocytesDisp1 the protein dispatched (DISP1), a regulator of ShhDll a family of genes Delta proteins, which are type-1 cytokine

receptor family proteinDlx distalless gene family in vertebrates, for example,

Dlx1DOPA 3, 4-dihydroxyphenylalanine, a catecholamine precursorDRG dorsal root gangliaDsh Disheveled gene and protein productD–V dorsoventral axis/polarity of embryonic regions/organ

rudiments (e.g., pharyngeal arches, limb bud), organs (e.g.,limbs) or organism. Sometimes referred to in the literatureas medio-lateral or proximo-distal polarity.

EECM extracellular matrixEDAR Ectodysplasin 1, anhidrotic receptorEdn3 endothelin-3, a mitogenic peptideEgf epithelial growth factor genes and their proteinseIF-4AIII Eukaryotic translation initiation factor 4AIIIEMT epithelial-mesenchymal transformation (sometimes shown as

epithelial —> mesenchymal transformation)En Engrailed gene family, for example, En1EphA, EphB eph receptor tyrosine kinases A and B, members of large

subfamilies of receptor protein-tyrosine kinases consists ofreceptors related to Eph, a receptor expressed in anerythropoietin-producing human hepatocellular carcinomacell line.

FFar First- arch murine craniofacial mutationFgf fibroblast growth factor gene and protein familyFox forkhead transcription factor binding elementFrzb Frizzled-related protein precursor, a secreted antagonist of

Wnt signalingFUDR 5-fluoro-2′-deoxyuridine (blocks DNA synthesis)

GGdnf glial-cell-line-derived neurotrophic factorGFP green fluorescent proteinGnRH neurons gonadotropin-releasing hormone (GnRH) neurons; see also

LhRH neurons

Abbreviations xix

HHh Hedgehog gene family, for example, Sonic hedgehog (Shh)H.H. Hamilton–Hamburger stage of chick embryonic developmentHMG high-mobility group proteinsHnf3ß hepatocyte nuclear factor3ßHNK-1 a cell surface carbohydrate (known as CD-57 in immunology)

used as a marker for NCCsHox homeotic gene classes in vertebrate, for example, Hoxd10Hr prefix for genes in the western northern Pacific ascidian

Halocynthia roretzi

IIgf insulin-like growth factor genes and productsInsm1 insulinoma-associated 1 gene

JJag1 gene for the transmembrane protein Jagged1, which functions

via the Notch pathway

KkDa kilo daltonsKrox20 a gene encoding a zinc-finger transcription factor

LLa-N-5 human neuroblastoma cell lineLhRH neurons luteinizing hormone releasing neurons; see also GnRH neuronsLp the Loop-tail mutant mouse, in which hindbrain and spinal

cord fail to close and so NCCs fail to migrateLRD lysinated rhodamine dextran

MMAPK ras/mitogen-activated protein kinase, a signaling pathway

involved in the phosphorylation of target molecules such astranscription factors and other kinases in cell membrane,cytoplasm, and nucleus

Mash1 Mouse achaete-scute homologue 1 geneMdkb midkine-b (a heparin-binding growth factor)MEN1 Multiple endocrine neoplasia type 1 in humans—characterized

by endocrine neoplasia of the parathyroids, pituitary, andpancreas

MIF Macrophage inhibitory factorMitf microphthalmia-associated transcription factorMmp matrix metalloprotease familyMsh melanocyte stimulating hormoneMsx homeobox genes (e.g., Msx1, Msx2) of vertebrates of the

Drosophila msh (melanocyte-stimulating hormone) familyMTN Mesencephalic Trigeminal NucleusM.W. molecular weight

xx Abbreviations

NNC neural crestN-CAM neural cell adhesion moleculeNCCs neural crest cellsNF1 the neurofibromin1 gene responsible for von Recklinghausen

neurofibromatosis (type 1 neurofibromatosis)NF1 von Recklinghausen neurofibromatosis (type 1

neurofibromatosis)NF2 bilateral acoustic neurofibromatosisNgf nerve growth factor family of genes and their productsNkx family of transcription factors that function downstream of ShhNof No-fin mutant in zebrafish, which lacks pectoral fins and gill

cartilagesNrp1, Nrp2 neuropilin1, neuropilin2 (co-receptors for semaphorins)Nt3 neurotrophin3, a nerve growth factor

OOca2 oculocutaneous albinism2 geneOsf2 osteoblast-stimulating factor2; see Runx2Otx orthodenticle family of genes in vertebrates, for example, Otx1

Pp27 cell cycle inhibitorPax a family of nine mammalian genes containing a paired-type

homeodomain as a DNA-binding motif; for example, Pax1,Pax9

P–D proximo-distal axis/polarity of embryonic regions/organrudiments (e.g., pharyngeal arches, limb bud), organs (e.g.,limbs) or organism

Pdgf platelet-derived growth factor genes and gene productsPdgfR platelet-derived growth factor receptor genes and gene

productsPitx2 Pituitary homeobox gene-2 in mouse related to bicoid in

Drosophila. Also known as Ptx.PNA peanut agglutinin lectinPRE pigmented retinal epitheliumPtch Patched, a binding protein for hedgehog gene productsPTEN tumour-suppressor gene, phosphatase and tensin

homologuePtx see Pitx

QQCPN quail non-chicken perinuclear antigen

Rr rhombomeres, a segment of the hindbrain in vertebratesRA retinoic acid, a biologically active form of vitamin A

Abbreviations xxi

Raldh2 a gene for retinaldehyde dehydrogenase, required for synthesisof retinoic acid

RaLP a member of the Src family of tyrosine kinase substratesR–B neurons Rohon–Beard neuronsRhob a low-molecular-weight GTPase in the Ras protein familyRTK receptor tyrosine kinaseRunx2 runt-related transcriptional factor-2; older names are cbfa-1

and osf2

SSEM scanning electron microscopyShh Sonic hedgehog geneSix2 sine oculis-related homeobox 2Snail1, 2 zinc-finger transcription factor-encoding genes, orthologues of

Drosophila Snail homologue 1 and Snail homologueSNC sacral neural crestSNCCs sacral neural crest cellssof short fin, a zebrafish mutantSox multigene families that encode transcription factors with

high-mobility group DNA-binding domains, the acronymcoming from coming from sex-determining regionhomeobox

S phase the phase of cell division during which DNA issynthesized

Suc the gene sucker in zebrafish, Danio rerio, which disruptsEndothelin-1. Also known as endothelin-1 (edn1)

TT-box a family of genes encoding transcription factors, for example,

Brachyury, Tbx1, Tbx5Tbx, a class of genes within the T-box family of transcription

factors, for example, Tbx6Tcf/Lef T-cell specific/lymphoid enhancer binding factor (transcription

factors)TCOF1 Treacher-Collins Franceschetti syndrome 1 gene coding for

nucleolar phosphoprotein TreacleTEM transmission electron microscopyTgfß transforming growth factor beta genes and their productsTgfßR transforming growth factor beta receptorsTimp tissue inhibitor of metalloproteaseTNC trunk neural crestTNCCs trunk neural crest cellsTrk a family of tyrosine kinases receptors for neurotropinsTsp thrombospondins (family of five glycoproteins involved in cell

migration and proliferation)

xxii Abbreviations

VVegf vascular endothelial growth factor gene and proteinVER ventral ectodermal (epithelial) ridge on developing tail budsVgr1 older name for Bmp6VMA vanillinemandelic acid (4-hydroxy-3-methoxymandelic acid, a

metabolite of catecholaminev-myc a proto-oncogene from retrovirus-associated DNA sequences

originally isolated from an avian myelocytomatosis virusVNC vagal neural crestVNCCs vagal neural crest cellsVNT ventral neural tubevt the vestigial tail tailless mouse mutant

WWnt a large gene family orthologous to wingless in Drosophila that

produce secreted molecules involved in intercellularsignaling. Wnt is a combination of Drosophila wingless andint1 for Wnt1, the first vertebrate (mouse) family memberdiscovered