Developmental Biology 11th Edition

Book Preface

From Scott Gilbert

A BIOLOGIST, A PHILOSOPHER, AND A THEOLOGIAN WALK INTO A BAR. Yes, it actually happened, in the chill of a winter night in Finland! A group of enthusiastic people listened as the moderator asked what each of them considered to be the most important story people need to know. The Christian theologian said that the most important story was salvation through God’s grace. The analytic philosopher disagreed, saying that the most important story for mankind was that of the Enlightenment. The developmental biologist knew that he was supposed to say “evolution.” But evolution is the consequence of another, more fundamental story. So the biologist claimed that most inspiring and meaningful story was how the embryo constructs itself. You pass from unformed zygote to the adult organism with its heart, brain, limbs, and gut all properly differentiated and organized. It is a story of how newness is created, how one keeps one’s identity while building oneself, and how global forces and local forces work together to generate a functional entity. This is the story we tell in this book. In the Ninth and Tenth editions of Developmental Biology, we speculated that the study of animal development was undergoing metamorphosis. The field has not reached the climax phaseyet, but certain differences between the previous edition and one in your hands (or on your screen) are definitely apparent. The first can be seen on the cover. Developmental biology has been charged with a huge undertaking—nothing less than discovering the anatomical and genetic bases of neural organization and behaviors. This task was part of developmental biology when it was reformulated in the early 1900s (especially by the American C. O. Whitman), but it had dropped out of the portfolio as being “too complicated” and not amenable for study. Today, however, developmental neurobiology is an increasingly large part of developmental biology. Among many other things, developmental biology is becoming necessary for cognitive science.

The second difference between this and previous editions is the prominence of stem cells. From being a small area of developmental biology, stem cell research has grown so fast as to have its own scientific societies. Not only do stem cells provide explanations for organ development, they also hold the tantalizing possibility of organ regeneration. Recent work, detailed in this book, shows how knowledge of developmental biology has been critical in turning adult cells into stem cells that can functionally replace missing and damaged tissue in laboratory animals. A third difference is the incredible revolution in lineage studies made possible by in vivo labeling. We can look at each cell developing in an early, living, embryo and discern which adult cells are its descendants. The techniques of computerenhanced visualization have given scientists amazing new technologies to see embryonic development.

A fourth difference is the idea that animal development, even that of mammals, is significantly influenced by the environment. The data that have accumulated for developmental plasticity and the roles of microbes in normal development have increased remarkably over the past several years. Finally, a fifth difference concerns the way science is taught. The “sage on the stage” model, where lectures generate the flow of information down a gradient from higher concentration to lower, has been supplemented by the “guide on the side.” Here, the professor becomes a facilitator or capacitator of discussion while the students are encouraged to discover the information for themselves.

Indeed, education is sometimes referred to as “development,” and there are many similarities between education and embryology. The two fields have exchanged metaphors constantly for the past two centuries, and two German words that have been used for both development and education—Bildung and Entwicklung—connote education by experience and education by instruction, respectively. Both work in different situations. So in this edition of Developmental Biology, we havetried to facilitate those professors who wish to experiment with different teaching methods. As in embryology, we don’t expect one method to be best for all occasions.

To all these ends, this book has metamorphosed to embrace a co-author. Michael J. F. Barresi is expert in all these areas of stem cells, developmental neurobiology, and new techniques of learning and teaching. It’s been 30 years since the first edition of this book was published, and I wanted a young professor to reconfigure this book into a learning tool that a new generation of teachers could use to inspire a new generation of students. Enter Michael. Michael did not want just cosmetic changes in the book. He proposed a radical re-envisioning of its mission: to educate students to appreciate and participate in developmental biology. Michael convinced us that we needed to rearrange the order of the chapters, add some chapters and shorten others, alter the ways that the material is presented within the chapters, and give all chapters more supplemental material for “flipped” classes, case studies, and other means of learning. The extra thought and effort that went into incorporating Michael’s new approaches have clearly been worth it.

One other thing that has changed in the past decade is the realization of how much our understanding of biology depends on our knowledge of development. If “nothing in biology makes sense except in the light of evolution,” we now find that “nothing in morphological evolution makes sense without knowledge of development.” Changes in adult anatomy and physiology are predicated on changes in morphogenesis and differentiation during development.

This is also true of the history of biology, where developmental biology can be seen to play the unique role of “the stem cell of biological disciplines,” constantly regenerating its own identity while simultaneously producing lineages that can differentiate in new directions. As Fred Churchill noted, cell biology “derived from descriptive embryology.” The founders of cell biology were each trying to explain development, and their new conception of the cell helped them do it. The original theories of evolution concerned themselves with how new variants arose from the altered development of ancestors. Charles Darwin’s friend and champion Thomas Huxley, expanded on this idea, which would eventually flourish into the field of evolutionary developmental biology.

Also during this Victorian age, a variant of developmental biology grew to become the field of immunology. Elie Metchnikoff (who showed the pole cells of flies to be germ cell precursors and who studied gastrulation throughout the animal kingdom) proposed a new cell theory of immunology in his attempt to find universal characters of the embryonic and larval mesoderm. Similarly, but with more anguish, genetics directly descended from a generation of embryologists who dealt with whether the nucleus or cytoplasm contained the determinants of embryonic development. Before his association with Drosophila, Thomas Hunt Morgan was a well-known embryologist who worked on sea urchin embryos, wrote a textbook on frog development, and was an authority on regeneration. Many of the first geneticists were originally embryologists, and it was only in the 1920s that Morgan formally separated the two fields. And regeneration is still intimately linked with development, for regeneration often is a recapitulation of embryonic processes. Ross Granville Harrison and Santiago Ramon y Cajal founded the science of neurobiology by showing how the brain and axons develop. To this day, neurology requires an understanding of the developmental origins of the central and peripheral nervous systems.

Brief Contents
I Patterns and Processes of Becoming: A Framework for Understanding Animal Development
Chap ter 1  Making New Bodies: Mechanisms of Developmental Organization 1
Chap ter 2  Specifying Identity: Mechanisms of Developmental Patterning 29
Chap ter 3  Differential Gene Expression: Mechanisms of Cell Differentiation 45
Chap ter 4  Cell-to-Cell Communication: Mechanisms of Morphogenesis 95
Chap ter 5  Stem Cells: Their Potential and Their Niches 143
II Gametogenesis and Fertilization: The Circle of Sex
Chap ter 6  Sex Determination and Gametogenesis 181
Chap ter 7  Fertilization: Beginning a New Organism 217
III Early Development: Cleavage, Gastrulation, and Axis Formation
Chap ter 8  Rapid Specification in Snails and Nematodes 251
Chap ter 9  The Genetics of Axis Specification in Drosophila 277
Chap ter 10  Sea Urchins and Tunicates: Deuterostome Invertebrates 311
Chap ter 11  Amphibians and Fish 333
Chap ter 12  Birds and Mammals 379
IV Building with Ectoderm: The Vertebrate Nervous System and Epidermis
Chap ter 13  Neural Tube Formation and Patterning 413
Chap ter 14  Brain Growth 439
Chap ter 15  Neural Crest Cells and Axonal Specificity 463
Chap ter 16  Ectodermal Placodes and the Epidermis 517
V Building with Mesoderm and Endoderm: Organogenesis
Chap ter 17  Paraxial Mesoderm: The Somites and Their Derivatives 539
Chap ter 18  Intermediate and Lateral Plate Mesoderm: Heart, Blood, and Kidneys 581
Chap ter 19  Development of the Tetrapod Limb 613
Chap ter 20  The Endoderm: Tubes and Organs for Digestion and Respiration 653
VI Postembryonic Development
Chap ter 21  Metamorphosis: The Hormonal Reactivation of Development 671
Chap ter 22  Regeneration 693
Chap ter 23  Aging and Senescence 723
VII Development in Wider Contexts
Chap ter 24  Development in Health and Disease: Birth Defects, Endocrine Disruptors, and Cancer 735
Chap ter 25  Development and the Environment: Biotic, Abiotic, and Symbiotic Regulation of Development 763
Chap ter 26  Development and Evolution: Developmental Mechanisms of Evolutionary Change 785