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Although it is the defining organ of the Chordata, the notochord and its cells are one of the least understood vertebrate organs. This may be because large parts of the notochord are often replaced with cartilaginous or bony vertebral bodies. The presence of cartilage in the notochord raises questions about the evolutionary relationships between notochord cells and cartilage cells. This book integrates classical analytical studies with recent palaeontological, experimental, and molecular studies in both developmental and evolutionary contexts. For example, although the early signaling function of the notochord is conserved across the vertebrates, many will be surprised to find that the role of the notochord in vertebral body development in tetrapods is not the blueprint for all vertebrates. Recent studies on zebrafish and medaka embryos have uncovered the molecular mechanisms of a somite-independent notochord-driven segmentation process that establishes vertebral centra and intervertebral spaces. As this process is not restricted to teleosts, the authors have written a general discussion about the role of the notochord in vertebral formation. Modularity and segmentation of the vertebral column are related topics. Further overarching themes are the structure, function and fate of the notochord in adult vertebrates and notochord–cartilage relationships.Key Features The first book devoted to notochord development, function and evolution Includes and integrates information on the notochord from studies going back 169 years Integrates developmental, molecular, functional, experimental and palaeontological studies Documents the fate of the notochord across the vertebrates Extensively illustrated with classical and new images Related TitlesBard, J. Evolution: The Origins and Mechanisms of Diversity (ISNB 978-0-3673-5701-6)Leys, S. and Hejnol. A. Origin and Evolution of Metazoan Cell Types (ISBN 978-1-1380-3269-9)

Advances in the development and application of electron microscopic techniques have occurred recently such that the electron microscope has evolved to become an essential tool in both basic and clinical research. Use of this instrument has contributed significantly to the formation of new perspectives and concepts concerning cell fine structure. These structural perspectives are now being integrated with specific functional, biochemical and pathophysiological events and processes of cells and tissues. Most recently, utilization of innovative electron microscopic techniques such as freeze-fracture, freeze­ etching, and scanning and high-voltage electron microscopy offers both the basic and clinical scientist potentially fundamental insights into many morphodynamic processes related to the activities of cells and tissues. Such an approach has been especially rewarding when applied to the dynamic events of gametogenesis and early embryonic development. The chapters comprising this book have been selected and edited with the aim of providing an up-to-date and comprehensive account of the most important aspects of vertebrate gamets and embryos as revealed by the integration of several different submicroscopic methods. The organization of the chapters is designed to indicate present gaps in our knowledge of the developmental and reproductive biology of gametes and the developing embryo and possible Iines of research which may lead to a lessening of these gaps.

Externally the vertebrate body plan presents a bilateral symmetry in relation to the midline. However, inside the body the distribution of the visceral organs follows a very particular pattern that is not symmetrical in relation to the midline. The last 10 years have seen remarkable advances in our understanding of how the internal asymmetries typical of the vertebrate body are established and controlled. The use of different development models has permitted to uncover fascinating ways of creating asymmetry, like the activity of the nodal cilia. A host of studies has also unravelled the involvement of many genes in the left right patterning pathway. Based on this knowledge the genetic basis of human laterality defects are beginning to be revealed. It is a major challenge now to understand how all these genes control left right development as well as the complex set of interactions established between them.

Epithelial phenotype is a dynamic stage of differentiation that can be modulated during several physiological or pathological events. The rapid conversion to a mesenchymal-like phenotype is called an epithelial-mesenchymal transition (EMT). The Rise and Fall of Epithelial Phenotype is the first book to comprehensively introduce the concept of EMT. The first part of this volume describes main examples and models and explains their physiological relevance. These examples include hydra morphogenesis, gastrulation in mouse, drosophila and sea urchin, as well as neural crest cell migration and heart morphogenesis in vertebrates. Part two reviews in detail, specific EMT molecular pathways covering extracellular induction, transduction and transcription response and modulation of cell-cell adhesion structures. It emphasizes new specific pathways with potential medical applications. EMTs can also be linked to pathological events such as wound healing and cancer progression, as detailed in this section of the book.