Gene Expression At The Beginning Of Animal Development

The beginning of life may be a miracle to some, and a mystery to others, but it is certainly one of the most exciting and perhaps controversial fields of scientific investigation in the 21st century. Among the metazoa, life begins when an egg is fertilized by a sperm. The sperm provides a genetic blueprint from the father and perhaps some critical proteins. The egg provides a genetic blueprint from the mother together with a large reservoir of mRNAs and proteins that are required for DNA replication, cell division and the onset of zygotic gene expression. All of the thousands of genes in these two mature gametes are transcriptionally silent and remain so until fertilization. This work focuses on three biological systems, providing the reader with a clear understanding of the current state of affairs, and the ability to identify common principles as well as critical differences that are responsible for beginning the process of animal development. The essays presented will be of practical value to all those who are interested in improving fertilization in vitro, in designing novel methods of contraception, in developing preimplantation genetic diagnosis for various diseases, in cloning animals by transplanting nuclei from adult cells to an enucleated egg, and in the application of embryonic stem cells to curing genetic diseases or replacing damaged tissues. But above all, this volume is offered to those who simply have an insatiable curiosity about life and its beginnings.

Four of the major animal systems studied for the mechanisms of their early embryonic development are treated in this volume. The articles address the specific questions studied in the various systems, discuss the fundamental questions raised by the particular organism and explain the techniques used to find answers to these questions. Questions of patternformation, early organogenesis and the genetics of the early development arecovered as well as the question of parental imprinting phenomena in mammals which are important for the early differentiation. The development of the mouse, Drosophila, Caenorhabditis and the zebrafish is emphasized by leading experts of their fields, and current problems in each system are exposed. For the zebrafish the advantages of this new system for developmental biology studies are summarized and discussed in their values, while in the other system the emphasis is laid on one of the actual field of research.

Updated and expanded to address the latest trends in developmental genetics by examining the developmental biology of three model animal systems with a vast range of complexity and phylogenetic distance--the nematode, fruitfly and mouse. This edition places greater emphasis on molecular approaches to pattern and development formation; introduces key issues and questions involving developmental biology; explores the final stages of patterning.

Eggs of all animals contain mRNAs and proteins that are supplied to or deposited in the egg as it develops during oogenesis. These maternal gene products regulate all aspects of oocyte development, and an embryo fully relies on these maternal gene products for all aspects of its early development, including fertilization, transitions between meiotic and mitotic cell cycles, and activation of its own genome. Given the diverse processes required to produce a developmentally competent egg and embryo, it is not surprising that maternal gene products are not only essential for normal embryonic development but also for fertility. This review provides an overview of fundamental aspects of oocyte and early embryonic development and the interference and genetic approaches that have provided access to maternally regulated aspects of vertebrate development. Some of the pathways and molecules highlighted in this review, in particular, Bmps, Wnts, small GTPases, cytoskeletal components, and cell cycle regulators, are well known and are essential regulators of multiple aspects of animal development, including oogenesis, early embryogenesis, organogenesis, and reproductive fitness of the adult animal. Specific examples of developmental processes under maternal control and the essential proteins will be explored in each chapter, and where known conserved aspects or divergent roles for these maternal regulators of early vertebrate development will be discussed throughout this review. Table of Contents: Introduction / Oogenesis: From Germline Stem Cells to Germline Cysts / Oocyte Polarity and the Embryonic Axes: The Balbiani Body, an Ancient Oocyte Asymmetry / Preparing Developmentally Competent Eggs / Egg Activation / Blocking Polyspermy / Cleavage/ Mitosis: Going Multicellular / Maternal-Zygotic Transition / Reprogramming: Epigenetic Modifications and Zygotic Genome Activation / Dorsal-Ventral Axis Formation before Zygotic Genome Activation in Zebrafish and Frogs / Maternal TGF-β and the Dorsal-Ventral Embryonic Axis / Maternal Control After Zygotic Genome Activation / Compensation by Stable Maternal Proteins / Maternal Contributions to Germline Establishment or Maintenance / Perspective / Acknowledgments / References