Molecules take center stage

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All animals, including humans, begin life as a single cell. During the first few hours of development, that initial cell and its progeny make a series of crucial decisions that ultimately lead to the formation of organs and structures of the adult organism. The principal aim of developmental biology is to understand how these amazing processes occur.In the past two decades, the explosion of information and novel techniques in molecular biology and genetics has armed modern embryologists with powerful tools with which to dissect the molecular basis of development. Recent studies have illustrated a remarkable conservation of molecular and cellular developmental strategies among embryos of different species. The future of developmental biology therefore relies on a comparative approach, especially in the post-genome era.Molecular Principles of Animal Development stands perfectly within this context. Martinez Arias and Stewart's rationale is to approach developmental biology, primarily from a molecular perspective. Thus far,traditional textbooks have begun with a description of developmental processes(such as axis formation, gastrulation and organogenesis) in different model systems. Molecular explanations were subsequently provided along the way. In Molecular Principles of Developmental Biology, however, molecules take center stage rather than the embryo or its constituent parts.The book is split into three sections. After a general introduction about the fundamental questions of developmental biology over the past few centuries, chapters 2-5 provide a basic course of molecular biology surveying topics such as transcription, signaling molecules and receptors, signaling pathways, and networks. These four chapters should give the reader the tools to understand the molecular mechanisms underlying developmental events. It is hard to predict, however, if this general overview is rigorous enough to teach a molecular understanding of development to a reader lacking any previous background in molecular biology or genetics. The next section, chapters 6-9,describes the integration of basic molecular mechanisms into cellular and developmental processes such as cell adhesion, polarity, movement, cell divisions or cell death. Finally, the last three chapters focus on selected topics: how specific cell types are generated (e.g. myogenesis, neurogenesis);and then how specific cell types become organized in two- or three-dimensional patterns (e.g. development of the C. elegans vulva, vertebrate limb development, patterning and growth of the Drosophilawing).FIG1The final challenging aim of the book, which is very valid, argues for the need to re-interpret all the developmental processes within a molecular framework. The amateur embryologist, however, might be better served with a broader view of events that gradually focuses at the molecular level. For example, it is useless to build up a gene map of embryos without having a clear concept of the fate map and the ability to correlate gene expression with the spatiotemporal coordinates of the embryo. The Wnt signaling pathway,for example, can exert opposite effects depending on where and when the embryo is exposed to it.In conclusion, this textbook should be considered as a companion to more traditional texts about developmental biology, and it is clearly useful for advanced graduate students and teachers who already have a background of embryology. Readers will further benefit from the figures and suggested readings. Ultimately, however, we should leave the embryo on the center stage and build up the molecular networks around it. What matters at the end, is not only the understanding of the molecular components, but the overall strategies that an embryo uses to guide its own development.