Genet. Res., Camb (1998), 71, pp. 277–279. Printed in the United Kingdom # 1998 Cambridge University Press 277

Book Reviews

the revelation of sonic hedgehog? Just why has a The Origin of Body Plans: A Study in generation of developmental biologists been buzzing EŠolutionary DeŠelopmental Biology. By W with excitement? And what made these pioneers of A. Cambridge University Press. 1997. ISBN the model systems approach return to their old 052155014 9. 338 pages. Price £45. textbooks to remind themselves what onyco- Every biologist must have heard of and phorans, malacostracans, enteropneusts and amphi- hedgehog . Most are probably aware that oxus look like? In the same vein, I found Arthur’s modern developmental research has something to say choice of milestones in evolutionary developmental about . But what exactly? What is this new biology particularly strange; it omits Lewis’ Bithorax discipline of ‘evolutionary ’ Complex insights, Field et al.’s pioneering assault on that has emerged (or re-emerged) in biology? Wallace molecular phylogeny and even the dis- Arthur’s new book tackles these questions, and covery of the ! Comparative developmental concludes that the new discipline is far from mature. biology is buoyant and fast-moving, but the reader It is not yet a full integration of would hardly guess so from this book. and developmental biology. He notes that there is Fortunately, there are better things in store if you ample dialogue between embryologists, molecular stick with the task or, dare I say it, skip these initial biologists, phylogeneticists and even palaeontologists, chapters entirely (better still, start by reading Rudy but laments the fact that evolutionary or population Raff’s ‘The Shape of ’ published by University of geneticists have been noticeably late to the party. Why Chicago Press). The final few chapters deal with the has research into paid so little crux of the problem in Arthur’s view: how to integrate attention to recent findings in development? And does comparative developmental biology into mainstream it matter? Arthur argues that it certainly does matter, evolutionary thinking (or vice versa). He points out since the implications of modern developmental that current evolutionary thinking focuses heavily on biology are so profound (and so consistently ignored the destruction of variation, rather than its creation. I by standard evolutionary theory) that the so-called agree strongly with this point, which emphasises the New Synthesis is starting to look distinctly jaded. constraints imposed by the genotype on the kinds of Perhaps it is time for a New Improved Synthesis in variants that will be viable, and therefore available for evolutionary biology. Arthur’s book does not provide natural selection. A second point stressed by Arthur is this synthesis, but it does try to set out the agenda. that selective forces need not be just external. Internal Before tackling this, Arthur takes the reader co- of genetic pathways or developmental through a careful, but rather slow, review of some key mechanisms may strongly influence which variants are aspects of developmental biology, expression successful; this would represent a new face of natural analysis, , invertebrate palaeontology selection, rooted in developmental biology. Again, I and , whilst trying to draw out agree, although just how important ‘internal selection’ threads for his later holistic overview. I was dis- has been is hard to gauge. In fact, Arthur suggests that appointed by these sections of the book. My dis- its importance may have changed considerably over satisfaction was not due to the presence of errors, evolutionary time. He speculates that the develop- although inevitably there are a few (the cognoscenti mental control pathways of Vendian may will, for example, spot the omission of Hoxb-13 and of have been far less well integrated that those of modern zen\Hox3 , and most would disagree that phyla, in which case evolution had a freer rein to Hox cluster duplications occurred by local remodel body plans in the than has ever processes). My main criticism is that these first eight been possible since. This idea is not new, and is likely chapters simply do not convey the genuine excitement to remain a plausible viewpoint if only because it is so of the subject. What happened to the romance of the difficult to test! homeobox, the passion of the explosion, or Other suggestions and speculations made by Arthur

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are certainly testable, and the final chapter sets out an to nutrient availability and rapidly becoming agenda for future research. It is an eclectic choice, and cellularized. The basic cellular building blocks like one far from comprehensive, but it is worth reading. actin and myosin are found in virtually all eukaryotic If it further stimulates the fusion of evolutionary and cells, yet the proteins have been modified to produce developmental biology then it will have served a the diversity. Secretory mechanisms are also well useful purpose. I simply hope it does not do the conserved. The authors describe how conserved opposite. Arthur’s book does tend to stress how far developmental pathways can be used in new combin- we have to go to achieve a true integration, and this ations to bring about novel structures such as wings may prove daunting to some. This should not be the and limbs, and how there are common transcription case, since so much rapid progress has already been factors involved in eye development from to made. I hope that readers of this book will spice it up , despite the huge differences in the anat- a little with forays into the primary literature, and omy of the eyes and their methods of receiving light. thereby gain a more balanced outlook. Evolutionary The book goes on to look in detail at how cells developmental biology is alive and well, and really respond to the extracellular and intracellular con- rather exciting; the field may benefit from some ditions in which they find themselves. It shows how steering along the lines that Arthur suggests, but let’s core proteins or processes respond in very specific not kill the excitement. ways to the passing of time or changes in the  . .  environment. As an organism develops, cells need to School of Animal and Microbial Sciences respond to a variety of signals by the control of cell The UniŠersity of Reading cycles, translational control, kinase signalling path- Whiteknights ways and other key regulatory mechanisms that link Reading RG6 6AJ signals to responses, with overall coordination achieved through the nervous and endocrine systems. The authors discuss the roles of G-protein signalling, transcription factors and ion channels. Eukaryotic Cells, Embryos and EŠolution.ByJ G and promoters have evolved to accommodate a large M K. Blackwell Science 1997. ISBN 0 number of binding factors with different sequence 86542 574 4. 642 pages. Price £29.50, paper. specificities and binding affinities to allow temporal Understanding how cells and their products actually and spatial control of gene expression. These complex bring about evolutionary differences is a key aim of control regions allow elaborate developmental pro- this excellent text book. The immense research activity gramming. Among other topics explored by the in recent years in molecular biology and develop- authors are the capacity of organisms to respond to mental genetics has shown just how well conserved new environments, animal behaviour, the immune many genes and control pathways are. The initially system, sensory perception and the evolution of the surprising findings that the same signalling pathways brain. and transcriptional regulators are used time and time About a third of the way into the book the again to make cellular decisions during the devel- emphasis shifts to protein evolution, with a fresh look opment of an individual and are well conserved in a at such topics as exon shuffling and novel controls of wide variety of species are now well documented. Yet protein functions. Cell differentiation and compart- alone these do not contribute to our understanding of mentalization is covered in depth and the evolution of evolution. How do organisms use cellular processes to multicellularity investigated. Of particular interest adapt their form to their environment? This book here are discussions on the segregation of the germ links together evolution, cell biology and develop- line, which remains capable of meiosis, from the rest mental biology in an original and thought-provoking of the somatic cells, and how localized cell–cell way. interactions lead to the specific development and The book covers a huge diversity of topics beginning differentiation of particular structures. A lot of with a look at how well conserved cellular processes emphasis is placed on the development of are, even between organisms differing most in body imaginal disks and how a specific position is selected plan, nervous system and the relationship of the to for the generation of a bristle using a complex set of reproductive strategies. It shows how conserved positive and negative regulators. This shows how first building blocks are used to build the great diversity of a field of cells becomes competent to differentiate and cell structures and cell types present within and then how cell–cell interactions and lateral inhibition between organisms; and also how the decision-making within the cluster, with further refinements and machinery, such as that regulating the cell cycle, is well commitments, finally cause one bristle or sensory conserved, even between organisms using widely dif- to differentiate. This section emphasises the fering strategies for controlling cell division – for importance of the cell’s position within a population example single celled organisms dividing in response of cells, its stage in development and its sex and how

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these factors call into play specific subsets of the cell’s this is often exemplified using the studies of Drosophila genetic repertoire. The evolution of mechanisms to imaginal disks, where organizing centres are set up generate spatial patterns is a crucial step in the and gradually refined using transcription regulation evolution of diversity of form. and cell–cell signalling interactions. They also address There are large sections on the development of the how these kinds of fundamental, compartmentalized, body plan and on axis specification, both of which are and robust but flexible processes allow evolution to excellent in their coverage, but not too different from occur in response to selective pressures and en- what one could find in other developmental biology vironmental change. texts. and the final development of the The book is not for the faint-hearted. It makes no organism has to be built up starting from the compromises and to read it you need to be at ease with with its defined axes and body plan. The transcription all the molecular, developmental, cellular, genetic and factor cascades used in to biochemical details needed to understand the data on activate different genes in different regions of the which their ideas are based. At times reading is embryo are described and related to the body plan therefore slow, but it is worth it. I think it will be of genes and the processes of gastrulation and neural interest and value to the best students. It is a pleasure development. Much of the research area described in to see a topic tackled in a new way and I would these sections centres on Drosophila as would be certainly recommend that it should be read by all expected, but the organizing centre of amphibians and those teaching or doing research in cell biology, neural development in higher organisms are also well developmental biology, evolution or molecular bi- represented. ology. The final chapters look at how body plans have   diversified during evolution and how, for example, Institute of Cell and Molecular Biology evolution has occurred. Again at the genetic level UniŠersity of Edinburgh EH9 3JR

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