Molecular Biology of Circadian Rhythms

Abstract

Amita Sehgal (Ed.) Wiley-Liss, 2004. $89.95, 283 pp. ISBN 0–471–41824–2 At the intersection of Genes, Brain and Behavior are Time, Love and Memory (Weiner 1999). The study of the genetic basis of these ‘simple’ behaviors, championed by Seymour Benzer in the 1960s and early 1970s, has paid rich dividends. The greatest progress has been made in understanding the molecular basis for circadian rhythms. Tremendous advances have been made in understanding the molecular feedback loops that underlie the capacity of organisms to measure the 24 h day and anticipate the next dawn. Painstaking work in the 1970s and 1980s led to the identification of mutants affecting circadian timing in model organisms, but as recently as 10 years ago, there were only two identified genes, period in Drosophila and frequency in Neurospora, that were routinely accepted as ‘clock genes’, genes essential for proper circadian timekeeping. The 1990s was a decade of explosive growth in the field, as workers exploited ‘new’ molecular methods including the polymerase chain reaction and genomic databases, combined with the faithful standby, the mutagenesis screen. As molecular information emerged, the similarity in the molecular basis of clocks in Drosophila and mammalian systems became apparent, fueling further advances. Not to be outdone, our colleagues studying organisms without brains (prokaryotic cyanobacteria, plants and bread mold) also made tremendous strides. While a review of the molecular bases for circadian clocks fit quite nicely into a 20-page review 5 years ago (Dunlap 1999), the expansion in the area has created a need for a text such as the one edited by Amita Sehgal. The volume by Sehgal and colleagues is aimed at an advanced undergraduate/graduate student level. The introductory chapter introduces concepts and terminology. In my view, portions of the opening three chapters of another recent text (Dunlap et al. 2003) provide a much more readable, clear and well-illustrated introduction to the field. The second chapter of this volume reviews methods to identify or study circadian genes and is likely essential for the target audience. The core of the book consists of six chapters devoted to describing the current understanding of the molecular control of circadian rhythms in animal models (Drosophila, non-mammalian vertebrates and mammals) and in cyanobacteria, Neurospora and plants. These chapters present useful information about the methods for studying each of these organisms and review the mutants and genes involved in the clockwork of each species. Many illustrations are stylized versions of data from published papers but often without providing a citation to the original source. Indeed, the chapters average only 15 references each; those encouraging students to pursue the primary literature will find this book dissatisfying. The illustrations and one-stop shopping convenience of this volume make it a useful complement to detailed, well-referenced reviews published by others (Allada et al. 2001; Johnson 2001; Loros & Dunlap 2001; Reppert & Weaver 2002; Williams & Sehgal 2001; compendia of review articles have also appeared recently in Cell and Tissue Research[volume 309, 2002] and in Novartis Foundation Symposia[volume 253, 2003]). The final section of the book is three chapters on ‘circadian organization in complex organisms’ that discuss selected physiological aspects of rhythmicity. These chapters do not appear to be well integrated with the remainder of the book or each other. The book includes a reasonable but not exhaustive index. As acknowledged by Dr Sehgal in the foreword, authors of several of the chapters have no direct experience working with the organism that they write about. The authors seem to have been selected for current or past research or institutional affiliation rather than on expertise with the specific model organism. To their credit, however, these authors have gone to tremendous effort to bring the information together, and indeed I believe that some chapters benefit from taking advantage of the opportunity to bring together and illustrate old and newer information, rather than being a revision of a review written by a more recognizable name. Overall, this volume does a good job of providing a timely snapshot of the molecular mechanisms of biological timekeeping as we understand it today and will be a good introduction to the topic for those interested in how genes and their products control rhythmic physiology and behavior. Experts in the field may have quibbles with specific points and with the emphasis of some chapters, but the book succeeds in its aim for its target audience.