Germ cell development is essential for sexually reproducing organisms and,with due respect to Monty Python, fertilization is just the culmination of a vast repertoire of developmental accomplishments by these cells. Upon fertilization, germ cells directly contribute to both the genetic and epigenetic programs of the progeny, and have been designated as `the guardians of the genome'. Because of their totipotency, germ cells are also referred to as the `mother of all stem cells'. Accordingly, germ cell development is a vibrant and important area of research that crosses the boundaries of many disciplines: their inherent scientific value as specialized cell types; the unique development and fates of their stem cells; the social and ethical issues associated with reproductive biology, human health and assisted reproductive technologies; and their use in animal conservation approaches exemplify this importance. The challenges that lie ahead for us in each area of this field are enormous. However, the tackling of such challenges at the bench could become a little easier with the recent publication of Germ Cell Protocols.
The book is divided into two volumes. With 21 and 25 chapters,respectively, they cover a wide array of important germ cell topics among many animals, such as C. elegans, zebrafish, sea urchins, amphibians,ascidians, avians and numerous mammals, including humans. In total, the two-volume set thoroughly covers most research areas. Experts in the field will find these volumes useful when considering how to improve their own methodology by comparison with other cell/species types, and novices will benefit from the protocol nature of the book, which allows them to find rapidly many essential steps to conduct experiments for the first time.
The most attractive features of Germ Cell Protocols are the diversity of model systems and experimental strategies that are described by leading experts in each discipline to address the unique complexities of germ cell development. Current trends in the publication of primary research papers include the presentation of an abundance of experimental data combined with a lack of sufficient detail about the methodology for the reader to execute similar studies. In addition, the recent revolution in technological advances has made many complex procedures much easier to achieve, and technical problems that were previously impenetrable can now be overcome. Each chapter in the book is organized into Introduction, Materials, Methods and Notes. This simple and clever organization not only allows germ cell researchers to find the methods they need to employ more effectively, but also to identity the exact reagents and equipment they require, and to understand the intellectual basis of the methodology. As specific areas of research become more integrated with multiple disciplines, a precise guide to these new advances is an extremely valuable tool to have in the laboratory.
Volume 1 (Sperm and Oocyte Analysis) effectively describes how to manipulate mature germ cells, sperm and oocytes, from diverse organisms such as ascidians and pigs. The chapters in this volume largely deal with aspects of sperm and oocyte purification and manipulation, and instruct researchers on how to manipulate specific aspects of fertilization experimentally. For example, protocols on how to study sperm and oocyte maturation in vitro are described that use common techniques of fluorescence microscopy; several chapters describe how to purify biochemically membrane-associated kinase activities in the egg and sperm. Together, these methods allow researchers to study how germ cells become competent for fertilization in diverse animals and also explain how to visualize and assay the biochemical mechanisms associated with normal fertilization. But the understanding of how fertilization is achieved in vitro without a better understanding of how mature germ cells have arisen in the first place is unsatisfying to the developmental biologists among us.
Hence, Volume 2 (Molecular Embryo Analysis, Live Imaging, Transgenesis, and Cloning) contains detailed descriptions of how to ascertain and study early germ cell development that occurs during embryogenesis. Primordial germ cells(PGCs) are the precursors to gametes that arise during embryonic development. Studying PGCs in any organism is an enormous feat because they are often limited in number and difficult to identify. The combined recent advances in imaging, transgenesis and stem cell technology have been used in many creative ways to visualize and manipulate the earliest aspects of germ cell development, PGC formation and migration. Chapter 1 of Volume 2, written by Hans Scholer and his associates, is a stellar example of the types of integrative methods that are being used to study germ-cell development. The use of various approaches, the detailed documentation of reagents and conditions, and descriptions of the wide-ranging effects of these approaches ensure that the reader will be able to take this work to the next level of understanding and application. In addition, many of the other chapters describe intricate nuclear cloning methods that are key to understanding how germ cells are programmed and reprogrammed for development, and how totipotency is achieved and manipulated. Overall, the protocols within Volume 2 guide researchers on how to use sophisticated tools in order to understand the molecular and cellular basis of the earliest events in germ cell development.
Despite the strengths that this set has to offer, several shortcomings could be considered when updating future volumes. With all the genomic resources and genome data that are now available for several of the organisms covered in this book, it is unfortunate that a significant presentation of such resources is missing here. We could envision at least two chapters on the genomic resources and databases that are available to the community, and on how researchers can integrate bioinformatics-based approaches with the biochemical and cellular protocols currently discussed in these volumes. A table of antibody/reagent/cell line resources would be useful to assist readers with identifying and obtaining essential elements for their work. As the germ cell is a cell type that, in some species, is synonymous with rarity,a greater availability of community resources is important if the field is to make rapid and efficient progress.
Although we realize that these volumes are intended to be protocols,chapters do sometimes suffer from a lack of comparison to or integration with each other, or even a lack of cross-referencing. As a result, they often appear to stand alone and sometimes to lack the `big picture' that is important for a first-time user of a protocol. The protocols are also generally just that – methodology. Although chapters end with a `Notes'section, which contains helpful tidbits about each protocol discussed, little is presented by way of troubleshooting or explaining why one approach is used instead of another, or the consequences of using alternatives. It is often these types of discussions that make a protocol dynamic and that contribute to improvements by other investigators. Several chapters could also be enhanced with figures or diagrams to help the reader understand the protocol better, or to see sample outcomes from the documented steps. In the chapters that are well illustrated, the illustrations largely take the form of black and white photos, which do not portray the richness of the cell type when viewed under the microscope.
Overall, both volumes of Germ Cell Protocols have widespread appeal, from basic developmental biologists, to veterinarians and to human clinicians, and will become a highly valuable resource in our respective laboratories.