“Epigenetics” – the New Testament of chromatin biology
In the past fifteen years several books have attempted to provide a coherent overview of the rapid and exciting advances in chromatin biology. Of these “Chromatin structure and function” by Alan Wolffe (Academic Press, 1995) is perhaps the far most popular and widely read book. Our current understanding of chromatin organization and the impact of various chromatin-related phenomena on gene expression, chromosome structure, development, cell differentiation and human disease has expanded into a much wider field of research currently known as “epigenetics”. Although the debates on the precise definition of this term and what it should or should not include are still ongoingReference Ptashne1, it is clear that what we call epigenetics nowadays is quite different from what this term meant when used by C. H. Waddington to describe how genotypes give rise to phenotypes during developmentReference Waddington2.
The recent advanced textbook “Epigenetics” edited by C. David Allis, Thomas Jenuwein and Danny Reinberg and published by Cold Spring Harbor Press is a monumental 500-page effort to collate, describe and explain the most essential concepts in modern chromatin biology and to bring these up to date. The book also provides a detailed account of specific molecular mechanisms underlying epigenetic phenomena in different organisms from bacteria to mammals.
“Epigenetics” contains 24 chapters, written by an international team of 47 experts. The book opens with an interesting historical perspective which follows the emergence of epigenetics from a collection of seemingly random observations into an exciting field of research that affects many areas of modern biology and “is founded upon trying to explain the unexpected – perhaps more than any other field of biological research”. The general layout of the book roughly follows the phylogenetic tree of eukaryotic model organisms, starting with budding yeast Saccharomyces cerevisiae, Drosophila melanogaster and plants, research on which has shaped the framework and the most basic perceptions of chromatin research in the past decades. It is not a surprise that these species still dominate the scientific landscape as the most commonly used models for high-throughput epigenetic studies. The chapters dedicated to individual model organisms are punctuated by others that focus in more detail on specific mechanisms that regulate chromatin structure and gene expression or participate in the formation of specialized chromosomal domains. These chapters describe the role of RNA interference in the assembly of heterochromatin, transcriptional gene regulation by Polycomb and Trithorax group proteins, the role of chromatin modifications and chromatin variants in the organization and function of genomes as well as more complex phenomena related to dosage compensation of gene expression in Drosophila and mammals. The last 8 chapters of the book are fully dedicated to mammalian epigenetics, with specific focus on DNA methylation, genomic imprinting and the involvement of chromatin in specification of the pluripotent state of germ and stem cells and the control of cellular differentiation. Last but not least, the final two chapters of the book summarize the current knowledge of changes in post-synthetic modifications of DNA and histone proteins that lead to complex human disease states such as ICF Syndrome, Rett Syndrome and cancer. Beautifully illustrated, this book is a rich resource of information for a diverse pool of readers, ranging from graduate students making their first steps in a new field of knowledge to more experienced scientists whose research has led them to unfamiliar grounds.
One may argue that in a rapidly developing field such as epigenetics any textbook written today is bound to be out of date the very day it is published. However, what makes “Epigenetics” a truly remarkable and, I believe, a long-lasting achievement is the clear and accessible overview of the major concepts and mechanisms that lay in the foundation of contemporary chromatin research. New details of how specific enzymes and proteins shape chromatin structure and composition may emerge, but the general principles that define how chromatin impacts on many cellular processes are likely to hold true.
