Jonathan Weitzman relishes two accounts of how environment can influence the script of our genome.
Epigenetics: The Ultimate Mystery of Inheritance
- Richard C. Francis
As an identical twin, I have always been fascinated by what determines who we are. Nature's clones are never truly identical, so what explains the differences between my brother and myself? How much of our identity is inherited; how much acquired by interacting with the environment? The field of epigenetics, standing at the interface between our environment and our genes, is beginning to offer answers.
Epigenetics explores how genetically identical entities, whether cells or whole organisms, display different characteristics, and how these are inherited. The past century witnessed amazing advances in our understanding of genetics, but secrets remain hidden within the genome. Epigenetics research is now blossoming, offering a potential panacea for these post-genome blues.
Two timely books open up this emergent field: Epigenetics by Richard Francis and The Epigenetics Revolution by Nessa Carey offer very different takes. Francis's thoughtful and succinct book focuses on the narrative and the excitement of discovery, rather than on the nitty-gritty details at the molecular level. His personal tour includes anecdotes from his travels around the world and allusions to popular culture.
The Epigenetics Revolution: How Modern Biology is Rewriting Our Understanding of Genetics, Disease and Inheritance
- Nessa Carey
Carey's book is more DNA-centric, focusing on epigenetic mechanisms and the chemistry of chromatin, which defines how DNA is packaged around proteins in the nucleus. Her book combines an easy style with a textbook's thoroughness.
Conveying epigenetics to a broad readership presents challenges. The field is in flux and the concepts are abstract and technically demanding. Researchers struggle to come up with a unanimously accepted definition of the term epigenetics. And there is confusion in the literature between epigenetic phenomena and epigenetic mechanisms. The first describes the transmission of heritable characteristics, thereby resembling genetics; the second focuses on how genes are regulated, and is more aligned with molecular biology. Francis is interested in the modes of inheritance and how these are affected by environmental events. Carey refers more to the mechanistic events that change how genes are switched on and off without altering the genes themselves.
What makes the field so exciting is that we have new tools to address old questions.
Epigenetics, for Francis, is a form of cellular control over gene activity. He presents the cell as a theatrical production, noting that the standard view — with genes as directors, proteins as actors and other biochemicals as stagehands — needs to be reassessed. As an alternative to the 'executive gene' idea, in which the genome is in control, he urges readers to think about the 'executive cell'. Francis relegates genes to members of the cast, and insists that they are regulated by, not regulators of, cellular states.
A seasoned science writer, Francis is at his best when describing abstract concepts in a historical context. A chapter on developmental biology reminds us that the idea that form emerges gradually during development (known as epigenesis) arose in response to an earlier concept, which held that form is predetermined from the beginning (preformationism). Francis cautions us not to fall into the trap of using the 'genetic blueprint' or 'genetic program' metaphors, which he sees as contemporary preformationism or genomic determinism. He ends with an interesting concept — the 'Janus gene' — which has both the outward causal aspect of gene function and an inward aspect that is responsive to external cues.
Carey's book is full of illustrations and entertaining metaphors. She describes the nucleosome as DNA wrapped around “eight ping-pong balls ... like a long liquorice whip around marshmallows”, and sees DNA as a film script, with plenty of room for interpretation and retakes. Carey's experience of the biotechnology industry shows in her concluding remarks on the pros and cons of our growing understanding of epigenetics for drug discovery, and on understanding the impact of diet and environment on disease.
These two bold attempts to bring epigenetics to a wide audience are at the vanguard: more books will follow as the field matures. But future authors should avoid using the words 'mystery' and 'revolution' in their titles. What makes the field so exciting is that we have new tools to address old questions. Unravelling life's mysteries? That's not revolution, it is why we become scientists in the first place. My twin brother and I are both professors studying genetics — I still wonder whether that choice was determined by genetics or the environment.
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Weitzman, J. Epigenetics: Beyond face value. Nature 477, 534–535 (2011). https://doi.org/10.1038/477534a
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