In June a discussion came up on Twitter about scientific terms that are overused. I began to wonder whether I was contributing to the problem and may need to tighten up my use of the word â€œepigenetics.â€ (Thanks to Brendan Maher for bringing it up and Helen Pearson for writing part of thisÂ 2008 Nature piece.)
As a starting point, geneticist Peng Jin recently set the stage with a review on â€œUnlocking epigenetic codes in neurogenesisâ€ in the journal Genes & Development:
The word â€œepigeneticsâ€ was first proposed by Waddington in the middle of the 20th century; the term is derived from the Greek words for â€œoverâ€ or â€œaboveâ€ genetics to describe the molecular events involved in early undifferentiated embryonic development. Epigenetics is now broadly defined as the heritable changes in gene expression and function that do not alter DNA sequence.
The key word there is heritable: transmitted from parent to child, or at the cellular level, from parent cell to daughter cell.
We have to think about what makes any cell in the body have the pattern of gene activity it does. A big part of that comes fromÂ all the proteins, such as transcription factors, bound to the chromosomal DNA. FormingÂ a sperm or egg takes all that structure and information away. Cell division takes SOME of the information away. Epigenetics has to provide information that is maintained through these disruptive processes.
Thus, phenomena like the Dutch Hunger Winter, the imprinting involved in Prader-Willi vs Angelman syndrome, or the recent discovery of inheritance of smell sensitivityÂ in mice here at Emory qualify unambiguously. However, any time DNA methylation is involved, is the term epigenetic appropriate? What about histone modifications or noncoding RNAs? Consider this postÂ an invitation for anyone with an informed opinion to agree or disagree.