Hunting for Darwin's gemmules and Lamarck's fluid: Transgenerational signaling and histone methylation

Recent studies have discovered phenotypes induced by a transient treatment or mutation that persist for multiple generations without mutations in DNA. Both invertebrates and vertebrates exhibit such inheritance, and a range of environmental factors can act as a trigger. Now referred to as transgenerational epigenetic inheritance or TEI, this emerging field faces a big challenge—what molecular mechanisms account for inheritance of TEI phenotypes? This review describes examples of TEI and focuses on the possible role of histone methylation and small RNAs in mediating TEI. This article is part of a Special Issue entitled: Methylation: A Multifaceted Modification — looking at transcription and beyond. •Transient environmental conditions can alter phenotypes for up to four generations.•The molecules that mediate transgenerational epigenetic inheritance (TEI) are largely unknown.•Modified histones in chromatin, methyltransferases and small, noncoding RNAs may be inherited cues.•TEI occurs in organisms that lack DNA methylation, indicating DNA methylation is not essential for TEI.•Nucleosomes are not stable within chromatin in vivo; they turn over on the order of hours.