Paramutation: Heritable in trans effects

Paramutation is the heritable transfer of epigenetic information from one allele of a gene to another allele of the same gene. In general, the consequence of this trans-communication is a change in gene expression. Paramutation has been observed in plants, fungi and mammals, but is most extensively studied in maize thanks to the long-standing history of maize genetics. For decades, paramutation has been a mystery, but recent progress has shed light on the mechanisms underlying this phenomenon. The identification of MOP1 as an RNA-dependent RNA polymerase shows that RNA plays a crucial role in the trans-inactivation process. RNA however appears not the only player in the paramutation process. In this chapter, potential mechanisms will be discussed in light of characteristics that the various paramutation phenomena have in common.