Epigenetics in C. elegans: facts and challenges.

Epigenetics is defined as the study of heritable changes in gene expression that are not accompanied by changes in the DNA sequence. Epigenetic mechanisms include histone post-translational modifications, histone variant incorporation, non-coding RNAs, and nucleosome remodeling and exchange. In addition, the functional compartmentalization of the nucleus also contributes to epigenetic regulation of gene expression. Studies on the molecular mechanisms underlying epigenetic phenomena and their biological function have relied on various model systems, including yeast, plants, flies, and cultured mammalian cells. Here we will expose the reader to the current understanding of epigenetic regulation in the roundworm C. elegans. We will review recent models of nuclear organization and its impact on gene expression, the biological role of enzymes modifying core histones, and the function of chromatin-associated factors, with special emphasis on Polycomb (PcG) and Trithorax (Trx-G) group proteins. We will discuss how the C. elegans model has provided novel insight into mechanisms of epigenetic regulation as well as suggest directions for future research.