Nuclear actin-related proteins as epigenetic regulators of development

Eukaryotic genomes encode several ancient classes of nuclear ARPs that participate in macromolecular machines affecting chromatin dynamics. Nuclear ARPs are variously required for assembly chromatin binding, and/or the enzymatic activities of different complexes. ARP-containing chromatin-modifying complexes carry out NR, chemical modifications of histones, or HVE reactions. These activities exert epigenetic control over cell proliferation and multicellular development along with controlling basal levels of transcription. In Arabidopsis, developmental pathways affecting every plant organ require normal levels of ARP4, ARP6, and/or ARP7 expression, providing strong evidence for this role. Diverse isoforms of ARP complexes may provide the greater target gene specificity and wider variety of chromatin-modifying activities needed for multicellular development, relative to development of single-celled organisms like yeast. © 2005 American Society of Plant Biologists.