The epigenetics of rRNA genes: from molecular to chromosome biology.
In eukaryotes, the genes encoding ribosomal RNAs (rDNA) exist in two distinct epigenetic states that can be distinguished by a specific chromatin structure that is maintained throughout the cell cycle and is inherited from one cell to another. The fact that even in proliferating cells with a high demand of protein synthesis a fraction of rDNA is silenced provides a unique possibility to decipher the mechanism underlying epigenetic regulation of rDNA. This chapter summarizes our knowledge of the molecular mechanisms that establish and propagate the epigenetic state of rRNA genes, unraveling a complex interplay of DNA methyltransferases and histone-modifying enzymes that act in concert with chromatin remodeling complexes and RNA-guided mechanisms to define the transcriptional state of rDNA. We also review the critical role of the RNA polymerase I transcription factor UBF in the formation of active nucleolar organizer regions (NORs) and maintenance of the euchromatic state of rRNA genes.
McStay
Brian
B
Biomedical Research Center, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, United Kingdom. b.m.mcstay@dundee.ac.uk
Grummt
Ingrid
I
D000818:Animals; D042002:Chromatin Assembly and Disassembly; D002875:Chromosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D033481:Chromosomes, Mammalian / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D021901:DNA, Intergenic; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D020459:Genes, rRNA; D006570:Heterochromatin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008322:Mammals; D009697:Nucleolus Organizer Region; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D021901:DNA, Intergenic; D006570:Heterochromatin; D014157:Transcription Factors; D045643:DNA Repair Enzymes