Wisely chosen paths - regulation of rRNA synthesis

All cells, from prokaryotes to vertebrates, synthesize enormous amounts of rRNA to produce 1-2 million ribosomes per cell cycle, which are required to maintain the protein synthesis capacity of the daughter cells. In recent years, considerable progress has been made in the elucidation of the basic principles of transcriptional regulation and the pathways that adapt cellular rRNA synthesis to metabolic activity, a process that is essential for understanding the link between nucleolar activity, cell growth, proliferation, and apoptosis. I will survey our present knowledge of the highly coordinated networks that regulate transcription by RNA polymerase I, coordinating rRNA gene transcription and ribosome production with environmental cues. Moreover, I will discuss the epigenetic mechanisms that control the chromatin structure and transcriptional activity of rRNA genes, in particular the role of noncoding RNA in DNA methylation and transcriptional silencing.