Structure and Epigenetics of Nucleoli in Comparison With Non-nucleolar Compartments

Abstract

The nucleolus is a nuclear compartment that plays an important role in ribosome biogenesis. Some structural features and epigenetic patterns are shared between nucleolar and non-nucleolar compartments. For example, the location of transcriptionally active mRNA on extended chromatin loop species is similar to that observed for transcriptionally active ribosomal DNA (rDNA) genes on so-called Christmas tree branches. Similarly, nucleolus organizer region-bearing chromosomes located a distance from the nucleolus extend chromatin fibers into the nucleolar compartment. Specific epigenetic events, such as histone acetylation and methylation and DNA methylation, also regulate transcription of both rRNA- and mRNA-encoding loci. Here, we review the epigenetic mechanisms and structural features that regulate transcription of ribosomal and mRNA genes. We focus on similarities in epigenetic and structural regulation of chromatin in nucleoli and the surrounding non-nucleolar region and discuss the role of proteins, such as heterochromatin protein 1, fibrillarin, nucleolin, and upstream binding factor, in rRNA synthesis and processing.

Basic concepts of epigenetics

“…153 In euchromatin, abundant ribosomal unit transcription factories called nucleoli are easily visualized, which synthesize ribosomal subunit proteins that will be assembled later into the small and large subunits of ribosomes. 67,154 Heterochromatin and lamins. Silenced heterochromatin is comprised of two categories.…”

“…N-CoR1 is a member of the ISWI class of ATPase/Snf2 h nucleosomal remodeling proteins (discussed below) and contains TIP5, which is capable of interacting with DNMTs and Sin3 and of recruiting constrictive HDACs and methyltransferases to silence promoter regions of DNA. 32,46,48,[67][68][69] N-CoR is also reported to bind to un-liganded nuclear hormone receptors, which block the hormonal activated dissociation of the Sin3 complex (inducing nucleosomal expansion) and inhibit the recruitment of HATs (inducing histone relaxation) involved with gene activation. 70 Other human MBD proteins.…”

Ribosomal Genes Activity in Aged Down Syndrome Subjects

“…Furthermore, ribosomal RNA synthesis by Pol I is crucially dependent upon nutrient availability and drives ribosome biogenesis, a process close linked to cell growth and proliferation [24][25][26][27].…”

“…These epigenetic regulation mechanisms also involve a reallocation of the majority of rDNA from perinucleolar heterochromatin into the nucleolus [25,28].…”

Nucleolin antisense oligodeoxynucleotides induce apoptosis and may be used as a potential drug for nasopharyngeal carcinoma therapy

“…Nucleolin, which is also known as C23 or NCL, is a phosphoprotein with many functions, such as acting as an RNA-binding protein, an autoantigen, a transcriptional repressor, a DNA and RNA helicase as well as a DNA-dependent ATPase (5,6). The synthesis of nucleolin is positively correlated with increased rates of cell division.…”