Heterochromatin and gene positioning: inside, outside, any side?

Abstract

All cellular processes depend on the expression and repression of the right sets of genes at the right time. As each cell contains the same DNA, transcriptional and epigenetic factors have to maintain tight control over gene expression. Even a small divergence from the correct transcriptional program can lead to severe defects and even death. Having deciphered the complete linear genetic information, we need to clarify how this information is organized into the dynamic and highly heterogeneous three-dimensional space of the eukaryotic cell nucleus. Observations on the higher order organization of DNA into differentiated condensation levels date back to the early twentieth century, and potential implications of these structural features to gene expression were postulated shortly after. In particular, proximity of genes to condensed regions of heterochromatin was proposed to negatively influence their expression and, henceforward, the concept of heterochromatin as subnuclear silencing compartment emerged. Methodological advances fueled a flurry of recent studies, which only, in part, led support to this concept. In this review, we address how (hetero)chromatin structure and proximity might influence gene expression and discuss the challenges and means to unravel this fundamental biological question.

Fatty acid binding proteins have the potential to channel dietary fatty acids into enterocyte nuclei

“…The spatial organization of eukaryotic genomes in the cell nucleus is linked to their transcriptional regulation ( 70,71 ). However, it has been diffi cult to fi nd general rules on the involvement of nuclear organization in transcriptional regulation.…”

Epigenetic modifications in sex heterochromatin of vole rodents

“…Two higher-order chromatin structures are typically observed, euchromatin and heterochromatin, which are defined by a complex interplay between condensation state, chromatin modifications, associated proteins, and transcriptional activity, all referred to as epigenetic marks (Richards and Elgin 2002;Francastel et al 2000;Jost et al 2012).…”

The Heterochromatin Condensation State in Peripheral “Gene Poor” and Central “Gene Rich” Nuclear Regions of Less Differentiated and Mature Human Leukemic Cells: A Mini-Review with Additional Original Observations

“…At this occasion it must be mentioned that the image optical densitometry used in the present study does not provide further information on the genes present in studied nuclear regions. It should be added that that methodical approach also does not facilitate to distinguish the constitutive and facultative heterochromatin regions [8,10,41,[43][44][45][46]. However, it might still provide useful and complementary information on the heterochromatin for further studies of chromosomal territories in different nuclear regions using other methodical approaches [45,47,48].…”

“…It should be added that that methodical approach also does not facilitate to distinguish the constitutive and facultative heterochromatin regions [8,10,41,[43][44][45][46]. However, it might still provide useful and complementary information on the heterochromatin for further studies of chromosomal territories in different nuclear regions using other methodical approaches [45,47,48]. In addition, it might be also useful to detect pathological abnormalities of the individual cells including various differentiation and maturation asynchronies or alterations, which are common in malignant disorders including leukemias [2,49].…”