#LAMINA DE MULTIPANEL ACTIVATOR#

One possible scenario is that activation of a single gene inside a LAD leads to movement of the whole surrounding LAD to the nuclear interior. It has therefore remained unclear what the impact of these repositioning events is on the surrounding chromosomal regions.

For example, do the size of the gene and its level of transcription matter? Moreover, the previous studies of individual loci have only been based on microscopy-based assays such as fluorescence inВ situ hybridization (FISH) or LacO tagging and have only visualized the targeted genes themselves, but not the flanking DNA sequences. It is thus unclear whether the observed detachment from the NL after transcription activation is universal, or limited to genes with particular features. The molecular signals that cause detachment of a locus from the NL are still poorly understood.ДЄnalysis of NL detachment that follows forced activation of a gene has so far been limited to a handful of loci. Another study found that activation of the long non-coding RNA gene ThymoD in mouse T-cell progenitors contributed to the detachment of the neighboring gene Bcl11b from the NL (Isoda etВ al, 2017). Similar observations were made when VP64 (a tetramer of VP16) was tethered to promoters of three distinct genes in LADs in mouse embryonic stem (mES) cells (Therizols etВ al, 2014).

#LAMINA DE MULTIPANEL ACTIVATOR#

Tethering of the transcriptional activator peptide VP16 to these arrays caused repositioning away from the NL (Tumbar & Belmont, 2001). This was initially suggested by experiments with fluorescently tagged lacO arrays that were integrated in a locus near the NL. This, however, does not rule out that the contacts of genes with the NL are the consequence of a lack of transcriptional activity, and vice versa, that genes detach from the NL in response to their activation. In support of this notion, depletion of lamins can lead to derepression of specific genes (primarily in Drosophila) (Shevelyov etВ al, 2009 Kohwi etВ al, 2013 Chen etВ al, 2014) transfer of human inactive promoters from LADs to a neutral chromatin environment can lead to activation of these promoters (Leemans etВ al, 2019) and artificial tethering of some genes to the NL can reduce their activity (Finlan etВ al, 2008 Kumaran & Spector, 2008 Reddy etВ al, 2008 Dialynas etВ al, 2010). These observations raise the interesting possibility that the NL helps to establish a repressive environment. When cells differentiate, detachment of genes from the NL often coincides with transcriptional activation, while increased NL interactions correlate with reduced transcription (Peric-Hupkes etВ al, 2010 Lund etВ al, 2013 Robson etВ al, 2016, 2017).

Most genes inside LADs have very low transcriptional activity (Guelen etВ al, 2008 Peric-Hupkes etВ al, 2010 Leemans etВ al, 2019). How LAD-NL contacts are regulated is poorly understood.

The NL contacts of some LADs are highly consistent between cell types, while other LADs interact in cell-type-specific (facultative) manners with the NL. Mammalian genomes have roughly one thousand of such lamina-associated domains (LADs), which are typically hundreds of kb or even a few Mb in size. In metazoan cell nuclei, large chromatin domains are associated with the nuclear lamina (NL) (Gonzalez-Sandoval & Gasser, 2016 van Steensel & Belmont, 2017 de Leeuw etВ al, 2018 Kim etВ al, 2019 Lochs etВ al, 2019). These extensive datasets are a resource for the analysis of LAD rewiring by transcription and reveal a remarkable flexibility of interphase chromosomes. Inactivation of active genes can lead to increased NL contacts. Loss of NL interactions coincides with a switch from late to early replication timing, but the latter can involve longer stretches of DNA. The degree of detachment depends on the expression level and the length of the activated gene. Gene activation inside LADs typically causes NL detachment of the entire transcription unit, but rarely more than 50вЂ“100В kb of flanking DNA, even when multiple neighboring genes are activated. We addressed these questions by systematic activation or inactivation of individual genes, followed by detailed genome-wide analysis of NL interactions, replication timing, and transcription patterns. How this process works and how it impacts flanking chromosomal regions are poorly understood. Activation of such genes is often accompanied by repositioning toward the nuclear interior. Transcriptionally inactive genes are often positioned at the nuclear lamina (NL), as part of large lamina-associated domains (LADs).

Lamina de multipanel