Project description:The nuclear lamina provides a repressive chromatin environment at the nuclear periphery. However, whereas most genes in lamina-associated domains (LADs) are repressed, approximately ten percent reside in local euchromatic contexts and are expressed. How these genes are regulated and whether they are able to contact regulatory elements in LADs or outside LADs remains unclear. Here, we integrate transcriptomic, chromatin states, microscopy and publicly available enhancer-capture Hi-C data to show that expressed genes in LADs are able to connect to enhancers in LADs and inter-LADs. Our data favor a model where the spatial topology of chromatin at the nuclear lamina is compatible with transcriptional regulation in this dynamic nuclear compartment.
Project description:The nuclear lamina is a proteinaceous network of filaments that provide both structural and gene regulatory functions by tethering proteins and large domains of DNA, so-called lamin associated domains (LADs), to the periphery of the nucleus. LADs are a large fraction of the mammalian genome that are repressed, in part, by their association to the nuclear periphery. The genesis and maintenance of LADs is poorly understood as are the proteins that participate in these functions. In an effort to identify proteins that reside at the nuclear periphery and potentially interact with LADs, we have taken a two-pronged approach. First, we have undertaken an interactome analysis of the inner nuclear membrane bound LAP2β to further characterize the nuclear lamina proteome. To accomplish this, we have leveraged the BioID system, which previously has been successfully used to characterize the nuclear lamina proteome. Second, we have established a system to identify proteins that bind to LADs by developing a chromatin directed BioID system. We combined the BioID system with the m6A-tracer system which binds to LADs in live cells to identify LAD proximal and nuclear lamina proteins. In combining these datasets, we have further characterized the protein network at the nuclear lamina as well as identified putative LAD proximal proteins. Our analysis identifies many heterochromatin related proteins related to H3K9 methylation processes as well as many proteins related to cell cycle regulation identifying important proteins essential for LAD function.
Project description:A large fraction of the mammalian genome is organized into inactive chromosomal domains associated with the nuclear lamina. Using genomic repositioning assays we show that Lamina associated domains (LADs), spanning the developmentally regulated IgH and Cyp3a loci, contain transportable DNA regions that associate chromatin with the nuclear lamina and repress gene activity in fibroblasts. We characterized DNA regions within LADs that are functionally capable of positioning chromatin domains at the inner nuclear membrane (INM) lamina. We mapped and characterized the IgH and other LADs in murine fibroblasts. We show that these murine LADs have a unique chromatin structure with discrete boundaries. We demonstrate DNA regions within LADs that are capable of directing the association of chromatin domains with the INM-lamina as well as the silencing of a co-integrated reporter gene.
Project description:Purpose: To compare the effects on Lamina Associated Domains (LADs) of shRNA treatment against lamin isotypes. Results: Using an optimized data analysis workflow (LADetector, available at https://github.com/thereddylab/LADetector), We found near identical sequences within the genome-wide maps indicating that ensemble methods are not effective for measuring random perturbations - perturbations that vary from cell to cell.
Project description:Lamina-associated domains (LADs) are large chromatin regions that are associated with the nuclear lamina and form a repressive environment for transcription. The molecular players that mediate gene repression in LADs are currently unknown. Here we performed a full-genome genetic screen in human cells using LAD-integrated fluorescent reporters to identify such regulators. Surprisingly, the screen identified very few lamina proteins, but revealed roles for dozens of known chromatin regulators. Among these are the negative elongation factor (NELF) complex and interacting factors, suggesting that regulation of RNA polymerase pausing can be a mechanism to repress transcription in LADs. Furthermore, the chromatin remodeler complex BAF and the activation complex Mediator can work both as activators and repressors in LADs, depending on the local context and possibly rewiring of heterochromatin. Our data suggest that fundamental regulatory steps of the transcription process and chromatin remodeling, rather than interaction with NL proteins, have a major role in the regulation of transcription in LADs.
Project description:Lamina-associated domains (LADs) are large chromatin regions that are associated with the nuclear lamina and form a repressive environment for transcription. The molecular players that mediate gene repression in LADs are currently unknown. Here we performed a full-genome genetic screen in human cells using LAD-integrated fluorescent reporters to identify such regulators. Surprisingly, the screen identified very few lamina proteins, but revealed roles for dozens of known chromatin regulators. Among these are the negative elongation factor (NELF) complex and interacting factors, suggesting that regulation of RNA polymerase pausing can be a mechanism to repress transcription in LADs. Furthermore, the chromatin remodeler complex BAF and the activation complex Mediator can work both as activators and repressors in LADs, depending on the local context and possibly rewiring of heterochromatin. Our data suggest that fundamental regulatory steps of the transcription process and chromatin remodeling, rather than interaction with NL proteins, have a major role in the regulation of transcription in LADs.