Nucleus (Austin, Tex.)最新文献

The nuclear envelope plays an indispensable role in the spatiotemporal organization of chromatin and transcriptional regulation during the intricate process of cell differentiation. This review outlines the distinct regulatory networks between nuclear envelope proteins, transcription factors and epigenetic modifications in controlling the expression of cell lineage-specific genes during differentiation. Nuclear lamina with its associated nuclear envelope proteins organize heterochromatin via Lamina-Associated Domains (LADs), proximal to the nuclear periphery. Since nuclear lamina is mechanosensitive, we critically examine the impact of extracellular forces on differentiation outcomes. The nuclear envelope is spanned by nuclear pore complexes which, in addition to their central role in transport, are associated with chromatin organization. Furthermore, mutations in the nuclear envelope proteins disrupt differentiation, resulting in developmental disorders. Investigating the underlying nuclear envelope controlled regulatory mechanisms of chromatin remodelling during lineage commitment will accelerate our fundamental understanding of developmental biology and regenerative medicine.

Maintaining genome integrity is essential for the proper functioning and development of organisms. An intriguing aspect is that neocentromeres can form at non-centromeric sites. CENP-A, a key epigenetic marker of centromeres, is often mislocalized to ectopic sites in cancers when overexpressed. Its deposition on centromeres relies on transcription of centromeric non-coding RNAs. Subsequently, ectopic CENP-A is frequently found at transcriptionally active and chromosome breakpoint regions. We previously engineered a stable ectopic CENP-A site on a naïve chromosome by overexpressing PCAT2, a non-centromeric oncogenic lncRNA that recruits CENP-A to its transcribing locus. We tracked cells with this transgene to analyze the longevity of ectopic CENP-A. We discovered that this induced epigenetic memory was lost due to suppression by epigenetic silencing mechanisms, restoring CENP-A to previous levels. These findings suggest that cells have mechanisms to prevent neocentromere formation at ectopic sites by suppressing transcription unless selective pressure favors it.

We performed a comparative study of the non-ribosomal gene content of nucleoli from seven cancer cell lines, using identical methods of purification and analysis. We identified unique chromosomal domains associated with the nucleolus (NADs) and genes within these domains (NAGs). Four cell lines have relatively few NAGs, which appears mostly transcriptionally inactive, consistent with literature. The remaining three lines formed a separate group with nucleoli with unique features and NADS. They constitute larger number of common NAGs, marked by ATAC-seq and having accessible promoters, with histone markers for transcriptional activity and detectable RNA Pol II bound at their promoters. The transcripts of these genes are almost entirely exported from the nucleolus. These results indicate that RNA Pol II dependent transcription in NADs can vary widely in different cell types, presumably dependent on the cell's developmental stage. Nucleolus-associated genes are likely to be distinguished marks reflecting the cell's metabolism.

Myofibers are the building block of skeletal muscle cells providing its capacity to contract and produce movement. The microtubule (MT) network sustains myofiber formation and its spatial organization is remodel during myofiber formation. This muscle-related MT network with specific partners, actively drive myonuclei localization in myofiber. In pathological conditions, myonuclei and MT patterning are affected and contribute to skeletal muscle mis-functionality. In this review, we classified myopathies depending on myonuclei positioning within myofibers and reported that 72% of myopathies exhibit myonuclei positioning alterations. We explored how this impairment can be analyzed according to muscle disease development, MT alterations and association with various partners. We highlighted how MT modifications impact muscle-specific mechanotransduction status and myofiber functional integrity. We then reported genes involved in myonuclei shape and positioning maintenance. Finally, we discussed technical contribution advances in the field to improve knowledge on muscle physiology and its challenges in disease context.

Chromatin is a dynamic polymer in constant motion. These motions are heterogeneous between cells and within individual cell nuclei and are profoundly altered in response to DNA damage. The shifts in chromatin motions following genomic insults depend on the temporal and physical scales considered. They are also distinct in damaged and undamaged regions. In this review, we emphasize the role of chromatin tethering and loop formation in chromatin dynamics, with the view that pulsing loops are key contributors to chromatin motions. Chromatin tethers likely mediate micron-scale chromatin coherence predicted by polymer models and measured experimentally, and we propose that remodeling of the tethers in response to DNA breaks enables uncoupling of damaged and undamaged chromatin regions.

The dynamic regulation of RNA metabolism plays a crucial part in cellular function, with emerging evidence suggesting an important role for RNA modifications in this process. This study explores the relationship between RNA splicing and the TET dioxygenase activity, shedding light on the role of hm5C (RNA 5-hydroxymethylcytosine), and TET proteins in RNA metabolism. Integrating data from mass spectrometry, AlphaFold structural modeling, microscopic analysis, and different functional assays, including in vitro splicing, TET proteins were found to regulate splicing. We show that TET1, TET2, and TET3 interact with the splicing factors U2AF1 and U2AF2. Interestingly, TET dioxygenases localize in splicing speckles in mammalian and Drosophila cells. TET speckles association was found to be RNA-dependent, but also rely on its interaction with splicing factors. Furthermore, cellular splicing assays revealed that all three TET proteins promote splicing efficiency independent of their catalytic activity. Interestingly, though, the oxidation of m5C to hm5C restores splicing efficiency in vitro. The latter highlights the regulatory role of cytosine modifications in RNA metabolism. These findings provide insights into the complex interplay between RNA modifications and splicing, suggesting a multifaceted role for TET proteins in RNA metabolism beyond their canonical function in the oxidation of 5mC in DNA.

Actin was first observed in the nucleus more than sixty years ago but research on nuclear actin did not receive significant attention for the next forty years. It only started to accelerate around the year 2000, when the first convincing experimental data emerged indicating that actin participates in essential nuclear processes. Today, we know that actin is involved in transcription, replication, DNA repair, chromatin remodeling, and participates in the determination of nuclear shape and size. In this paper we review the results of the last five years of increasingly intensive research on nuclear actin, because on one hand, the field has expanded with several new directions during this time, and on the other hand, the enrichment of our picture of nuclear actin will certainly provide a more solid foundation and new impetus for its future investigation.

Aberrant nuclear morphology is a hallmark of human disease and causes nuclear dysfunction. Perturbed nuclear mechanics via reduced heterochromatin weakens the nucleus resulting in nuclear blebbing and rupture. While the role of heterochromatin is known, the separate roles of constitutive heterochromatin methylation states remains elusive. Using MEF and HT1080 cells, we isolated the individual contribution of constitutive heterochromatin H3K9 methylation states through histone methyltransferase inhibitors. Inhibition of SUV39H1 via Chaetocin downregulates H3K9 trimethylation (me3), while inhibition of G9a via BIX01294 downregulates H3K9 dimethylation (me2). Overall, the loss of H3K9me3 increased nuclear blebbing and rupture in interphase nuclei due to decreased nuclear rigidity from decompaction of chromocenters. Oppositely, loss of H3K9me2 decreased nuclear blebbing and rupture with increased nuclear rigidity and more compact chromocenters. We show that facultative heterochromatin and HP1α are non-essential for chromocenter compaction. Constitutive heterochromatin provides essential nuclear mechanical support to maintain nuclear shape and integrity through chromocenter compaction.