The INO80 complex activates the transcription of S-phase genes in a cell cycle-regulated manner

The INO80 Chromatin Remodeling Complex Regulates Histone H2A.Z Mobility and the G1-S Transition in Oligodendrocyte Precursors

Chromatin remodeling complexes (CRCs) participate in oligodendrocyte (OL) differentiation, survival, and maintenance. We asked whether CRCs also control the proliferation of OL precursors (OPs)-focusing on the INO80 complex, which is known to regulate the proliferation of a variety of other cell types during development and disease. CRISPR/Cas9-mediated inactivation of Ino80 in vitro, or Cre-mediated deletion in vivo, slowed the OP cell cycle substantially by prolonging G1. RNAseq analysis revealed that E2F target genes were dysregulated in OPs from INO80-deficient mice, but correlated RNAseq and ATAC-seq uncovered no general correlation between gene expression and altered nucleosome positioning at transcription start sites. Fluorescence photobleaching experiments in cultured OPs demonstrated that histone H2A.Z mobility increased following the loss of INO80, suggesting that INO80 regulates the cell cycle machinery in OPs through H2A.Z/H2A exchange. We also present evidence that INO80 associates with OLIG2, a master regulator of OL development.

Human chromatin remodelers regulating HIV-1 transcription: a target for small molecule inhibitors

HIV-1 can establish a lifelong infection by incorporating its proviral DNA into the host genome. Once integrated, the virus can either remain dormant or start active transcription, a process governed by the HIV Tat protein, host transcription factors and the chromatin landscape at the integration site. Histone-modifying enzymes and chromatin-remodeling enzymes play crucial roles in regulating this chromatin environment. Chromatin remodelers, a group of ATP-dependent proteins, collaborate with host proteins and histone-modifying enzymes to restructure nucleosomes, facilitating DNA repair, replication, and transcription. Recent studies have highlighted the importance of chromatin remodelers in HIV-1 latency, spurring research focused on developing small molecule modulators that can either reactivate the virus for eradication approaches or induce long-term latency to prevent future reactivation. Research efforts have primarily centered on the SWI/SNF family, though much remains to be uncovered regarding other chromatin remodeling families. This review delves into the general functions and roles of each chromatin remodeling family in the context of HIV and discusses recent advances in small molecule development targeting chromatin remodelers and the HIV Tat protein, aiming to improve therapeutic approaches against HIV.

INO80 Is Required for the Cell Cycle Control, Survival, and Differentiation of Mouse ESCs by Transcriptional Regulation

Precise regulation of the cell cycle of embryonic stem cells (ESCs) is critical for their self-maintenance and differentiation. The cell cycle of ESCs differs from that of somatic cells and is different depending on the cell culture conditions. However, the cell cycle regulation in ESCs via epigenetic mechanisms remains unclear. Here, we showed that the ATP-dependent chromatin remodeler Ino80 regulates the cell cycle genes in ESCs under primed conditions. Ino80 loss led to a significantly extended length of the G1-phase in ESCs grown under primed culture conditions. Ino80 directly bound to the transcription start site and regulated the expression of cell cycle-related genes. Furthermore, Ino80 loss induced cell apoptosis. However, the regulatory mechanism of Ino80 in differentiating ESC cycle slightly differed; an extended S-phase was detected in differentiating inducible Ino80 knockout ESCs. RNA-seq analysis of differentiating ESCs revealed that the expression of genes associated with organ development cell cycle is persistently altered in Ino80 knockout cells, suggesting that cell cycle regulation by Ino80 is not limited to undifferentiated ESCs. Therefore, our study establishes the function of Ino80 in ESC cycle via transcriptional regulation, at least partly. Moreover, this Ino80 function may be universal to other cell types.

INO80 requires a polycomb subunit to regulate the establishment of poised chromatin in murine spermatocytes

INO80 is the catalytic subunit of the INO80-chromatin remodeling complex that is involved in DNA replication, repair and transcription regulation. Ino80 deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes due to incomplete synapsis and aberrant DNA double-strand break repair, which leads to apoptosis. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WT spermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Furthermore, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment and, in turn, showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Furthermore, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.

SWI/SNF and RSC remodeler complexes bind to MBF-dependent genes

In fission yeast, MBF-dependent transcription is required for cells to complete S phase. The MBF transcription factor is regulated through a complex feedback mechanism that involves the co-repressors Yox1 and Nrm1 that are loaded onto MBF at the end of S phase, while positive transactivation is achieved through the constitutive binding of the co-activator Rep2. Here we show that Rep2 is required to fully recruit the chromatin remodelers SWI/SNF and RSC to MBF-regulated promoters. On the contrary, Nrm1 and Yox1, when bound to the MBF complex, block the approximation of these chromatin remodelers to MBF-regulated promoters. We propose that SWI/SNF and RSC are recruited to MBF-regulated genes, and RSC together with SAGA complex are important to regulate the G1-to-S transcriptional wave. Mutants of these remodeler complexes are highly sensitive when cells are exposed to insults that challenge DNA synthesis.

High-Throughput Flow Cytometry Combined with Genetic Analysis Brings New Insights into the Understanding of Chromatin Regulation of Cellular Quiescence

Cellular quiescence is a reversible differentiation state when cells are changing the gene expression program to reduce metabolic functions and adapt to a new cellular environment. When fission yeast cells are deprived of nitrogen in the absence of any mating partner, cells can reversibly arrest in a differentiated G₀-like cellular state, called quiescence. This change is accompanied by a marked alteration of nuclear organization and a global reduction of transcription. Using high-throughput flow cytometry combined with genetic analysis, we describe the results of a comprehensive screen for genes encoding chromatin components and regulators that are required for the entry and the maintenance of cellular quiescence. We show that the histone acetylase and deacetylase complexes, SAGA and Rpd3, have key roles both for G₀ entry and survival during quiescence. We reveal a novel function for the Ino80 nucleosome remodeling complex in cellular quiescence. Finally, we demonstrate that components of the MRN complex, Rad3, the nonhomologous end-joining, and nucleotide excision DNA repair pathways are essential for viability in G_0.

Gcn5-mediated acetylation at MBF-regulated promoters induces the G1/S transcriptional wave

In fission yeast, MBF-dependent transcription is inactivated at the end of S phase through a negative feedback loop that involves the co-repressors, Yox1 and Nrm1. Although this repression system is well known, the molecular mechanisms involved in MBF activation remain largely unknown. Compacted chromatin constitutes a barrier to activators accessing promoters. Here, we show that chromatin regulation plays a key role in activating MBF-dependent transcription. Gcn5, a part of the SAGA complex, binds to MBF-regulated promoters through the MBF co-activator Rep2 in a cell cycle-dependent manner and in a reverse correlation to the binding of the MBF co-repressors, Nrm1 or Yox1. We propose that the co-repressors function as physical barriers to SAGA recruitment onto MBF promoters. We also show that Gcn5 acetylates specific lysine residues on histone H3 in a cell cycle-regulated manner. Furthermore, either in a gcn5 mutant or in a strain in which histone H3 is kept in an unacetylated form, MBF-dependent transcription is downregulated. In summary, Gcn5 is required for the full activation and correct timing of MBF-regulated gene transcription.

Transcriptional responses to DNA damage

In response to the threat of DNA damage, cells exhibit a dramatic and multi-factorial response spanning from transcriptional changes to protein modifications, collectively known as the DNA damage response (DDR). Here, we review the literature surrounding the transcriptional response to DNA damage. We review differences in observed transcriptional responses as a function of cell cycle stage and emphasize the importance of experimental design in these transcriptional response studies. We additionally consider topics including structural challenges in the transcriptional response to DNA damage as well as the connection between transcription and protein abundance.