Human PSF concentrates DNA and stimulates duplex capture in DMC1-mediated homologous pairing

PSF is considered to have multiple functions in RNA processing, transcription and DNA repair by mitotic recombination. In the present study, we found that PSF is produced in spermatogonia, spermatocytes and spermatids, suggesting that PSF may also function in meiotic recombination. We tested the effect of PSF on homologous pairing by the meiosis-specific recombinase DMC1, and found that human PSF robustly stimulated it. PSF synergistically enhanced the formation of a synaptic complex containing DMC1, ssDNA and dsDNA during homologous pairing. The PSF-mediated DMC1 stimulation may be promoted by its DNA aggregation activity, which increases the local concentrations of ssDNA and dsDNA for homologous pairing by DMC1. These results suggested that PSF may function as an activator for the meiosis-specific recombinase DMC1 in higher eukaryotes

GEMIN2 promotes accumulation of RAD51 at double-strand breaks in homologous recombination

RAD51 is a key factor in homologous recombination (HR) and plays an essential role in cellular proliferation by repairing DNA damage during replication. The assembly of RAD51 at DNA damage is strictly controlled by RAD51 mediators, including BRCA1 and BRCA2. We found that human RAD51 directly binds GEMIN2/SIP1, a protein involved in spliceosome biogenesis. Biochemical analyses indicated that GEMIN2 enhances the RAD51–DNA complex formation by inhibiting RAD51 dissociation from DNA, and thereby stimulates RAD51-mediated homologous pairing. GEMIN2 also enhanced the RAD51-mediated strand exchange, when RPA was pre-bound to ssDNA before the addition of RAD51. To analyze the function of GEMIN2, we depleted GEMIN2 in the chicken DT40 line and in human cells. The loss of GEMIN2 reduced HR efficiency and resulted in a significant decrease in the number of RAD51 subnuclear foci, as observed in cells deficient in BRCA1 and BRCA2. These observations and our biochemical analyses reveal that GEMIN2 regulates HR as a novel RAD51 mediator

Reversing SKI-SMAD4-mediated suppression is essential for TH17 cell differentiation

T helper 17 (TH17) cells are critically involved in host defence, inflammation, and autoimmunity. Transforming growth factor β (TGFβ) is instrumental in TH17 cell differentiation by cooperating with interleukin-6 (refs 6, 7). Yet, the mechanism by which TGFβ enables TH17 cell differentiation remains elusive. Here we reveal that TGFβ enables TH17 cell differentiation by reversing SKI-SMAD4-mediated suppression of the expression of the retinoic acid receptor (RAR)-related orphan receptor γt (RORγt). We found that, unlike wild-type T cells, SMAD4-deficient T cells differentiate into TH17 cells in the absence of TGFβ signalling in a RORγt-dependent manner. Ectopic SMAD4 expression suppresses RORγt expression and TH17 cell differentiation of SMAD4-deficient T cells. However, TGFβ neutralizes SMAD4-mediated suppression without affecting SMAD4 binding to the Rorc locus. Proteomic analysis revealed that SMAD4 interacts with SKI, a transcriptional repressor that is degraded upon TGFβ stimulation. SKI controls histone acetylation and deacetylation of the Rorc locus and TH17 cell differentiation via SMAD4: ectopic SKI expression inhibits H3K9 acetylation of the Rorc locus, Rorc expression, and TH17 cell differentiation in a SMAD4-dependent manner. Therefore, TGFβ-induced disruption of SKI reverses SKI-SMAD4-mediated suppression of RORγt to enable TH17 cell differentiation. This study reveals a critical mechanism by which TGFβ controls TH17 cell differentiation and uncovers the SKI-SMAD4 axis as a potential therapeutic target for treating TH17-related diseases

High-quality ChIP-seq analysis of MBD3 in human breast cancer cells

Chromatin accessibility is tightly regulated by multiple factors/mechanisms to establish different cell type-specific gene expression programs from a single genome. Dysregulation of this process can lead to diseases including cancer. The Mi-2/nucleosome remodeling and deacetylase (NuRD) complex is thought to orchestrate chromatin structure using its intrinsic nucleosome remodeling and histone deacetylase activities. However, the detailed mechanisms by which the NuRD complex regulates chromatin structure in vivo are not yet known. To explore the regulatory mechanisms of the NuRD complex, we mapped genome-wide localization of MBD3, a structural component of NuRD, in a human breast cancer cell line (MDA-MB-231) using a modified ChIP-seq protocol. Our data showed high quality localization information (i.e., high mapping efficiency and low PCR duplication rate) and excellent consistency between biological replicates. The data are deposited in the Gene Expression Omnibus (GSE76116). Keywords: ChIP-seq, Mi-2/NuRD, Breast cance

Human PSF binds to RAD51 and modulates its

homologous-pairing and strand-exchange activitie

Interaction of the pioneer transcription factor GATA3 with nucleosomes

GATA 3 functions as a pioneer factor during cellular reprogramming. Here the authors delineate nucleosome positioning relative to GATA3 binding motifs and describe the structure of a GATA3–nucleosome complex; providing insight into how a pioneer factor interacts with nucleosomes and catalyze their local remodelling to produce an accessible enhancer