A novel lncRNA Discn fine-tunes replication protein A (RPA) availability to promote genomic stability.

RPA is a master regulator of DNA metabolism and RPA availability acts as a rate-limiting factor. While numerous studies focused on the post-translational regulations of RPA for its functions, little is known regarding how RPA availability is controlled. Here we identify a novel lncRNA Discn as the guardian of RPA availability in stem cells. Discn is induced upon genotoxic stress and binds to neucleolin (NCL) in the nucleolus. This prevents NCL from translocation into nucleoplasm and avoids undesirable NCL-mediated RPA sequestration. Thus, Discn-NCL-RPA pathway preserves a sufficient RPA pool for DNA replication stress response and repair. Discn loss causes massive genome instability in mouse embryonic stem cells and neural stem/progenigor cells. Mice depleted of Discn display newborn death and brain dysfunctions due to DNA damage accumulation and associated inflammatory reactions. Our findings uncover a key regulator of DNA metabolism and provide new clue to understand the chemoresistance in cancer treatment.

XBP1s repression regulates Kupffer cell polarization leading to immune suppressive effects protecting liver allograft in rats.

BACKGROUND: Polarized kupffer cells (KCs) influence the immune response after liver transplantation. We report an undiscovered immune regulatory role of X-box binding protein 1 (XBP1) on immune function of kupffer cells (KCs). METHODS: Acute rejection model using rats. RESULTS: We found that suppression of XBP1s in lipopolysaccharide (LPS) -activated KCs could increase the expression of arginase-1 (Arg-1) and CD204 but also decrease the expression levels of MHC-II and CD40 and shift the phenotype markers of KCs toward M2 via the janus kinase (JAK) 3- Signal Transducer And Activator Of Transcription (STAT) 6 pathway, presenting an immunosuppressive function by enhancing anti-inflammatory cytokine secretion and accelerating apoptosis of activated T cells. XBP1s over-expression in KCs shift the phenotype markers on KCs towards M1 via the JAK1-STAT1 pathway and have shown a strong pro-inflammatory property. Down-regulation of XBP1s in KCs changed the phenotype and cytokine secretion profile towards M2 and markedly protected the function and structure of allograft liver, prolonging the recipient's survival compared with control and normal saline groups in rats. CONCLUSIONS: Our findings reveal a novel regulatory mechanism of XBP1 in an induced immuno-suppressive state to protect rat's liver allograft via JAK-STAT mediated KCs polarization.

Genome integrity and neurogenesis of postnatal hippocampal neural stem/progenitor cells require a unique regulator Filia.

Endogenous DNA double-strand breaks (DSBs) formation and repair in neural stem/progenitor cells (NSPCs) play fundamental roles in neurogenesis and neurodevelopmental disorders. NSPCs exhibit heterogeneity in terms of lineage fates and neurogenesis activity. Whether NSPCs also have heterogeneous regulations on DSB formation and repair to accommodate region-specific neurogenesis has not been explored. Here, we identified a regional regulator Filia, which is predominantly expressed in mouse hippocampal NSPCs after birth and regulates DNA DSB formation and repair. On one hand, Filia protects stalling replication forks and prevents the replication stress-associated DNA DSB formation. On the other hand, Filia facilitates the homologous recombination-mediated DNA DSB repair. Consequently, Filia-/- mice had impaired hippocampal NSPC proliferation and neurogenesis and were deficient in learning, memory, and mood regulations. Thus, our study provided the first proof of concept demonstrating the region-specific regulations of DSB formation and repair in subtypes of NSPCs.

Identification of the primate-specific gene BTN3A2 as an additional schizophrenia risk gene in the MHC loci.

BACKGROUND: Schizophrenia is a complex mental disorder resulting in poor life quality and high social and economic burden. Despite the fact that genome-wide association studies (GWASs) have successfully identified a number of risk loci for schizophrenia, identifying the causal genes at the risk loci and elucidating their roles in disease pathogenesis remain major challenges. METHODS: The summary data-based Mendelian randomization analysis (SMR) was used to integrate a large-scale GWAS of schizophrenia with brain expression quantitative trait loci (eQTL) data and brain methylation expression quantitative trait loci (meQTL) data, to identify novel risk gene(s) for schizophrenia. We then analyzed the mRNA expression and methylation statuses of the gene hit BTN3A2 during the early brain development. Electrophysiological analyses of CA1 pyramidal neurons were performed to evaluate the excitatory and inhibitory synaptic activity after overexpression of BTN3A2 in rat hippocampal slices. Cell surface binding assay was used to test the interaction of BTN3A2 and neurexins. FINDINGS: We identified BTN3A2 as a potential risk gene for schizophrenia. The mRNA expression and methylation data showed that BTN3A2 expression in human brain is highest post-natally. Further electrophysiological analyses of rat hippocampal slices showed that BTN3A2 overexpression specifically suppressed the excitatory synaptic activity onto CA1 pyramidal neurons, most likely through its interaction with the presynaptic adhesion molecule neurexins. INTERPRETATION: Increased expression of BTN3A2 might confer risk for schizophrenia by altering excitatory synaptic function. Our result constitutes a paradigm for distilling risk gene using an integrative analysis and functional characterization in the post-GWAS era. FUND: This study was supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB02020003 to Y-GY), the National Natural Science Foundation of China (31730037 to Y-GY), and the Bureau of Frontier Sciences and Education, Chinese Academy of Sciences (QYZDJ-SSW-SMC005 to Y-GY).

Maternal gene Ooep may participate in homologous recombination-mediated DNA double-strand break repair in mouse oocytes.

DNA damage in oocytes can cause infertility and birth defects. DNA double-strand breaks (DSBs) are highly deleterious and can substantially impair genome integrity. Homologous recombination (HR)-mediated DNA DSB repair plays dominant roles in safeguarding oocyte quantity and quality. However, little is known regarding the key players of the HR repair pathway in oocytes. Here, we identified oocyte-specific gene Ooep as a novel key component of the HR repair pathway in mouse oocytes. OOEP was required for efficient ataxia telangiectasia mutated (ATM) kinase activation and Rad51 recombinase(RAD51)focal accumulation at DNA DSBs. Ooep null oocytes were defective in DNA DSB repair and prone to apoptosis upon exogenous DNA damage insults. Moreover, Ooep null oocytes exhibited delayed meiotic maturation. Therefore, OOEP played roles in preserving oocyte quantity and quality by maintaining genome stability. Ooep expression decreased with the advance of maternal age, suggesting its involvement in maternal aging.

Mouse embryonic stem cells have increased capacity for replication fork restart driven by the specific Filia-Floped protein complex.

Pluripotent stem cells (PSCs) harbor constitutive DNA replication stress during their rapid proliferation and the consequent genome instability hampers their applications in regenerative medicine. It is therefore important to understand the regulatory mechanisms of replication stress response in PSCs. Here, we report that mouse embryonic stem cells (ESCs) are superior to differentiated cells in resolving replication stress. Specifically, ESCs utilize a unique Filia-Floped protein complex-dependent mechanism to efficiently promote the restart of stalled replication forks, therefore maintaining genomic stability. The ESC-specific Filia-Floped complex resides on replication forks under normal conditions. Replication stress stimulates their recruitment to stalling forks and the serine 151 residue of Filia is phosphorylated in an ATR-dependent manner. This modification enables the Filia-Floped complex to act as a functional scaffold, which then promotes the stalling fork restart through a dual mechanism: both enhancing recruitment of the replication fork restart protein, Blm, and stimulating ATR kinase activation. In the Blm pathway, the scaffolds recruit the E3 ubiquitin ligase, Trim25, to the stalled replication forks, and in turn Trim25 tethers and concentrates Blm at stalled replication forks through ubiquitination. In differentiated cells, the recruitment of the Trim25-Blm complex to replication forks and the activation of ATR signaling are much less robust due to lack of the ESC-specific Filia-Floped scaffold. Thus, our study reveals that ESCs utilize an additional and unique regulatory layer to efficiently promote the stalled fork restart and maintain genomic stability.