Reduced chromatin accessibility correlates with resistance to Notch activation

ETS1 and RBPJ transcriptionally regulate METTL14 to suppress TGF-β1-induced epithelial-mesenchymal transition in human bronchial epithelial cells

Asthma is a chronic respiratory disease characterized by airway inflammation and remodeling. Epithelial-mesenchymal transition (EMT) of bronchial epithelial cells is considered to be a crucial player in asthma. Methyltransferase-like 14 (METTL14), an RNA methyltransferase, is implicated in multiple pathological processes, including EMT, cell proliferation and migration. However, the role of METTL14 in asthma remains uncertain. This research aimed to explore the biological functions of METTL14 in asthma and its underlying upstream mechanisms. METTL14 expression was down-regulated in asthmatic from three GEO datasets (GSE104468, GSE165934, and GSE74986). Consistent with this trend, METTL14 was decreased in the lung tissues of OVA-induced asthmatic mice and transforming growth factor-β1 (TGF-β1)-stimulated human bronchial epithelial cells (Beas-2B) in this study. Overexpression of METTL14 caused reduction in mesenchymal markers (FN1, N-cad, Col-1 and α-SMA) in TGF-β1-treated cells, but caused increase in epithelial markers (E-cad), thus inhibiting EMT. Also, METTL14 suppressed the proliferation and migration ability of TGF-β1-treated Beas-2B cells. Two transcription factors, ETS1 and RBPJ, could both bind to the promoter region of METTL14 and drive its expression. Elevating METTL14 expression could reversed EMT, cell proliferation and migration promoted by ETS1 or RBPJ deficiency. These results indicate that the ETS1/METTL14 and RBPJ/METTL14 transcription axes exhibit anti-EMT, anti-proliferation and anti-migration functions in TGF-β1-induced bronchial epithelial cells, implying that METTL14 may be considered an alternative candidate target for the treatment of asthma.

The Neurog2-Tbr2 axis forms a continuous transition to the neurogenic gene expression state in neural stem cells

Neural stem cells (NSCs) differentiate into neuron-fated intermediate progenitor cells (IPCs) via cell division. Although differentiation from NSCs to IPCs is a discrete process, recent transcriptome analyses identified a continuous transcriptional trajectory during this process, raising the question of how to reconcile these contradictory observations. In mouse NSCs, Hes1 expression oscillates, regulating the oscillatory expression of the proneural gene Neurog2, while Hes1 expression disappears in IPCs. Thus, the transition from Hes1 oscillation to suppression is involved in the differentiation of NSCs to IPCs. Here, we found that Neurog2 oscillations induce the accumulation of Tbr2, which suppresses Hes1 expression, generating an IPC-like gene expression state in NSCs. In the absence of Tbr2, Hes1 expression is up-regulated, decreasing the formation of IPCs. These results indicate that the Neurog2-Tbr2 axis forms a continuous transcriptional trajectory to an IPC-like neurogenic state in NSCs, which then differentiate into IPCs via cell division.

Notch induces transcription by stimulating release of paused RNA Polymerase II

Notch proteins undergo ligand-induced proteolysis to release a nuclear effector that influences a wide range of cellular processes by regulating transcription. Despite years of study, however, how Notch induces the transcription of its target genes remains unclear. Here, we comprehensively examined the response to human Notch1 across a time course of activation using high-resolution genomic assays of chromatin accessibility and nascent RNA production. Our data reveal that Notch induces target gene transcription primarily by releasing paused RNA polymerase II (RNAPII). Moreover, in contrast to prevailing models suggesting that Notch acts by promoting chromatin accessibility, we found that open chromatin was established at Notch-responsive regulatory elements prior to Notch signal induction, through SWI/SNF-mediated remodeling. Together, these studies show that the nuclear response to Notch signaling is dictated by the pre-existing chromatin state and RNAPII distribution at the time of signal activation.

HOPX-associated molecular programs control cardiomyocyte cell states underpinning cardiac structure and function

Genomic regulation of cardiomyocyte differentiation is central to heart development and function. This study uses genetic loss-of-function human-induced pluripotent stem cell-derived cardiomyocytes to evaluate the genomic regulatory basis of the non-DNA-binding homeodomain protein HOPX. We show that HOPX interacts with and controls cardiac genes and enhancer networks associated with diverse aspects of heart development. Using perturbation studies in vitro, we define how upstream cell growth and proliferation control HOPX transcription to regulate cardiac gene programs. We then use cell, organoid, and zebrafish regeneration models to demonstrate that HOPX-regulated gene programs control cardiomyocyte function in development and disease. Collectively, this study mechanistically links cell signaling pathways as upstream regulators of HOPX transcription to control gene programs underpinning cardiomyocyte identity and function.

Notch Signaling Plays a Dual Role in Regulating the Neuron-to-Oligodendrocyte Switch in the Developing Dorsal Forebrain

Neural progenitor cells in the developing dorsal forebrain generate excitatory neurons followed by oligodendrocytes (OLs) and astrocytes. However, the specific mechanisms that regulate the timing of this neuron-glia switch are not fully understood. In this study, we show that the proper balance of Notch signaling in dorsal forebrain progenitors is required to generate oligodendrocytes during late stages of embryonic development. Using ex vivo and in utero approaches in mouse embryos of both sexes, we found that Notch inhibition reduced the number of oligodendrocyte lineage cells in the dorsal pallium. However, Notch overactivation also prevented oligodendrogenesis and maintained a progenitor state. These results point toward a dual role for Notch signaling in both promoting and inhibiting oligodendrogenesis, which must be fine-tuned to generate oligodendrocyte lineage cells at the right time and in the right numbers. We further identified the canonical Notch downstream factors HES1 and HES5 as negative regulators in this process. CRISPR (clustered regularly interspaced short palindromic repeat)/Cas9-mediated knockdown of Hes1 and Hes5 caused increased expression of the pro-oligodendrocyte factor ASCL1 and led to precocious oligodendrogenesis. Conversely, combining Notch overactivation with ASCL1 overexpression robustly promoted oligodendrogenesis, indicating a separate mechanism of Notch that operates synergistically with ASCL1 to specify an oligodendrocyte fate. We propose a model in which Notch signaling works together with ASCL1 to specify progenitors toward the oligodendrocyte lineage but also maintains a progenitor state through Hes-dependent repression of Ascl1 so that oligodendrocytes are not made too early, thus contributing to the precise timing of the neuron-glia switch.SIGNIFICANCE STATEMENT Neural progenitors make oligodendrocytes after neurogenesis starts to wind down, but the mechanisms that control the timing of this switch are poorly understood. In this study, we identify Notch signaling as a critical pathway that regulates the balance between progenitor maintenance and oligodendrogenesis. Notch signaling is required for the oligodendrocyte fate, but elevated Notch signaling prevents oligodendrogenesis and maintains a progenitor state. We provide evidence that these opposing functions are controlled by different mechanisms. Before the switch, Notch signaling through Hes factors represses oligodendrogenesis. Later, Notch signaling through an unknown mechanism promotes oligodendrogenesis synergistically with the transcription factor ASCL1. Our study underscores the complexity of Notch and reveals its importance in regulating the timing and numbers of oligodendrocyte production.

Hypocretin-1 suppresses malignant progression of glioblastoma cells through Notch1 signaling pathway

Hypocretin-1 is a multifunctional neuropeptide that has been identified as a potential antitumor agent for its role in inhibiting tumor growth, including in colon cancer, neuroendocrine tumor, and prostate cancer. However, the role and mechanism of hypocretin-1 in the occurrence and development of malignant glioma have not been well studied. Therefore, we investigated the effect of hypocretin-1 on glioblastoma proliferation, apoptosis, migration and invasion and its mechanism. We found that the hypocretin-1 receptor was expressed in both glioma cell lines and glioma tissues. Hypocretin-1 treatment can inhibit glioblastoma cell proliferation, migration and invasion, and induce cell apoptosis. Meanwhile, hypocretin-1 treatment significantly reduces tumor growth rate and tumor weight. In addition, mechanistic studies have found that hypocretin-1 exerts antitumor effects by inhibiting NOTCH signaling pathway. Overexpression of NICD significantly reversed the antitumor effect of hypocretin on glioblastoma. Taken together, these findings suggest that hypocretin-1 inhibits glioblastoma proliferation, migration and invasion and induces apoptosis in vitro and in vivo through NOTCH signaling pathway.

Mitochondrial respiration and dynamics of in vivo neural stem cells

Neural stem cells (NSCs) in the developing and adult brain undergo many different transitions, tightly regulated by extrinsic and intrinsic factors. While the role of signalling pathways and transcription factors is well established, recent evidence has also highlighted mitochondria as central players in NSC behaviour and fate decisions. Many aspects of cellular metabolism and mitochondrial biology change during NSC transitions, interact with signalling pathways and affect the activity of chromatin-modifying enzymes. In this Spotlight, we explore recent in vivo findings, primarily from Drosophila and mammalian model systems, about the role that mitochondrial respiration and morphology play in NSC development and function.