<em>In Vitro</em> Differentiation of Mouse Granulocyte-macrophage-colony-stimulating Factor (GM-CSF)-producing T Helper (T<sub>H</sub>GM) Cells

The granulocyte-macrophage-colony-stimulating factor (GM-CSF)-producing T helper (THGM) cell is a newly identified T helper cell subset that predominantly ...

National University of Singapore

SMAD4 serves as a common mediator for signaling of TGF-β superfamily. Previous studies illustrated that SMAD4-null mice die at embryonic day 6.5 (E6.5) due to failure of mesoderm induction and extraembryonic defects; however, functions of SMAD4 in each germ layer remain elusive. To investigate this, we disrupted SMAD4 in the visceral endoderm and epiblast, respectively, using a Cre-loxP mediated approach. We showed that mutant embryos lack of SMAD4 in the visceral endoderm (Smad4(Co/Co);TTR-Cre) died at E7.5-E9.5 without head-fold and anterior embryonic structures. We demonstrated that TGF-β regulates expression of several genes, such as Hex1, Cer1, and Lim1, in the anterior visceral endoderm (AVE), and the failure of anterior embryonic development in Smad4(Co/Co);TTR-Cre embryos is accompanied by diminished expression of these genes. Consistent with this finding, SMAD4-deficient embryoid bodies showed impaired responsiveness to TGF-β-induced gene expression and morphological changes. On the other hand, embryos carrying Cre-loxP mediated disruption of SMAD4 in the epiblasts exhibited relatively normal mesoderm and head-fold induction although they all displayed profound patterning defects in the later stages of gastrulation. Cumulatively, our data indicate that SMAD4 signaling in the epiblasts is dispensable for mesoderm induction although it remains critical for head patterning, which is significantly different from SMAD4 signaling in the AVE, where it specifies anterior embryonic patterning and head induction.

Anterior visceral endoderm SMAD4 signaling specifies anterior embryonic patterning and head induction in mice.

Cardiovascular inflammation has been regarded as a major cause for heart failure. However, the mechanisms that are involved in the regulation of cardiovascular inflammation are not well understood. In this chapter, we review the recent progress in revealing the roles of STAT3 in cardiovascular inflammation. Particularly, we discuss cardiomyocyte-specific STAT3-deficient mice and their phenotypes. An emerging view is that STAT3 plays a key role not only in cardiac protection but also in the control of cardiac-related inflammation.

Multiple roles of STAT3 in cardiovascular inflammatory responses.

Histone arginine methylation has emerged as an important histone modification involved in gene regulation. Protein arginine methyltransferase (PRMT) 4 and 5 have been shown to play essential roles in early embryonic development and in embryonic stem (ES) cells. Recently, it has been reported that PRMT6-mediated di-methylation of histone H3 at arginine 2 (H3R2me2) can antagonize tri-methylation of histone H3 at lysine 4 (H3K4me3), which marks active genes. However, whether PRMT6 and PRMT6-mediated H3R2me2 play crucial roles in early embryonic development and ES cell identity remain unclear. Here, we have investigated their roles using gain and loss of function studies with mouse ES cells as a model system. We report that Prmt6 and histone H3R2 methylation levels increased when ES cells are induced to differentiate. Consistently, we find that differentiation of ES cells upon upregulation of Prmt6 is associated with decreased expression of pluripotency genes and increased expression of differentiation markers. We also observe that elevation of Prmt6 increases the methylation level of histone H3R2 and decreases H3K4me, Chd1, and Wdr5 levels at the promoter regions of Oct4 and Nanog. Surprisingly, knockdown of Prmt6 also leads to downregulation of pluripotency genes and induction of expression of differentiation markers suggesting that Prmt6 is important for ES cell pluripotency and self-renewal. Our results indicate that a critical level of Prmt6 and histone H3R2me must be maintained in mouse ES cells to sustain their pluripotency.

Protein arginine methyltransferase 6 regulates embryonic stem cell identity.

The Müller cell is the only glial cell type generated from the retinal neuroepithelium. This cell type controls normal retina homeostasis and has been suggested to play a neuroprotective role. Recent evidence suggests that mammalian Müller cells can de-differentiate and return to a progenitor or stem cell stage following injury or disease. In vivo exploration of the molecular mechanisms of Müller cell differentiation and proliferation will add essential information to manipulate Müller cell functions. Signal transduction pathways that regulate Müller cell responses and activity are a critical part of their cellular machinery. In this study, we focus on mitogen-activated protein kinase (MAPK) signaling pathway during Müller glial cell differentiation and proliferation. We found that both MAPK and STAT3 signaling pathways are present during Müller glial cell development. Ciliary neurotrophic factor (CNTF)-stimulated Müller glial cell proliferation is associated with early developmental stages. Specific inhibition of MAPK phosphorylation significantly reduced the number of Müller glial cells with or without CNTF stimulation. These results suggested that the MAPK signal transduction pathway is important in the formation of Müller glial cells during retina development.

MAPK signaling during Müller glial cell development in retina explant cultures.

Although it is known that OCT4-NANOG are required for maintenance of pluripotent cells in vitro, the upstream signals that regulate this circuit during early development in vivo have not been identified. Here we demonstrate, for the first time, signal transducers and activators of transcription 3 (STAT3)-dependent regulation of the OCT4-NANOG circuitry necessary to maintain the pluripotent inner cell mass (ICM), the source of in vitro-derived embryonic stem cells (ESCs). We show that STAT3 is highly expressed in mouse oocytes and becomes phosphorylated and translocates to the nucleus in the four-cell and later stage embryos. Using leukemia inhibitory factor (Lif)-null embryos, we found that STAT3 phosphorylation is dependent on LIF in four-cell stage embryos. In blastocysts, interleukin 6 (IL-6) acts in an autocrine fashion to ensure STAT3 phosphorylation, mediated by janus kinase 1 (JAK1), a LIF- and IL-6-dependent kinase. Using genetically engineered mouse strains to eliminate Stat3 in oocytes and embryos, we firmly establish that STAT3 is essential for maintenance of ICM lineages but not for ICM and trophectoderm formation. Indeed, STAT3 directly binds to the Oct4 and Nanog distal enhancers, modulating their expression to maintain pluripotency of mouse embryonic and induced pluripotent stem cells. These results provide a novel genetic model of cell fate determination operating through STAT3 in the preimplantation embryo and pluripotent stem cells in vivo. 

A genetic and developmental pathway from STAT3 to the OCT4-NANOG circuit is essential for maintenance of ICM lineages in vivo.

Embryonic stem cells (ESCs) derived from the inner cell mass (ICM) of blastocysts are pluripotent. Pluripotency is maintained by a transcriptional network in which Oct4 and Nanog are master regulators. Notably, several zinc finger transcription factors have important roles in this network. Patz1, a BTB/POZ-domain-containing zinc finger protein, is expressed at higher levels in the ICM relative to the trophectoderm. However, its function in pluripotency has been poorly studied. Here, we show that Patz1 is an important regulator of pluripotency in ESCs. Patz1 RNAi, chromatin immunoprecipitation (ChIP), and reporter assays indicate that Patz1 directly regulates Pou5f1 and Nanog. Global transcriptome changes upon Patz1 knockdown largely involve upregulation of apoptotic genes and downregulation of cell cycle and cellular metabolism genes. Patz1 ChIP sequencing further identified more than 5,000 binding sites of Patz1 in mouse genome, from which two binding motifs were extracted. Further, gene ontology analysis of genes associated with the binding sites displays enrichment for proximity to developmental genes. In addition, embryoid body assays suggest that Patz1 represses developmental genes. Together, these results propose that Patz1 is important for ESC pluripotency. 

Patz1 regulates embryonic stem cell identity.

Signal transducers and activators of transcription (STAT) proteins are key signalling molecules in metazoans, implicated in various cellular processes. Increased research in the field has resulted in the accumulation of STAT sequence and structure data, which are scattered across various public databases, missing extensive functional annotations, and prone to effort redundancy because of the dearth of community sharing. Therefore, there is a need to integrate the existing sequence, structure and functional data into a central repository, one that is enriched with annotations and provides a platform for community contributions. Herein, we present STATdb (publicly available at http://statdb.bic.nus.edu.sg/), the first integrated resource for STAT sequences comprising 1540 records representing the known STATome, enriched with existing structural and functional information from various databases and literature and including manual annotations. STATdb provides advanced features for data visualization, analysis and prediction, and community contributions. A key feature is a meta-predictor to characterise STAT sequences based on a novel classification that integrates STAT domain architecture, lineage and function. A curation policy workflow has been devised for regulated and structured community contributions, with an update policy for the seamless integration of new data and annotations. 

STATdb: a specialised resource for the STATome.

T helper (TH)-cell subsets, such as TH1 and TH17, mediate inflammation in both peripheral tissues and central nervous system. Here we show that STAT5 is required for T helper-cell pathogenicity in autoimmune neuroinflammation but not in experimental colitis. Although STAT5 promotes regulatory T cell generation and immune suppression, loss of STAT5 in CD4+ T cells resulted in diminished development of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Our results showed that loss of encephalitogenic activity of STAT5-deficient autoreactive CD4+ T cells was independent of IFN-γ or interleukin 17 (IL-17) production, but was due to the impaired expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), a crucial mediator of T-cell pathogenicity. We further showed that IL-7-activated STAT5 promotes the generation of GM-CSF-producing CD4+ T cells, which were preferentially able to induce more severe EAE than TH17 or TH1 cells. Consistent with GM-CSF-producing cells being a distinct subset of TH cells, the differentiation program of these cells was distinct from that of TH17 or TH1 cells. We further found that IL-3 was secreted in a similar pattern as GM-CSF in this subset of TH cells. In conclusion, the IL-7-STAT5 axis promotes the generation of GM-CSF/IL-3-producing TH cells. These cells display a distinct transcriptional profile and may represent a novel subset of T helper cells which we designate as TH-GM.

STAT5 programs a distinct subset of GM-CSF-producing T helper cells that is essential for autoimmune neuroinflammation.

Chemical RNA modifications are central features of epitranscriptomics, highlighted by the discovery of modified ribonucleosides in mRNA and exemplified by the critical roles of RNA modifications in normal physiology and disease. Despite a resurgent interest in these modifications, the biochemistry of 3-methylcytidine (mC) formation in mammalian RNAs is still poorly understood. However, the recent discovery of  as the second gene responsible for mC presence in RNA in fission yeast raises the possibility that multiple enzymes are involved in mC formation in mammals as well. Here, we report the discovery and characterization of three distinct mC-contributing enzymes in mice and humans. We found that methyltransferase-like (METTL) 2 and 6 contribute mC in specific tRNAs and that METTL8 only contributes mC to mRNA. MS analysis revealed that there is an ∼30-40% and ∼10-15% reduction, respectively, in  and  null-mutant cells, of mC in total tRNA, and primer extension analysis located METTL2-modified mC at position 32 of tRNA isoacceptors and tRNA We also noted that METTL6 interacts with seryl-tRNA synthetase in an RNA-dependent manner, suggesting a role for METTL6 in modifying serine tRNA isoacceptors. , however, modified only mRNA, as determined by biochemical and genetic analyses in  null-mutant mice and two human  mutant cell lines. Our findings provide the first evidence of the existence of mC modification in mRNA, and the discovery of METTL8 as an mRNA mC writer enzyme opens the door to future studies of other mC epitranscriptomic reader and eraser functions.

Three distinct 3-methylcytidine (mC) methyltransferases modify tRNA and mRNA in mice and humans.

Axonal injury is a common feature of central nervous system insults. Upregulation of amyloid precursor protein (APP) is observed following central nervous system neurotrauma and is regarded as a marker of central nervous system axonal injury. However, the underlying mechanism by which APP mediates neuronal death remains to be elucidated. Here, we used mouse optic nerve axotomy (ONA) to model central nervous system axonal injury replicating aspects of retinal ganglion cell (RGC) death in optic neuropathies. APP and APP intracellular domain (AICD) were upregulated in retina after ONA and APP knockout reduced Tuj1 RGC loss. Pathway analysis of microarray data combined with chromatin immunoprecipitation and a luciferase reporter assay demonstrated that AICD interacts with the JNK3 gene locus and regulates JNK3 expression. Moreover, JNK3 was found to be upregulated after ONA and to contribute to Tuj1 RGC death. APP knockout reduced the ONA-induced enhanced expression of JNK3 and phosphorylated JNK (pJNK). Gamma-secretase inhibitors prevented production of AICD, reduced JNK3 and pJNK expression similarly, and protected Tuj1 RGCs from ONA-induced cell death. Together these data indicate that ONA induces APP expression and that gamma-secretase cleavage of APP releases AICD, which upregulates JNK3 leading to RGC death. This pathway may be a novel target for neuronal protection in optic neuropathies and other forms of neurotrauma.

APP upregulation contributes to retinal ganglion cell degeneration via JNK3.

The capacity of embryonic stem cells (ESCs) to differentiate into all lineages of mature organism is precisely regulated by cellular signaling factors. STAT3 is a crucial transcription factor that plays a central role in maintaining ESC identity. However, the underlying mechanism by which STAT3 directs differentiation is still not completely understood. Here, we show that STAT3 positively regulates gene expression of methyltransferase-like protein 8 (Mettl8) in mouse ESCs. We found that METTL8 is dispensable for pluripotency but affects ESC differentiation. Subsequently, we discovered that METTL8 interacts with Mapkbp1's mRNA, which is an intermediate factor in c-Jun N-terminal kinase (JNK) signaling, and inhibits the translation of the mRNA. Thereby, METTL8 prohibits the activation of JNK signaling and enhances the differentiation of mouse ESCs. Collectively, our study uncovers a STAT3 target, Mettl8, which regulates mouse ESC differentiation via JNK signaling.

The STAT3 Target Mettl8 Regulates Mouse ESC Differentiation via Inhibiting the JNK Pathway.

Characterising the activated oncogenic signalling that leads to advanced breast cancer is of clinical importance. Here, we showed that SET domain, bifurcated 1 (SETDB1), a histone H3 lysine 9 methyltransferase, is aberrantly expressed and behaves as an oncogenic driver in breast cancer. SETDB1 enhances c-MYC and cyclin D1 expression by promoting the internal ribosome entry site (IRES)-mediated translation of MYC/CCND1 mRNA, resulting in prominent signalling of c-MYC to promote cell cycle progression, and provides a growth/self-renewal advantage to breast cancer cells. The activated c-MYC-BMI1 axis is essential for SETDB1-mediated breast tumourigenesis, because silencing of either c-MYC or BMI1 profoundly impairs the enhanced growth/colony formation conferred by SETDB1. Furthermore, c-MYC directly binds to the SETDB1 promoter region and enhances its transcription, suggesting a positive regulatory interplay between SETDB1 and c-MYC. In this study, we identified SETDB1 as a prominent oncogene and characterised the underlying mechanism whereby SETDB1 drives breast cancer, providing a therapeutic rationale for targeting SETDB1-BMI1 signalling in breast cancer. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Xin-Yuan Fu

Cancer Science Institute of Singapore,
Yong Loo Lin School of Medicine,
Cancer Science Institute of Singapore, Yong Loo Lin School of Medicine

National University of Singapore

In Vitro Differentiation of Mouse Granulocyte-macrophage-colony-stimulating Factor (GM-CSF)-producing T Helper (T_HGM) Cells

Xin-Yuan Fu

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National University of Singapore

In Vitro Differentiation of Mouse Granulocyte-macrophage-colony-stimulating Factor (GM-CSF)-producing T Helper (THGM) Cells

Cancer Science Institute of Singapore,
Yong Loo Lin School of Medicine,
Cancer Science Institute of Singapore, Yong Loo Lin School of Medicine

In Vitro Differentiation of Mouse Granulocyte-macrophage-colony-stimulating Factor (GM-CSF)-producing T Helper (T_HGM) Cells