Implication of retinoic acid receptor selective signaling in myogenic differentiation.
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ABSTRACT: Signaling molecules are important for committing individual cells into tissue-specific lineages during early vertebrate development. Retinoic acid (RA) is an important vertebrate morphogen, in that its concentration gradient is essential for correct patterning of the vertebrate embryo. RA signaling is mediated through the activation of retinoic acid receptors (RARs), which function as ligand-dependent transcription factors. In this study, we examined the molecular mechanisms of RAR-selective signaling in myogenic differentiation. We found that just like natural ligand RA, a RAR-selective ligand is an effective enhancer in the commitment of skeletal muscle lineage at the early stage of myogenic differentiation. Interestingly, the kinetics and molecular basis of the RAR-selective ligand in myogenic differentiation are similar to that of natural ligand RA. Also similar to natural ligand RA, the RAR-selective ligand enhances myogenic differentiation through β-catenin signaling pathway while inhibiting cardiac differentiation. Furthermore, while low concentrations of natural ligand RA or RAR-selective ligand regulate myogenic differentiation through RAR function and coactivator recruitment, high concentrations are critical to the expression of a model RA-responsive gene. Thus our data suggests that RAR-mediated gene regulation may be highly context-dependent, affected by locus-specific interaction or local chromatin environment.
Project description:Whether or not the process of somitogenesis and myogenesis is affected by excessive caffeine intake still remains ambiguous. In this study, we first showed that caffeine treatment results in chest wall deformities and simultaneously reduced mRNA expressions of genes involved in myogenesis in the developing chicken embryos. We then used embryo cultures to assess in further detail how caffeine exposure affects the earliest steps of myogenesis, and we demonstrated that the caffeine treatment suppressed somitogenesis of chicken embryos by interfering with the expressions of crucial genes modulating apoptosis, proliferation, and differentiation of myogenic progenitors in differentiating somites. These phenotypes were abrogated by a retinoic acid (RA) antagonist in embryo cultures, even at low caffeine doses in C2C12 cells, implying that excess RA levels are responsible for these phenotypes in cells and possibly in vivo. These findings highlight that excessive caffeine exposure is negatively involved in regulating the development of myogenic progenitors through interfering with RA signaling. The RA somitogenesis/myogenesis pathway might be directly impacted by caffeine signaling rather than reflecting an indirect effect of the toxicity of excess caffeine dosage.
Project description:Retinoids play key roles in development, differentiation, and homeostasis through regulation of specific target genes by the retinoic acid receptor/retinoid X receptor (RAR/RXR) nuclear receptor complex. Corepressors and coactivators contribute to its transcriptional control by creating the appropriate chromatin environment, but the precise composition of these nuclear receptor complexes remains to be elucidated. Using an RNA interference-based genetic screen in mouse F9 cells, we identified the transcriptional corepressor CTBP2 (C-terminal binding protein 2) as a coactivator critically required for retinoic acid (RA)-induced transcription. CTBP2 suppression by RNA interference confers resistance to RA-induced differentiation in diverse murine and human cells. Mechanistically, we find that CTBP2 associates with RAR/RXR at RA target gene promoters and is essential for their transactivation in response to RA. We show that CTBP2 is indispensable to create a chromatin environment conducive for RAR/RXR-mediated transcription by recruiting the histone acetyltransferase p300. Our data reveal an unexpected function of the corepressor CTBP2 as a coactivator for RAR/RXR in RA signaling.
Project description:T helper 9 (Th9) cells are interleukin 9 (IL-9)-producing cells that have diverse functions ranging from antitumor immune responses to allergic inflammation. Th9 cells differentiate from naïve CD4+ T cells in the presence of IL-4 and transforming growth factor-beta (TGF-β); however, our understanding of the molecular basis of their differentiation remains incomplete. Previously, we reported that the differentiation of another subset of TGF-β-driven T helper cells, Th17 cells, is highly dependent on de novo lipid biosynthesis. On the basis of these findings, we hypothesized that lipid metabolism may also be important for Th9 cell differentiation. We therefore investigated the differentiation and function of mouse and human Th9 cells in vitro under conditions of pharmacologically or genetically induced deficiency of the intracellular fatty acid content and in vivo in mice genetically deficient in acetyl-CoA carboxylase 1 (ACC1), an important enzyme for fatty acid biosynthesis. Both the inhibition of de novo fatty acid biosynthesis and the deprivation of environmental lipids augmented differentiation and IL-9 production in mouse and human Th9 cells. Mechanistic studies revealed that the increase in Th9 cell differentiation was mediated by the retinoic acid receptor and the TGF-β-SMAD signaling pathways. Upon adoptive transfer, ACC1-inhibited Th9 cells suppressed tumor growth in murine models of melanoma and adenocarcinoma. Together, our findings highlight a novel role of fatty acid metabolism in controlling the differentiation and in vivo functions of Th9 cells.
Project description:Herein, we report the first evidence that c-SRC is required for retinoic acid (RA) receptor (RAR) signaling, an observation that suggests a new paradigm for this family of nuclear hormone receptors. We observed that CSK negatively regulates RAR functions required for neuritogenic differentiation. CSK overexpression inhibited RA-mediated neurite outgrowth, a result which correlated with the inhibition of the SFK c-SRC. Consistent with an extranuclear effect of CSK on RAR signaling and neurite outgrowth, CSK overexpression blocked the downstream activation of RAC1. The conversion of GDP-RAC1 to GTP-RAC1 parallels the activation of c-SRC as early as 15 min following all-trans-retinoic acid treatment in LA-N-5 cells. The cytoplasmic colocalization of c-SRC and RARgamma was confirmed by immunofluorescence staining and confocal microscopy. A direct and ligand-dependent binding of RAR with SRC was observed by surface plasmon resonance, and coimmunoprecipitation studies confirmed the in vivo binding of RARgamma to c-SRC. Deletion of a proline-rich domain within RARgamma abrogated this interaction in vivo. CSK blocked the RAR-RA-dependent activation of SRC and neurite outgrowth in LA-N-5 cells. The results suggest that transcriptional signaling events mediated by RA-RAR are necessary but not sufficient to mediate complex differentiation in neuronal cells. We have elucidated a nongenomic extranuclear signal mediated by the RAR-SRC interaction that is negatively regulated by CSK and is required for RA-induced neuronal differentiation.
Project description:Deciphering the molecular mechanisms underpinning myoblast differentiation is a critical step in developing the best strategy to promote muscle regeneration in patients suffering from muscle-related diseases. We have previously established that a rexinoid x receptor (RXR)-selective agonist, bexarotene, enhances the differentiation and fusion of myoblasts through a direct regulation of MyoD expression, coupled with an augmentation of myogenin protein. Here, we found that RXR signaling associates with the distribution of myogenin at poised enhancers and a distinct E-box motif. We also found an association of myogenin with rexinoid-responsive gene expression and identified an epigenetic signature related to histone acetyltransferase p300. Moreover, RXR signaling augments residue-specific histone acetylation at enhancers co-occupied by p300 and myogenin. Thus, genomic distribution of transcriptional regulators is an important designate for identifying novel targets as well as developing therapeutics that modulate epigenetic landscape in a selective manner to promote muscle regeneration.
Project description:All-trans retinoic acid (RA) signals via binding to retinoic acid receptors (RARs ?, ?, and ?). RA directly influences expression of Pdx1, a transcription factor essential for pancreatic development and beta-cell (?-cell) maturation. In this study we follow the differentiation of cultured wild-type (WT) vs. RAR? knockout (KO) embryonic stem (ES) cells into pancreatic islet cells. We found that RAR? KO ES cells show greatly reduced expression of some important endocrine markers of differentiated islet cells, such as glucagon, islet amyloid polypeptide (Iapp), and insulin 1 (Ins1) relative to WT. We conclude that RAR? activity is essential for proper differentiation of ES cells to pancreatic endocrine cells.
Project description:FOXP2 was the first gene shown to cause a Mendelian form of speech and language disorder. Although developmentally expressed in many organs, loss of a single copy of FOXP2 leads to a phenotype that is largely restricted to orofacial impairment during articulation and linguistic processing deficits. Why perturbed FOXP2 function affects specific aspects of the developing brain remains elusive. We investigated the role of FOXP2 in neuronal differentiation and found that FOXP2 drives molecular changes consistent with neuronal differentiation in a human model system. We identified a network of FOXP2 regulated genes related to retinoic acid signaling and neuronal differentiation. FOXP2 also produced phenotypic changes associated with neuronal differentiation including increased neurite outgrowth and reduced migration. Crucially, cells expressing FOXP2 displayed increased sensitivity to retinoic acid exposure. This suggests a mechanism by which FOXP2 may be able to increase the cellular differentiation response to environmental retinoic acid cues for specific subsets of neurons in the brain. These data demonstrate that FOXP2 promotes neuronal differentiation by interacting with the retinoic acid signaling pathway and regulates key processes required for normal circuit formation such as neuronal migration and neurite outgrowth. In this way, FOXP2, which is found only in specific subpopulations of neurons in the brain, may drive precise neuronal differentiation patterns and/or control localization and connectivity of these FOXP2 positive cells.
Project description:All-trans retinoic acid (ATRA) promotes myoblast differentiation into myotubes. Leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6) is a candidate ATRA-responsive gene; however, its role in skeletal muscles remains unclear. Here, we demonstrated that during the differentiation of murine C2C12 myoblasts into myotubes, Lgr6 mRNA expression transiently increased before the increase in the expression of the mRNAs encoding myogenic regulatory factors, such as myogenin, myomaker, and myomerger. The loss of LGR6 decreased the differentiation and fusion indices. The exogenous expression of LGR6 up to 3 and 24 h after the induction of differentiation increased and decreased the mRNA levels of myogenin, myomaker, and myomerger, respectively. Lgr6 mRNA was transiently expressed after myogenic differentiation in the presence of a retinoic acid receptor α (RARα) agonist and an RARγ agonist in addition to ATRA, but not in the absence of ATRA. Furthermore, a proteasome inhibitor or Znfr3 knockdown increased exogenous LGR6 expression. The loss of LGR6 attenuated the Wnt/β-catenin signaling activity induced by Wnt3a alone or in combination with Wnt3a and R-spondin 2. These results indicate that LGR6 promotes myogenic differentiation and that ATRA is required for the transient expression of LGR6 during differentiation. Furthermore, LGR6 expression appeared to be downregulated by the ubiquitin-proteasome system involving ZNRF3.
Project description:Centroacinar cells (CACs) are ductal Notch-responsive progenitors that in the larval zebrafish pancreas differentiate to form new islets and ultimately contribute to the majority of the adult endocrine mass. Uncovering the mechanisms regulating CAC differentiation will facilitate understanding how insulin-producing β cells are formed. Previously we reported retinoic acid (RA) signaling and Notch signaling both regulate larval CAC differentiation, suggesting a shared downstream intermediate. Sox9b is a transcription factor important for islet formation whose expression is upregulated by Notch signaling in larval CACs. Here we report that sox9b expression in larval CACs is also regulated by RA signaling. Therefore, we hypothesized that Sox9b is an intermediate between both RA- and Notch-signaling pathways. In order to study the role of Sox9b in larval CACs, we generated two cre/lox based transgenic tools, which allowed us to express full-length or truncated Sox9b in larval CACs. In this way we were able to perform spatiotemporal-controlled Sox9b gain- and loss-of-function studies and observe the subsequent effect on progenitor differentiation. Our results are consistent with Sox9b regulating CAC differentiation by being a downstream intermediate of both RA- and Notch-signaling pathways. We also demonstrate that adult zebrafish with only one functional allele of sox9b undergo accelerated β-cell regeneration, an observation consistent with sox9b regulating CAC differentiation in adults.
Project description:CD8 tissue-resident memory T (TRM) cells provide frontline protection at barrier tissues; however, mechanisms regulating TRM cell development are not completely understood. Priming dictates the migration of effector T cells to the tissue, while factors in the tissue induce in situ TRM cell differentiation. Whether priming also regulates in situ TRM cell differentiation uncoupled from migration is unclear. Here, we demonstrate that T cell priming in the mesenteric lymph nodes (MLN) regulates CD103+ TRM cell differentiation in the intestine. In contrast, T cells primed in the spleen were impaired in the ability to differentiate into CD103+ TRM cells after entry into the intestine. MLN priming initiated a CD103+ TRM cell gene signature and licensed rapid CD103+ TRM cell differentiation in response to factors in the intestine. Licensing was regulated by retinoic acid signaling and primarily driven by factors other than CCR9 expression and CCR9-mediated gut homing. Thus, the MLN is specialized to promote intestinal CD103+ CD8 TRM cell development by licensing in situ differentiation.