Project description:Spalt-Like Transcription Factor 1 (Sall1) is a critical regulator of organogenesis and microglia identity. Despite its known biological importance, mechanisms that specify the cell-specific expression of Sall1 and its transcriptional functions remain poorly understood. Here, we demonstrate that targeted deletion of a conserved microglia-specific super enhancer interacting with the Sall1 promoter results in complete and specific loss of Sall1 expression in microglia, thereby identifying an essential regulatory element that transduces brain environmental signals required for microglia-specific gene expression. By determining the genomic binding sites of SALL1 and leveraging Sall1 enhancer knock out (EKO) mice to probe how SALL1 shapes the regulatory landscape of microglia, we provide evidence that SALL1 functions to both directly activate microglia-specific genes and repress genes that are associated with inflammation and aging. Unexpectedly, motifs for SMAD proteins that mediate transcriptional effects of TGFb signaling were enriched within the set of enhancers predicted to be directly activated by SALL1, suggesting that collaborative interactions between SALL1 and SMADs are required to establish microglia-specific gene expression. To test this hypothesis, we determined the transcriptional consequences of a conditional knockout of the common co-SMAD Smad4 and defined the genome-wide locations of SMAD4 in wild type and EKO microglia. These studies revealed two layers of functional interdependence. First, we found that SMAD4 binds directly to the Sall1 super enhancer and is required for Sall1 expression, consistent with the requirement of the TGFb and SMAD homologues Dpp and Mad for cell-specific expression of Spalt in the Drosophila wing. Second, we extend this paradigm by demonstrating that SALL1 in turn promotes binding and function of SMAD4 at microglia-specific enhancers while simultaneously suppressing binding of SMAD4 to enhancers of genes that become inappropriately activated in EKO microglia. Collectively, these results suggest molecular mechanisms by which SALL1 enforces microglia-specific functions of the TGFb-SMAD signaling axis that may be relevant to roles of SALL1 in other developmental contexts.

Project description:Murine BV2 microglia cells were transfected either with siRNA negative control or siRNA against caspase-3 for 48h. Later on some the of the BV2 transfected cells were co-cultured with C6 glioma cells during 6h. We used the SA Biosciences Mouse Wound Healing PCR Array (PAMM-121Z) to quantitate gene expression of relevant genes related to the wound healing process Glioma cells recruit and exploit microglia, resident immune cells of the brain, for their proliferation and invasion capability. The underlying molecular mechanism used by glioma cells to transform microglia into a tumor-supporting phenotype remains elusive. Here, we report that glioma-induced microglia conversion is coupled to a reduction of basal microglial caspase-3 activity, increased S-nitrosylation of mitochondria-associated caspase-3 through inhibition of thioredoxin-2 activity, and demonstrate that caspase-3 inhibition regulates microglial tumor-supporting function. Further, we identified nitric oxide synthase-2 (NOS2) activity originating from the glioma cells as a driving stimulus in the control of microglial caspase-3 activity. Repression of glioma NOS2 expression in vivo led to reduction in both microglia recruitment and tumor expansion, whereas depletion of the microglial caspase-3 gene promoted tumor growth. This study provides evidence that the inhibition of Trx2-mediated denitrosylation of SNO-procaspase-3 is part of the microglial pro-tumoral activation pathway initiated by glioma cancer cells. qPCR gene expression profiling. Three independent experiments of siControl BV2 monoculture, siCaspase3 BV2 monoculture, siControl BV2 cocultured 6h with C6 glioma cells and siCaspase3 BV2 cocultured 6h with C6 glioma cells. Equal amount total RNA from each culture was used for the gene expression analysis. Please note that the raw data for three independent experiments (prior to averaging the data) is provided in the 'Raw_Data_File_with_the_Ct_values_for_3_indep_experiments.txt'.

Project description:Microglia colonize the brain parenchyma at early stages of development and accumulate in specific regions where they actively participate in cell death, angiogenesis, neurogenesis and synapse elimination. A recurring feature of embryonic microglial distribution is their association with developing axon tracts which, together with in vitro data, supports the idea of a physiological role for microglia in neurite development. Yet the demonstration of this role of microglia is still lacking. Here, we have studied the consequences of microglial dysfunction on the formation of the corpus callosum, the largest connective structure in the mammalian brain, which shows consistent microglial accumulation during development. We studied two models of microglial dysfunction: the loss-of-function of DAP12, a key microglial-specific signaling molecule, and a model of maternal inflammation by peritoneal injection of LPS at E15.5. We performed transcriptional profiling of maternally inflamed and Dap12-mutant microglia at E17.5. We found that both treatments principally down-regulated genes involved in nervous system development and function, particularly in neurite formation. We then analyzed the functional consequences of these microglial dysfunctions on the formation of the corpus callosum. We also took advantage of the Pu.1-/- mouse line, which is devoid of microglia. We now show that all three models of altered microglial activity resulted in the same defasciculation phenotype. Our study demonstrates that microglia are actively involved in the fasciculation of corpus callosum axons. To investigate possible roles for microglial during brain development, we challenged microglial function by two complementary approaches. First, we induced maternal inflammation by peritoneal injection of LPS into pregnant dams. Next, we analyzed the consequences of a loss of function of DAP12, a signaling molecule specifically expressed in microglia that is crucial for several aspects of microglia biology (references in Wakselman et al., 2008). We compared the gene expression profiles of microglia from control, maternally-inflamed by LPS (MI), and Dap12-mutated embryos. We isolated RNA from FACS sorted maternally inflamed (by LPS) and Dap12-mutant microglia at E17.5 pooled per pregnant dam; as a control we included PBS treated and untreated (UT) microglia. We compared gene expression between maternally inflamed microlgia (PBSvsLPS) and DAP12-mutant microglia (UTvsDAP12KO).

Dataset Information

Radial glia promote microglial development through aVb8 -TGFb1 signaling [ChIP-seq]

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