Molecular Neurobiology
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The assembly of a fully functional nervous system, with all its diversity and complexity, depends on the coordinate generation of both neurons and glia from differentiating multipotent neural stem cells in the developing embryo. The progression of this differentiation process is associated and controlled by changes in gene expression programs that need to be very tightly regulated. For the moment we are mostly interested in understanding how such regulation takes place at the transcription level, by focusing our studies on the role played by various transcription factors in neurogenesis.
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Browsing Molecular Neurobiology by Subject "Ascl1"
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- Ascl1 Coordinately Regulates Gene Expression and the Chromatin Landscape during NeurogenesisPublication . Raposo, Alexandre A.S.F.; Vasconcelos, Francisca F.; Drechsel, Daniela; Marie, Corentine; Johnston, Caroline; Dolle, Dirk; Bithell, Angela; Gillotin, Sébastien; van den Berg, Debbie L.C.; Ettwiller, Laurence; Flicek, Paul; Crawford, Gregory E.; Parras, Carlos M.; Berninger, Benedikt; Buckley, Noel J.; Guillemot, François; Castro, Diogo S.The proneural transcription factor Ascl1 coordinates gene expression in both proliferating and differentiating progenitors along the neuronal lineage. Here, we used a cellular model of neurogenesis to investigate how Ascl1 interacts with the chromatin landscape to regulate gene expression when promoting neuronal differentiation. We find that Ascl1 binding occurs mostly at distal enhancers and is associated with activation of gene transcription. Surprisingly, the accessibility of Ascl1 to its binding sites in neural stem/progenitor cells remains largely unchanged throughout their differentiation, as Ascl1 targets regions of both readily accessible and closed chromatin in proliferating cells. Moreover, binding of Ascl1 often precedes an increase in chromatin accessibility and the appearance of new regions of open chromatin, associated with de novo gene expression during differentiation. Our results reveal a function of Ascl1 in promoting chromatin accessibility during neurogenesis, linking the chromatin landscape at Ascl1 target regions with the temporal progression of its transcriptional program.
- MyT1 Counteracts the Neural Progenitor Program to Promote Vertebrate NeurogenesisPublication . Vasconcelos, Francisca F.; Sessa, Alessandro; Laranjeira, Cátia; Raposo, Alexandre A.S.F.; Teixeira, Vera; Hagey, Daniel W.; Tomaz, Diogo M.; Muhr, Jonas; Broccoli, Vania; Castro, Diogo S.The generation of neurons from neural stem cells requires large-scale changes in gene expression that are controlled to a large extent by proneural transcription factors, such as Ascl1. While recent studies have characterized the differentiation genes activated by proneural factors, less is known on the mechanisms that suppress progenitor cell identity. Here, we show that Ascl1 induces the transcription factor MyT1 while promoting neuronal differentiation. We combined functional studies of MyT1 during neurogenesis with the characterization of its transcriptional program. MyT1 binding is associated with repression of gene transcription in neural progenitor cells. It promotes neuronal differentiation by counteracting the inhibitory activity of Notch signaling at multiple levels, targeting the Notch1 receptor and many of its downstream targets. These include regulators of the neural progenitor program, such as Hes1, Sox2, Id3, and Olig1. Thus, Ascl1 suppresses Notch signaling cell-autonomously via MyT1, coupling neuronal differentiation with repression of the progenitor fate.
- A transcription factor network specifying inhibitory versus excitatory neurons in the dorsal spinal cordPublication . Borromeo, M. D.; Meredith, D. M.; Castro, D. S.; Chang, J. C.; Tung, K.-C.; Guillemot, F.; Johnson, J. E.The proper balance of excitatory and inhibitory neurons is crucial for normal processing of somatosensory information in the dorsal spinal cord. Two neural basic helix-loop-helix transcription factors (TFs), Ascl1 and Ptf1a, have contrasting functions in specifying these neurons. To understand how Ascl1 and Ptf1a function in this process, we identified their direct transcriptional targets genome-wide in the embryonic mouse neural tube using ChIP-Seq and RNA-Seq. We show that Ascl1 and Ptf1a directly regulate distinct homeodomain TFs that specify excitatory or inhibitory neuronal fates. In addition, Ascl1 directly regulates genes with roles in several steps of the neurogenic program, including Notch signaling, neuronal differentiation, axon guidance and synapse formation. By contrast, Ptf1a directly regulates genes encoding components of the neurotransmitter machinery in inhibitory neurons, and other later aspects of neural development distinct from those regulated by Ascl1. Moreover, Ptf1a represses the excitatory neuronal fate by directly repressing several targets of Ascl1. Ascl1 and Ptf1a bind sequences primarily enriched for a specific E-Box motif (CAGCTG) and for secondary motifs used by Sox, Rfx, Pou and homeodomain factors. Ptf1a also binds sequences uniquely enriched in the CAGATG E-box and in the binding motif for its co-factor Rbpj, providing two factors that influence the specificity of Ptf1a binding. The direct transcriptional targets identified for Ascl1 and Ptf1a provide a molecular understanding of how these DNA-binding proteins function in neuronal development, particularly as key regulators of homeodomain TFs required for neuronal subtype specification.