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Transcriptional Mechanisms of Proneural Factors and REST in Regulating Neuronal Reprogramming of Astrocytes.

ABSTRACT: Direct lineage reprogramming induces dramatic shifts in cellular identity, employing poorly understood mechanisms. Recently, we demonstrated that expression of Neurog2 or Ascl1 in postnatal mouse astrocytes generates glutamatergic or GABAergic neurons. Here, we take advantage of this model to study dynamics of neuronal cell fate acquisition at the transcriptional level. We found that Neurog2 and Ascl1 rapidly elicited distinct neurogenic programs with only a small subset of shared target genes. Within this subset, only NeuroD4 could by itself induce neuronal reprogramming in both mouse and human astrocytes, while co-expression with Insm1 was required for glutamatergic maturation. Cultured astrocytes gradually became refractory to reprogramming, in part by the repressor REST preventing Neurog2 from binding to the NeuroD4 promoter. Notably, in astrocytes refractory to Neurog2 activation, the underlying neurogenic program remained amenable to reprogramming by exogenous NeuroD4. Our findings support a model of temporal hierarchy for cell fate change during neuronal reprogramming.

SUBMITTER: Masserdotti G

PROVIDER: S-EPMC4509553 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Transcriptional mechanisms of proneural factors and REST in regulating neuronal reprogramming of astrocytes

Project description:Reprogramming offers the possibility to study cell fate acquisitions otherwise difficult to address in vivo. By monitoring the dynamics of gene expression during direct reprogramming of astrocytes into different neuronal subtypes via the activation of Neurog2 and Ascl1, we demonstrate that these proneural factors control largely different neurogenic programs. Among the cascades induced, however, we identified a common subset of transcription factors required for both Neurog2- and Ascl1-induced reprogramming, and combinations of these factors comprising NeuroD4 were sufficient to generate functional neurons. Notably, during astrocyte maturation REST prevents Neurog2 from binding to the NeuroD4 locus that becomes then enriched with histone H4 lysine 20 tri-methylation. As combinations of downstream targets are sufficient to induce reprogramming in Neurog2-resistant cultures, our data support a model of a temporal hierarchy in shutting off alternative fate in astrocyte differentiation.

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Project description:A truncating mutation in the mouse Srrm4 gene, which encodes a neuronal splicing factor, causes alternative splicing defects selectively in the ear. The mechanism by which splicing is preserved in the brain of these mice is not known. Here, we show that SRRM3 limits the Srrm4 mutation-associated defects to the ear and that, in cortical neurons, overlapping SRRM3-SRRM4 activity regulates the development of interneuronal inhibition. In vitro, SRRM3 and SRRM4 regulate the same splicing events, but a mutation in mouse Srrm3 causes tremors and mild defects in neuronal alternative splicing, demonstrating unique SRRM3 roles in vivo. Mice harboring mutations in both Srrm3 and Srrm4 die neonatally and exhibit severe splicing defects. In these mice, splicing alterations prevent inactivation of the gene repressor REST, which maintains immature excitatory GABAergic neurotransmission by repressing K-Cl cotransporter 2. Thus, our data reveal that SRRM3 and SRRM4 act redundantly to regulate GABAergic neurotransmission by inactivating REST.

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