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The Repression of Atoh1 by Neurogenin1 during Inner Ear Development.

ABSTRACT: Atonal homolog 1 (Atoh1) and Neurogenin1 (Neurog1) are basic Helix-Loop-Helix (bHLH) transcription factors crucial for the generation of hair cells (HCs) and neurons in the inner ear. Both genes are induced early in development, but the expression of Atoh1 is counteracted by Neurog1. As a result, HC development is prevented during neurogenesis. This work aimed at understanding the molecular basis of this interaction. Atoh1 regulation depends on a 3'Atoh1-enhancer that is the site for Atoh1 autoregulation. Reporter assays on chick embryos and P19 cells show that Neurog1 hampers the autoactivation of Atoh1, the effect being cell autonomous and independent on Notch activity. Assay for Transposase-Accessible Chromatin with high throughput sequencing (ATAC-Seq) analysis shows that the region B of the 3'Atoh1-enhancer is accessible during development and sufficient for both activation and repression. Neurog1 requires the regions flanking the class A E-box to show its repressor effect, however, it does not require binding to DNA for Atoh1 repression. This depends on the dimerization domains Helix-1 and Helix-2 and the reduction of Atoh1 protein levels. The results point towards the acceleration of Atoh1 mRNA degradation as the potential mechanism for the reduction of Atoh1 levels. Such a mechanism dissociates the prevention of Atoh1 expression in neurosensory progenitors from the unfolding of the neurogenic program.

SUBMITTER: Galvez H

PROVIDER: S-EPMC5655970 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Breaking the Atoh1 autoregulatory loop in hair cells: the repression of Atoh1 by Neurogenin1 during ear development

Project description:The functional unit of the inner ear consists of hair cells (HCs) and neurons in the inner ear. Both genes are induced early in development, but Atoh1 expression is counteracted by Neurog1. As a result, HC development is prevented during neurogenesis. This work aimed at understanding the molecular basis of this interaction. Atoh1 regulation depends on a 3’Atoh1-enhancer that is the site for Atoh1 autoregulation. This enhancer recapitulates Atoh1 expression in the embryo and contains putative binding sites for several transcription factors, including basic helix-loop-helix (bHLH) factors like Atoh1, Neurog1 and Hes/Hey repressors. Reporter assays on chick embryos and P19 cells show that Neurog1 hampers the autoactivation of Atoh1, the effect being cell autonomous and independent on Notch activity. ATAC-seq analysis shows that the region B of the 3’Atoh1-enhancer is accessible during development and sufficient for both activation and repression. Neurog1 requires the regions flanking the class A E-box bound by Atoh1 to show its repressor effect. However, Neurog1 does not require binding to DNA for Atoh1 repression and prevention of HC formation, but the dimerization domains Helix-1 and Helix-2. The repression of Atoh1 by Neurog1 does not involve the direct interaction between Atoh1 and Neurog1, but rather an indirect effect on the levels of Atoh1 protein. The results suggest that Neurog1 induces the acceleration of Atoh1 mRNA degradation and the consequent reduction of protein levels. Such a mechanism dissociates the prevention of Atoh1 expression in neuro-sensory progenitors from the unfolding of the neurogenic program.

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