In Vivo Neuronal Subtype-Specific Targets of Atoh1 (Math1) in Dorsal Spinal Cord

Department of Neuroscience, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 07/2011; 31(30):10859-71. DOI: 10.1523/JNEUROSCI.0445-11.2011
Source: PubMed

ABSTRACT Neural basic helix-loop-helix (bHLH) transcription factors are crucial in regulating the differentiation and neuronal subtype specification of neurons. Precisely how these transcription factors direct such processes is largely unknown due to the lack of bona fide targets in vivo. Genetic evidence suggests that bHLH factors have shared targets in their common differentiation role, but unique targets with respect to their distinct roles in neuronal subtype specification. However, whether neuronal subtype-specific targets exist remains an unsolved question. To address this question, we focused on Atoh1 (Math1), a bHLH transcription factor that specifies distinct neuronal subtypes of the proprioceptive pathway in mammals including the dI1 (dorsal interneuron 1) population of the developing spinal cord. We identified transcripts unique to the Atoh1-derived lineage using microarray analyses of specific bHLH-sorted populations from mouse. Chromatin immunoprecipitation-sequencing experiments followed by enhancer reporter analyses identified five direct neuronal subtype-specific targets of Atoh1 in vivo along with their Atoh1-responsive enhancers. These targets, Klf7, Rab15, Rassf4, Selm, and Smad7, have diverse functions that range from transcription factors to regulators of endocytosis and signaling pathways. Only Rab15 and Selm are expressed across several different Atoh1-specified neuronal subtypes including external granule cells (external granule cell layer) in the developing cerebellum, hair cells of the inner ear, and Merkel cells. Our work establishes on a molecular level that neuronal differentiation bHLH transcription factors have distinct lineage-specific targets.

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    • "The trhlmodel is the result of anEMS induced hypomorphic allele of the Atoh1 geneon the C57BL/6J (B6) mouse strain[13]. The phenotype of these hypomorphic mutant mice includes a trembling gait and hearing loss (symbol: trhl). "
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    ABSTRACT: Atoh1 is a transcription factor that regulates neural development in multiple tissues and is conserved among species. Prior mouse models of Atoh1, though effective and important in the evolution of our understanding of the gene, have been limited by perinatal lethality. Here we describe a novel point mutation of Atoh1 (designated Atoh1(trhl) ) underlying a phenotype of trembling gait and hearing loss. Histology revealed inner ear hair cell loss and cerebellar atrophy. Auditory Brainstem Response (ABR) and Distortion Product Otoacoustic Emission (DPOAE) showed functional abnormalities in the ear. Normal lifespan and fecundity of Atoh1(trhl) mice provide a complementary model to facilitate elucidation of ATOH1 function in hearing,central nervous system and cancer biology.
    PLoS ONE 11/2013; 8(11):e79791. DOI:10.1371/journal.pone.0079791 · 3.23 Impact Factor
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    • "Together, our observations support the view that Npn2 regulates commissural axon guidance in a population-specific manner and raise the possibility that Atoh1 or another transcription factor expressed by post-mitotic dI1 neurons directly regulates the expression of Npn2. However, our preliminary studies indicate that Npn2 expression is unaltered in mice lacking Atoh1 (EC and ZK, unpublished observation) and Npn2 was not identified in a systematic screen for direct lineage-specific in vivo targets of Atoh1[43]. "
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    ABSTRACT: Spinal commissural axons represent a model system for deciphering the molecular logic that regulates the guidance of midline-crossing axons in the developing central nervous system (CNS). Whether the same or specific sets of guidance signals control the navigation of molecularly distinct subtypes of these axons remains an open and largely unexplored question. Although it is well established that post-crossing commissural axons alter their responsiveness to midline-associated guidance cues, our understanding of the repulsive mechanisms that drive the post-crossing segments of these axons away from the midline and whether the underlying guidance systems operate in a commissural axon subtype-specific manner, remains fragmentary at best. Here, we utilize axonally targeted transgenic reporter mice to visualize genetically distinct dorsal interneuron (dI)1 and dI4 commissural axons and show that the repulsive class 3 semaphorin (Sema3) guidance receptor Neuropilin 2 (Npn2), is selectively expressed on the dI1 population and is required for the guidance of post-crossing dI1, but not dI4, axons. Consistent with these observations, the midline-associated Npn2 ligands, Sema3F and Sema3B, promote the collapse of dI1, but not dI4, axon-associated growth cones in vitro. We also identify, for the first time, a discrete GABAergic population of ventral commissural neurons/axons in the embryonic mouse spinal cord that expresses Npn2, and show that Npn2 is required for the proper guidance of their post-crossing axons. Together, our findings indicate that Npn2 is selectively expressed in distinct populations of commissural neurons in both the dorsal and ventral spinal cord, and suggest that Sema3-Npn2 signaling regulates the guidance of post-crossing commissural axons in a population-specific manner.
    Neural Development 07/2013; 8(1):15. DOI:10.1186/1749-8104-8-15 · 3.45 Impact Factor
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    • "Although the targets of Atoh1 in developing hair cells are largely unknown , Atoh1 is known to bind to its own promoter region to initiate a positive-feedback loop that will act to maintain or increase expression of the gene (Helms et al. 2000). Recent work using new techniques to assess gene expression and Atoh1–DNA interactions in both the cerebellum and dorsal spinal cord has led to the generation of " Atoh1 targetomes " (Klisch et al. 2011; Lai et al. 2011) that include genes such as Barhl1 and Hes6 that are expressed in hair cells; however, whether Atoh1 acts to directly regulate these genes within the inner ear remains to be determined. Considering the importance of regulating the number of cells that develop as hair cells, it is likely that multiple levels of regulatory control determine how many cells will express Atoh1. "
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    ABSTRACT: The inner ear is a structurally complex vertebrate organ built to encode sound, motion, and orientation in space. Given its complexity, it is not surprising that inner ear dysfunction is a relatively common consequence of human genetic mutation. Studies in model organisms suggest that many genes currently known to be associated with human hearing impairment are active during embryogenesis. Hence, the study of inner ear development provides a rich context for understanding the functions of genes implicated in hearing loss. This chapter focuses on molecular mechanisms of inner ear development derived from studies of model organisms.
    Cold Spring Harbor perspectives in biology 08/2012; 4(8):a008409. DOI:10.1101/cshperspect.a008409 · 8.68 Impact Factor
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