RESUMEN
In Drosophila, commitment of a cell to a sense organ precursor (SOP) fate requires bHLH proneural transcription factor upregulation, a process that depends in most cases on the interplay of proneural gene autoregulation and inhibitory Notch signaling. A subset of SOPs are selected by a recruitment pathway involving EGFR signaling to ectodermal cells expressing the proneural gene atonal. We show that EGFR signaling drives recruitment by directly facilitating atonal autoregulation. Pointed, the transcription factor that mediates EGFR signaling, and Atonal protein itself bind cooperatively to adjacent conserved binding sites in an atonal enhancer. Recruitment is therefore contingent on the combined presence of Atonal protein (providing competence) and EGFR signaling (triggering recruitment). Thus, autoregulation is the nodal control point targeted by signaling. This exemplifies a simple and general mechanism for regulating the transition from competence to cell fate commitment whereby a cell signal directly targets the autoregulation of a selector gene.
Asunto(s)
Drosophila/embriología , Receptores ErbB/metabolismo , Regulación del Desarrollo de la Expresión Génica , Órganos de los Sentidos/embriología , Transducción de Señal , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Sitios de Unión , Proteínas de Unión al ADN/metabolismo , Drosophila/genética , Proteínas de Drosophila , Ensayo de Cambio de Movilidad Electroforética , Elementos de Facilitación Genéticos , Glutatión Transferasa/metabolismo , Proteínas Fluorescentes Verdes/metabolismo , Inmunohistoquímica , Proteínas de la Membrana/metabolismo , Modelos Biológicos , Modelos Moleculares , Proteínas del Tejido Nervioso , Proteínas Proto-Oncogénicas/metabolismo , Receptores Notch , Proteínas Recombinantes de Fusión/metabolismo , Factores de Transcripción/metabolismo , Regulación hacia ArribaRESUMEN
For a particular functional family of basic helix-loop-helix (bHLH) transcription factors, there is ample evidence that different factors regulate different target genes but little idea of how these different target genes are distinguished. We investigated the contribution of DNA binding site differences to the specificities of two functionally related proneural bHLH transcription factors required for the genesis of Drosophila sense organ precursors (Atonal and Scute). We show that the proneural target gene, Bearded, is regulated by both Scute and Atonal via distinct E-box consensus binding sites. By comparing with other Ato-dependent enhancer sequences, we define an Ato-specific binding consensus that differs from the previously defined Scute-specific E-box consensus, thereby defining distinct E(Ato) and E(Sc) sites. These E-box variants are crucial for function. First, tandem repeats of 20-bp sequences containing E(Ato) and E(Sc) sites are sufficient to confer Atonal- and Scute-specific expression patterns, respectively, on a reporter gene in vivo. Second, interchanging E(Ato) and E(Sc) sites within enhancers almost abolishes enhancer activity. While the latter finding shows that enhancer context is also important in defining how proneural proteins interact with these sites, it is clear that differential utilization of DNA binding sites underlies proneural protein specificity.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila/genética , Elementos E-Box/genética , Regulación del Desarrollo de la Expresión Génica , Sistema Nervioso/metabolismo , Neuronas/metabolismo , Factores de Transcripción/metabolismo , Región de Flanqueo 3'/genética , Región de Flanqueo 5'/genética , Animales , Secuencia de Bases , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , ADN/genética , ADN/metabolismo , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/genética , Drosophila/citología , Drosophila/embriología , Drosophila/metabolismo , Proteínas de Drosophila/química , Proteínas de Drosophila/genética , Proteínas del Tejido Nervioso , Sistema Nervioso/citología , Sistema Nervioso/embriología , Factores de Transcripción/química , Factores de Transcripción/genéticaRESUMEN
Proneural genes encode basic-helix-loop-helix (bHLH) transcription factors required for neural precursor specification. Recently amos was identified as a new candidate Drosophila proneural gene related to atonal. Having isolated the first specific amos loss-of-function mutations, we show definitively that amos is required to specify the precursors of two classes of olfactory sensilla. Unlike other known proneural mutations, a novel characteristic of amos loss of function is the appearance of ectopic sensory bristles in addition to loss of olfactory sensilla, owing to the inappropriate function of scute. This supports a model of inhibitory interactions between proneural genes, whereby ato-like genes (amos and ato) must suppress sensory bristle fate as well as promote alternative sense organ subtypes.