RESUMO
At the core of the primary transcriptional network regulating ciliary gene expression in Caenorhabditis elegans sensory neurons is the RFX/DAF-19 transcription factor, which binds and thereby positively regulates 13-15 bp X-box promoter motifs found in the cis-regulatory regions of many ciliary genes. However, the variable expression of direct RFX-target genes in various sets of ciliated sensory neurons (CSNs) occurs through as of yet uncharacterized mechanisms. In this study the cis-regulatory regions of 41 direct RFX-target genes are compared using in vivo genetic analyses and computational comparisons of orthologous nematode sequences. We find that neither the proximity to the translational start site nor the exact sequence composition of the X-box promoter motif of the respective ciliary gene can explain the variation in expression patterns observed among different direct RFX-target genes. Instead, a novel enhancer element appears to co-regulate ciliary genes in a DAF-19 dependent manner. This cytosine- and thymidine-rich sequence, the C-box, was found in the cis-regulatory regions in close proximity to the respective X-box motif for 84% of the most broadly expressed direct RFX-target genes sampled in this study. Molecular characterization confirmed that these 8-11 bp C-box sequences act as strong enhancer elements for direct RFX-target genes. An artificial promoter containing only an X-box promoter motif and two of the C-box enhancer elements was able to drive strong expression of a GFP reporter construct in many C. elegans CSNs. These data provide a much-improved understanding of how direct RFX-target genes are differentially regulated in C. elegans and will provide a molecular model for uncovering the transcriptional network mediating ciliary gene expression in animals.
Assuntos
Proteínas de Caenorhabditis elegans/genética , Caenorhabditis elegans/genética , Regiões Promotoras Genéticas/genética , Sequências Reguladoras de Ácido Nucleico/genética , Fatores de Transcrição/genética , Animais , Animais Geneticamente Modificados , Sequência de Bases , Sítios de Ligação/genética , Caenorhabditis elegans/crescimento & desenvolvimento , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/metabolismo , Cílios/genética , Elementos Facilitadores Genéticos/genética , Perfilação da Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Microscopia Confocal , Mutação , Motivos de Nucleotídeos/genética , Células Receptoras Sensoriais/metabolismo , Fatores de Transcrição/metabolismoRESUMO
DCDC2 is one of the candidate susceptibility genes for dyslexia. It belongs to the superfamily of doublecortin domain containing proteins that bind to microtubules, and it has been shown to be involved in neuronal migration. We show that the Dcdc2 protein localizes to the primary cilium in primary rat hippocampal neurons and that it can be found within close proximity to the ciliary kinesin-2 subunit Kif3a. Overexpression of DCDC2 increases ciliary length and activates Shh signaling, whereas downregulation of Dcdc2 expression enhances Wnt signaling, consistent with a functional role in ciliary signaling. Moreover, DCDC2 overexpression in C. elegans causes an abnormal neuronal phenotype that can only be seen in ciliated neurons. Together our results suggest a potential role for DCDC2 in the structure and function of primary cilia.