ABSTRACT
Notch proteins are the receptors for an evolutionarily highly conserved signalling pathway that regulates numerous cell fate decisions during development. Signal transduction involves the presenilin-dependent intracellular processing of Notch and nuclear translocation of the intracellular domain of Notch, Notch-IC. Notch-IC associates with the DNA-binding protein RBP-Jkappa/CBF-1 to activate transcription of Notch target genes. In the absence of Notch signalling, RBP-Jkappa/CBF-1 acts as a transcriptional repressor through the recruitment of histone deacetylase (HDAC) corepressor complexes. We identified SHARP as an RBP-Jkappa/CBF-1-interacting corepressor in a yeast two-hybrid screen. In cotransfection experiments, SHARP-mediated repression was sensitive to the HDAC inhibitor TSA and facilitated by SKIP, a highly conserved SMRT and RBP-Jkappa-interacting protein. SHARP repressed Hairy/Enhancer of split (HES)-1 promoter activity, inhibited Notch-1-mediated transactivation and rescued Notch-1-induced inhibition of primary neurogenesis in Xenopus laevis embryos. Based on our data, we propose a model in which SHARP is a novel component of the HDAC corepressor complex, recruited by RBP-Jkappa to repress transcription of target genes in the absence of activated Notch.
Subject(s)
Adaptor Proteins, Signal Transducing , DNA-Binding Proteins/metabolism , Membrane Proteins/metabolism , Neuropeptides/metabolism , Nuclear Proteins , Receptors, Cell Surface , Transcription Factors/metabolism , Animals , Basic Helix-Loop-Helix Transcription Factors , Carrier Proteins/genetics , Carrier Proteins/metabolism , Cell Line , DNA-Binding Proteins/genetics , Gene Expression , HeLa Cells , Histone Deacetylases/metabolism , Homeodomain Proteins/genetics , Humans , Immunoglobulin J Recombination Signal Sequence-Binding Protein , In Vitro Techniques , Membrane Proteins/genetics , Mice , Neuropeptides/chemistry , Neuropeptides/genetics , Phenotype , Promoter Regions, Genetic , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptor, Notch1 , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Signal Transduction , Transcription Factor HES-1 , Transcription Factors/chemistry , Transcription Factors/genetics , Transfection , Two-Hybrid System Techniques , Xenopus laevisABSTRACT
We report on the temporal and spatial expression pattern of two novel genes of the Xenopus fork head/winged helix family, xFoxB2 and xFoxI1c. xFoxB2 is activated at the late blastula stage and first expressed within the dorsolateral ectoderm except for the organiser territory. During gastrulation, xFoxB2 is found in two ectodermal stripes adjacent to the dorsal midline. Expression is completely down-regulated during neurulation. However, two distinct sets of cells expressing xFoxB2 re-appear in the rhombencephalon of swimming tadpoles. xFoxI1c is initially expressed at the early neurula stage in an epidermal ring around the neural field. Subsequent expression is found to be increased, and is exclusively localised to placodal precursor cells. The placodal expression remains until stage 40, when it is restricted to a distinct region in the lateral body wall behind the gills.
