XB-ART-7054Genes Dev June 1, 2002; 16 (11): 1397-411.
Mastermind mediates chromatin-specific transcription and turnover of the Notch enhancer complex.
Signaling through the Notch pathway activates the proteolytic release of the Notch intracellular domain (ICD), a dedicated transcriptional coactivator of CSL enhancer-binding proteins. Here we show that chromatin-dependent transactivation by the recombinant Notch ICD-CBF1 enhancer complex in vitro requires an additional coactivator, Mastermind (MAM). MAM provides two activation domains necessary for Notch signaling in mammalian cells and in Xenopus embryos. We show that the central MAM activation domain (TAD1) recruits CBP/p300 to promote nucleosome acetylation at Notch enhancers and activate transcription in vitro. We also find that MAM expression induces phosphorylation and relocalization of endogenous CBP/p300 proteins to nuclear foci in vivo. Moreover, we show that coexpression with MAM and CBF1 strongly enhances phosphorylation and proteolytic turnover of the Notch ICD in vivo. Enhanced phosphorylation of the ICD and p300 requires a glutamine-rich region of MAM (TAD2) that is essential for Notch transcription in vivo. Thus MAM may function as a timer to couple transcription activation with disassembly of the Notch enhancer complex on chromatin.
PubMed ID: 12050117
PMC ID: PMC186317
Article link: Genes Dev
Genes referenced: crebbp ep300 itch maml1 notch1 nrarp rbpj smpx tubb2b
Article Images: [+] show captions
|Figure 4. Both TAD1 and the C-terminal activation domain (TAD2) of MAM are required for Notch signaling in injected Xenopusembryos. Xenopus embryos at the two-cell stage were injected with RNA encoding wild-type (Full-length) or mutant human MAM proteins (HMMδ74–301; HMM1–301) along with lacZ RNA as a tracer. The embryos were fixed and stained for β-galactosidase expression and double-labeled by whole-mount in situ hybridization for a neural-specific tubulin. Notch signaling was assessed by counting the number of primary neurons on the neural plate for the half of the embryo that was injected (inj) relative to that for the uninjected control (cont). (m) Midline; (i) interneuron; (l) lateral neuron.|