The Neural RNA-Binding Protein Musashi1 Translationally Regulates Mammalian numb Gene Expression by Interacting with Its mRNA

Abstract

Musashi1 (Msi1) is an RNA-binding protein that is highly expressed in neural progenitor cells, including neural stem cells. In this study, the RNA-binding sequences for Msi1 were determined by in vitro selection using a pool of degenerate 50-mer sequences. All of the selected RNA species contained repeats of (G/A)U n AGU (n ‫؍‬ 1 to 3) sequences which were essential for Msi1 binding. These consensus elements were identified in some neural mRNAs. One of these, mammalian numb (m-numb), which encodes a membrane-associated antagonist of Notch signaling, is a likely target of Msi1. Msi1 protein binds in vitro-transcribed m-numb RNA in its 3-untranslated region (UTR) and binds endogenous m-numb mRNA in vivo, as shown by affinity precipitation followed by reverse transcription-PCR. Furthermore, adenovirus-induced Msi1 expression resulted in the down-regulation of endogenous m-Numb protein expression. Reporter assays using a chimeric mRNA that combined luciferase and the 3-UTR of m-numb demonstrated that Msi1 decreased the reporter activity without altering the reporter mRNA level. Thus, our results suggested that Msi1 could regulate the expression of its target gene at the translational level. Furthermore, we found that Notch signaling activity was increased by Msi1 expression in connection with the posttranscriptional down-regulation of the m-numb gene.

Differential Distribution of Stem Cells in the Auditory and Vestibular Organs of the Inner Ear

“…Another indication of the immature status of differentiated sphere cell populations arises from the expression of Musashi1, an RNA binding protein associated with asymmetric cell divisions (Imai et al 2001;Murata et al 2004). Cells with strong cytoplasmic Musashi1-immunoreactivity were often juxtaposed to hair cell marker-positive cells that did not express Musashi1 [ Fig.…”

Attributes of adult stem cells

“…Msi-1 is expressed by neural progenitors, enhancing the effects of Notch signalling, maintaining the undifferentiated state [64,65]. Msi-1 has also been advocated as a stem cell marker in the gut; in the rat stomach Msi-1-expressing cells are located just beneath the foveolar region (the putative niche), although there was some expression in parietal cells [66].…”

Novel Double-negative Feedback Loop between Adenomatous Polyposis Coli and Musashi1 in Colon Epithelia

“…For Msi1 overexpression, pCDNA3-Flag-Msi1 (Flag-Msi1) and pCDNA3-FlagMsi1mutR1 (Flag-mutR1) were generously provided by Hideyuki Okano (Tokyo, Japan). The mutR1 Msi1 mutant contains three phenylalanine-to-leucine substitutions in the first RNA binding domain (8). These phenylalanines are required for RNA binding and subsequent translational inhibition by Msi1, and these substitutions have been shown to ablate binding of the mutant to Numb mRNA (8,20).…”

“…The two best characterized targets of mammalian MSI1 are the Notch antagonist Numb and the cyclin-dependent kinase inhibitor p21 (7,8). Msi1 2 maintains cells in a more undifferentiated state, in part, through activation of Notch signaling and cell cycle progression (9).…”