The neural RNA-binding protein Musashi1 translationally regulates mammalian numb gene expression by interacting with its mRNA.
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.
Imai
T
T
Department of Physiology, Keio University School of Medicine, Shinjuku, Tokyo 160-8582.
Tokunaga
A
A
Yoshida
T
T
Hashimoto
M
M
Mikoshiba
K
K
Weinmaster
G
G
Nakafuku
M
M
Okano
H
H
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D015536:Down-Regulation; D005656:Fungal Proteins / Q000235:genetics; D017930:Genes, Reporter; D066298:In Vitro Techniques; D008024:Ligands; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D014176:Protein Biosynthesis; D012313:RNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D051880:Receptors, Notch; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D015533:Transcriptional Activation; D000098825:Oxysterol Binding Proteins
D017931:DNA Primers; D005656:Fungal Proteins; D008024:Ligands; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012313:RNA; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D051880:Receptors, Notch; D029701:Saccharomyces cerevisiae Proteins; C087902:HES1 protein, S cerevisiae; D000098825:Oxysterol Binding Proteins; C104786:Msi1h protein, mouse; C106293:Numb protein, mouse