In contrast, MSI2 is ubiquitous, but with high levels in some tissues such as hematopoietic stem and progenitor cells, where its downregulation coincides with stem cell differentiation ( 3). Of the two MSI homologues, MSI1 is expressed primarily in neurons ( 2). MSI proteins are thought to bind to the 3′ untranslated region (3′UTR) of specific transcripts and regulate their translation. The Musashi proteins (MSI1 and its homologue MSI2) are highly conserved across metazoans and contain two distinct RNA recognition motifs ( 1). RNA binding proteins (RBPs) encompass a diverse group of proteins that regulate all aspects of RNA biology. Our results also underscore the challenges in defining functional targets of RBPs since mere binding does not imply a discernible functional interaction. We propose that MSI2 downregulation of EIF3A amplifies these effects on translation. Using complementary approaches, we determined eukaryotic translation initiation factor 3A (EIF3A) to be an immediate, direct target. Surprisingly, only 50 transcripts were found to undergo translational induction on acute loss. To further distinguish direct and indirect targets, MSI2 was acutely depleted. Instead, the functional targets identified here were bound at higher density and contain more ‘UAG’ motifs compared to targets bound nonproductively. iCLIP revealed specific MSI2 binding to thousands of mRNAs largely in 3′UTRs, but translational differences were restricted to a small fraction of these transcripts, indicating that MSI2 regulation is not triggered by simple binding.

Here, we used individual nucleotide resolution cross-linking and immunoprecipitation (iCLIP) to identify direct RNA binding partners of MSI2 and integrated these data with polysome profiling to obtain insights into MSI2 function. MSI2 appears to repress translation by binding to 3′ untranslated regions (3′UTRs) of mRNA, but the identity of functional targets remains unknown.

Musashi 2 (MSI2) is an RNA binding protein (RBP) that regulates asymmetric cell division and cell fate decisions in normal and cancer stem cells.

Iclip biotin