Ringo/cyclin-dependent kinase and mitogen-activated protein kinase signaling pathways regulate the activity of the cell fate determinant Musashi to promote cell cycle re-entry in Xenopus oocytes.

Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, Arkansas 722205, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 01/2012; 287(13):10639-49. DOI: 10.1074/jbc.M111.300681
Source: PubMed

ABSTRACT Cell cycle re-entry during vertebrate oocyte maturation is mediated through translational activation of select target mRNAs, culminating in the activation of mitogen-activated protein kinase and cyclin B/cyclin-dependent kinase (CDK) signaling. The temporal order of targeted mRNA translation is crucial for cell cycle progression and is determined by the timing of activation of distinct mRNA-binding proteins. We have previously shown in oocytes from Xenopus laevis that the mRNA-binding protein Musashi targets translational activation of early class mRNAs including the mRNA encoding the Mos proto-oncogene. However, the molecular mechanism by which Musashi function is activated is unknown. We report here that activation of Musashi1 is mediated by Ringo/CDK signaling, revealing a novel role for early Ringo/CDK function. Interestingly, Musashi1 activation is subsequently sustained through mitogen-activated protein kinase signaling, the downstream effector of Mos mRNA translation, thus establishing a positive feedback loop to amplify Musashi function. The identified regulatory sites are present in mammalian Musashi proteins, and our data suggest that phosphorylation may represent an evolutionarily conserved mechanism to control Musashi-dependent target mRNA translation.

1 Bookmark
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mRNA binding protein, Musashi, has been shown to regulate translation of select mRNAs and control cellular identity in both stem cells and cancer cells. Within mammalian cells, Musashi has traditionally been characterized as a repressor of translation. However, we have demonstrated that Musashi is an activator of translation in progesterone-stimulated oocytes of the frog Xenopus laevis, and recent evidence has revealed the capability of Musashi to function as an activator of translation in mammalian systems. The molecular mechanism by which Musashi directs activation of target mRNAs has not been elucidated. Here, we report a specific association of Musashi with the noncanonical poly[A] polymerase Germline Development-2 (GLD2) and map the association domain to 30 amino acids within the C-terminal domain of Musashi. We show that loss of GLD2 interaction through deletion of the binding domain, or treatment with antisense oligonucleotides compromises Musashi function. Additionally, we demonstrate that overexpression of both Musashi and GLD2 significantly enhances Musashi function. Finally, we report a similar co-association also occurs between murine Musashi and GLD2 orthologs, suggesting that coupling of Musashi to the polyadenylation apparatus is a conserved mechanism to promote target mRNA translation.
    Journal of Biological Chemistry 03/2014; · 4.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Spermatogenesis is a complex developmental process whereby diploid spermatogenic stem cells become haploid and undergo a series of morphological changes to produce physically mature spermatozoa. Crucial to this process are a number of RNA binding proteins, responsible for the post-transcriptional control of essential mRNAs; particularly pertinent to the two periods of inactive transcription which occur in spermatogenesis. One such group of RNA binding proteins is the Musashi family, specifically Musashi-1 (MSI1) and Musashi-2 (MSI2), which act as key translational regulators in various stem cell populations and have been linked with the induction of tumorigenesis. In the present study, we examined the differential expression of mammalian MSI1 and MSI2 during germ cell development in the mouse testis. MSI1 was found to be predominately localized in mitotic gonocytes and spermatogonia, while MSI2 was detected in meiotic spermatocytes and differentiating spermatids. Extensive examination of the function of Musashi in spermatogenesis was achieved through the use of two transgenic mouse models with germ cell specific over-expression of full-length isoforms of Msi1 or Msi2. These models demonstrated that aberrant expression of either Msi1 or Msi2 has deleterious effects on normal spermatogenesis, with the Msi2 over-expression resulting in male sterility. Studies undertaken on human testicular seminoma tumors provide further insights into the relevance of MSI1 and MSI2 over-expression as diagnostic markers to human stem cell cancers. Overall this study provides further evidence for the unique functions that RNA-binding protein isoforms occupy within spermatogenesis, and introduces the potential manipulation of the Musashi family proteins to elucidate the mechanisms of post-transcriptional gene expression during germ cell development.
    Biology of Reproduction 03/2014; · 3.45 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Hematopoietic stem cells (HSCs) are maintained through the regulation of symmetric and asymmetric cell division. We report that conditional ablation of the RNA-binding protein Msi2 results in a failure of HSC maintenance and engraftment caused by a loss of quiescence and increased commitment divisions. Contrary to previous studies, we found that these phenotypes were independent of Numb. Global transcriptome profiling and RNA target analysis uncovered Msi2 interactions at multiple nodes within pathways that govern RNA translation, stem cell function, and TGF-β signaling. Msi2-null HSCs are insensitive to TGF-β-mediated expansion and have decreased signaling output, resulting in a loss of myeloid-restricted HSCs and myeloid reconstitution. Thus, Msi2 is an important regulator of the HSC translatome and balances HSC homeostasis and lineage bias.
    Journal of Experimental Medicine 01/2014; · 13.91 Impact Factor


Available from
Oct 7, 2014