A novel role for the RNA-binding protein FXR1P in myoblasts cell-cycle progression by modulating p21/Cdkn1a/Cip1/Waf1 mRNA stability

PLoS Genet. 2013 Mar;9(3):e1003367. doi: 10.1371/journal.pgen.1003367. Epub 2013 Mar 21.


The Fragile X-Related 1 gene (FXR1) is a paralog of the Fragile X Mental Retardation 1 gene (FMR1), whose absence causes the Fragile X syndrome, the most common form of inherited intellectual disability. FXR1P plays an important role in normal muscle development, and its absence causes muscular abnormalities in mice, frog, and zebrafish. Seven alternatively spliced FXR1 transcripts have been identified and two of them are skeletal muscle-specific. A reduction of these isoforms is found in myoblasts from Facio-Scapulo Humeral Dystrophy (FSHD) patients. FXR1P is an RNA-binding protein involved in translational control; however, so far, no mRNA target of FXR1P has been linked to the drastic muscular phenotypes caused by its absence. In this study, gene expression profiling of C2C12 myoblasts reveals that transcripts involved in cell cycle and muscular development pathways are modulated by Fxr1-depletion. We observed an increase of p21--a regulator of cell-cycle progression--in Fxr1-knocked-down mouse C2C12 and FSHD human myoblasts. Rescue of this molecular phenotype is possible by re-expressing human FXR1P in Fxr1-depleted C2C12 cells. FXR1P muscle-specific isoforms bind p21 mRNA via direct interaction with a conserved G-quadruplex located in its 3' untranslated region. The FXR1P/G-quadruplex complex reduces the half-life of p21 mRNA. In the absence of FXR1P, the upregulation of p21 mRNA determines the elevated level of its protein product that affects cell-cycle progression inducing a premature cell-cycle exit and generating a pool of cells blocked at G0. Our study describes a novel role of FXR1P that has crucial implications for the understanding of its role during myogenesis and muscle development, since we show here that in its absence a reduced number of myoblasts will be available for muscle formation/regeneration, shedding new light into the pathophysiology of FSHD.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Cycle / genetics
  • Cell Differentiation
  • Cell Line
  • Cyclin-Dependent Kinase Inhibitor p21* / genetics
  • Cyclin-Dependent Kinase Inhibitor p21* / metabolism
  • Humans
  • Mice
  • Muscle Development / genetics
  • Muscle Development / physiology
  • Muscular Dystrophies* / genetics
  • Muscular Dystrophies* / metabolism
  • Myoblasts* / cytology
  • Myoblasts* / metabolism
  • RNA Stability / genetics
  • RNA, Messenger / metabolism
  • RNA-Binding Proteins / genetics*
  • RNA-Binding Proteins / metabolism


  • Cyclin-Dependent Kinase Inhibitor p21
  • FXR1 protein, human
  • Fxr1h protein, mouse
  • RNA, Messenger
  • RNA-Binding Proteins

Grant support

LD was funded by CNRS, the FRAXA Research Foundation 2010-12, and the Marie Curie European Community Program (FP6 MEIF-CT-2006-41096 and FP7-PEOPLE-ERG-2008-239290). BB was funded by CNRS, LIA “NEOGENEX,” INSERM, Agence Nationale de la Recherche (ANR) grant ANR-09-RARE-02-05, and by two French charities: Fondation Recherche Médicale call TEAM FRM 2009 and AFM (Association Française contre les Myopathies) Call MNMP2010 grant NR 13536. BB and LD were supported by Conseil Général Region PACA. OK was supported by a “Ville de Nice” post-doctoral fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.