Fmr1 Deficiency Alters Self-Renewal And Proliferation Of Mouse Embryonic Cells

The regulation of embryonic stem (ES) cell self-renewal and pluripotency is based upon highly orchestrated transcription factor networks. RNA inhibition has been demonstrated to affect ES cell function by altering gene expression levels that are critical to the maintenance and differentiation of ES cells. Fragile X mental retardation protein (FMRP) is a selective RNA-binding protein that can act as a translational repressor for bound mRNA and regulates the expression of a variety of gene transcripts in numerous adult cells. The absence of FMRP results in the most common form of inherited intellectual disability, Fragile X syndrome. In an effort to determine the role of FMRP during development, we silenced the FMRP gene (FMR1) using short hairpin RNA (shRNA). Prior to differentiation induction, we analyzed the phenotype of FMR1 knock down (FMR1-kd) mouse ES cells in their undifferentiated state. Herein, we report that FMR1-kd ES cells proliferate at a greater rate than wild-type ES cells resulting in a 25% reduction in doubling time. FMR1-kd ES cells were found to have an increased expression of three self-renewal genes (OCT-4, Sox2, Nanog) in the undifferentiated state. Moreover, FMR1-kd ES cells failed to downregulate OCT-4 during differentiation programs resulting in abnormal fate decisions in vitro. These results demonstrate an unexpected correlation between FMR1 expression and OCT-4 regulation suggesting that FMRP is involved in the silencing of OCT-4 during the commencement of differentiation programs.