Abstract
Fragile X syndrome results from the loss of expression of the Fragile X Mental Retardation Protein (FMRP). FMRP and RNA helicase Moloney Leukemia virus 10 (MOV10) are important Argonaute (AGO) cofactors for miRNA-mediated translation regulation. We previously showed that MOV10 functionally associates with FMRP. Here we quantify the effect of reduced MOV10 and FMRP expression on dendritic morphology. Murine neurons with reduced MOV10 and FMRP phenocopied Dicer1 KO neurons which exhibit impaired dendritic maturation Hong J (2013), leading us to hypothesize that MOV10 and FMRP regulate DICER expression. In cells and tissues expressing reduced MOV10 or no FMRP, DICER expression was significantly reduced. Moreover, the Dicer1 mRNA is a Cross-Linking Immunoprecipitation (CLIP) target of FMRP Darnell JC (2011), MOV10 Skariah G (2017) and AGO2 Kenny PJ (2020). MOV10 and FMRP modulate expression of DICER1 mRNA through its 3'untranslated region (UTR) and introduction of a DICER1 transgene restores normal neurite outgrowth in the Mov10 KO neuroblastoma Neuro2A cell line and branching in MOV10 heterozygote neurons. Moreover, we observe a global reduction in AGO2-associated microRNAs isolated from Fmr1 KO brain. We conclude that the MOV10-FMRP-AGO2 complex regulates DICER expression, revealing a novel mechanism for regulation of miRNA production required for normal neuronal morphology.
Highlights
We cultured hippocampal neurons from Mov10 Het mice and showed that they have significantly reduced dendritic arborization compared to wild type (WT) [(p < .0001, Fig 1A and 1C) and [15]
DICER is the primary producer of miRNAs and its mRNA is directly bound by Fragile X Mental Retardation Protein (FMRP), Moloney Leukemia virus 10 (MOV10) and AGO2 [15, 59, 60]
We observed significantly reduced levels of AGO2-associated miRNAs in the Fmr1 knockout brain compared to wild type, initially suggesting a global defect in miRNA production in the absence of FMRP; that was not the case based on miRNA-seq of both WT and Fmr1 ko brains, showing that the global miRNA levels were unchanged
Summary
Neuronal architecture is affected in many neurodevelopmental disorders. Fragile X syndrome (FXS) is caused by loss of the RNA binding protein (RBP) FMRP [1]. Extensive characterization of FMRP loss in Drosophila, mice and humans has led to robust observations revealing the role of FMRP in the development of abnormal dendritic spines [2]. FMRP has been shown to play an important role in neuronal maturation. FXS patient-derived neurons from induced pluripotent stem cells (iPSCs) and hippocampal neurons from neonatal Fmr knockout (KO) mice and adult Fmr knockdown (KD) exhibit defects in neurite extension and dendritic maturation [3–7].
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