title: Single-Molecule Imaging of PSD-95 mRNA Translation in Dendrites and Its Dysregulation in a Mouse Model of Fragile X Syndrome.
abstract: Fragile X syndrome (FXS) is caused by the loss of the fragile X mental retardation protein (FMRP), an RNA binding protein that regulates translation of numerous target mRNAs, some of which are dendritically localized. Our previous biochemical studies using synaptoneurosomes demonstrate a role for FMRP and miR-125a in regulating the translation of PSD-95 mRNA. However, the local translation of PSD-95 mRNA within dendrites and spines, as well as the roles of FMRP or miR-125a, have not been directly studied. Herein, local synthesis of a Venus-PSD-95 fusion protein was directly visualized in dendrites and spines using single-molecule imaging of a diffusion-restricted Venus-PSD-95 reporter under control of the PSD-95 3'UTR. The basal translation rates of Venus-PSD-95 mRNA was increased in cultured hippocampal neurons from Fmr1 KO mice compared with WT neurons, which correlated with a transient elevation of endogenous PSD-95 within dendrites. Following mGluR stimulation with (S)-3,5-dihydroxyphenylglycine, the rate of Venus-PSD-95 mRNA translation increased rapidly in dendrites of WT hippocampal neurons, but not in those of Fmr1 KO neurons or when the binding site of miR125a, previously shown to bind PSD-95 3'UTR, was mutated. This study provides direct support for the hypothesis that local translation within dendrites and spines is dysregulated in FXS. Impairments in the regulated local synthesis of PSD-95, a critical regulator of synaptic structure and function, may affect the spatiotemporal control of PSD-95 levels and affect dendritic spine development and synaptic plasticity in FXS.
authors.affiliation: Departments of Cell Biology and Neurology, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Marius F
authors.identifier: http://orcid.org/0000-0001-9172-3180
authors.initials: MF
authors.lastname: Ifrim
authors.affiliation: Departments of Cell Biology and Neurology, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Kathryn R
authors.initials: KR
authors.lastname: Williams
authors.affiliation: Departments of Cell Biology and Neurology, Emory University School of Medicine, Atlanta, Georgia 30322 gary.bassell@emory.edu.
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Bassell
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003712:Dendrites / Q000737:chemistry / Q000378:metabolism*; D004195:Disease Models, Animal; D000076122:Disks Large Homolog 4 Protein; D005600:Fragile X Syndrome / Q000378:metabolism*; D051528:Guanylate Kinases / Q000032:analysis / Q000096:biosynthesis*; D006624:Hippocampus / Q000737:chemistry / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000032:analysis / Q000096:biosynthesis*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D057054:Molecular Imaging / Q000379:methods*; D014176:Protein Biosynthesis / Q000502:physiology*
chemical_list: D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; D008565:Membrane Proteins; D051528:Guanylate Kinases
keywords: FMRP; Fragile X syndrome; PSD-95; PSD-95 mRNA; local translation; single-molecule imaging