FMRP phosphorylation and interactions with Cdh1 regulate association with dendritic RNA granules and MEF2-triggered synapse elimination

• Type of Material: Article
• Authors: Julia R Wilkerson, UT Southwestern Medical Center, Dallas; Marius F Ifrim, State University of New York; Arielle Valdez, Emory University; Patricia Hahn, UT Southwestern Medical Center, Dallas; Jacob E Bowles, UT Southwestern Medical Center, Dallas; Gemma Molinaro, UT Southwestern Medical Center, Dallas; Aleksandra Janusz-Kaminska, Emory University; Gary J Bassell, Emory University; Kimberly M Huber, UT Southwestern Medical Center, Dallas
• Language: English
• Date: 2023-05-03
• Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE
• Publication Version: Final Published Version
• Copyright Statement: © 2024 Elsevier B.V., its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies. For all open access content, the Creative Commons licensing terms apply.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/j.nbd.2023.106136
• Title of Journal or Parent Work: NEUROBIOLOGY OF DISEASE
• Volume: 182
• Start Page: 106136
• End Page: 106136
• Grant/Funding Information: This work was supported by NIH grants (HD052731, HD104461; KMH) and (MH109026; GJB)
• Keywords: REVEALS; DEGRADATION; Neurosciences & Neurology; Hippocampal CA1; MEF2; FLUORESCENT PROTEIN; MOUSE MODEL; MGLUR; COMPLEMENTATION BIFC ANALYSIS; Life Sciences & Biomedicine; Synapse elimination; Neurosciences; FMRP; TRANSCRIPTION; MENTAL-RETARDATION PROTEIN; Science & Technology; TRANSLATION; ARC/ARG3.1; Cdh1
• Research Categories: Psychology, Developmental; Biology, Cell; Biology, Neuroscience

Abstract

Fragile X Messenger Ribonucleoprotein (FMRP) is necessary for experience-dependent, developmental synapse elimination and the loss of this process may underlie the excess dendritic spines and hyperconnectivity of cortical neurons in Fragile X Syndrome, a common inherited form of intellectual disability and autism. Little is known of the signaling pathways that regulate synapse elimination and if or how FMRP is regulated during this process. We have characterized a model of synapse elimination in CA1 neurons of organotypic hippocampal slice cultures that is induced by expression of the active transcription factor Myocyte Enhancer Factor 2 (MEF2) and relies on postsynaptic FMRP. MEF2-induced synapse elimination is deficient in Fmr1 KO CA1 neurons, and is rescued by acute (24 h), postsynaptic and cell autonomous reexpression of FMRP in CA1 neurons. FMRP is an RNA binding protein that suppresses mRNA translation. Derepression is induced by posttranslational mechanisms downstream of metabotropic glutamate receptor signaling. Dephosphorylation of FMRP at S499 triggers ubiquitination and degradation of FMRP which then relieves translation suppression and promotes synthesis of proteins encoded by target mRNAs. Whether this mechanism functions in synapse elimination is not known. Here we demonstrate that phosphorylation and dephosphorylation of FMRP at S499 are both necessary for synapse elimination as well as interaction of FMRP with its E3 ligase for FMRP, APC/Cdh1. Using a bimolecular ubiquitin-mediated fluorescence complementation (UbFC) assay, we demonstrate that MEF2 promotes ubiquitination of FMRP in CA1 neurons that relies on activity and interaction with APC/Cdh1. Our results suggest a model where MEF2 regulates posttranslational modifications of FMRP via APC/Cdh1 to regulate translation of proteins necessary for synapse elimination.