FUS-ALS mutants alter FMRP phase separation equilibrium and impair protein translation

Abstract

FUsed in Sarcoma (FUS) is a multifunctional RNA binding protein (RBP). FUS mutations lead to its cytoplasmic mislocalization and cause the neurodegenerative disease amyotrophic lateral sclerosis (ALS). Here, we use mouse and human models with endogenous ALS-associated mutations to study the early consequences of increased cytoplasmic FUS. We show that in axons, mutant FUS condensates sequester and promote the phase separation of fragile X mental retardation protein (FMRP), another RBP associated with neurodegeneration. This leads to repression of translation in mouse and human FUS-ALS motor neurons and is corroborated in vitro, where FUS and FMRP copartition and repress translation. Last, we show that translation of FMRP-bound RNAs is reduced in vivo in FUS-ALS motor neurons. Our results unravel new pathomechanisms of FUS-ALS and identify a novel paradigm by which mutations in one RBP favor the formation of condensates sequestering other RBPs, affecting crucial biological functions, such as protein translation.

ALS-related FUS mutations alter axon growth in motoneurons and affect HuD/ELAVL4 and FMRP activity

“…In both FUS P525L hiPSC-derived MNs and Fus-Δ14 mice, however, mutant FUS is expressed at physiological levels and does not form aggregates 9 , 33 , 50 . Second, FUS mutations might promote phase separation of FMRP by sequestering it in FUS-containing cytoplasmic ribonucleoprotein complexes (RNPs) 51 . Third, mutant FUS might directly compete with FMRP for 3′UTR binding.…”

Axonal Length Determines Distinct Homeostatic Phenotypes in Human iPSC Derived Motor Neurons on a Bioengineered Platform

“…To maintain and regulate both translation and RNA metabolism within the axon, a number of RNA binding proteins (RBPs) are localized within the axon, [41] coordinating transport, granule formation and delivery of the mRNA to sites of local protein translation, [42] subsequently influencing the production rate of proteins at these sides. [43] Moreover, RBPs exhibit a broad influence on RNA splicing, stability, and transcription, wherefore it is not surprising that their malfunction makes them key player in neurodegenerative diseases. [18,22,44] We focused on two of these key RBPs, fused in sarcoma (FUS) and transactive DNA response binding protein 43 (TDP-43), as they are required in the healthy axon and are known to cause ALS.…”

BIAPSS: A Comprehensive Physicochemical Analyzer of Proteins Undergoing Liquid–Liquid Phase Separation

“…The summary page contains a high-quality image of the experimentally confirmed cellular location (left panel in Figure 3 ). Due to its multifunctionality in RNA processing, FUS is mostly observed in the nucleus [ 38 ]. In physiological conditions, the low levels of the protein are distributed in the cytoplasm [ 39 ], where FUS transports and manages RNA through the dynamic liquid-like subcellular compartments, such as ribonucleoprotein or stress granules [ 40 ].…”