Fast Transport of RNA Granules by Direct Interactions with KIF5A/KLC1 Motors Prevents Axon Degeneration

Abstract

20Complex neural circuitry requires stable connections formed by lengthy axons. To maintain these 21 functional circuits, fast transport delivers RNAs to distal axons where they undergo local translation. 22However, the mechanism that enables long distance transport of non-membrane enclosed organelles 23 such as RNA granules is not known. Here we demonstrate that a complex containing RNA and the RNA-24 binding protein (RBP) SFPQ interacts directly with a tetrameric kinesin containing the adaptor KLC1 and 25 the motor KIF5A. We show that binding of SFPQ to KIF5A/KLC1 motor complex is required for axon survival 26 and is impacted by KIF5A mutations that cause Charcot-Marie-Tooth (CMT) Disease. Moreover, 27 therapeutic approaches that bypass the need for local translation of SFPQ-bound proteins prevent axon 28 degeneration in CMT models. Collectively, these observations show that non-membrane enclosed 29 organelles can move autonomously and that replacing axonally translated proteins provides a therapeutic 30 approach to axonal degenerative disorders. 31 Results 75SFPQ granule, a non-membrane enclosed organelle, undergoes fast axonal transport. 77The RBP SFPQ is found in both cell bodies and axons of sensory neurons. However, the 78 mechanisms by which SFPQ and its critical RNA cargos are transported between these two locations is 79 not known. We utilized live cell imaging of DRG sensory neurons expressing Halo-tagged SFPQ to directly 80 visualize transport dynamics (Video 1). Fluorescent signal was enriched in the nucleus and was also 81 evident as discrete granules in the soma and axons, a pattern similar to the distribution of endogenous 82 SFPQ (Cosker et al., 2016). Consistent with the presence of intrinsically disordered regions within the 83 SFPQ coding sequence, Halo-tagged SFPQ granules exhibited liquid like properties during time-lapse 84 imaging (Gopal, Nirschl, Klinman, & Holzbaur, 2017), as the size and shape of SFPQ granules remained 85 constant at approximately 1 µm in diameter during the stationary phase, but the granules expanded and 86 elongated as they move ( Figure 1A and 1B). The majority of the Halo-tagged SFPQ granules in axons 87 were motile, either moving by retrograde transport (~48%), or anterograde transport (~28%), with the 88 remainder in stationary phase (~25%) ( Figure 1C and Figure 1-figure supplement 1A). SFPQ granules 89 exhibit an average anterograde velocity of 0.89 ± 0.08 μm/sec and average anterograde cumulative 90 displacement of 21.02 ± 2.49 μm, with an average retrograde velocity of 0.80 ± 0.04 μm/sec retrograde 91 and average retrograde cumulative displacement of 32.02 ± 2.45 μm (Figure 1D, Figure 1-figure 92 supplement 1B-E). Together, the velocity and the characteristics of movement indicate that the SFPQ-93 granules are non-membrane enclosed organelles that move in both directions by microtubule-94 dependent fast axonal transport, using a kinesin motor for anterograde and the more highly processive95 dynein motor for retrograde movements.96 97 98 99 5 SFPQ preferentiall...

Coiled-Coil Motifs of RNA-Binding Proteins: Dynamicity in RNA Regulation

“…This coiled-coil interaction allows for movement of cargo proteins, lipids, and RNAs within membrane-bound and membraneless organelles via motor protein binding, along the microtubule cytoskeletal network. For example, the microtubule-associated kinesin-1 cargo adaptor complex (KLC1) moves ribonucleoprotein granules by interacting with the RBP SFPQ via a coiled-coil motif, an interaction that is necessary for axonal transport (Fukuda et al, 2020). Large, membrane-bounded organelles, such as the lysosome, can be trafficked throughout the cell via similar coiled-coil protein-protein interactions.…”

A Picture Worth a Thousand Molecules—Integrative Technologies for Mapping Subcellular Molecular Organization and Plasticity in Developing Circuits

“…Microdissection and TRAP approaches for isolating RNA have revealed important roles for transcript UTR sequence motifs and transcript trafficking proteins in local translation. mRNAs are transported in phase-separated ribonucleoprotein (RNP) granules over long distances to dendrites and axons to establish local transcriptome pools (Nalavadi et al, 2012;Jung et al, 2014;Das et al, 2019;Liao et al, 2019;Pushpalatha and Besse, 2019;Fukuda et al, 2020;Rhine et al, 2020;Wu et al, 2020; Figure 3). The spatial control of transcript trafficking is based on mRNA sequences found in 3 and 5 untranslated regions (UTRs; Figure 3A) that act as binding sites for trans-acting RBPs (Sahoo et al, 2018;Bae and Miura, 2020).…”

The Emerging Role of the RNA-Binding Protein SFPQ in Neuronal Function and Neurodegeneration

“…More recently, it has been demonstrated that a complex containing RNA and SFPQ directly interacts with a tetrameric kinesin complex containing the motor, KIF5A, and the adaptor, KLC1 [ 59 ], further evidencing the SFPQ-dependent mRNA transport in neurons. Defects in kinesin-driven transport of SFPQ led to axon degeneration in the dorsal root ganglion sensory neurons, indicating that the interaction of SFPQ with the kinesin motor complex sustains axon survival by transporting relevant mRNA towards the distal end of the dorsal root ganglion sensory neurons for translation.…”

“…Defects in kinesin-driven transport of SFPQ led to axon degeneration in the dorsal root ganglion sensory neurons, indicating that the interaction of SFPQ with the kinesin motor complex sustains axon survival by transporting relevant mRNA towards the distal end of the dorsal root ganglion sensory neurons for translation. Interestingly, the authors found that the interaction of the kinesin motor complex and SFPQ is RNA-dependent, suggesting that KIF5A/KLC1 bind and transport SFPQ when it is part of large RNP transport granules [ 59 ].…”