Myosin-V Induces Cargo Immobilization and Clustering at the Axon Initial Segment

Abstract

The selective transport of different cargoes into axons and dendrites underlies the polarized organization of the neuron. Although it has become clear that the combined activity of different motors determines the destination and selectivity of transport, little is known about the mechanistic details of motor cooperation. For example, the exact role of myosin-V in opposing microtubule-based axon entries has remained unclear. Here we use two orthogonal chemically-induced heterodimerization systems to independently recruit different motors to cargoes. We find that recruiting myosin-V to kinesin-propelled cargoes at approximately equal numbers is sufficient to stall motility. Kinesin-driven cargoes entering the axon were arrested in the axon initial segment (AIS) upon myosin-V recruitment and accumulated in distinct actin-rich hotspots. Importantly, unlike proposed previously, myosin-V did not return these cargoes to the cell body, suggesting that additional mechanism are required to establish cargo retrieval from the AIS.

F‐actin patches associated with glutamatergic synapses control positioning of dendritic lysosomes

“…Next, we tested a potential contribution of the processive motors myosins V and VI in lysosome stalling. They are known to mediate cargo transport into and inside dendritic spines (Correia et al, 2008;Esteves da Silva et al, 2015), and dendritic cargo sorting at the axon initial segment is based on the presence of myosin V (Janssen et al, 2017). Thus, it is very likely that many dendritic cargos are associated with myosins.…”

Role of actin in organelle trafficking in neurons

“…The AIS is an actin‐rich region that aids in halting dendritic cargo (Balasanyan et al, ; K. Watanabe et al, ). Specifically Myosin V motors present at the AIS cause stalling of dendritic cargo at the actin‐enriched AIS of neurons in culture (Al‐Bassam et al, ; Janssen et al, ) (Figure b). Artificially recruited Myosin V to axonally targeted Rab3 vesicles led to clustering of these vesicles at the AIS (Janssen et al, ).…”

“…Specifically Myosin V motors present at the AIS cause stalling of dendritic cargo at the actin‐enriched AIS of neurons in culture (Al‐Bassam et al, ; Janssen et al, ) (Figure b). Artificially recruited Myosin V to axonally targeted Rab3 vesicles led to clustering of these vesicles at the AIS (Janssen et al, ). Thus, actin enrichment at the AIS can aid polarized cargo transport by halting dendritic cargo entry into axons through Myosin V. However, it is unclear how the actomyosin network at the AIS distinguishes between dendritic and axonal cargo.…”

“…Although, transport through myosins and transport mediated by actin flow have been described in neurons, force-based propulsion of cargos by actin polymerization in neurons has not been reported. Janssen et al, 2017;Pathak, Sepp, & Hollenbeck, 2010;van Bommel et al, 2019;Wagner et al, 2011) or (b) a physical roadblock created by a network of actin filaments that may halt moving cargo (Chada & Hollenbeck, 2004;Gutnick, Banghart, West, & Schwarz, 2019;Kuromi & Kidokoro, 1998;Sood et al, 2018).…”

“…Specifically Myosin V motors present at the AIS cause stalling of dendritic cargo at the actin-enriched AIS of neurons in culture Janssen et al, 2017) (Figure 3b). Artificially recruited Myosin V to axonally targeted Rab3 vesicles led to clustering of these vesicles at the AIS (Janssen et al, 2017). Thus, actin enrichment at the AIS can aid polarized cargo transport by halting dendritic cargo entry into axons through Myosin V. However, it is unclear how the Early studies done on mitochondrial transport in neurons suggest that actin filaments could play a role in docking and positioning these organelles along the axon as disruption of actin caused an increase in the velocity and duty cycle (moving/stationary time) of moving mitochondria (Morris & Hollenbeck, 1995).…”