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Steady axonal cargo flow is central to the functioning of healthy neurons. However, a substantial fraction of cargo in axons remains stationary up to several minutes. We examine the transport of precursors of synaptic vesicles (pre‐SVs), endosomes and mitochondria in Caenorhabditis elegans touch receptor neurons, showing that stationary cargo are predominantly present at actin‐rich regions along the neuronal process. Stationary vesicles at actin‐rich regions increase the propensity of moving vesicles to stall at the same location, resulting in traffic jams arising from physical crowding. Such local traffic jams at actin‐rich regions are likely to be a general feature of axonal transport since they also occur in Drosophila neurons. Repeated touch stimulation of C. elegans reduces the density of stationary pre‐SVs, indicating that these traffic jams can act as both sources and sinks of vesicles. This suggests that vesicles trapped in actin‐rich regions are functional reservoirs that may contribute to maintaining robust cargo flow in the neuron. A video abstract of this article can be found at: Video S1; Video S2 [ABSTRACT FROM AUTHOR]

Microtubules stimulate contractile-ring formation in the equatorial cortex and simultaneously suppress contractility in the polar cortex; how they accomplish these differing activities is incompletely understood. We measured the behavior of GFP-actin in mammalian cells treated with nocodazole under conditions that either completely eliminate microtubules or selectively disassemble astral microtubules. Selective disassembly of astral microtubules resulted in functional contractile rings that were wider than controls and had altered dynamic activity, as measured by FRAP. Complete microtubule disassembly or selective loss of astral microtubules resulted in wave-like contractile behavior of actin in the non-equatorial cortex, and mislocalization of myosin II and Rho. FRAP experiments showed that both contractility and actin polymerization contributed to the wave-like behavior of actin. Wave-like contractile behavior in anaphase cells was Rho-dependent. We conclude that dynamic astral microtubules function to suppress Rho activation in the nonequatorial cortex, limiting the contractile activity of the polar cortex. [ABSTRACT FROM AUTHOR]