Actin-dependent organelle movement in squid axoplasm

Abstract

Studies of organelle movement in axoplasm extruded from the squid giant axon have led to the basic discoveries of microtubule-dependent organelle motility and the characterization of the microtubule-based motor proteins kinesin and cytoplasmic dynein. Rapid organelle movement in higher animal cells, especially in neurons, is considered to be microtubule-based. The role of actin filaments, which are also abundant in axonal cytoplasm, has remained unclear. The inhibition of organelle movement in axoplasm by actin-binding proteins such as DNase I, gelsolin and synapsin I has been attributed to their ability to disorganize the microtubule domains where most of the actin-filaments are located. Here we provide evidence of a new type of organelle movement in squid axoplasm which is independent of both microtubules and microtubule-based motors. This movement is ATP-dependent, unidirectional, actin-dependent, and probably generated by a myosin-like motor. These results demonstrate that an actomyosin-like mechanism can be directly involved in the generation of rapid organelle transport in nerve cells.

Microtubule-based filopodium-like protrusions form after axotomy

“…However, filopodia generally do not contain microtubules, being rich in actin filaments instead (Letourneau and Ressler, 1983;Tosney and Wessells, 1983). Also, there is evidence that membranous organelles can move along actin filaments in axoplasm (Kuznetsov et al, 1992), and a recent report suggested that actin filaments can power the transport of swellings in growth cone filopodia (Sheetz et al, 1990). In occasional optically favorable situations, VEC-DIC microscopy revealed a fiber extending from the living axon into an FLP and even bending or moving from side to side.…”

Short-term regulation of bile acid uptake by microfilament-dependent translocation of rat ntcp to the plasma membrane

“…Organelle movement along actin filaments has been demonstrated in algae, 28 squid axoplasm, 29 and in rat neuronal tissue. 30 Moreover, Kuznetsov et al demonstrated in a cell-free system that an individual organelle could move from microtubules directly to microfilaments.…”

Direct Interaction of the trans-Golgi Network Membrane Protein, TGN38, with the F-actin Binding Protein, Neurabin

“…It mediates several essential roles during mitosis (37); together with adhesion molecules, it regulates cell-cell and cell-substrate interactions (38,39) and participates in transmembrane signaling (40), endocytosis (41,42), and secretion (43). Actin filament integrity has been shown to be required for the normal positioning and morphology of the Golgi complex (44).…”