Gliding movement of and bidirectional transport along single native microtubules from squid axoplasm: evidence for an active role of microtubules in cytoplasmic transport.

TLDR

Native microtubules isolated from squid axoplasm can transport organelles and vesicles unidirectionally in fresh preparations and bidirectionally in older ones, with particles adhering, moving along, and switching between intersecting microtubules while gliding and carrying cargo in either direction. The authors aim to propose two models that explain the observed microtubule‑driven transport phenomena and fast axoplasmic transport. The study uses gently homogenized 1–30 µm microtubule segments that glide over glass, carrying particles in an ATP‑dependent, taxol‑insensitive motion, and proposes two mechanistic models for this activity. The experiments show that 1–30 µm microtubule segments glide hundreds of micrometers on glass, carrying particles in an ATP‑dependent, taxol‑insensitive manner, suggesting that the motive force originates from the microtubule or its associated proteins and that these findings could inform a broad range of microtubule‑based motility processes.

Abstract

Native microtubules prepared from extruded and dissociated axoplasm have been observed to transport organelles and vesicles unidirectionally in fresh preparations and more slowly and bidirectionally in older preparations. Both endogenous and exogenous (fluorescent polystyrene) particles in rapid Brownian motion alight on and adhere to microtubules and are transported along them. Particles can switch from one intersecting microtubule to another and move in either direction. Microtubular segments 1 to 30 microns long, produced by gentle homogenization, glide over glass surfaces for hundreds of micrometers in straight lines unless acted upon by obstacles. While gliding they transport particles either in the same (forward) direction and/or in the backward direction. Particle movement and gliding of microtubule segments require ATP and are insensitive to taxol (30 microM). It appears, therefore, that the mechanisms producing the motive force are very closely associated with the native microtubule itself or with its associated proteins. Although these movements appear irreconcilable with several current theories of fast axoplasmic transport, in this article we propose two models that might explain the observed phenomena and, by extension, the process of fast axoplasmic transport itself. The findings presented and the possible mechanisms proposed for fast axoplasmic transport have potential applications across the spectrum of microtubule-based motility processes.