Motility in Echinosphaerium nucleofilum. I. An analysis of particle motions in the axopodia and a direct test of the involvement of the axoneme.

Abstract

The motion of particles in the axopodia of Echinosphaerium nucleofilum is saltatory. In the present study, photokymograph records of 123 motions from six axopodia have been analyzed. Particles followed rectilinear paths of from 1 to 15 am while in continuous motion at an average velocity of 0.66 • 0.32 #m/s. The velocity of the particles was variable in 36% of the cases measured. Some motions were punctuated by pauses either before continuing in the same direction or reversing. Frequently, several particles were moving at the same velocity, but neighboring particles showed no motion or moved in the opposite direction. Two particles occasionally contacted one another and travelled as a unit for varying lengths of time but subsequently moved independently. These motions reflect the underlying mechanism of motive force production. Furthermore, a glass microneedie can be substituted for the microtubular axoneme in the axopodia. In these artificial axopodia, bidirectional particle motions occurred which were similar to those in normal axopodia. Colchicine, at the threshold dose for axonemal dissolution, had no affect on these particle motions. It is concluded that the microtubular axoneme is not responsible for particle motions and also that individual microtubules are unlikely candidates for motive force production in this system. The axopodia of Echinosphaerium nucleofilumare needle-like projections up to 300/~m in length that radiate from the cytosome and are supported longitudinally by two coiled sheets of cross-linked microtubules, the axoneme (5, 9, 12). In Echinosphaerium the prevalence of cytoplasmic microtubules has suggested a possible role for microtubules in intracellular motility. The majority of ultrastructural studies have shown microtubules to be the only linear element present in the cytoplasm. However, Hovasse (4) has reported "skeins of microfibrils," as well as microtubules, to be present in the axopodia, an observation that more recent works have not confirmed. Thus, since alternatives are lacking, cytoplasmic motility has been attributed to the microtubules.The axopodia constitute a convenient system for studying particle motions because their geometry confines the motions to the long axis of the axopodia. The one-dimensional motions are readily analyzed with a photokymograph.

Video microscopy of fast axonal transport in extruded axoplasm: A new model for study of molecular mechanisms

“…It is possible that the glass surface can serve as an artificial substrate for ordering components of the transport machinery. The hypothesis that the motile machinery can interact with glass surfaces gains further support from observations by Edds [1975] that a glass microneedle can support particle movement in axopodia depleted of microtubules. We routinely preincubate our preparations at 4°C prior to observation because it appears to increase the consistency of the preparations and provides a convenient method of short-term storage (2040 minutes) prior to observation.…”

Differential distribution and function of microtubules and microfilaments in sea urchin coelomocytes

“…Similar findings involving actin in cellular morphogenesis have been reported in other cell types [see Allison et al, 1971;Amato et al, 1983;Boyles and Bainton, 1979;Clarke et al, 1975;Nachmias, 1980;Small and Celis, 1978;Tilney, 19761. The role of microtubules, however, is less well agreed upon. In some protozoans-Echinosphaerium, for example-MT's are absolutely essential for protrusive activity of the axopodia [Edds, 1975;Tilney, 19681. In another protozoan with a MT based cytoskeleton, Allogromia, a recent study has reported the visualization of sliding MT's poking outward against the cell membrane and the concomitant formation of filopodia [Travis et al, 19831.…”

Towards a new classification of intracellular particle movements based on quantitative analyses

“…From recent studies on the details of movements of axonal organelles it becomes increasingly evident that many other animal cells possess mechanisms very similar to those that are found to be microtubule-dependent in axons [Schliwa, 1984;Allen et al, 19851. On the other hand, certain cells show saltatory particle movement that is not dependent on microtubules but rather on the presence of actin filaments [Edds, 1975;Schliwa, 19841. Recently the use of the newly developed and most powerful technique of video-enhanced contrast, differential interference contrast (AVEC-DIC) microscopy [Allen et al, 1981;Allen and Allen, 1983;Allen, 19851 led to several reports on axonal systems where a class of 0 1986 Alan R. Liss, Inc.…”