Evidence that cell surface motility in Allogromia is mediated by cytoplasmic microtubules

We have previously shown that reticulopods of Allogromia sp. (strain NF) and Allogromia laticollaris display rapid, bidirectional saltatory transport of plasma membrane surface markers (i.e., polystyrene microspheres). Correlative video microscopic and electron microscopic methods were used to determine whether cytoskeletal components are involved in this surface transport. Such transport was observed only where the plasma membrane overlay cytoplasmic fibrils, which have been shown to be involved in organelle transport. Ultrastructural analysis indicated that these fibrils contain microtubules and an associated flocculent fibrillar material. In studies with nonionic detergents the surface marker particles remained bound to these microtubule-containing fibrils, even after the plasma membrane had been removed. Surface transport was inhibited when reticulopods were treated with agents that induce microtubule disassembly. Together these observations provide strong evidence that surface motility in Allogromia is mediated by labile cytoplasmic microtubules.