Radial extension of macrophage tubular lysosomes supported by kinesin

Abstract

THE centrifugal elongation of membranes to form extended tubular structures is a widespread form of intracellular organelle movement. Tubular lysosomes¹ and the endoplasmic reticulum², for example, undergo such extension in association with micro-tubules, and this process has been mimicked in vitro by combining purified microtubules with isolated membranes and the mechano-chemical ATPase kinesin^3,4. This, along with evidence that kinesin is associated with the endoplasmic reticulum⁵, has led to the suggestion that kinesin provides the motive force for the formation and maintenance of elongated tubulovesicular structures in cells^6,7. We have addressed this hypothesis in murine macrophages, which have prominent tubular lysosomes whose form depends on the integrity of microtubules. Here we report that two antikinesin antibodies which disrupt in vitro motility will each cause centripetal collapse of the array of tubular lysosomes when scrape-loaded into macrophages. To our knowledge this provides the first in vivo evidence that kinesin is responsible for extension of tubulovesicular structures along microtubules.