Organelle movements in the wild type and wall-less fz;sg;os-1 mutants of Neurospora Crassa are mediated by cytoplasmic microtubules

ABSTRACT The cellular basis of organelle transport in filamentous fungi is still unresolved. Here we have studied the intra-cellular movement of mitochondria and other organelles in the fungus Neurospora crassa. Four different model systems were employed: hyphae, protoplasts, a cell wallless mutant, and experimentally generated small, flattened cell fragments of the mutant cells. Organelle movements were visualized by DIC optics and computer-enhanced video microscopy. In all cell models the transport of organelles was vectorial and saltatory in nature. The mean velocities for mitochondria, particles and nuclei were 1.4, 2.0, and 0.9 m/s, respectively. Treatment with 10 M nocodazole for 30 minutes caused a complete disappearance of microtubules and reversibly blocked directed transport of virtually all organelles, whereas cytochalasin D up to 20 M was without effect. Correlative video and immunofluorescence microscopy of small fragments of wall-less mutant cells revealed a clear match between microtubule distribution and the tracks of moving organelles. We conclude that organelle movement in the filamentous fungus Neurospora crassa is a microtubule-dependent process.