SELF-CENTRING ACTIVITY OF CYTOPLASM

Fish melanophore cells aggregate pigment granules at the centre or red isperse them throughout the cytoplasm. The granules move along radial microtubules by means of molecular motors(1-3) Cytoplasmic fragments o f melanophores organize a radial array of microtubules and aggregate p igment at its centre(4-7). Here we report self-centring in microsurgic ally produced cytoplasmic fragments of black tetra melanophores. We ob served rapid (10 min) formation of a radial microtubule array after st imulation of aggregation. Arrangement of microtubules in the fragments returned to random during pigment redispersion. Apparently, formation of the radial array does not depend on a pre-existing microtubule-org anizing centre. The array did not form in granule-free fragments nor i n fragments treated with inhibitors of the intracellular motor protein cytoplasmic dynein. We conclude that formation of the radial microtub ule array is induced by directional motion of pigment granules along m icrotubules and present evidence that its position is defined by inter action of microtubules with the surface.