Self-Centering Activity of Cytoplasm V.I.Rodionov and G.G. Borisy Nature 386:170-172, 1997

Fish melanophores aggregate pigment granules at the center or redisperse them throughout the cytoplasm. The granules move along radial microtubules (MTs) by means of molecular motors (ref. 1-3). Cytoplasmic fragments of melanophores organize a radial array of MTs and aggregate pigment at its center (ref. 4-7). Here we studied self centering in microsurgically produced cytoplasmic fragments of black tetra melanophores. We observed rapid (10 min) formation of a radial MT array after stimulation of aggregation. Arrangement of MTs in the fragments returned to random during pigment redispersion. Apparently, formation of the radial array did not depend on a pre-existing MT organizing center. The array did not form in granule-free fragments nor in fragments treated with inhibitors of the intracellular motor, cytoplasmic dynein. We conclude that formation of the radial MT array is induced by directional motion of pigment granules along microtubules and present evidence that its position is defined by interaction of MTs with the surface.

	Figure 1(500K) - Formation of radial MT array in melanophore fragments does not depend on MT nucleation at a new center and requires pigment granules.
	Figure 2(88K) - Inhibitors of motor activity interfere with MT rearrangement in melanophore fragments.
	Figure 3(171K) - Pigment motion in a toroidal-shaped fragment.
	Figure 4(110K) - Photobleaching of MTs in the course of centripetal motion of pigment aggregate in nascent fragment.

	Movie 1 (2.8 M) - Pattern of pigment motion in nascent fragment.
	Movie 2 (2.5 M) - Pattern of pigment motion in nascent fragment after treatment with taxol.
	Movie 3 (1.7 M) - Pigment motion in incubated fragment.
	Movie 4 (1.7 M) - Pigment motion in incubated fragment treated with taxol.
	Movie 5 (1.8 M) - Pigment motion in toroidal fragment.