Abstract. Hook decoration with pig brain tubulin was used to assess the polarity of microtubules which mainly have 15 protofilaments in the transcellular bundles of late pupal Drosophila wing epidermal cells. The microtubules make end-on contact with cell surfaces. Most microtubules in each bundle exhibited a uniform polarity. They were oriented with their minus ends associated with their hemidesmosomal anchorage points at the apical cuticle-secreting surfaces of the cells. Plus ends were directed towards, and were sometimes connected to, basal attachment desmosomes at the opposite ends of the cells.The orientation of microtubules at cell apices, with minus ends directed towards the cell surface, is opposite to the polarity anticipated for microtubules which have elongated centrifugally from centrosomes. It is consistent, however, with evidence that microtubule assembly is nucleated by plasma membrane-associated sites at the apical surfaces of the cells (Mogensen, M. M., and J. B. Tucker. 1987. J. Cell Sci. 88:95-107) after these cells have lost their centriole-containing, centrosomal, microtubule-organizing centers

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The nutritive tubes of telotrophic insect ovaries are cytoplasmic channels along which ribosomes are transported over distances of several mm from trophic cells to the developing oocytes. The presence within the nutritive tubes of a massive number of orientated microtubules renders them strongly birefringent in polarised light, a property which, together with their size, rendered them amenable to isolation by microdissection. Ultrastructurally the isolated tubes were indistinguishable from undissected controls. Polyacrylamide gels revealed a consistent pattern of some 30 bands of which tubulin was the most prominent. The tubes also contained a band which comigrated with the major high molecular weight microtubule associated protein (MAP) from mouse brain but no detectable actin, myosin or dynein. Microtubules in the isolated tubes were not depolymerised by treatments (cold, calcium and colchicine) which typically disrupt cytoplasmic microtubules. Following extraction of the membrane enclosing the tubes and the cytoplasmic matrix the microtubule cytoskeleton persisted, retaining its cylindrical organisation although no bridges between the microtubules were detected in the electron microscope. The possibility that the stability and spatial deployment of the nutritive tube microtubules is conferred by specific microtubule accessory proteins is discussed.