The arrangement of microtubules in the cells of Drosophila primary embryonic cultures and the cell line Cl.8+. D.M. Cottam, J.B. Tucker, M.J. Milner. School of Biology, University of St. Andrews, St. Andrews, Fife, UK.

   We have been using the Drosophila primary embryonic culture system to examine the arrangement of microtubules in different cell types and under different circumstances.
    Firstly, the anatomy of tendon and muscle cells and their junctions in vitro allowed us to investigate the mechanisms involved during the positioning and capture of microtubule ends at the apical and basal surfaces of the tendon cells. We propose a mechanism for capture and positioning of microtubules in these cells.
    Secondly, we present evidence for the reversible cold-induced rearrangement of microtubule assemblages. This rearrangement has been observed in flattened muscle cells in primary embryonic culture using both fixed wild-type cells stained with anti--tubulin and in living cells expressing a GFP-tau fusion protein that decorates the microtubules. A similar phenomenon has been observed in Cl.8+ cells. These approaches reveal that lengths of microtubules are concentrated in irregular star-shaped arrangements that form after cultures have been cooled to 0C for 3 hours or longer. In some cells, but not others, these assemblages appear to be associated with -tubulin. Such assemblages dissociate rapidly after warming to normal culture temperature (25C) and the microtubule arrangement becomes indistinguishable from that of uncooled control cells within 24 hours.