On the mechanism of anaphase spindle elongation in Diatoma vulgare

Abstract

Central spindles from 5 dividing cells (1 metaphase, 3 anaphase, and 1 telophase) of Diatoma vulgare were reconstructed from serial sections. Each spindle is made up of 2 half spindles that are composed almost entirely of polar microtubules. A small percentage of continuous microtubules and free microtubules were present in every stage except telophase. The half spindles interdigitate at the midregion of the central spindle, forming a zone of overlap where the microtubules from 1 pole intermingle with those of the other. At metaphase the overlap zone is fairly extensive, but as elongation proceeds, the spindle poles move apart and the length of the overlap decreases because fewer microtubules are sufficiently long to reach from the pole to the zone of interdigitation. At telophase, only a few tubules are long enough to overlap at the midregion. Concurrent with the decrease in the length of the overlap zone is an increase in the staining density of the intermicrotubule matrix at the same region. These changes in morphology can most easily be explained by assuming some mechanochemical interaction between microtubules in the overlap zone which results in a sliding apart of the 2 half spindles.