Fig. 3.

Acentrosomal spindle organization in C. elegans female meiosis. a Schematic representation (above) of the first meiotic division (β-tubulin::GFP; lower panels). Microtubules form around the chromatin and become organized into a bipolar array (only three bivalents are drawn). At this stage, KLP-18 is required for microtubule bundling and pole focusing. Chromosomes align on the metaphase plate in a rosette pattern (shown above), and KLP-19 (red strip) is implicated in providing an anti-poleward force that could exert a torque on the paired chromosomes to ensure their proper alignment (yellow arrows). The redistribution of microtubules in metaphase-anaphase and telophase is represented schematically. By telophase, microtubules begin to accumulate around chromatin to assemble the second meiotic spindle. b Electron micrographs showing the formation of the first polar body with an enlarged view of a kinetochore region (mid panel). c Three-dimensional reconstruction of one half of a meiotic wild-type spindle (microtubules in red, pole–proximal ends as white spheres, pole–distal ends as blue spheres, chromatin in green; p is spindle pole, from [132]). d Tomographic slice showing lateral disruption of the lattice of a spindle microtubule (arrows). e Model explaining the role of katanin (shown as stars) in female meiotic spindle assembly. One half spindle is shown; chromatin is green. Katanin converts a few long microtubules into many short microtubule fragments that may become bundled and arranged into the bipolar array. f Gallery of microtubule pole–distal, and g gallery of microtubule pole–proximal ends showing a variety of open, flared morphologies. Scale bars are 5 μm in a, 500 nm in c, and 50 nm in d