In the present study, we examined cytokinesis in ammonia-activated sea urchin eggs, which lack paternally derived centrosomes and undergo mitosis mediated by unusual anastral, bipolar mini-spindles.
Earlier, we showed that these eggs form anastral, bipolar "mini-spindles" that can segregate chromosomes, along with non-spindle-associated microtubule arrays (Henson et al., 2008; see also Paweletz and Mazia, 1979; Bestor and Schatten, 1982; Harris and Clason, 1992).
The origin, development, and function of the diffuse anastral spindle of land plants are fundamental questions in evolutionary and developmental biology.
The diversity in spindle origin seen in bryophytes is in stark contrast to the uniformity of anastral spindle origin in "higher plants" and centrosomal spindle origin in algal and animal cells.
Based on the mechanisms of asymmetric division in mitotic cells (Kaltschmidt et al., 2000; Gonczy, 2002), a growing number of studies in meiosis have revealed female meiosis-specific mechanisms regulating either astral or anastral
meiotic spindle movement during asymmetric division: aside from the cytoskeleton itself, molecules associated with cytoskeletal organization as well as molecules that have no direct relationships with the cytoskeleton are involved in these processes.
[gamma]-Tubulin localization changes from discrete polar organizers to anastral
spindles and phragmoplasts in mitosis of Marchantia polymorpha L.
These spindles were small, anastral
, capable of anaphase-like chromosome segregation, and overall very reminiscent of meiotic spindles.