[
Trends Cell Biol,
2001]
In vertebrates and higher eukaryotes such as Caenorhabditis elegans and Drosophila melanogaster, microtubules are in each cell primarily nucleated and organized by the centrosome, which has as its center a pair of centrioles. In recent years, it has become clear that bipolar spindle assembly is possible without centrosomes, and it appears that the centrosome might be required for proper spindle positioning rather than for spindle assembly.