FOCUSING ON SPINDLE POLES

Spindle poles are discernible by light microscopy as the sites where m icrotubules converge at the ends of both mitotic and meiotic spindles. In most cell types centrosomes are present at spindle poles due to th eir dominant role ire microtubule nucleation. However, in some special ized cell types microtubules converge into spindle poles in the absenc e of centrosomes. Thus, spindle poles in centrosomal and acentrosomal cell types are structurally different, and it is this structural dicho tomy that has created confusion as to the mechanism by which microtubu les are organized into spindle poles. This review summarizes a series of recent articles that begin to resolve this confusion by demonstrati ng that spindle poles are organized through a common mechanism by a co nserved group of nonproteins in the presence or absence of centrosomes .