Figure 3.
(A–H) Selected video images of a PtK1 cell 20 hr after fusing. This cell contains independent bipolar (left side of A) and tripolar (right side of A) spindles. In this example anaphase started in the bipolar spindle (B) 24 min after its last monooriented chromosome initiated congression (arrow in A), and anaphase was initiated in the presence of a monooriented chromosome on the tripolar spindle (arrow in B). The tripolar spindle then entered anaphase 25 min later (D) even though it still contained a monooriented chromosome (arrow in D and E). This cell cleaved between the poles of the bipolar spindle (arrowheads in D). It then also initiated cleavage between two spindle poles in the tripolar spindle (open arrowhead in F) and also between the independent spindles (arrowheads in F–H). Note that this latter furrow did not contain a midbody, and that it completely cleaved the cell between two spindle poles that lacked intervening chromosomes. (Bar = 10 μm.)