Mitosis in vertebrate somatic cells with two spindles: implications for the metaphase/anaphase transition checkpoint and cleavage - PubMed (original) (raw)

Mitosis in vertebrate somatic cells with two spindles: implications for the metaphase/anaphase transition checkpoint and cleavage

C L Rieder et al. Proc Natl Acad Sci U S A. 1997.

Abstract

During mitosis an inhibitory activity associated with unattached kinetochores prevents PtK1 cells from entering anaphase until all kinetochores become attached to the spindle. To gain a better understanding of how unattached kinetochores block the metaphase/anaphase transition we followed mitosis in PtK1 cells containing two independent spindles in a common cytoplasm. We found that unattached kinetochores on one spindle did not block anaphase onset in a neighboring mature metaphase spindle 20 microm away that lacked unattached kinetochores. As in cells containing a single spindle, anaphase onset occurred in the mature spindles x = 24 min after the last kinetochore attached regardless of whether the adjacent immature spindle contained one or more unattached kinetochores. These findings reveal that the inhibitory activity associated with an unattached kinetochore is functionally limited to the vicinity of the spindle containing the unattached kinetochore. We also found that once a mature spindle entered anaphase the neighboring spindle also entered anaphase x = 9 min later regardless of whether it contained monooriented chromosomes. Thus, anaphase onset in the mature spindle catalyzes a "start anaphase" reaction that spreads globally throughout the cytoplasm and overrides the inhibitory signal produced by unattached kinetochores in an adjacent spindle. Finally, we found that cleavage furrows often formed between the two independent spindles. This reveals that the presence of chromosomes and/or a spindle between two centrosomes is not a prerequisite for cleavage in vertebrate somatic cells.

PubMed Disclaimer

Figures

Figure 1

Figure 1

Differential interference contrast (A) and epifluorescent (B) photomicrographs of a fused PtK1 cell that contains independent bipolar and tripolar spindles. Note that the two spindles do not share a common chromosome and that their microtubule arrays do not overlap. (Bar = 10 μm.)

Figure 2

Figure 2

(A–F) Selected video images from an untreated PtK1 cell with independent bipolar and monopolar spindles. In this cell the bipolar spindle entered anaphase (C) 24 min after its last monooriented chromosome initiated congression (arrow in A), and in the presence of numerous monooriented chromosomes on the monopolar spindle. Arrows in D and E indicate unattached anaphasic chromatids on the monopolar spindle. Note that a cleavage furrow is initiated between the poles of the bipolar spindle, and also between the poles of the bipolar and monopolar spindles where no chromosomes were present (arrowheads in F). (Bar = 10 μm.)

Figure 3

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.)

Comment in

References

    1. Wells W A E. Trends Cell Biol. 1996;6:228–234. - PubMed
    1. Hardwick K G, Murray A W. J Cell Biol. 1995;131:709–720. - PMC - PubMed
    1. Rieder C L, Cole R W, Khodjakov A, Sluder G. J Cell Biol. 1995;130:941–948. - PMC - PubMed
    1. Zhang D, Nicklas R B. Nature (London) 1996;382:466–468. - PubMed
    1. Chen R-H, Waters J C, Salmon E D, Murray A W. Science. 1996;274:242–246. - PubMed

Publication types

MeSH terms

Grants and funding

LinkOut - more resources