Anaphase spindles

Koshland D, Hartwell LH 1987 The structure of sister minichromosome DNA before anaphase in Saccharomjces cerevisiae. Science 238 1713—1716 KumadaK, Nakamura T, Nagao K, Funabiki H, Nakagawa T, Yanagida M 1998 Cutl is loaded onto the spindle by binding to Cut2 and promotes anaphase spindle movement upon Cut2 proteolysis. Curr Biol 8 633—641... 

Cell polarity and anaphase spindle positioning in the wild-type one-cell stage C. elegans embryo... 

The phase of the cell cycle where the sister chromatids are separated and distributed onto two daughter nuclei. First, upon entry into mitosis the chromosomes are condensed followed by the breakdown of the nuclear-envelope (prophase). The two centrosomes are separated and induce the formation of the mitotic spindle. Then, the chromosomes are captures by the spindle and aligned on the metaphase plate (metaphase). The sister-chromatids are separated and pulled to the poles of the spindle (anaphase). In telophase, two new nuclei are formed around the separated chromatids. 

The processes of meiosis and mitosis involve many motile events, from the separation of the daughter chromosomes to the final act of cell separation at cytokinesis (Wadsworth, 1993). DNA replication itself may be considered as a motile event, because the polymerase complex moves along the linear DNA. One of the most obvious motile events is the separation of the chromosomes along the mitotic spindle at anaphase. Details of the structure and polarity of microtubules in the spindle apparatus in meiosis and mitosis are known through electron and light microscopy, but it is not yet clear whether the chromosomes are pushed, pulled or... 

Loss of sister chromatid cohesion would therefore be sufficient for the sudden movement of chromatids to opposite poles at the metaphase to anaphase transition. According to this hypothesis, a specific apparatus binds chromatids together during replication, holds them in an orientation that facilitates the attachment of sister kinetochores to spindles extending to opposite poles, and resists the splitting force that results from this bipolar attachment to the spindle. Destruction of this specialized cohesive structure triggers movement of chromatids to opposite poles at the onset of anaphase. 

Hunt Normally cyclin A goes away very early in mitosis—almost as soon as the nuclear envelope breaks down. If it doesn t go away, what seems to happen is that the spindle doesn t organize itself properly, yet it goes through anaphase. It is peculiar the spindles look horrible. These are spindles with both cyclin A and cyclin B. The cyclin A seems to be necessary to get it up to that point, but then you need to get rid of it in order for the cyclin B to take over. 

Aist JR, Liang H, Berns MW 1993 Astral and spindle forces in PtK2 cells during anaphase B a laser microbeam study. J Cell Sci 104 1207-1216 Bohm H, Brinkmann V, Drab M, Henske A, Kurzchalia TV 1997 Mammalian homologues of C. elegant PAR-1 are asymmetrically localized in epithelial cells and may influence their polarity. Curr Biol 7 603-606... 

Phosphorylation also plays an evident part in cell division. Specifically, cytoskeleton-associated protein 2 (CKAP2) has a phosphorylation site at threonine 596. This threonine has been tracked and gets phosphorylated between prophase and metaphase, and dephosphorylated a short time later before anaphase, suggesting that the protein is phosphorylated during the formation of mitotic spindles. ... 

Anaphase TPX2 Localization of Aurora A kinase to mitotic spindles 353... 

Figure 20.28 Diagrammatic representation of mitosis in a cell with a single pair of homologous chromosomes. In prophase, the chromatin condenses into chromosomes, each of which consists of a pair of chromatids that have been formed by replication during interphase, and the nuclear envelope disappears. In metaphase, each chromatid attaches to the spindle fibres (microtubules) at a centre point, the centromere. In anaphase, the two chromatids of each chromosome become detached from each other and move to opposite poles of the cell along the microtubules. In telophase, the chromatids have reached the poles. Two nuclear envelopes then form and enclose each new set of chromatids, now once again called chromosomes. The microtubules disappear and the chromosomes uncoil and re-form into the long chromatin threads. Finally the cell membrane is drawn inward by a band of microfilaments to form a complete constriction between the newly formed nuclei, and two new cells are formed. The process is called cytokinesis.

---