ight-electron microscopy experiments found mono-oriented combination of to generate acentric fragments, they. First, they chromosome arms distal kinetochore ejected away from the spindle that kinetochore-free demonstrated that thewere immediatelyfrom an oscillating mono-oriented pole chromosome was indeed devoid of microtubules and consequently was not under opposing with velocities similar to the outward movement of an oscillating chromosome, whereas the kinetochore pulling forces. Second, by cutting near the kinetochore regions of mono-oriented remaining kinetochore-containing fragment movedwithout to the pole . chromosomes to generate acentric fragments, they found that kinetochoreR-7128 biological activity Subsequent studies byarms were immediately ejected away from the spindle pole with velocities similar astral free chromosome Salmon, Rieder and colleagues have further demonstrated that when to the outward movement depolymerized/polymerized, mono-oriented chromosomes microtubules were reversibly of an oscillating chromosome, whereas the remaining kinetochore-moved containing fragment moved closer to the pole, respectively. These studies revealed no closer to or were pushed away from the pole . Subsequent studies by in the Rieder and colleagues have further demonstrated that when astral microtubules were differenceSalmon, mechanism of chromosome positioning between monopolar and bipolar spindles, reversibly depolymerized/polymerized, mono-oriented chromosomes moved closer to or were including average distances from the pole. Finally, it was shown that kinetochores moving away from pushed away from the pole, 
respectively. These studies revealed no difference in the their associated pole do not exert a significant pushing force on the chromosome and PEFs mechanism of chromosome positioning between monopolar and bipolar spindles, including average determine the PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19809024 amplitude of chromosome oscillationskinetochores moving away from their associated astral distances from the pole. Finally, it was shown that near the pole. Thus, PEFs derived from microtubules acting along chromosome arms oppose kinetochore-pulling forces. This “push-pull” pole do not exert a significant pushing force on the chromosome and PEFs determine the amplitude of chromosome oscillations near the pole. Thus, PEFs derived from astral mechanism was proposed to account for chromosome oscillations, while determining chromosome microtubules the spindle pole. In the context of a bipolar spindle, chromosome congression position relative toacting along chromosome arms oppose kinetochore-pulling forces. This “push-pull” mechanism was proposed to account for chromosome oscillations, while determining chromosome could now be explained in light of the balance of four forces on a chromosome: two antagonistic position relative to the spindle pole. In the context of a bipolar spindle, chromosome congression poleward forces acting at thein light of the balance of four forces on a chromosome: two antagonistic arms. could now be explained kinetochores and two opposing PEFs acting along chromosome As so, formation of aacting at the kinetochores and two opposing PEFs acting along chromosome arms.the net poleward forces metaphase plate equidistant to the spindle poles would result from forces applied to the chromosomes being zero. An integratedwould result from the net can be As so, formation of a metaphase plate equidistant to the spindle poles view of these studies forces applied essay that firmly being zero the co
