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Micrograph showing condensed chromosomes in blue and the mitotic spindle in green during prometaphase of mitosis

The spindle apparatus is a structure of the eukaryotic cytoskeleton involved in mitosis and meiosis, often referred to as the mitotic spindle during mitosis and the meiotic spindle during meiosis. Its function is to segregate chromosomes during cell division (either mitosis or meiosis) to the daughter cells . It consists of a bundle of microtubules joined at the ends but spread out in the middle, vaguely ellipsoid in shape. In the wide middle portion, known as the spindle midzone, antiparallel microtubules are bundled by kinesins. At the pointed ends, known as spindle poles, microtubules are nucleated by the centrosomes.

During spindle assembly in prometaphase, some of the spindle's microtubules attach to the kinetochores that assemble on the centromere portion of the chromosomes. The chromosomes are pulled into alignment along the spindle midzone to form the metaphase spindle. Once all the chromosomes are aligned with sister chromatids pointing to opposite ends of the spindle, the cell enters anaphase, in which the chromatids separate and move toward their respective poles. Since the center of the spindle specifies the plane along which the cell will divide during cytokinesis, this ensures that each daughter cell will receive one of each chromatid. The mitotic kinase Aurora A is required for proper spindle assembly and separation.

According to a recent publication^[1], Lamin B is a key component of the spindle matrix helping microtubule assembly, the mitotic spindle will not form without it.

1. ^ Tsai MY, Wang S, Heidinger JM, Shumaker DK, Adam SA, Goldman RD, Zheng Y. A mitotic lamin B matrix induced by RanGTP required for spindle assembly Science 2006 Mar 31;311(5769):1887-93. PMID 16543417

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