 At a certain point during the cell cycle in open mitosis , the cell divides to form two cells . In order for this process to be possible , each of the new daughter cells must have a full set of genes , a process requiring replication of the chromosomes as well as segregation of the separate sets . This occurs by the replicated chromosomes , the sister chromatids , <unk> to microtubules , which in turn are attached to different centrosomes . The sister chromatids can then be pulled to separate locations in the cell . In many cells , the <unk> is located in the cytoplasm , outside the nucleus ; the microtubules would be unable to attach to the chromatids in the presence of the nuclear envelope . Therefore , the early stages in the cell cycle , beginning in <unk> and until around <unk> , the nuclear membrane is dismantled . Likewise , during the same period , the nuclear lamina is also <unk> , a process regulated by <unk> of the lamins by protein <unk> such as the <unk> protein kinase . Towards the end of the cell cycle , the nuclear membrane is reformed , and around the same time , the nuclear lamina are reassembled by <unk> the lamins . 
