Spindle fibres

Spindle fibres consist of microtubules that are polymeric chains made from the protein Tublin. They form during the Prometaphase stage of Mitosis and both the Metaphase 1 and 2 stages of Meiosis, and they originate from the centrosomes located at the poles of the dividing cell, which help organize the microtubules as Tublin in polymerized. During cell replication, these fibres would form and attach to the Kinetochores located at the centromeres of the 2 sister chromatid strands. This stabilises the growing end of the polymer and prevents them from depolymerizing. They then retract during the Anaphase stage of Mitosis or Meiosis, pulling the sister chromatids apart towards the opposite poles of the cell.