The spindle attaches primarily to the chromosome structures known as kinetochores, which form at the centromere region of each duplicated chromosome during cell division.

Spindle Attachment Sites

• Kinetochores : These are protein complexes assembled at the centromere of each chromosome. Microtubules from the spindle apparatus bind to these sites, ensuring that each chromosome is properly connected to the spindle for accurate segregation.

• Centromeres : The centromere is the region on the chromosome where the kinetochore forms and acts as the physical platform for spindle attachment.

• Spindle Poles/Centrosomes : The microtubules' minus-ends are anchored at the spindle poles (centrosomes), providing the structural orientation for chromosome movement. Astral microtubules also extend from these poles to anchor the spindle to the cell cortex.

Key Functional Connections

• The spindle is a dynamic microtubule structure crucial for chromosome alignment and segregation during cell division, attaching directly to the chromosome at the kinetochore and indirectly stabilizing the division process via connections to spindle poles and the cell cortex.

• Overlap microtubules at the spindle equator interact to maintain spindle stability and bipolarity, but do not attach to chromosomes directly.

In summary, the spindle attaches to chromosomes via kinetochores, which are located at the centromeres, and is anchored at the spindle poles within the cell.