Figure 4.

The spindle checkpoint. Proper chromosome alignment in metaphase and microtubule attachment to the kinetochores induces the activation of APC, which mediates the degradation of proteins acting as a ‘molecular glue’ to hold together sister chromatids, thus allowing sister chromosomes separation. Defects in microtubule attachment result in activation of the Mad and Bub proteins, that phosphorylate the regulatory subunit of APC inhibiting its activity, with the result of preventing metaphase‐anaphase transition. Loss of function of these sensor proteins results in chromosome segregation even in conditions of a defective spindle, leading to aneuploidy.