Securin

Following bi-orientation of chromosome pairs and inactivation of the spindle checkpoint system, the underlying regulatory system, which includes securin, produces an abrupt stimulus that induces highly synchronous chromosome separation in anaphase.

[1] Securin is initially present in the cytoplasm and binds to separase, a protease that degrades the cohesin rings that link the two sister chromatids.

[1][2] It is thought that securin integrates multiple regulatory inputs to make separase activation switch like, resulting in sudden, coordinated anaphase.

One proposed signaling pathway generating switch-like behavior contains a positive feedback loop for activation of Cdc14 by separase,[3] leading to dephosphorylation and degradation of securin (Figure 3).

In addition, these mutant strains exhibited very high rates of mis-segregation compared to normal behavior.

Figure 1
Figure 1: Securin and separase are widely conserved
Figure 2
Figure 2: Five identified phosphorylation sites on securin
network diagram
Figure 3: Network diagram with feedback loops to generate switch-like activation of anaphase
network diagram
Figure 4: Potential network diagram involving securin to generate switch-like activation of anaphase