A Novel Hyperactive Nud1 Mitotic Exit Network Scaffold Causes Spindle Position Checkpoint Bypass in Budding Yeast

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Mitotic exit is essential for genome integrity, involving coordinated nuclear positioning and cyclin B destruction.
• The mitotic exit network (MEN) pathway regulates this process during anaphase in budding yeast.
• MEN activation requires Dbf2-Mob1 kinase complex recruitment and activation by the Nud1 scaffold protein at spindle pole bodies (SPBs).

Purpose of the Study:

• To investigate the mechanism of Cdc15 recruitment to SPBs for MEN activation.
• To characterize a hyperactive Nud1 allele (nud1-A308T) and its effect on MEN signaling.
• To understand the role of scaffold protein regulation in preventing aberrant pathway activation.

Main Methods:

• Identification and characterization of a hyperactive Nud1 allele (nud1-A308T).
• Analysis of Cdc15 and Dbf2-Mob1 recruitment to SPBs using the nud1-A308T allele.
• Assessment of the impact of nud1-A308T on nuclear positioning and mitotic exit coupling.

Main Results:

• The nud1-A308T allele causes constitutive recruitment of Cdc15 to SPBs, independent of Cdc5.
• This leads to premature Dbf2-Mob1 recruitment during metaphase.
• The nud1-A308T mutation disrupts the coupling between nuclear position and mitotic exit, particularly in cells with mispositioned spindles.

Conclusions:

• Scaffold protein regulation is critical for timely and spatially controlled activation of signaling pathways like the MEN.
• Aberrant activation of MEN due to scaffold mutations can compromise cell cycle fidelity and genome stability.
• Proper regulation of Nud1 function is essential for maintaining the coordination between nuclear positioning and mitotic exit.