A memory system of negative polarity cues prevents replicative aging

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Cdc42 is a master regulator of cell polarity.
• Understanding how cells establish and maintain polarity is crucial for cell division and function.
• Previous growth sites (cytokinesis remnants, CRMs) are typically avoided for subsequent polarization events.

Purpose of the Study:

• To investigate the mechanism by which yeast cells avoid re-establishing polarity at previously used sites (CRMs).
• To elucidate how Cdc42-inhibitory polarity cues are established and maintained.
• To understand the role of Nba1 in preventing re-polarization.

Main Methods:

• Yeast genetics and live-cell imaging.
• Analysis of protein localization and interactions.
• Characterization of "memory loss" mutants.

Main Results:

• A two-step mechanism for loading the Cdc42 antagonist Nba1 into CRMs was identified.
• Nba1, with a cortically tethered adaptor protein, creates a "memory" of past polarization events.
• This mechanism ensures the local singularity of Cdc42 activation, preventing re-use of CRMs.
• "Memory loss" mutants exhibit nuclear segregation defects and reduced lifespan.

Conclusions:

• Cytokinesis remnants (CRMs) act as negative polarity cues, preventing Cdc42 reactivation.
• This mechanism ensures the spatial singularity of cell polarization.
• Maintaining polarity site fidelity is essential for cellular fitness and proper cell division.