Dynamics of SIN asymmetry establishment

Area of Science:

• Cell Biology
• Molecular Biology
• Systems Biology

Background:

• Cell division timing in fission yeast is regulated by the Septation Initiation Network (SIN).
• SIN activation initiates at spindle pole bodies (SPBs) during metaphase.
• Asymmetric SIN activity, with inactivation at one SPB by Cdc16-Byr4, is established by anaphase.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the rapid asymmetric distribution of SIN regulators at SPBs.
• To develop a computational model integrating known SIN regulators to understand asymmetry establishment.
• To experimentally validate model predictions regarding SIN mutant behavior and protein phosphorylation.

Main Methods:

• Computational modeling of a minimal two-antagonist system.
• Incorporation of detailed molecular knowledge of key SIN regulators into an extended model.
• Experimental validation of model predictions, including testing double and triple SIN mutants.
• Investigating the role of Cdc11 phosphorylation by SIN kinase and Cyclin-dependent kinase (Cdk).

Main Results:

• The computational model successfully captured known experimental findings on asymmetry establishment.
• The model predicted the behavior of double and triple SIN mutants.
• Experimental tests confirmed that Cdc11 phosphorylation by SIN kinase and Cdk can partially compensate for Cdc16 mutations.
• One model prediction failed, suggesting a gap in current knowledge regarding SIN regulation.

Conclusions:

• SIN asymmetry is established through antagonistic interactions between SIN and its inhibitor, Cdc16-Byr4.
• Regulation of Cdc11 phosphorylation states plays a partial role in establishing SIN asymmetry.
• Further research is needed to fully understand the complex regulatory network governing SIN asymmetry.