A novel checkpoint pathway controls actomyosin ring constriction trigger in fission yeast

Area of Science:

• Cell biology
• Molecular and Cellular Physiology
• Biochemistry

Background:

• The septation initiation network (SIN) in fission yeast coordinates cell division processes, including actomyosin ring (CAR) constriction, membrane ingression, and septum synthesis.
• Regulation of CAR constriction under cellular stress, particularly cell wall stress, remains incompletely understood.
• The cell integrity pathway (CIP) is crucial for responding to cell wall stress.

Purpose of the Study:

• To investigate the role of Rgf1p (Rho1p GEF) in regulating CAR constriction during cell wall stress.
• To elucidate the involvement of the cell integrity pathway (CIP) and the septation initiation network (SIN) in mediating cytokinesis delay under stress.

Main Methods:

• Utilized fission yeast strains, including wild-type, rgf1Δ, and Pmk1p (CIP MAPK) deficient mutants.
• Applied cell wall stress using blankophor (BP).
• Observed CAR assembly, constriction timing, and cytokinesis progression using microscopy.
• Assessed SIN signaling maintenance.

Main Results:

• Blankophor (BP) induced a delay in the onset of CAR constriction in wild-type cells, but not in rgf1Δ cells.
• This BP-induced delay was abolished in the absence of Pmk1p, leading to premature abscission and a multi-septated phenotype.
• The observed cytokinesis delay correlated with maintained SIN signaling, indicating a functional checkpoint.

Conclusions:

• Rgf1p (Rho1p GEF) is involved in delaying cytokinesis under cell wall stress.
• The cell integrity pathway (CIP), through Pmk1p, participates in a checkpoint that triggers CAR constriction delay via the SIN pathway.
• This coordinated delay ensures the successful termination of cytokinesis, maintaining cellular integrity under stress.