Involvement of Septation Initiation Network (SIN) in events during cytokinesis in fission yeast

Abstract

The Septation Initiation Network (SIN) consisting of a GTPase and a cascade of three protein kinases regulates cell division in fission yeast S. pombe, but questions remain about its influence on cytokinesis. We made quantitative measurements of Cdc7p kinase (a marker for SIN activity) on SPBs and on the timing of assembly, maturation and constriction of contractile rings with six different proteins tagged with fluorescent proteins. When SIN activity is low in spg1-106 mutant cells at 32°C, cytokinetic nodes formed contractile rings ∼3 min slower than wild-type cells. During the maturation period these rings maintained normal numbers of myosin-II mEGFP-Myo2p but accumulated less F-BAR protein Cdc15p-GFP than wild-type cells. The Cdc15p-GFP fluorescence then disintegrated into spots as mEGFP-Myo2p dissociated slowly. Some rings started to constrict at the normal time, but most failed to complete constriction. When high SIN activity persists far longer than normal on both SPBs in cdc16-116 mutant cells at 32°C contractile rings assembled and constricted normally, but disassembled slowly, delaying cell separation.