The septation initiation network controls the assembly of nodes containing Cdr2p for cytokinesis in fission yeast

Abstract

In the fission yeast S. pombe cortical protein structures called interphase nodes help to prepare for cytokinesis by positioning precursors of the cytokinetic contractile ring, while the septation initiation network (SIN) regulates the onset of cytokinesis and septum formation. Previous work noted that one type of interphase node disappears during mitosis providing SIN activity is high. Here we used time-lapse fluorescence microscopy to provide evidence that SIN activity is necessary and sufficient to disperse the type 1 node proteins Cdr2p and Mid1p into the cytoplasm, so these nodes assemble only during interphase through early mitosis when SIN activity is low. Activating the SIN in interphase cells dispersed Cdr2p and anillin Mid1p from type 1 nodes a few minutes after the SIN kinase Cdc7p-GFP accumulated at spindle pole bodies. If the SIN was then turned off in interphase cells, Cdr2p and Mid1p reappeared in nodes in parallel with the decline in SIN activity. Hyperactivating SIN during mitosis dispersed type 1 nodes earlier than normal, and prolonged SIN activation prevented nodes from reforming at the end of mitosis.