Spatial control of cytokinesis by Cdr2 kinase and Mid1/anillin nuclear export.

Maintaining genome integrity and cellular function requires proper positioning of the cell division plane. In most eukaryotes, cytokinesis relies on a contractile actomyosin ring positioned by intrinsic spatial signals that are poorly defined at the molecular level. Fission yeast cells assemble a medial contractile ring in response to positive spatial cues from the nucleus at the cell center and negative spatial cues from the cell tips. These signals control the localization of the anillin-like protein Mid1, which defines the position of the division plane at the medial cortex, where it recruits contractile-ring components at mitosis onset. Here we show that Cdr2 kinase anchors Mid1 at the medial cortex during interphase through association with the Mid1 N terminus. This association underlies the negative regulation of Mid1 distribution by cell tips. We also demonstrate that the positive signaling from the nucleus is based on Mid1 nuclear export, which links division-plane position to nuclear position during early mitosis. After nuclear displacement, Mid1 nuclear export is dominant over Cdr2-dependent positioning of Mid1. We conclude that Cdr2- and nuclear export-dependent positioning of Mid1 constitute two overlapping mechanisms that relay cell polarity and nuclear positional information to ensure proper division-plane specification.