Rewiring Mid1p-Independent Medial Division in Fission Yeast

Correct positioning of the cell division machinery is key to genome stability. Schizosaccharomyces pombe is an attractive organism to study cytokinesis as it, like higher eukaryotes, divides using a contractile actomyosin ring. In S. pombe, many actomyosin ring components assemble at the medial cortex into node-like structures before coalescing into a ring [1, 2]. Assembly of cytokinetic nodes requires Midi p, which recruits IQGAP-related Rng2p to the division site, after which other node components accumulate at the division site in a characteristic sequence [3-6]. How cytokinetic nodes assemble, whether the order of assembly of ring components is important, and whether Mid1p solely participates in ring positioning are poorly understood. Here, we show that synthetic targeting of IQGAP-related Rng2p, formin-Cdc12p, and myosin II (Myo2p) restores medial division in midi mutants, suggesting that ring proteins need not assemble at the division site in an invariant order. Unlike in wild-type cells, actomyosin rings in cells rewired to divide medially in the absence of Midi p assemble late in anaphase. Furthermore, the rewiring process affects the ability of the actomyosin ring to track the nucleus upon perturbation of nuclear position. Our work reveals the power of synthetic rewiring studies in deciphering roles performed by multifunctional proteins.