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Plastin and Β-Heavy-Spectrin Cooperate to Stabilize the Actomyosin Cortex During Cytokinesis

Cytokinesis, the process that partitions the mother cell into two daughter cells, requires the assembly and constriction of an equatorial actomyosin network. Different types of non-motor F-actin crosslinkers localize to the network, but their functional contribution remains poorly understood. Here, we describe a synergy between the small rigid crosslinker plastin and the large flexible crosslinker spectrin in the C. elegans one-cell embryo. In contrast to single inhibitions,  co-inhibition of the two crosslinkers results in cytokinesis failure, which live imaging shows is due to the progressive disorganization and eventual collapse of the equatorial actomyosin network. The synergy is specific for the heavy isoform of β-spectrin and requires its actin binding domain but neither its capacity to anchor F-actin at the plasma membrane nor SH3 domain-mediated signaling. Localization dynamics of non-muscle myosin II in co-inhibited embryos mimic those observed after drug-induced F-actin depolymerization, suggesting that the combined action of plastin and spectrin stabilizes actin filaments in the contractile ring. Our findings provide the first evidence that spectrin contributes to cytokinesis and highlight the importance of crosslinker interplay for actomyosin network integrity.