The TAO kinase KIN-18 regulates contractility and establishment of polarity in the C. elegans embryo.

Cell polarity is crucial for many aspects of cell and developmental biology. Cytoskeleton remodeling plays an essential role in the establishment of cell polarity. In the Caenorhabditis elegans one-cell embryo, while the actomyosin cytoskeleton is required for asymmetric localization of the PAR proteins, anterior PAR proteins exert a feedback regulation on contractility. Here we identify the TAO kinase KIN-18 as a regulator of cortical contractility in the early embryo. KIN-18 negatively regulates cortical contractions in a RHO-1 dependent manner and regulates RHO-1 cortical localization. KIN-18 contributes to polarity establishment by regulating the position of the boundary between anterior and posterior PAR proteins. Although KIN-18 is involved in polarity establishment, depletion of KIN-18 restores contractions in a par-3 mutant indicating that kin-18 is epistatic to par-3. We suggest a model in which KIN-18 provides a link between the cytoskeleton remodeling and polarity machineries, uncovering a role for TAO kinases in the regulation of cell polarity.