PI(4,5)P2 forms dynamic cortical structures and directs actin distribution as well as polarity in C. elegans embryos

Abstract

Asymmetric division is crucial for embryonic development and stem cell lineages. In the one-cell C. elegans embryo, a contractile cortical actomyosin network contributes to asymmetric division by segregating PAR proteins to discrete cortical domains. Here, we discovered that the plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2) localizes to polarized dynamic structures in C. elegans zygotes, distributing in a PAR-dependent manner along the anterior-posterior (A-P) embryonic axis. PIP2 cortical structures overlap with F-actin, and coincide with the actin regulators RHO-1, CDC-42 as well as ECT-2. Particle image velocimetry analysis revealed that PIP2 and F-actin cortical movements are coupled, with PIP2 structures moving slightly ahead. Importantly, we established that PIP2 cortical structure formation and movement is actin-dependent. Conversely, we found that decreasing or increasing the level of PIP2 results in severe F-actin disorganization, revealing interdependence between these components. Furthermore, we uncovered that PIP2 and F-actin regulate the sizing of PAR cortical domains, including during the maintenance phase of polarization. Overall, our work establishes that a lipid membrane component, PIP2, modulates actin organization and cell polarity in C. elegans embryos.