Deciphering the role of PI(4,5)P2 and its modulators PPK-1 and CSNK-1 in nematode asymmetric division

ended

The first embryonic division of Caenorhabditis elegans is a powerful system to dissect the mechanisms governing asymmetric division, which relies on PAR-proteins for cell polarity and on dynein-dependant forces for centrosome and spindle positioning. In contrast to the extensive knowledge regarding proteins regulating asymmetric division, the contribution of plasma membrane tension, as well as of PIP2 and its modulators PPK-1 and CSNK-1 is poorly understood. I propose to decipher these questions as follows: 1) PIP2 is enriched in the embryo anterior in microdomains of the plasma membrane. I will test the contribution of PPK-1, the only kinase from the proteome converting PIP into PIP2 in formation of PIP2 microdomains distribution, cell polarity and pulling force. This will be achieved through ppk-1(RNAi) as well as two complementary optogenetic approaches to obtain acute spatiotemporal inactivation of PIP2. 2) I will decipher how the casein kinase CSNK-1 interacts with and phosphorylates PPK-1, thereby presumably regulating PIP2 microdomain distribution and function, as well as identify and characterize up to three CSNK-1 phospho-substrates with. 3) I will test whether PIP2 undergoes phase separation driven by a decrease in plasma membrane tension, and, if so, investigate the consequences on asymmetric division. Moreover, I will study the relationship between membrane tension and cortex contractility. 4) I will analyze asymmetric cell division in the one-cell Pristiochus pacificus embryo I will then use the knowledge acquired in C. elegans to conduct related experiments in P. pacificus, thus investigating potential conserved and divergent themes governing asymmetric division across nematode evolution. Overall, these experiments will shed critical light on the poorly understood contribution of PIP2 and its modulators to asymmetric division, an evolutionarily conserved process fundamental for development and stem cell lineages.