Targeted RNAi screen reveals novel regulators of RNA-binding protein phase transitions in Caenorhabditis elegans oocytes

Abstract

The ability of oocytes to maintain their quality is essential for successful reproduction. One critical aspect of oocyte quality and successful embryogenesis after fertilization is the proper regulation of the stores of maternal mRNA by RNA-binding proteins. Many RNA-binding proteins undergo regulated phase transitions during oogenesis, and alterations of the protein phase can disrupt its ability to regulate mRNA stability and translation. In C. elegans, genetic screens have identified regulators of RNA-binding protein condensation in arrested oocytes of females and in embryos, but less attention has focused on phase transitions in maturing oocytes of young adult hermaphrodites. Interestingly, of the relatively few regulators of RNA-binding protein phase transitions identified to date in maturing oocytes, several genes overlap with those required for clearance of protein aggregates in maturing oocytes. To determine the extent to which the temporally linked processes of clearance of damaged proteins and maintenance of RNP complexes are coordinated at a molecular level, we conducted a targeted RNAi screen of genes required for removal of protein aggregates in maturing oocytes. We identified six novel regulators of phase transitions of the KH-domain protein MEX-3 and obtained strong evidence that the regulatory network of protein aggregate clearance overlaps with, but is distinct from, the regulation of MEX-3 phase transitions in the oocyte.