Probing P granule Assembly and Dynamics with Optogenetic Tools

Abstract

P granules represent a canonical example of intracellular condensates that form through liquid-liquid phase separations. During the first mitosis in the Caenorhabditis elegans embryo, these germ granules consisting of specific sets of RNA and protein undergo asymmetric localization to the posterior side of the embryo, which is hypothesized to be important in germ line specification. However, a lack of experimental approaches to control granule dynamics in a spatiotemporal manner has hampered further understanding of this process and its implication on C. elegans’ embryonic development. Here, two optogenetic systems (Cryptochrome-2 based “optoDroplet” and iLID based “Corelet” systems) are introduced into the C. elegans model organism in order to study the assembly and dynamics of P granules during early embryonic development. Using these optogenetic platforms, P granule-like droplets are created in the early embryo with precise spatiotemporal control. Localized light activation of the embryo leads to novel patterning of P granule proteins, including PGL-1. Quantitative tracking and analysis of these structures show that light-sensitive creation of P granule-like droplets can affect native assembly dynamics of endogenous granules. The interaction of these light-activated P granule-like droplets in relation to endogenous P granule proteins such as MEG-3, LAF-1, and PGL-1 is also investigated. These results establish that optogenetic control of intracellular condensates can be used to influence asymmetric cell divisions and potentially cell fate determination during development.