Polar Positioning of Phase-Separated Liquid Compartments in Cells Regulated by an mRNA Competition Mechanism

• Published in: Cell 2016-09, Vol.166 (6), p.1572-1584.e16
• Main Authors: Saha, Shambaditya, Weber, Christoph A., Nousch, Marco, Adame-Arana, Omar, Hoege, Carsten, Hein, Marco Y., Osborne-Nishimura, Erin, Mahamid, Julia, Jahnel, Marcus, Jawerth, Louise, Pozniakovski, Andrej, Eckmann, Christian R., Jülicher, Frank, Hyman, Anthony A.
• Format: Article
• Language: English
• Subjects: Animals; Caenorhabditis elegans - metabolism; Caenorhabditis elegans Proteins - analysis; Caenorhabditis elegans Proteins - metabolism; Cell Polarity; Embryo, Nonmammalian; Intracellular Space - chemistry; Intracellular Space - metabolism; Models, Theoretical; Protein Binding; RNA, Messenger - metabolism; RNA-Binding Proteins - analysis; RNA-Binding Proteins - metabolism
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2016.08.006

P granules are non-membrane-bound RNA-protein compartments that are involved in germline development in C. elegans. They are liquids that condense at one end of the embryo by localized phase separation, driven by gradients of polarity proteins such as the mRNA-binding protein MEX-5. To probe how polarity proteins regulate phase separation, we combined biochemistry and theoretical modeling. We reconstitute P granule-like droplets in vitro using a single protein PGL-3. By combining in vitro reconstitution with measurements of intracellular concentrations, we show that competition between PGL-3 and MEX-5 for mRNA can regulate the formation of PGL-3 droplets. Using theory, we show that, in a MEX-5 gradient, this mRNA competition mechanism can drive a gradient of P granule assembly with similar spatial and temporal characteristics to P granule assembly in vivo. We conclude that gradients of polarity proteins can position RNP granules during development by using RNA competition to regulate local phase separation. [Display omitted] •The protein PGL-3 can phase separate into P-granule-like droplets in vitro•Assembly of PGL-3 droplets at physiological concentration requires mRNA binding to PGL-3•MEX-5 inhibits mRNA-dependent droplet assembly by competing with PGL-3 for binding mRNA•Competition among MEX-5 and PGL-3 for mRNA can account for P granule segregation in vivo Asymmetric positioning of cellular compartments formed by phase separation can be driven by competition between two mRNA binding proteins, one of which forms a spatial concentration gradient.