eLife digest | Spatial patterning of P granules by RNA-induced phase separation of the intrinsically-disordered protein MEG-3

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Spatial patterning of P granules by RNA-induced phase separation of the intrinsically-disordered protein MEG-3

eLife digest

Affiliation details

Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, United States

Animal cells contain many smaller compartments known as organelles that perform particular roles. For example, a compartment called the nucleus stores most of the cell’s genetic information. The nucleus and many other organelles form inside layers of membrane that physically separate them from the rest of the cell. However, some organelles, such as the germ granule, do not have a membrane. It is thought that these organelles may form in the same way that oil droplets tend to come together when mixed with water. However, oil droplets form in water spontaneously and do not fall apart, so it is not clear how cells could control the assembly and destruction of such organelles.

The germ granules inside the cells of a worm called C. elegans are destroyed and reassembled in cycles. Smith et al. investigated how the worm cells control these cycles. The experiments show that a protein called MEG-3 is required to allow the components of granules to transition from behaving like individual molecules dissolved in water (similar to being dissolved in cell fluid) to assembling into droplets. When MEG-3 is mixed with molecules of ribonucleic acid (RNA) it can bind very tightly to the RNA and then separate out from the rest of the fluid to form distinct droplets.

Smith et al. also show that another protein called MEX-5 can destroy these droplets by attaching itself to RNA in place of MEG-3, which causes MEG-3 to dissolve back into the rest of the fluid. The physical properties of the MEG-3 droplets are still not known and so the next step following on from this work will be to find out whether germ granules behave like liquids, gels or hard solids.

DOI: http://dx.doi.org/10.7554/eLife.21337.002