Spontaneous confinement of mRNA at RNP granule interfaces

Cellular membraneless organelles termed ribonucleoprotein (RNP) granules often are enriched in messenger RNA (mRNA) molecules relative to the surrounding cytoplasm. Yet, the spatial localization and diffusion of mRNAs in close proximity to phase separated RNP granules is not well understood. In this study, we performed single molecule fluorescence imaging experiments of mRNAs in live cells in the presence of two types of RNP granules, stress granules (SG) and processing bodies (PB), which are distinct in their molecular composition and function. We developed a new colocalization imaging algorithm that was employed to determine the accurate positions of individual mRNAs relative to the granules boundaries. We found that mRNA is often localized at granule boundaries, an observation consistent with recently published data1,2. We suggest that mRNA molecules become spontaneously confined at the RNP granule boundary similar to the adsorption of polymer molecules at liquid-liquid interfaces, which is observed in various technological and biological processes.