Abstract
mRNAs enriched in membraneless condensates provide functional compartmentalization within cells. The mechanisms that recruit transcripts to condensates are under intense study; however, how mRNAs organize once they reach a granule remains poorly understood. Here, we report on a self-sorting mechanism by which multiple mRNAs derived from the same gene assemble into discrete homotypic clusters. We demonstrate that invivo mRNA localization to granules and self-assembly within granules are governed by different mRNA features: localization is encoded by specific RNA regions, whereas self-assembly involves the entire mRNA, does not involve sequence-specific, ordered intermolecular RNA:RNA interactions, and is thus RNA sequence independent. We propose that the ability of mRNAs to self-sort into homotypic assemblies is an inherent property of an messenger ribonucleoprotein (mRNP) that is augmented under conditions that increase RNA concentration, such as upon enrichment in RNA-protein granules, a process that appears conserved in diverse cellular contexts and organisms.
Highlights
We addressed the molecular parameters of homotypic mRNA assembly within RNA granules in vivo
Our data suggest that models relying on specific trans RNA:RNA interactions generated by RNA binding proteins (RBPs) or by base-paired RNA sequences observed for osk and bcd messenger ribonucleoprotein (mRNP) and the human immunodeficiency virus (HIV) genome cannot explain the specificity for homotypic mRNA assembly in Drosophila germ granules
We show that RNA:RNA interactions among clustered nos and gcl are sequence independent and disordered
Summary
Markus Grosch, ..., Hari Shroff, Eli Rothenberg, Ruth Lehmann. In Brief mRNAs enriched in Drosophila germ granules form homotypic assemblies. In vivo, this assembly is not specified by germ granule proteins but instead relies on the mRNA. MRNA self-assembly involves the entire mRNP and is RNA sequence independent and sequence specific. Ordered intermolecular RNA:RNA interactions among clustered transcripts were not observed. Highlights d Germ-granule-enriched mRNA organization was probed by super-resolution imaging in vivo d Many mRNAs from the same gene self-assemble into homotypic clusters in germ granules d Homotypic self-assembly relies on properties of an mRNP, but not specific RNA sequences d Sequence-specific trans-RNA:RNA interactions among clustered mRNAs are not detected.
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