Mechanism For Paraspeckles To Enhance Pri-miRNA Processing

Paraspeckles are discrete nuclear bodies organized by the IncRNA NEAT1 adjacent to nuclear speckles where most pre-mRNA splicing factors are enriched.Paraspeckles contain RNAs with inverted repeats and>30 RNA binding proteins(RBPs),thus thought to serve as sites for RBP sequestration.Here we present evidences that paraspeckles function as global hubs for enhancing primary microRNA(pri-miRNA)processing by the Microprocessor Drosha/DGCR8.Disruption of paraspeckles by knocking down NEAT1 or key organizing RBPs,such as PSF and NONO,impairs processing of most,if not all,pri-miRNAs;CLIP-seq reveals that the PSF/NONO heterodimer binds nearly all expressed pri-miRNAs;and biochemical studies suggest that NEAT1 not only provides loading docks for RBPs,but also uses various hairpins,including a "pseudo pri-miRNA" near its 3' end,to attract the Microprocessor.Together,these findings highlight an IncRNA-organized nuclear subdomain for orchestrating pri-miRNA processing,and as?80%miRNAs are intron-derived,coordinated pri-miRNA and pre-mRNA processing may account for the formation of paraspeckles near nuclear speckles.