Drosophila wingless and pair-rule transcripts localize apically by dynein-mediated transport of RNA particles.

Asymmetric mRNA localization targets proteins to their cytoplasmic site of function. We have elucidated the mechanism of apical localization of wingless and pair-rule transcripts in the Drosophila blastoderm embryo by directly visualizing intermediates along the entire path of transcript movement. After release from their site of transcription, mRNAs diffuse within the nucleus and are exported to all parts of the cytoplasm, regardless of their cytoplasmic destinations. Endogenous and injected apical RNAs assemble selectively into cytoplasmic particles that are transported apically along microtubules. Cytoplasmic dynein is required for correct localization of endogenous transcripts and apical movement of injected RNA particles. We propose that dynein-dependent movement of RNA particles is a widely deployed mechanism for mRNA localization.