Subcellular mRNA localisation is used in many cell types to control where proteins operate. Whilst it has long been recognised that cytoskeletal motors play a central role in mRNP trafficking, it is unclear how mRNAs are recruited to motors and how motor activity is regulated in these assemblies. I will present our efforts to address these questions using two experimental models: early Drosophila development and human cancer cells. High-resolution cryo-EM structures of the Drosophila RNA adaptor Egalitarian (Egl) complexed with the dynein motor activator Bicaudal-D (BicD) and three double-stranded RNA targets reveal the basis of mRNA recognition in this system. The results of single-molecule resolution in vitro motility assays show that two RNA stem-loops are required to activate dynein motility, a finding rationalised by Alphafold-assisted modelling of RNA-protein complexes. I will also present evidence that the RNA-binding proteins FXR1 and FXR2 are long-sought-after adaptors between dynein and mRNAs in human cells. Like Drosophila Egl, FXR1 and FXR2 associate directly with a BicD family member and enable its dynein-activating functions. Collectively, our work reveals similar organisational principles of mRNA transport complexes in divergent eukaryotic cell types, with the RNA cargo determined by the specificity of interchangeable RNA-binding proteins.