title: Kinesin-3 and dynein mediate microtubule-dependent co-transport of mRNPs and endosomes.
abstract: Long-distance transport of mRNAs is important in determining polarity in eukaryotes. Molecular motors shuttle large ribonucleoprotein complexes (mRNPs) containing RNA-binding proteins and associated factors along microtubules. However, precise mechanisms including the interplay of molecular motors and a potential connection to membrane trafficking remain elusive. Here, we solve the motor composition of transported mRNPs containing the RNA-binding protein Rrm4 of the pathogen Ustilago maydis. The underlying transport process determines the axis of polarity in infectious filaments. Plus-end-directed Kin3, a kinesin-3 type motor, mediates anterograde transport of mRNPs and is also present in transport units moving retrogradely. Split dynein Dyn1-Dyn2 functions in retrograde movement of mRNPs. Plus-end-directed conventional kinesin Kin1 is indirectly involved by transporting minus-end-directed dynein back to plus ends. Importantly, we additionally demonstrate that Rrm4-containing mRNPs colocalise with the t-SNARE Yup1 on shuttling endosomes and that functional endosomes are essential for mRNP movement. Either loss of Kin3 or removal of its lipid-binding pleckstrin-homology domain abolishes Rrm4-dependent movement without preventing colocalisation of Rrm4 and Yup1-positive endosomes. In summary, we uncovered the combination of motors required for mRNP shuttling along microtubules. Furthermore, intimately linked co-transport of endosomes and mRNPs suggests vesicle hitchhiking as mode of mRNP transport.
authors.affiliation: Heinrich Heine University Düsseldorf, Institute for Microbiology, 40204 Düsseldorf,  Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Baumann
authors.forename: Thomas
authors.initials: T
authors.lastname: Pohlmann
authors.forename: Marc
authors.initials: M
authors.lastname: Jungbluth
authors.forename: Andreas
authors.initials: A
authors.lastname: Brachmann
authors.forename: Michael
authors.initials: M
authors.lastname: Feldbrügge
mesh_terms: D004398:Dyneins / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D016547:Kinesins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D021381:Protein Transport; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D014588:Ustilago / Q000166:cytology / Q000378:metabolism*
chemical_list: C092350:FM 4-64; D005656:Fungal Proteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; D004398:Dyneins; D016547:Kinesins