Cytoplasmic Dynamics of the General Nuclear Import Machinery in Apically Growing Syncytial Cells

Karyophenns are transporters involved in the bidirectional, selective and active transport of macromolecules through nuclear pores. Importin-beta 1 is the paradigm of karyopherins and together with its cargo-adapter importin-a mediates the general nuclear import pathway. Here we show the existence of different cellular pools of both imporkin-alpha and -beta 1. homologues, KapA and KapB, n the coenocytic ascomycete Aspergillus rildulans. Fluorescence analysis of hap bid and diploid strains expressing KapB::GFP and/or KapA::mRFP showed patches of both karyopherins concurrently translocating long distances in apically-growing cells. Anterograde and retrograde movements allowed those patches to reach cell tips and distal regions with an average speed in the range of mu m/s. This bidirectional traffic required rnicrotubules as well as kiriesin and dynein motors, since it is blocked by benomyl and also by the inactivation of the dynein/dynactin complex through nudA1 or nudK317 mutations. Deletion of Kinesin-3 motor UncA, required for the transport through detyrosinated microtubules, strongly inhibited KapA and KaplE3 movement along hyphae. Overall, this is the first report describing the bidirectional dynamics of the main nuclear import system in coenocytic fungi. A functional link is proposed between two key cellular machines of the filamentous fungal cell: nuclear transport and the tip-growth apparatusThis work has been supported by former Spanish Ministerio de Ciencia y Tecnologia and Ciencia e Innovacion, through grants BFU2006-04185 and BFU2009-08701, and current Ministerio de Economia y Competitividad through grant BFU2012-33142 to E.A.E. O.E. held a research contract associated to grant BFU2006-04185 at the CIB, a research contract at The University of The Basque Country (UPV/EHU) with funds from Ministerio de Educacion y Ciencia (BFU2010-17528) and is now a Lecturer at the UPV/EHU with funds from the Basque Government (IT599-13). Maria Villarino held a research contract associated to grant BFU-2009-08701. AM.-I. held a predoctoral F.P.I. fellowship from the Ministerio de Educacion y Ciencia and is now a contract researcher of The University of The Basque Country associated to a grant for Specialization of Researchers of the UPV/EHU(2012). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript