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Eukaryotic Cell, May 2009, p. 723-731, Vol. 8, No. 5
1535-9778/09/$08.00+0     doi:10.1128/EC.00018-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Microtubule-Nucleus Interactions in Dictyostelium discoideum Mediated by Central Motor Kinesins{triangledown} ,{dagger}

Irina Tikhonenko,1 Dilip K. Nag,1,2 Douglas N. Robinson,3 and Michael P. Koonce1,2*

Division of Translational Medicine, Wadsworth Center, Albany, New York 12201-0509,1 Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, New York 12201-0509,2 Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 212053

Received 12 January 2009/ Accepted 10 March 2009

Kinesins are a diverse superfamily of motor proteins that drive organelles and other microtubule-based movements in eukaryotic cells. These motors play important roles in multiple events during both interphase and cell division. Dictyostelium discoideum contains 13 kinesin motors, 12 of which are grouped into nine families, plus one orphan. Functions for 11 of the 13 motors have been previously investigated; we address here the activities of the two remaining kinesins, both isoforms with central motor domains. Kif6 (of the kinesin-13 family) appears to be essential for cell viability. The partial knockdown of Kif6 with RNA interference generates mitotic defects (lagging chromosomes and aberrant spindle assemblies) that are consistent with kinesin-13 disruptions in other organisms. However, the orphan motor Kif9 participates in a completely novel kinesin activity, one that maintains a connection between the microtubule-organizing center (MTOC) and nucleus during interphase. kif9 null cell growth is impaired, and the MTOC appears to disconnect from its normally tight nuclear linkage. Mitotic spindles elongate in a normal fashion in kif9– cells, but we hypothesize that this kinesin is important for positioning the MTOC into the nuclear envelope during prophase. This function would be significant for the early steps of cell division and also may play a role in regulating centrosome replication.

* Corresponding author. Mailing address: Wadsworth Center, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509. Phone: (518) 486-1490. Fax: (518) 474-7992. E-mail: Koonce{at}wadsworth.org

{triangledown} Published ahead of print on 13 March 2009.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

Eukaryotic Cell, May 2009, p. 723-731, Vol. 8, No. 5
1535-9778/09/$08.00+0     doi:10.1128/EC.00018-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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