Several fundamental processes rely on an accurately positioned Golgi including differentiation of myoblasts into myotubes, immunological synapse formation, neuronal arborization, and directed cell migration. The pericentrosomally positioned Golgi apparatus, in combination with oriented microtubule arrays, defines a physiologically important axis of secretion to the most proximate aspect of the plasma membrane. In response to a polarity cue, cells reorient their microtubule array and reposition the Golgi apparatus towards the stimulus defining the cell leading edge (Kupfer et al., 1982
; Pu and Zhao, 2005
). Specific disruption of Golgi positioning blocks polarized delivery of secretory cargo to the leading edge, resulting in a collapse of cell polarity and an inability to migrate and heal a wound (Yadav et al., 2009
Golgi positioning is dramatically regulated during these processes. When myoblasts fuse to form a myotube, the pericentrosomal Golgi ribbon fragments and is repositioned as isolated Golgi stacks that encircle each nucleus (Ralston, 1993
). This repositioning may be caused by a loss of Golgi membrane motility, and could be an obligate part of the muscle differentiation pathway (Lu et al., 2001
). When natural killer cells and cytotoxic T cells form an immunological synapse with target cells, the Golgi repositions towards the synapse to secrete lytic factors that kill the target cell (Kupfer et al., 1983
; Stinchcombe et al., 2006
). In hippocampal neurons, the Golgi aligns on the side facing a newly forming axon (de Anda et al., 2005
). In pyramidal neurons, the cell body-localized, or somatic, Golgi orients towards the apical dendrites (Horton et al., 2005
). Interestingly, neuronal Golgi elements are also present in dendrites as multiple Golgi “outposts”, whose positioning is required for dendritic arborization (Ye et al., 2007
Mitotic regulation of Golgi positioning is perhaps even more striking. As microtubules reorganize to form the spindle-pole body, the Golgi membrane network fragments and then completely vesiculates giving rise to a mixture of Golgi vesicles and Golgi vesicle clusters that are dispersed throughout the mitotic cytoplasm (Shorter and Warren, 2002
). The uncoupling of membranes from their microtubule-based positioning is thought to ensure their uniform partitioning during cell division (Yadav and Linstedt, 2011
). At the end of mitosis, the Golgi membranes once again move towards microtubule minus ends and reestablish their pericentrosomal position in each daughter cell.
Despite its importance, our understanding of the mechanisms that position the Golgi and move secretory cargo inward is incomplete. Particularly vexing is that the components that specifically link the dynein/dynactin complex to these membranes to confer pericentrosomal positioning remain unknown (Kardon and Vale, 2009
). Although there are several dynein-interacting proteins on the Golgi, none of these have been shown required for membrane association of the motor. Identifying the membrane receptor for the molecular motor is critical, as it will help us understand both the regulation of motor recruitment during membrane transport and organelle positioning, and the regulatory events that allow the motor to switch to its specialized roles during cell division.
Golgin160, a homodimeric coiled-coil protein localized primarily to cis Golgi cisternae (Hicks et al., 2006
; Hicks and Machamer, 2002
), is an excellent candidate receptor because its depletion blocks Golgi positioning and yields dispersed ministacks (Yadav et al., 2009
). Here, unlike all previously identified dynein interacting proteins, we show that golgin160 satisfies a list of stringent criteria expected from a candidate motor receptor on the Golgi. Golgin160 was specifically required for dynein recruitment and Golgi motility. It directly bound dynein and its dynein-binding site was required for Golgi positioning. Golgin160 was also sufficient to confer functional motor recruitment. Golgin160 directly bound the Arf1 GTPase and this interaction was responsible for membrane association of the golgin160 motor complex. Finally, golgin160 dissociated from Golgi membranes at mitosis and this dissociation was required for mitotic Golgi dispersal. Together, our data suggest that the Golgi positioning depends on constant motility provided by the recruitment of dynein by golgin-160, a cell cycle regulated motor receptor. The membrane attachment of this motor receptor, through the highly regulated GTPase Arf1, is likely a key control point for the dramatic changes in motility and organelle positioning observed during cell differentiation, polarization, and division.