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on the Golgi and maintain the integrity of this organelle by restricting access of
Golgi resident proteins to budding transport vesicles (Holleran and Holzbaur,
1998
). Furthermore, Golgi-associated spectrin may serve as a scaffold for the
recruitment of signaling proteins from the cytosol. The actin-related protein Arp1
is a good example for such a spectrin-binding protein (Holleran et al.
2001
).
Spectrin-dependent recruitment of Arp1, a central component of the dynactin
complex, to the Golgi may allow this protein to control dynein activity and con-
tribute to the regulation of Golgi positioning.
Golgi and centrosome-associated proteins also control the pericentrosomal
positioning of the Golgi. Loss of either Golgin-160, GMAP210 or Golgin-84, all
putative structural Golgi proteins, resulted in the dispersal of Golgi membranes
into ER-associated mini-stacks, producing a phenotype that is reminiscent of no-
codazole-treated cells (Diao et al.
2003
; Yadav et al.
2009
). Dispersal of Golgi
membranes was also observed in cells depleted of the centrosomal protein
TBCCD1 (Goncalves et al.
2010
). Interestingly, in these cells, the centrosome was
mislocalized away from the nucleus. In conclusion, diverse groups of proteins are
involved in, and required for, the proper positioning of the Golgi apparatus next to
the centrosome (Table
7.1
), suggesting that sustaining this specific localization
may be important for cell homeostasis.
7.3 A Role for the Pericentrosomal Golgi Apparatus
in Cell Polarity
Cell polarity is a feature of eukaryotic cells that allows them to carry out their
specialized functions. For example, neurons depend on their polarization to
transmit electrical signals from one cell to the next, whereas epithelial cells use
their polarized organization to protect the body from its environment. The Golgi
apparatus and the centrosome both have independent roles in the establishment of
cell polarity. Golgi membranes control the sorting of proteins, which is important
for their delivery to the leading edge of a cell (Bergmann et al.
1983
). This so-
called directional transport is a prerequisite for cell polarization, and was recently
shown to involve Golgi-nucleated microtubules (Bergmann et al.
1983
; Rivero
et al.
2009
). When Rivero and colleagues selectively disrupted this subset of
microtubules, there were defects in cell polarization and migration (Rivero et al.
2009
). Golgi membranes also recruit the Ste20-like kinase YSK1, a protein kinase
required for Golgi organization and cell polarization (Preisinger et al.
2004
). A
pathway that involves the interaction between STK25, the mouse homolog of
YSK1, and the Golgi protein GM130 is also required for Golgi organization and
polarization in cultured neurons and in vivo (Matsuki et al.
2010
).
Like the Golgi, the centrosome has long been anticipated to play an important role
in cell polarization. In many migrating cells, including fibroblasts and macrophages,
the centrosome localizes between the nucleus and the leading edge (Kupfer et al.
1982
; Nemere et al.
1985
), suggesting that the position of the centrosome may
