Biology Reference
In-Depth Information
for protein transport. In the yeast Saccharomyces cerevisiae, for example, individual
Golgi cisternae are dispersed throughout the cytosol (Preuss et al.
1992
; Rambourg
et al.
2001
). In the fission yeast Schizosaccharomyces pombe, Golgi mini-stacks
exist, but they are distributed throughout the cytoplasm and do not form a single
connected Golgi ribbon (Chappell and Warren
1989
). Interestingly, studies in
Drosophila have shown that Golgi organization can be cell type-specific (Stanley
et al.
1997
). In pre- and post-cellularized Drosophila embryos, as well as in S2 tissue
culture cells, Golgi membranes appear as dispersed punctate structures that corre-
spond to isolated Golgi mini-stacks (Kondylis and Rabouille
2009
; Stanley et al.
1997
). These mini-stacks localize close to the transitional ER, forming a unit for
translation and transport that is also seen in Toxoplasma, Plasmodium and plants
(Kondylis and Rabouille
2009
). However, the Drosophila Golgi has also been
observed as unstacked cisternae during distinct stages of development, or as a ribbon-
like structure in spermatids, indicating that Golgi membranes can be organized
differently within the same organism (Kondylis and Rabouille
2009
).
In this chapter, we will focus on the spatial and functional relationship between
the Golgi and the centrosome in mammalian cells. We will first discuss the
mechanism by which Golgi membranes are positioned in the pericentrosomal
region. We will then review studies on the functional connections between the
Golgi and the centrosome in interphase, including the role of the pericentrosomal
Golgi in directional protein secretion and cell polarization. Finally, we will discuss
the link between the Golgi and the centrosome during mitosis, the stage of the cell
cycle when the physical Golgi-centrosome connection is temporarily lost due to
extensive Golgi fragmentation and dispersal.
7.2 Mechanisms of Golgi Positioning in Interphase
Mammalian Cells
Although not essential for the typical function of the Golgi in protein and lipid
transport, the positioning of the Golgi apparatus in mammalian cells next to the
centrosome is actively maintained (Table
7.1
). The preservation of this specific
localization involves both the microtubule and actin cytoskeletal networks and
their associated motor proteins and regulators (Brownhill et al.
2009
). These
cytoskeletal networks are linked to the Golgi by binding to either structural Golgi
proteins, such as Hook3, or by directly associating with specialized phospholipids
in the Golgi membranes, such as PtdIns(4,5)P
2
(Godi et al.
1998
; Walenta et al.
2001
). Both microtubule- and actin-associated motor proteins have been detected
on the Golgi. Because microtubule motors actively contribute to the positioning of
the Golgi apparatus, they will be discussed in detail. In contrast, Golgi-localized
actin-associated motor proteins will not be covered because they function pre-
dominantly in the movement of vesicles to and from the Golgi, and do not seem to
control Golgi localization.
