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daughter cells. Second, fragmentation may promote the release of mitotic signaling
components that are normally sequestered on Golgi membranes. For example,
ACBD3, a critical regulator of numb signaling, is released from the Golgi during
mitotic fragmentation to promote asymmetric cell division (Zhou et al.
2007
). Third,
an intact Golgi ribbon may cause steric hindrance during centrosome maturation and
restrict centrosome movement necessary for mitotic spindle formation.
In addition, there is support for an association between mitotic Golgi mem-
branes and the mitotic spindle. In a careful live imaging study, Shima and col-
leagues detected the enrichment of mitotic Golgi fragments at spindle poles,
indicating that the mitotic spindle may facilitate the ordered inheritance of Golgi
fragments into daughter cells (Shima et al.
1998
). Spindle poles were also found to
contain factors that are important for Golgi ribbon formation (Wei and Seemann
2009
). In this study, cells were induced to divide asymmetrically, with both
spindle poles segregating into only one of the two daughter cells. Under these
conditions, the pericentrosomal Golgi ribbon reformed only in the spindle pole-
containing daughter cell, and not in the daughter cell that lacked a spindle pole.
This result supports the notion that Golgi ribbon determinants associate with
spindle poles for their inheritance into the daughter cells; however, the nature of
these ribbon determinants is not known. Finally, Golgi proteins appear to control
the formation of the mitotic spindle. Three functionally diverse, Golgi-associated
proteins have been identified as having a role in mitotic spindle formation. These
proteins include the poly-ADP ribosylase Tankyrase (Chang et al.
2005
), the
peripheral Golgi protein GRASP65 (Sütterlin et al.
2005
) and the phosphoinositide
phosphatase Sac1 (Liu et al.
2008
). RNAi-mediated depletion of each of these
proteins resulted in multi-polar spindles and defects in cell cycle progression.
Furthermore, GM130 was found to be required for meiotic spindle formation
during mouse oocyte maturation (Zhang et al.
2011
). However, the mechanisms by
which these diverse proteins regulate spindle formation are not understood.
7.6 Conclusion and Perspective
While a unique physical association between the mammalian Golgi apparatus and the
centrosome has been observed over many years, recent studies have found that these
two organelles are also linked functionally (Table
7.2
). Such interactions occur
primarily during interphase, when the Golgi and the centrosome are in close vicinity.
During this stage of the cell cycle, the Golgi-centrosome interaction is important for
cellular processes, such as the establishment of cell polarity, the nucleation of
microtubules, and the control of centrosome structure and function. Other functional
Golgi-centrosome interactions are independent of organelle proximity and occur
during mitosis, when the physical proximity is disrupted. These include the regu-
lation of mitotic entry and post-mitotic reassembly of the Golgi ribbon.
It has been a challenging task to determine which characteristic of the peri-
centrosomal Golgi apparatus is important for the regulation of processes such as
