| Sumario: | In mitosis, each daughter cell must receive a complete and equal set of cellular components. Cellular organelles that are single copy, such as endoplasmic reticulum, nuclear envelope and Golgi apparatus, have to break down to allow their correct distribution between daughter cells. The mammalian Golgi is a continuous membranous system formed by cistern stacks, tubules and small vesicles that are located in the perinuclear area. At the onset of mitosis, the Golgi apparatus undergoes a sequential fragmentation that is highly coordinated with mitotic progression and in which reversible phosphorylation plays a critical regulatory role. In fact, several kinases have been implicated in each stage of this fragmentation process. Before mitotic disassembly, the lateral connections between the stacks are severed resulting in the formation of isolated cisternae. Several kinases such as mitogen-activated protein kinase kinase 1(MEK1), Raf-1, ERK1c, ERK2, Plk3, VRK1, several Golgi matrix proteins (GRASP65 and GRASP55) and the membrane fission protein BARS have been shown to mediate signals in this first step that takes place in late G2 phase. As prophase progresses, the isolated cisternae are first unstacked followed by its breakage into smaller vesicles and tubules that accumulate around the two spindle poles at metaphase. Unstacking and vesiculation are triggered by several proteins including kinases (Plk1 and Cdc2), the GTPase ARF-1 and inactivation of membrane fusion complexes (VCP and NSF). Post-mitotic Golgi reassembly consists of two processes: membrane fusion mediated by two ATPases, VCP and NSF; and cistern restacking mediated by dephosphorylation of Golgi matrix proteins (GRASP65 and GM130) by phosphatase PP2A (B). Apart from the tight regulation by reversible phosphorylation, it seems that mitotic Golgi membrane dynamics also involves a cycle of ubiquitination during disassembly and deubiquitination during reassembly in part regulated by the VCP-mediated pathway.
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