Golgi ribbon unlinking -: An organelle-based G2/M checkpoint

Cell cycle checkpoints have been associated mostly with signaling mechanisms monitoring the genetic material for abnormalities and inaccuracy in partitioning, such as DNA lesions or failure in chromosome attachment to kinetochores. However, it becomes more evident that other checkpoints are turned on by cytoplasmic events, such as the cytoskeleton organization and the organelle structure. Here, we summarize recent evidence strongly suggesting that the integrity of the Golgi ribbon and more precisely the tubules interconnecting the Golgi stacks to form this ribbon, at late G(2)/early prophase, is linked to a Golgi-related G(2)/M checkpoint. A number of kinases phosphorylating a small subset of Golgi-localized proteins have been shown to promote the G(2)-specific Golgi ribbon unlinking, allowing the cell to enter mitosis. When these kinases are inactivated or when the substrates cannot be phosphorylated, Golgi unlinking is prevented and the cells are blocked or delayed in G(2) phase.