Figure 10.

The block of severing of the Golgi ribbon during G2 inhibits the recruitment and activation of Aur-A at the centrosome trough a novel mechanism. (A) In mammalian cells, the Golgi complex is organized as a continuous membranous system composed of stacks interconnected by tubules, a structure known as the Golgi ribbon (ribbon). During the G2 phase of the cell cycle, the severing of the Golgi ribbon into its constituent stacks (stacks) is a fragmentation step that is essential for mitotic entrance and is concomitant with the initial recruitment and activation of Aur-A kinase at the centrosomes (CE). A block in Golgi fragmentation (X) inhibits Aur-A recruitment and activation at the centrosome, and this in turn impairs the first activation of cycB-Cdk1 at the centrosome. The Golgi-dependent G2 block is not mediated by known Aur-A activators (i.e., Pak1), and neither it is indirectly mediated or Plk1 and the cycB–Cdk1 complex. (B) The Golgi-dependent G2 block is not regulated by known G2 checkpoint mediators (e.g., : Chk1 or p38), and neither it is mediated by Golgi-localized cell cycle regulators (e.g., : Myt-1), which act downstream the Golgi checkpoint. (C) At the onset of mitosis the kinases Aur-A, Plk1 and cycB-Cdk1 become functionally connected by a positive feedback loop, leading to irreversible progression into mitosis.