Coalescence of Golgi fragments in microtubule-deprived living cells

The process of stack coalescence, an important mechanism of Golgi recovery from mitosis, was examined using novel experimental paradigms. In living ce lls with disrupted (by nocodazole) microtubules, galactosyl transferase-GFP -labelled Golgi fragments constantly appeared, grew sometimes moved with a speed of 1-2 mu m/min, coalesced or gradually diminished and disappeared, T he rate of Golgi fragment turnover and coalescence was highly balanced to m aintain a constant number of Golgi units per cell. Moreover some Golgi isla nds appear and some received new GalTase-GFP after photobleaching of cell c ytoplasm, Short tubules extending from the rims of scattered Golgi fragment s frequently formed bridges between ministacks, inducing their coalescence. The frequency of coalescence could also be inhibited by disruption of acti n microfilaments. After the Golgi redistribution into endoplasmic reticulum induced by brefeldin A, either the growth of small Golgi fragments or thei r coalescence leads to compartmentalized stark formation without the partic ipation of microtubules, These results demonstrate that this coalescence be tween isolated Golgi stacks is microtubule-independent and could thus be me diated by membranous tubules.