Golgi Membranes Are Absorbed into and Reemerge from the ER during Mitosis

Abstract

Quantitative imaging and photobleaching were used to measure ER/Golgi recycling of GFP-tagged Golgi proteins in interphase cells and to monitor the dissolution and reformation of the Golgi during mitosis. In interphase, recycling occurred every 1.5 hr, and blocking ER egress trapped cycling Golgi enzymes in the ER with loss of Golgi structure. In mitosis, when ER export stops, Golgi proteins redistributed into the ER as shown by quantitative imaging in vivo and immuno-EM. Comparison of the mobilities of Golgi proteins and lipids ruled out the persistence of a separate mitotic Golgi vesicle population and supported the idea that all Golgi components are absorbed into the ER. Moreover, reassembly of the Golgi complex after mitosis failed to occur when ER export was blocked. These results demonstrate that in mitosis the Golgi disperses and reforms through the intermediary of the ER, exploiting constitutive recycling pathways. They thus define a novel paradigm for Golgi genesis and inheritance.

Rapid, Endoplasmic Reticulum-independent Diffusion of the Mitotic Golgi Haze

“…If, on the other hand, it depends on the endoplasmic reticulum, then it can be viewed as a dependent organelle, which exists only as a consequence of ER functioning (Zaal et al, 1999;Bevis et al, 2002;Munro, 2002).…”

“…Endogenous GalT was also localized to ER-like structures in mitotic cells, but the lack of quantitation and double-labeling to identify the ER precludes any firm conclusions. Blocking ER exit at the end of mitosis prevented Golgi reassembly arguing that critical Golgi components were relocated to the ER during the mitosis (Zaal et al, 1999).Perhaps the most supportive line of evidence came from experiments exploiting the properties of the lipid dye BODIPY ceramide, which has been used as a marker for the Golgi apparatus in interphase cells (Pagano et al, 1991). Lipids move much faster in membranes than proteins but should move at the same rate if both are present in common carriers such as small vesicles.…”

“…Fluorescence recovery after photobleaching (FRAP) analysis in mitotic cells showed that the rate of diffusion of this dye was 10 times higher than that of a GalT-GFP construct, arguing that both were present in a continuous membrane system rather than small vesicles. These membranes were identified as the ER because the diffusion coefficients for the GalT-GFP construct were the same in mitotic cells as in interphase cells treated with brefeldin A (BFA) (Zaal et al, 1999).Another model-related issue is the status of mitotic Golgi clusters (MGCs), which are visualized as bright resolvable puncta by fluorescence microscopy, and tubulo-vesicular clusters by EM (Lucocq et al, 1987(Lucocq et al, , 1989Misteli and Warren, 1995;Shima et al, 1998;Jokitalo et al, 2001). In the autonomous partitioning model, they are viewed as the mediators of Golgi partitioning (Shima et al, 1998).…”

“…This might help explain the variability in the amount of Golgi haze that is seen in different cell types. The status of the matrix is, however, still unclear, and its existence has been disputed (Zaal et al, 1999;Miles et al, 2001;Ward et al, 2001;Stroud et al, 2003). In the merged ER-Golgi model of partitioning, the MGCs are viewed as intermediates on the pathway leading to merger of the Golgi and the ER.…”

Golgi localization and dynamics of hyaluronan binding protein 1 (HABP1/p32/C1QBP) during the cell cycle

“…The dispersion pattern of HABP1 during mitosis is similar to most proteins of golgi-membrane and nucleus [17,18]. Most interestingly however, the distribution pattern and retention of HABP1 during different stages of mitosis resemble that of its primary ligand, HA [15].…”