Visualizing cisternal maturation in living yeast.
Catherine A. Reinke, Brooke J. Bevis, Eugene Losev, Daniel E. Strongin, Benjamin S. Glick
Mol. Gen. and Cell Bio., University of Chciago, 920 E. 58th St., Chicago, IL, 60637, USA
According to the cisternal maturation model, cisternae of the Golgi apparatus are transient compartments that form de novo, mature, and ultimately fragment into transport carriers. This model suggests that an individual Golgi cisterna progressively changes its identity. However, a definitive test of the maturation model has been elusive. Saccharomyces cerevisiae is an ideal system for analyzing Golgi dynamics because this yeast has a non-stacked Golgi apparatus, so individual early and late Golgi cisternae can be resolved by fluorescence microscopy. The maturation model predicts that an early Golgi cisterna should mature into a late cisterna. We set out to visualize the composition of individual Golgi cisternae over time using fast 4D confocal microscopy. GFP-Gos1p labels early to medial Golgi cisternae, whereas Sec7p-DsRed labels late Golgi cisternae. These two markers show partial overlap and thus occasionally occupy the same cisternae. In dual-color movies, we observe that an individual cisterna is first marked by GFP-Gos1p fluorescence, which then fades as the cisterna simultaneously gains Sec7p-DsRed fluorescence. We conclude that the identity of an individual cisterna changes over time. These results provide strong, direct support for the cisternal maturation model.
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