Live imaging of yeast Golgi cisternal maturation

Abstract

There is a debate over how protein trafficking is performed through the Golgi apparatus. In the secretory pathway, secretory proteins that are synthesized in the endoplasmic reticulum enter the early compartment of the Golgi apparatus called cis cisternae, undergo various modifications and processing, and then leave for the plasma membrane from the late (trans) cisternae. The cargo proteins must traverse the Golgi apparatus in the cis-to-trans direction. Two typical models propose either vesicular transport or cisternal progression and maturation for this process. The vesicular transport model predicts that Golgi cisternae are distinct stable compartments connected by vesicular traffic, whereas the cisternal maturation model predicts that cisternae are transient structures that form de novo, mature from cis to trans, and then dissipate. Technical progress in live-cell imaging has long been awaited to address this problem. Here we show, by the use of high-speed three-dimensional confocal microscopy, that yeast Golgi cisternae do change the distribution of resident membrane proteins from the cis nature to the trans over time, as proposed by the maturation model, in a very dynamic way.

The Actomyosin Ring Recruits Early Secretory Compartments to the Division Site in Fission Yeast

“…Our data provide further evidence supporting the cisternal progression model of Golgi maturation ( Figure 1G and Supplementary Movie 3). Time required for Golgi cisternae identity change in fission yeast ( Figure 1F) was consistent with maturation dynamics reported previously in S. cerevisiae (Losev et al, 2006;Matsuura-Tokita et al, 2006). As judged by the dynamics of the early Golgi marker protein, Anp1p-mCherry, cis-Golgi cisternae could also arise de novo (Figure 1, E and F, and Supplementary Movie 2), but the relationship of these biogenesis events to tER was more difficult to establish because of the large number of Sec24p-GFP entities.…”

Defining the boundaries: Rab GEFs and GAPs

“…Compartment maturation by Rab conversion is of special interest for the yeast Golgi complex, because live-cell video microscopy has shown that the yeast Golgi matures in a process analogous to endosome maturation in mammalian cells (9,10). Using live-cell video microscopy, Rivera-Molina and Novick (5) could also detect the conversion of a Ypt1p-enriched Golgi compartment into a Ypt32p-enriched compartment in a process that depended on the Ypt1 GAP, Gyp1p.…”

“…By using Rab GEFs and GAPs to generate late Golgi compartments from earlier Golgi compartments, yeast cells ensure vectorial and ordered transport within the secretory pathway. In rapidly growing baker's yeast cells that lack a stacked Golgi complex, Rab interconversion may provide the molecular basis for Golgi maturation in the secretory pathway (9,10). In mammalian cells in which early and late Golgi compartments seem to be more stably stacked, Rab conversion may represent part of the mechanism for vectorial transport, on top of conserved vesicle transfers between individual Golgi compartments.…”

P4-ATPase Requirement for AP-1/Clathrin Function in Protein Transport from the trans-Golgi Network and Early Endosomes

“…The yeast TGN appears to be a transient organelle with a half-life of only 1-2 min before it is consumed into many types of vesicles that are targeted to either the plasma membrane, early endosomes, late endosomes, the vacuole, or potentially earlier Golgi cisternae (Losev et al, 2006;Matsuura-Tokita et al, 2006). Thus, TGN residents rely on an active trafficking mechanism to maintain their TGN localization.…”