Cisternal progression
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Template:Clarify Cisternal progression is a theory of protein transport through the Golgi apparatus inside a cell, as opposed to the bulk flow model.
In cisternal progression, instead of vesicles continually budding and fusing to static cisternae carrying cargo molecules, the cisternae themselves would move towards the cell surface. Any resident of the Golgi not meant to travel to the cell surface or any other destination out of the Golgi, would be packaged in vesicles and moved back to the next cisternae. In this manner the cis (early most) cisternae would mature into the medial and the medial would mature into the trans cisternae by moving forward and receiving resident Golgi proteins from the preceding cisternae.
Both models of transport (cisternal progression and bulk flow) are considered to hold true. Some cargo proteins may take one route while others may choose the alternative route. For instance, a typical vesicle is 60-90nm in size. If a large protein is, say 400nm in length, it would be too big to fit in the vesicle and therefore may be left packaged in the cisternae itself. This is basically where the idea of cisternal progression came from, the study if algal sclaes and collagen transport.
This also brings up the idea that the Golgi may not be a static organelle. If the cisternae move forward and mature during transport, then what will happen if transport halts? Do the cisternae disappear or do they just stop transporting and stay where they are? The answer is, they disappear. Actually the recycling of Golgi into the endoplasmic reticulum (ER) continues and the Golgi fuses with the ER, becoming no more. Those favoring cisternal progression use this fact to explain their hypothesis. For if the Golgi were a static organelle with vesicles budding and fusing from it, then it would be an oranelle regardless of transport, but this is not the case.
Much controversy still continues aound the idea of cisternal progression vs. the bulk flow model.