This domain-based segregation of cargo is reminiscent of that seen in the endosomal pathway.
The process of autophagy begins with the autophagosome formation which involves the segregation of cargo macromolecules in the double-membrane vesicle.
The default pathway for molecules entering early endosomes is recycling back to the plasma membrane, a pathway that starts with the segregation of cargo into the tubular extensions of the early endosomes (Draye et al. 1988; Yamashiro et al. 1984).
We showed that these specific combinations of motors direct not only the motility of these endosomal domains but also dictate their morphology and the segregation of cargo within them.
Sequential activity of ESCRT-0, -I, -II and -III complexes sorts ubiquitylated membrane proteins into specific membrane domains, induces inward budding and mediates membrane abscission to form ILVs. Other studies have pointed to ceramide and other lipids as mediators of exosome biogenesis by driving lateral segregation of cargo into specialized endosomal membrane regions able to bend inwards.
At this time it was also recognized that the mechanism for segregation of cargo proteins (either soluble or membrane associated), or sorting into a particular pathway was an important issue, as was the identification of the precise location for the initiation of the sorting process.
The first step (the formation of the tubular export domains) also includes the segregation of the cargo proteins from the Golgi resident enzymes.
Analysis of the role of motor subunits in the endosomal system also led us to define a role in segregation of endocytic cargo into distinct functional domains (Hunt et al., 2013).
There are two key aspects to the formation of the PGC precursors: their morphogenesis at the TGN; and the segregation between different types of cargo proteins that are targeted for different destinations, as well as between the Golgi-resident proteins, such as the Golgi enzymes.
