Autophagosome maturation and lysosomal fusion.

Compartmentalization is essential in the eukaryotic cell and this is most often achieved by sequestering specific components that perform a related function in a membrane-bound organelle. To function normally these organelles must transiently fuse with other compartments in order to transfer protein and lipid that is needed for them to function. These events must be highly coordinated otherwise non-specific fusion could occur leading to loss of compartment identity and function. The autophagosome is a specialized membrane compartment that delivers cytosolic components to the lysosome for degradation. Likewise, this delivery is coordinated so that only when the autophagosome is fully formed is it imparted with the information to allow it to specifically fuse with the endocytic system and deliver its contents to the lysosome. In the present chapter, I discuss our current understanding of how this happens.