Late endosomal and lysosomal vesicles are important as a site of degradation, but also sites where intracellular bacteria grow, viruses enter the cell and MHC class II molecules find antigen fragments for alarming the immune system. Endosomal vesicles move and fuse and thus mature and recycle in cells. How such a process is controlled in time and space is complicated and largely not understood.

I will present data on the dynamics of late endosomes harbouring MHC class II molecules. I will show how cholesterol and the endoplasmic reticulum control the movement of these structures but also their fusion with other structures including autophagosomes. Late endosomes/lysosomes have a unique multivesicular structure with nanometer sized internal vesicles detectable by electronmicroscopy only. I will discuss the dynamics within such a structure using chemical biological technology. Finally, I will show how to use mass data to come to simple networks explaining the behaviour of endosomes in activated dendritic cells.

The talk will be focused on the dynamics in and between intracellular organelles in cells. It shows that biological processes do not occur in isolation but through interactive networks to control timed and spatial behavior.