Research Overview


Our laboratory is interested in the molecular mechanisms of endocytosis and synaptic vesicle protein trafficking in neurons. Synaptic vesicles are small membrane-bounded organelles that store and secrete non-peptide neurotransmitters (Figure 1).
Haucke Research Fig.1
Figure 1: Distribution of synaptotagmin (red, left) and synaptobrevin 2 (green, middle) in axons of differentiated P19 neurons analyzed by indirect immunofluorescence microscopy. Right, overlay of the middle and left images illustrating the co-localization of both synaptic vesicle proteins (image by Kathrin Kastning)


Following exocytosis and the concomitant insertion of synaptic vesicle proteins and lipids into the presynaptic plasmalemma synaptic vesicles are retrieved by clathrin-mediated endocytosis. During this process the clathrin adaptor complex AP-2 is recruited to the presynaptic plasmamembrane along with a growing number of accessory proteins which assist in the formation and maturation of clathrin-coated pits (Figure 2).
Haucke Research Fig.2
Figure 2: Formation of clathrin-coated endocytic pits on liposomes (from Takei et al.(1998) Cell, 94:131-141)


Coated pits eventually pinch off in a dynamin-dependent reaction giving rise to free clathrin-coated vesicles which become refilled with neurotransmitter and finally shed their coat resulting in the regeneration of synaptic vesicles.

We are interested in how the endocytic process is regulated at the molecular level both by proteins and lipids and how synaptic vesicles are formed in differentiating neuronal precursor cells. We have identified stonin 2, a novel component of the endocytic machinery which we hypothesize to regulate synaptic vesicle recycling by interacting with AP-2 and synaptotagmin. How this protein precisely acts at the synapse is currently under intense investigation by the combined use of molecular biological, biochemical, and physiological techniques. Other projects are directed towards dissecting the role of phosphoinositides, a certain class of membrane lipids which interact with several components of the endocytic machinery, in clathrin-mediated endocytosis at the synapse (Figure 3)
Haucke Research Fig.3
Figure 3: Hypothetical model for the cooperation of membrane phosphoinositides and the synaptic membrane protein in recruiting the clathrin adaptor complex AP-2 to the presynaptic plasmalemma (modified from Takei & Haucke (2001, Trends Cell Biol. 11: 385-391).


Finally, we are trying to understand the biogenesis pathway of synaptic vesicles during neuronal differentiation by establishing an in vitro system that allows the formation of neurons from differentiating non-neuronal precursor cells (see also Figure 1) We are also trying to establish novel adaptors that might serve as sorters for the directed delivery of synaptic vesicle proteins to the axonal targeting pathway.