Click to enlarge
Left panel: The picture shows a triple immunofluorescence staining of cultured neurons for the synaptic vesicle marker Synaptophysin
(red), and the active zone cytomatrix molecules Bassoon (green) and Piccolo (blue). White colour indicates colocalization of
all three markers and, thus, the location of presynaptic nerve terminals. Synaptic vesicles and active zone cytomatrix
molecules colocalize at synapses, but the cytomatrix molecules are enriched at the plasmamembrane in a way that can be deteced
even by light microscopy (see box). The scale bar is 10 µm.
Right panels: Schematic representations of key components of a presynaptic nerve terminal,
i.e. synaptic vesicles and active zone cytomatrix molecules: Active
zones are sites of neurotransmitter release. Depending on the protocols used,
electron microscopy reveals pyramid shaped structures or filaments located at or
originating from the plasmamembrane. The pyramids and the filaments,
respectively, are thought to represent or contain active zone cytomatrix
Questions: How do cytomatrix molecules restrict neurotransmitter release to active zones?
How do they control synaptic vesicle function?
Click to enlarge
The active zones of one axon can be visualized using transfection. The double
fluorescence image shows a culture stained for Piccolo (red). In the field of
view, one neuron has been transfected to express GFP-Bassoon. The green
fluorescent recombinant Bassoon should be targeted to active zones and
colocalize with Piccolo (colocalization is shown in yellow). The green picture
shows the punctate distribution of GFP-Bassoon in the axon of the transfected
The movie shows a live imaging time lapse taken from a double transfected culture: GFP-Bassoon is coexpressed with red
fluorescent Synaptophysin, a synaptic vesicle marker. In the field of view, two axons run along the soma and dendrite of a
postsynaptic neuron. Within the axons, GFP-Bassoon and red fluorescent Synaptophysin colocalize in large immobile spots
expected to be synaptic sites. In addition, small mobile puncta that contain only one fluorescence are trafficked along the
axon, suggesting that in this example Bassoon and Synaptophysin are trafficked as distinct packets. The current notion holds
that Bassoon is shipped on the surface of precursor vesicles.
Questions: How do cytomatrix molecules and synaptic
vesicles find their way to synapses?
What are the signals and mechanisms underlying protein and organelle targeting to synapses?
Click to enlarge
The synapses of young nerve cells must mature before they can release their neurotransmitters to the full extent and with
the speed and properties of a mature synapse. We found that the nerve terminals of mice lacking the postsynaptic cell
adhesion molecule Neuroligin-1 remain at an immature stage with respect to both structure and function. Synaptic cell
adhesion molecules have also been implicated in cases of autism.
The picture shows a neuronal culture stained for the
presynaptic marker Synaptophysin (red). One neuron expresses GFP-Neuroligin-1, a recombinant version of the cell adhesion
molecule that is targeted to dendritic spines.
Questions: How do Neuroligins stimulate presynaptic maturation? Does dysfunctional maturation
contribute to autism?
Click to enlarge
The fundamental mechanisms of synapse formation and function appear to be conserved across species and across types of
synapses. How are these fundamental mechanisms harnessed, in the brain, to equip specialized synapses for their specialized
tasks? To address this question, we have begun to study the synapses of the mammalian auditory system. Several types of
synapses are found along the auditory pathway, of which some are highly specialized. For example, the so-called endbulbs of
Held and the Calyx of Held are "giant" nerve terminals that harbor hundreds of active zones. Some of these terminals are large
enough to cover a major area of the cell body of their postsynaptic target. How can we explain the specific properties of
these synapses assuming that they rely on intricate modification of fundamental principles? Another specialization comes with
genes that occur only in vertebrates. Which functions do they add to the evolutionarily conserved set of synaptic proteins?
The sketch (by Donata Oertel, UW-Madison) illustrates the types of presynaptic terminals occurring at early stages of the
auditory pathway, where we have begun to study the molecular composition and function of endbulbs of Held.
See for example:
Kremer, T., Kempf, C., Wittenmayer, N., Nawrotzki, R., Kuner, T., Kirsch, J. and Dresbach, T. (2007) Mover is a novel vertebrate-specific presynaptic protein with differential distribution at subsets of CNS synapses. FEBS Lett. 581, 4727-4733.
Oertel D. (1999). The role of timing in the brain stem auditory nuclei of vertebrates. Annu Rev Physiol. 1999;61:497-519. Review.
We study synapse formation with particular focus on the biogenesis of presynaptic nerve terminals. Presynaptic boutons are
the principal sites of neurotransmitter release in the brain. They are generated during pivotal stages of brain
development, including initial wiring of the brain, after adult neurogenesis, and during remodeling of presynaptic input
in regions undergoing structural plasticity. Bouton generation is followed by maturation steps that fine-tune individual
synapses for specific tasks.
It is an emerging view that subtle aspects of presynaptic dysfunction are implicated in an increasing number of disorders
such as autism and schizophrenia. To unravel the molecular mechanisms involved, we study presynaptic bouton function at
three principal levels, i.e. at the level of bouton composition, bouton assembly, and bouton maturation.
Key questions driving our research are:
- What are the fundamental mechanisms underlying synapse formation and function?
- How are these fundamental mechanisms harnessed to equip specialized synapses in the brain with their specific properties?
- How are synapse formation and function controlled by transsynaptic signalling? How do subtle failures at each step -
including synapse assembly, maturation, and fine-tuning - affect brain function?
For an illustrated overview of projects please click on the items.
There is ample possibility for participation and training at all levels, including lab visits, individual practical courses,
lab rotation, bachelor-, master-, MD-, PhD- thesis work, and PostDoc work.
Training is offered in these methods:
- Molecular cloning, yeast-2-hybrid assay, western blotting, subcellular fractionation, pulldown, immuno precipitation, antibody
- Primary culture, cell lines, viral infection of neurons, various transfection methods, molecular perturbation
methods (knockout, knockdown, overexpression)
- Epifluorescence and confocal microscopy, live imaging, electron microscopy, DAB
photooxidation electron microscopy
- Patch clamp electrophysiology
Feel free to visit us.