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New Biological Frontiers Illuminated by Molecular Sensors and Actuators
Tuesday Speaker Abstracts
Molecular Choreography of Polarity Regulation in Cell Migration
Tobias Meyer
.
Stanford University, Stanford, USA.
We are investigating molecular mechanisms of polarization both in neutrophils and endothelial
cells using fluorescent reporters and chemical and genetic perturbations. I will be presenting
work on the order of events by which neutrophils rapidly transition from an unpolarized state to a
polarized migrating state in a series of steps involving the small GTPases Cdc42, RhoA, Rac as
well as Ras and PI3K. Once neutrophils are persistently migrating they steer their front towards
chemotactic sources using primarily local Cdc42 and RhoA activities. In contrast to neutrophils,
endothelial cells show two types of polarization, one operating in leader cells using a
combination of small GTPases, Ca2+ and diacylglycerol signals and one operating in follower
cells based on small GTPases that are locally directed by curved VE-cadherin-based membrane
invaginations that we termed "Cadherin fingers". I will be presenting results on how curved
membranes generated by these cadherin fingers help orient follower cells.
Synaptic Function Illuminated by a Hybrid-Type Fluorescent Glutamate Probe
Kenzo Hirose
.
UTokyo, Tokyo, Japan.
To facilitate our understanding of the basic features of synaptic transmission, we have been
developing a series of fluorescent glutamate probes named EOS. EOS is a hybrid type
fluorescent probe consisting of a fluorescent dye and a glutamate binding domain of AMPA-type
glutamate receptor. eEOS, our most recent version of EOS, was obtained by a combinatorial
screening. eEOS has good photostability and a large dynamic range. Using eEOS, we
successfully imaged glutamate release from single presynaptic terminals of cultured hippocampal
neurons. The amounts of glutamate release under various conditions were analyzed to evaluate
synaptic parameters that govern the quantal nature of neurotransmitter release. Results show that
there exist multiple release sites at each synaptic terminal. There are large varieties in the number
of the release sites as well as in release probability. Intriguingly the two synaptic parameters
were not correlated. Thus each synapse has its own 'personality' characterized by these
independent parameters. We then asked how nanoscale architectures formed by presynaptic
proteins control neurotransmitter release. We undertook STORM microscopy for nanoscale
visualization of presynaptic proteins. Notably, Mun13-1 molecules were found to assemble as
small clusters; there were multiple Mun13-1 clusters per active zone. By combining the
glutamate imaging technique and STORM microscopy, we directly counted and compared the
number of the release sites and the number of Mun13-1 clusters. We found that these numbers
were highly correlated. We also found that Muc13-1 clusters recruited syntaxin-1. These data
indicate that Munc13-1 clusters are molecular entities for functional release. Reconstitution
experiments in non-neuronal cells reveal that the formation of nanoclusters relies on self-
organizing properties of Munc13-1 molecules sites. The self-organizing property of presynaptic
molecule underlies presynaptic weights for synaptic computation.