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Actin has a molecular scaffolding, not propulsive, role in presynaptic function

Abstract

We used actin tagged with enhanced green fluorescent protein (EGFP–actin) to characterize the distribution and dynamics of actin in living presynaptic terminals in rat CNS neurons. Actin was preferentially concentrated around—and appeared to surround—the presynaptic vesicle cluster. In resting terminals, 30% of actin was found to be in a polymerized but dynamic state, with a remodeling time scale of 20 s. During electrical activity, actin was further polymerized and recruited from nearby axonal regions to the regions surrounding vesicles. Treatment of terminals with the actin monomer–sequestering agent latrunculin-A completely dispersed the actin network and abolished activity-dependent actin dynamics. We used a variety of methods to examine the role of actin in the presynaptic vesicle cycle. These data rule out a propulsive role for actin, either in maintaining the vesicle cluster or in guiding vesicle recycling. Instead, we propose that actin acts as a scaffolding system for regulatory molecules in the nerve terminal.

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Figure 1: Neurons expressing EGFP–actin are functionally intact.
Figure 2: EGFP–actin puncta seems to encompass the recycling vesicle cluster.
Figure 3: Activity-dependent recruitment of actin to synaptic terminals.
Figure 4: Latrunculin-A causes a dose-dependent disruption of EGFP–actin and abolishes the activity-dependent dynamics of actin.
Figure 5: Jasplakinolide (Jas) recruits EGFP–actin to synaptic terminals.
Figure 6: Disruption of EGFP–actin does not cause a disruption of the vesicle cluster.
Figure 7: Disruption of actin leads to slightly faster rates of exocytosis but has no effect on endocytosis or repriming.
Figure 8: Actin disruption reduces the steady-state levels of synapsin and increases its extent of activity-dependent dispersion at synapses.

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Acknowledgements

We would like to thank members of the Ryan lab for useful discussions and W. Yan for technical assistance. This work was supported by the National Institutes of Health (NS24692, GM61925) and the Irma T. Hisrchl Trust.

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Correspondence to Timothy A. Ryan.

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Sankaranarayanan, S., Atluri, P. & Ryan, T. Actin has a molecular scaffolding, not propulsive, role in presynaptic function. Nat Neurosci 6, 127–135 (2003). https://doi.org/10.1038/nn1002

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