Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Wednesday Speaker Abstracts

FUSION PORE DYNAMICS IN ENDOCRINE AND SYNAPTIC EXOCYTOSIS

Meyer B. Jackson ; 1 University of Wisconsin, Neuroscience, Madison, WI, USA

The exocytosis of single vesicles can be monitored in real time. In endocrine cells amperometry recording tracks the release of catecholamine, and analysis of the unitary events provides insight into the endocrine fusion pore. In neurons miniature synaptic currents track the release of neurotransmitter, and analysis of the unitary events provides insight into the synaptic fusion pore. Mutagenesis of SNARE transmembrane domains has been shown to alter flux through both of these fusion pores with striking parallels, indicating that immediately after opening, these two fusion pores share common structural features. The greater speed of synaptic release compared to endocrine release has made the study of synaptic fusion pores especially challenging. New methods are being developed to analyze miniature synaptic currents to use these signals to probe the mechanisms of exocytosis. A current focus of this laboratory is on establishing the role of diffusion within the synaptic cleft and determining its contribution in shaping unitary synaptic currents.

FUSION PORE REGULATION IN INSULIN-SECRETING BETA CELLS

Sebastian Barg 1 ; 1 Uppsala University, Medical Cell Biology, Uppsala, Sweden

Pancreatic beta cells co-secrete insulin and small transmitter molecules like ATP from dense core granules, and there is good evidence that the exocytotic fusion pore acts as molecular sieve that allows differential release of the two types of content. Widening of the fusion pore during exocytosis leads to insulin release, while its closure initiates kiss&run or cavicapture endocytosis after selective release of small molecules. I will present data from single insulin granule TIRF imaging experiments to demonstrate that the fusion pore is regulated by cAMP/Epac signaling and widely used antidiabetic drugs, and that transient synthesis and accumulation of PI(4,5)P 2 at the release site stalls fusion pore expansion by recruiting components of the endocytic fission machinery to the release site. The absence of clathrin differentiates this mechanism from clathrin-mediated endocytosis. Thus, local cAMP or phospholipid signaling inhibits fusion pore expansion and peptide release through an unconventional dynamin-dependent endocytic mechanism.

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