Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Thursday Speaker Abstracts

ADVANCED STATISTICS FOR SPATIO-TEMPORAL EVENTS OF EXOCYTOSIS Giuliana Cortese 1 ; 1 University of Padova, Padova, Italy Hormones and neurotransmitters are released when secretory granules or synaptic vesiclesfuse with the cell membrane, a process denoted exocytosis. Modern imaging techniques, inparticular total internal reflection fluorescence microscopy, allow the investigator tomonitor secretory granules at the plasma membrane, before and when they undergo exocytosis, and to observe their spatial relation. However, rigorous statistical approaches for temporal and spatial analysis of such exocytosisdata are still lacking. We show that various advanced statistical methods are well suited to analyse this biological process. We apply statistical regression models based on time-to- event analysis: granules are followed over time to occurrence of exocytosis events or to the end of the experiment, and the analysis can also be corrected for granules that dock during the experiment. We quantify the rate of exocytosis, as a function of time, in response to pulses of stimuli in insulin-secreting pancreatic ß-cell, and how it depends on proteins levels surrounding the granules. To study heterogeneity in granule populations, we exploit frailty models, which account for unobserved differences between granules, or between cells. Another important biological question is whether events of exocytosis are spatially correlated, and if this association depends on local levels of proteins such as syntaxin. For this scope, spatial survival models and statistical models for spatial point patterns were applied. Moreover, we extended the analysis to settings where multiple events act simultaneously (e.g., exocytosis and undocking) by using multivariate spatial point processes. Among the results, we find that the rate of exocytosis significantly increases when the local density of calcium channels is higher, it depends on syntaxin levels and exocytosis events are spatially correlated, with correlation being significant within a certain distance. This novel application of advanced statistical methods should be useful also for the study of other well-defined spatio-temporal events at the cellular level.

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