Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Poster Abstracts

41-POS Board 41 SPATIAL SURVIVAL ANALYSIS OF SECRETORY GRANULE BEHAVIOR RECORDED BY TIRF IMAGING IN HUMAN BETA-CELLS Thi Huong Phan 1 ; Giuliana Cortese 2 ; 1 University of Padova, Department of Information Engineering, Padova, Italy 2 University of Padova, Department of Statistical Sciences, Padova, Italy Exocytosis on beta-cells is one of the fundamental cellular processes that releases insulin from secretory granules. Studying survival of granules on the plasma membrane and their spatial correlation within cells during the exocytosis is of great interest. We analyze TIRF images recorded from 8 human beta-cells, containing granules and syntaxin information. One of the main objectives of this project is to investigate the relationship between the survival rates of granules and syntaxin levels, while adjusting for spatial correlation among granules within cells. To address the biological problem, an imaging procedure is performed to obtain survival datasets in which granules are followed from the first moment they arrive at the plasma membrane until they are no longer visualized in TIRF-images. Briefly, granule centroids are firstly detected in each single video image, then their trajectories are recorded by linking the same granules in subsequent frames. To study the concentration of syntaxin at granules in the plasma membrane, on-granule syntaxin levels are quantified for each single granule. In the survival analysis perspective, we propose a semiparametric proportional hazard model with individual frailties, where the clustering structure, as well as the spatial correlation between granules are modeled via the variance-covariance matrix of frailties. Finally, we apply the standard Cox model and our method to analyze the granule data. We discover that there exist two distinct groups of granules identified by their presence/absence at beginning of the experiment. For granules that are present at the beginning of the experiment, a higher level of syntaxin contributes to obtain a higher survival rate; moreover, disappearing of these granules from the plasma membrane are very strong spatially correlated within cells. In contrast, syntaxin level seems to have no effect on survival rates of granules that appear during the experiment and also no spatial correlation is found.

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