Figure 6. Binarized and Granger causality analysis corroborates the existence of super-connected leader cells in mouse islets in vivo.

a. Pooled data for average R and % connectivity measurements in mouse islets (n=5 in 5 different animals, individual datapoints shown) imaged over 60 minutes, with prolonged (>10 minute) exposure to high circulating glucose levels. Connectivity was recorded in the high glucose state (>10 mM), medium (6-10mM) and low (<4 mM) state from the same β cell ROIs. Prolonged exposure to high glucose levels does not abrogate the connectivity readout or result in dysynchrony. b. Topographic representation of connected β cells as extracted using the binarized and Monte Carlo data analysis approach for the same islet shown in Figure 5. Topographical representation of β cell connections in the remaining four islets imaged are shown in b’. The top 20-40% connected cells (reminiscent of previously-defined in vitro hubs) are highlighted in white. c. Log-log graph of the distribution of cell-cell connections pooled across all five islets imaged reveals a scale-free network (obeying a power-law distribution) whereby 8% cells serve the majority (60-100%) connections. d. Section of fluorescence intensity readouts for all 26 cells identified during a typical Ca²⁺ wave (superimposed in different colours) in a single islet. Data collected at 1.0 frame per second, the calcium waves shown here occurred in the high glucose state (25 mM). e. Close up of the fluorescent profiles for each individual cell taking part in the islet Ca²⁺ wave. “Leader cells” can be defined temporally as preceding the activity of “follower” cells. f. Yellow markers highlight the position of the temporally-defined “leaders”. Results are shown in Supplementary Table 1 (Animal #1). Note that temporally the four defined “leaders” are always the most connected on independent Granger Causality analysis.