Leader β-cells coordinate Ca2+ dynamics across pancreatic islets in vivo

Pancreatic β-cells form highly connected networks within isolated islets. Whether this behaviour pertains to the situation in vivo, after innervation and during continuous perfusion with blood, is unclear. In the present study, we used the recombinant Ca2+ sensor GCaMP6 to assess glucose-regulated connectivity in living zebrafish Danio rerio, and in murine or human islets transplanted into the anterior eye chamber. In each setting, Ca2+ waves emanated from temporally defined leader β-cells, and three-dimensional connectivity across the islet increased with glucose stimulation. Photoablation of zebrafish leader cells disrupted pan-islet signalling, identifying these as likely pacemakers. Correspondingly, in engrafted mouse islets, connectivity was sustained during prolonged glucose exposure, and super-connected ‘hub’ cells were identified. Granger causality analysis revealed a controlling role for temporally defined leaders, and transcriptomic analyses revealed a discrete hub cell fingerprint. We thus define a population of regulatory β-cells within coordinated islet networks in vivo. This population may drive Ca2+ dynamics and pulsatile insulin secretion

Ecophysiological strategies of Antarctic intertidal invertebrates faced with freezing stress

Recent studies have revealed a previously unanticipated level of biodiversity present in the Antarctic littoral. Here, we report research on the ecophysiological strategies adopted by intertidal species that permit them to survive in this environment, presenting cold-tolerance data for the widest range of invertebrates published to date from the Antarctic intertidal zone. We found significant differences in levels of cold tolerance between species within this zone. However, and contrary to expectations, intraspecific comparisons of subtidal and intertidal groups of eight species found significant differences between groups in only three species. One species, the nemertean Antarctonemertes validum, showed evidence of the presence of antifreeze proteins (thermal hysteresis proteins), with 1.4°C of thermal hysteresis measured in its haemolymph. We found a strong inverse relationship across species between mass and supercooling point, and fitted a power law model to describe the data. The scaling exponent (0.3) in this model suggests a relationship between an animal’s supercooling point and its linear dimensions