Dynamics of embryonic pancreas development using real-time imaging

Current knowledge about developmental processes in complex organisms has relied almost exclusively on analyses of fixed specimens. However, organ growth is highly dynamic, and visualization of such dynamic processes, e.g., real-time tracking of cell movement and tissue morphogenesis, is becoming increasingly important. Here, we use live imaging to investigate expansion of the embryonic pancreatic epithelium in mouse. Using time-lapse imaging of tissue explants in culture, fluorescently labeled pancreatic epithelium was found to undergo significant expansion accompanied by branching. Quantification of the real-time imaging data revealed lateral branching as the predominant mode of morphogenesis during epithelial expansion. Live imaging also allowed documentation of dynamic β-cell formation and migration. During in vitro growth, appearance of newly formed β-cells was visualized using pancreatic explants from MIP-GFP transgenic animals. Migration and clustering of β-cells were recorded for the first time using live imaging. Total β-cell mass and concordant aggregation increased during the time of imaging, demonstrating that cells were clustering to form "pre-islets". Finally, inhibition of Hedgehog signaling in explant cultures led to a dramatic increase in total β-cell mass, demonstrating application of the system in investigating roles of critical embryonic signaling pathways in pancreas development including β-cell expansion. Thus, pancreas growth in vitro can be documented by live imaging, allowing visualization of the developing pancreas in real-time.