Pax4-Ghrelin mediates the conversion of pancreatic ε-cells to β-cells after extreme β-cell loss in zebrafish

Pancreatic ε-cells producing ghrelin are one type of endocrine cell found in islets, which have been shown to influence other intra-islet cells, especially in regulating the function of β cells. However, the role of such cells during β-cell regeneration is currently unknown. Here, using a zebrafish nitroreductase (NTR)-mediated β-cell ablation model, we reveal that ghrelin-positive ε-cells in the pancreas act as contributors to neogenic β-cells after extreme β-cell loss. Further studies show that the overexpression of ghrelin or the expansion of ε-cells potentiates β-cell regeneration. Lineage tracing confirms that a proportion of embryonic ε-cells can transdifferentiate to β-cells, and that the deletion of Pax4 enhances this transdifferentiation of ε-cells to β-cells. Mechanistically, Pax4 binds to the ghrelin regulatory region and represses its transcription. Thus, deletion of Pax4 derepresses ghrelin expression and causes producing more ghrelin-positive cells, enhancing the transdifferentiation of ε-cells to β-cells and consequently potentiating β-cell regeneration. Our findings reveal a previously unreported role for ε-cells during zebrafish β-cell regeneration, indicating that Pax4 regulates ghrelin transcription and mediates the conversion of embryonic ε-cells to β-cells after extreme β-cell loss.