Fig. 3.

Fig. 3. Lineage tracing and targeted cell ablation using krt4 knock-in iCre line.

(A and B) Confocal images of krt4⁺ ductal cells in 6 dpf larvae (A) and 30 dpf juvenile fish (B). The brown, white, and cyan dashed lines indicate the pancreata, intestine, and the principal islet, respectively. The yellow arrows indicate large luminal krt4⁺ ducts throughout the pancreas, i.e., even in the pancreatic tail as the fish grow older. Scale bars, 100 μm. (C) The Cre/loxP strategy used to demonstrate krt4⁺ ductal cell–derived β cells. krt4-p2a-mNeonGreen-t2a-iCre was crossed to a color-switch line under the control of the insulin promoter. H2BmCherry is specifically induced in krt4-derived β cells, while β cells from other origins express CFP. (D and E) Z-projection showing differential distribution of β cells from krt4⁻ (green) and krt4⁺ (magenta) origins, 21 dpf (D) and 25 dpf (E). The ductal trees are visualized with anti-Vasnb staining. Scattered β cells budding out from the intermediate duct are highlighted with red arrows. White dashed lines indicate the principal islet. Scale bars, 40 μm. (F) Confocal images of krt4-derived β cells (magenta) in the secondary islets. Scale bars, 40 μm. (G to I) Design of targeted cell ablation of krt4-derived β cells by induction of DTA (G) with representative confocal images [(H) and (I)]. Cyan and yellow dashed lines in the Z-projection (H) indicate the area with surviving β cells at the posterior part of the principal islet and the β cell debris at the anterior part, respectively. The cell with orange arrow in (I) and magnified image (I′) is activated Caspase-3–positive, shown in single plane, indicating apoptosis. Scale bars, 80 μm.