Cytokeratin 18 (K18) expression during early embryonic stages. (A) At the one-celled stage, dorsal view. (B) At 8 h postfertilization (hpf), dorsal view. (C) Enlarged view of the same embryo in B. (D) At 10-hpf, dorsal view. (E) At 14-hpf, lateral view. (F) At 18-hpf, dorsal view. (G) At 20-hpf, lateral view. (H) Enlarged view of the same embryo in G; the arrow indicates the presumptive epithelial cells. (I) Detailed view of 48-hpf embryos; the arrow indicates the presumptive epithelial cells.

Red fluorescent protein (RFP) expression of the transgenic fish lines during early embryogenesis. The F2 offspring were produced by mating F1 female from Tg(k18(2.9):RFP) line with wild-type males (A, B, D, E) or by mating the F1 males from the Tg(k18(2.9):RFP) with wild-type females (C). (A) At the one-cell stage. (B) At 14 h postfertilization (hpf). (C) At 14 hpf. (D) At 3 days postfertilization (dpf); the arrows and arrow head indicate two different shapes of epithelial cells. (E) At 4 dpf, the red signals were gradually abolished to the undetectable level (upper). However, some of them still displayed red fluorescence (bottom). (F) Observation under the light field.

Cryosections of 48 h postfertilization (hpf) and 7 days postfertilization (dpf) larva from wild-type embryos and Tg(k18(2.9):RFP) transgenic line embryos. (A) Cryosection of the wild-type 48 hpf embryos, revealing that the endogenous k18 was expressed in the dorsal aorta, pronephric duct, and gut. (B) The comparable section from a 48 hpf k18(2.9):RFP transgenic embryo. (C) Head region. (D) Enlarged view of the same section in C. (D) Trunk section. DA, dorsal aorta; DF, dorsal fin; I, intestine; PD, pronephric duct; PF, pelvic fin; e, eye; i, inner plexiform layer; o, outer plexiform layer; r, rods and cones.

(A–E) Red fluorescent protein (RFP) expression patterns of transgenic lines in the adult fish. The arrow indicates that no red fluorescence was observed when the scale was removed. AF, anal fin; CF, caudal fin; DF, dorsal fin; PF, pelvic fin.