Fig. 2

Fig. 2 Developmental changes in morphology of the swimbladder. (A–F) EGFP expression in Et(krt4:EGFP)^sq33-2 at 3–5 dpf as shown in whole mount (A–C) and cross sections (D–F). EGFP is expressed in the swimbladder epithelium (e). White arrows indicate the primordium of anterior chamber. (G–L) EGFP expression in Et(krt4:EGFP)^sq3 at 3–5 dpf as shown in whole mount (G–I) and cross sections (J–L). Expression of EGFP is in the outer mesothelium (o) of swimbladder. (M–O) Cross section of swimbladder at 3–5 dpf stained with hematoxylin and eosin. (P) EGFP expression in Et(krt4:EGFP)^sq33-2 at 21 dpf, showing an inflated anterior chamber (white arrow). (Q) Cross section of swimbladder at 120 hpf, three different cell layers represent epithelium (e), mesenchyme (m), and outer mesothelium (o). (R–U) Schematic representation of three phases of swimbladder morphogenesis: budding phase (R), growth phase (S) and inflation phase (T, U). At, 2 dpf, the swimbladder bud evaginates out of the anterior foregut epithelium (blue dotted line) at the level of second somite (panel R). By 3 dpf, the swimbladder bud has elongated, forming a pneumatic duct, and the swimbladder epithelium forms a sac-like structure surrounded by the mesenchymal tissue (green) and outer mesothelium (red) (panel S). The second chamber primordium (arrow) is present at the anterior tip of the main chamber (panels S and T). Inflation of the main and posterior chamber occurs at 4–5 dpf (panel T) and inflation of the anterior chamber at 20 dpf (panel U). Abbreviations: 1–7, sequence numbers of anterior somites; e, epithelium; g, gut; lu, lumen of swimbladder; m, mesenchyme; n, notochord; o, outer mesothelium; pd, pneumatic duct; oe, oesophagus; ph, pharynx; sb, swimbladder. Numbers—anterior somites. Scale bars: 250 μm in whole mount and panels R–U; 100 μm in cross sections.