Fig. 1

Expression of wnt8a and pax2a. A) Left panel shows a lateral view of a whole mount 85% epiboly stage embryo stained for wnt8a, with the white arrow indicating wnt8a⁺ cells in the region of the posterior lateral mesoderm. The schematic in the middle highlights the position of the posterior lateral mesoderm in relation to the wnt8a⁺ cells at 85% epiboly. Right panel shows a sagittal section through the ventral midline with white arrows indicating wnt8a⁺ cells in the hypoblast layer. B) Panels show posterior views of 9.5 hpf stage embryos stained for wnt8a and pax2a transcripts. White arrow in left panel identifies wnt8a expression in the presumptive intermediate mesoderm; black arrow in the right panel identifies the intermediate mesoderm labelled by pax2a. C) Caudal view of 10 hpf stage embryo co-labelled for wnt8a (purple) and pax2a (red) transcripts. Right panel shows a high magnification view of the intermediate mesoderm, black arrows indicate co-staining of wnt8a and pax2a and white arrow highlights a more caudal and medial domain that is wnt8a⁺ but pax2a^-. D) Dorsal views of flat mounted 12 hpf and 16 hpf embryos (anterior to the left) showing wnt8a (purple) and pax2a (red) double labelling. Black arrow in the left panel identifies the posterior-most limit of the intermediate mesoderm; white arrow in right panel identifies caudal pax2a⁺/wnt8a⁺ cells. Abbreviations are: An, Animal; V, Ventral; D, Dorsal; Veg, Vegetal; PLM, Posterior Lateral Mesoderm; hpf, hours post fertilization.