Fig. 1. Heart field expression of the Nkx2-5::GFP transgenic line in Xenopus laevis.
A-C: Fluorescence from the Nkx2-5::GFP transgene is first observed during late neurula and early tailbud stages of development. A: Anterior ventral view of a stage 18 embryo. B: Stage 20 embryo. C: Ventral view of the anterior portion of a stage 22 embryo. The GFP fluorescence that is viewed on both anterior and posterior sides of the cement gland (A, C-arrows) actually forms a contiguous domain of pharyngeal GFP expression. D, E: The shape of the GFP domain changes as the tailbud stage embryo elongates along the anterior-posterior axis. D: Ventral view of the heart-forming region at stage 26. E: Stage 27. When viewed from the ventral side, the fluorescence appears brightest in a posterior part of the domain where the cardiac mesoderm and underlying pharyngeal endoderm both express GFP. F-K: During tadpole development, it becomes easier to discriminate between the cardiac mesoderm and pharyngeal endoderm components of the transgene activity and the heart commences beating. F: Stage 32. G: Stage 35. H: Stage 40. I: Stage 45. J: Stage 46. K: Detail view of the forming spleen in a stage 46 animal, an organ that expresses Nkx2-5 mRNA and also shows transgene activity. Melanocyte pigment formation was inhibited in this tadpole to give clearer photography. White arrows indicate the extent of the pharyngeal expression domain while red arrows point to the heart. A, anterior domain of GFP; H, heart; P, pharynx; GB, gall bladder; SP, spleen.
From: Sparrow, D. et al (2000) “Regulation of the tinman Homologues in Xenopus Embryos”, Dev. Biol. 227, 65–79.