Spinal GFP⁺ cells of transgenic <i>uts2b</i>-GFP <i>X. laevis</i> tadpoles project to tail myotomes.

<p>Confocal image of combined immuno-labeling of spinal GFP⁺ neurons (<b>A1</b>) and retrograde labeling of spinal motoneurons (<b>A2</b>) in a stage 50 <i>uts2b</i>-GFP tadpole whole-mount spinal cord preparation. <b>A3</b>. Merged image obtained when GFP staining and retrograde labeling were superimposed. Dorsal view with rostral up. Only the hemi-cord is shown. The dashed-line on the right side represents the midline. Axial motoneurons (Ax MN) innervating myotomes were labeled from tail muscles with rhodamine (RDA) dextran dye whereas appendicular motoneurons (Ap MN) innervating limbs were labeled from hindlimb buds with alexa dextran 647 dye (A.D. 647; see scheme on the left panel). The drawing at the top left panel illustrates the medio-lateral localization of Ax MN and developing Ap MN in larval spinal cord at stage 50. Yellow arrowheads indicate double stained cells. Cross-section confocal image of combined immuno-labeling of spinal GFP⁺ neurons (<b>B1</b>, <b>C1</b>) and retrograde labeling of dorsal thoracic motoneurons (dTh MN, <b>B2</b>) and Ap MN, (<b>C2</b>) in stage 60 metamorphosing <i>uts2b</i>-GFP tadpole. <b>B3</b>, <b>C3</b>. Merged images obtained GFP staining and retrograde labeling were superimposed. dTh MN were labeled from <i>dorsalis trunci</i> muscles with RDA whereas Ap MN were labeled from groups of extensor and flexor of the hindlimb with A.D. 647 (see scheme on the left side). The cross-section drawing at the bottom left panel illustrates the dorso-ventral localization of dTh MN and Ap MN in the future adult spinal cord at stage 60. sp.sgt 7–10, spinal segments 7 to 10, Vr, ventral root. D, dorsal; L, lateral.