Fig. 3. BMPRIB specifically mediates commissural axon outgrowth and guidance. (A-D) After the ubiquitous expression of caBMPRIA and GFP from the CMV enhancer, the (B) GFP⁺ (blue) and (C) Axonin1⁺ axons (green) cross the spinal cord normally at the FP (arrowhead, B). (D) The electroporated Axonin1⁺ axons also project around the circumference of the spinal cord similar to control axons. (E-H) By contrast, after misexpression of caBMPRIB and GFP from the CMV enhancer, (F) no GFP⁺ axons cross the FP (arrowhead), and (G,H) Axonin1⁺ axons are both mispolarized medially towards the lumen of the spinal cord (arrows, G,H) and stalled (open arrowhead) above the ventral midline. + indicates the electroporated side. Scale bar in A: 100 µm for A-H.