Fig. 3. Defects in muscle development, innervation and axon projections in Hoxc10^-/-/Hoxd10^-/- double-mutant embryos. (A) Cross-sections through mid-thigh and mid-shank of embryos stained for muscle (MyoD) and nerve (neurofilament 165). Two muscles, the anterior head of the biceps in the thigh and the extensor hallucis longus in the shank (arrows) are missing in this Hoxc10^-/-/Hoxd10^-/- mutant embryo. In the shank of these mutants, innervation is completely lost from muscles of the anterior group (A) and greatly reduced in the lateral group (L). (B) Whole-mount neurofilament staining of axons in the hindlimb (lateral view, rostral is to the left). Top panels show the contribution of spinal segments to the lumbar (L) and sacral (S) plexii. In control embryos, segments L1-L3 contribute to the lumbar plexus and L3-L5 to the sacral plexus. In double-mutant embryos, axons in the two plexii were derived from more-caudal segments; L3 and L4 contributed to the lumbar plexus and L4 and L5 to the sacral plexus. Bottom panels are higher magnification images showing that the dorsal peroneal nerve (p) of the sacral plexus is missing in Hoxc10^-/-/Hoxd10^-/- mutant embryos, whereas the ventral tibial nerve (t) is still present. Arrowhead indicates a cutaneous nerve. (C) Cross-sections of lumbar spinal cord and hindlimb, through the sacral plexus, stained for β-III-tubulin. In control embryos, both the dorsal (peroneal, p) and ventral (tibial, t) branches were present, whereas in Hoxc10^-/-/Hoxd10^-/- mutants only the ventral branch was detected. Scale bars: 200 µm.