Fig. 5. spt and ntl together are required for spinal cord medial floor plate formation. Expression of sonic hedgehog (shh) in ventral brain, medial floor plate (MFP), and posterior notochord and of krox20 in wild-type (A) and mutant (B-D) embryos at 24 hpf. Posterior MFP irregularities, such as broadening, are noted in ntl^– (B) and spt^– (C) embryos, but MFP is conspiciously missing in spt^–;ntl^– embryos (D), beginning approximately at the end of the hindbrain. Lateral views, with anterior to the left. Scale bar: 100 µm.

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