Figure 6.

 Failure of motor neuron and ventral interneuron development in the absence of Noggin. Section in situ hybridization at the level of the forelimb (A,B), between the limbs (C,D,G,J), and at the hindlimb (E–H) level in 10.5 dpc embryos heterozygous (A,C,E,G,I,K) or homozygous (B,D,F,H,J,L) for the targeted Noggin allele. Differentiating motor neurons or their precursors (short arrow) were detected with an Islet-1 probe (A–F), which also hybridizes to transcripts in dorsal root ganglia (barbed arrow) or with an Nkx2.2 probe (G,H). Differentiating ventral interneurons were detected by En-1 expression (I,J), and notochord and floor plate by Shh (K,L). (For abbreviations, see legend to Fig. 5.) Pairwise comparisons were photographed at the same magnification.