Fig. 4. Neither spt nor ntl function is required for most dorsal-ventral spinal cord patterning. (A,E,I,M) Wild-type, (B,F,J,N) ntl^–, (C,G,K,O) spt^–, and (D,H,L,P) spt^–;ntl^– embryos. (A-D) pax2.1 interneuron expression at 24 hpf, (E-L) islet1 expression at the 8-10 somite stage (13-14 hpf); arrowheads indicate primary motoneurons and arrows indicate Rohon-Beard neurons. (M-P) sonic hedgehog (shh) and krox20 expression at the late gastrula stage (9.5 hpf). Transverse sections (A-D; I-L) are approximately from midtrunk levels. Anterior is to the top. Scale bars: 25 µm (A-D and I-L), 100 µm (E-H and M-P).