Fig. 3. Removal of the presomitic mesoderm elicits premature neuronal differentiation and the down regulation of CNP-specific genes. (C,E,H,J,L,N,P,R are transverse sections.) (A) Diagram illustrating removal of PSM at stage 7+ and the embryo 6 hours later. (B,C) Depletion of NeuroM-expressing cells in neural tube developing following PSM removal. S1, most recently formed somite on un-operated side. (D,E) Sox2 expression is unaffected by PSM removal. (F) Diagram of the removal of somites at stage 8/8+ and the embryo 6 hours later. (G,H) Depletion of NeuroM-expressing cells following somite removal. S, first somite formed after removal on operated side. (I,J) Sox2 and (K,L) Delta 1 are unaffected by somite removal. (M,N) NeuroM expression extends into the PNT in the absence of PSM. (O,P) Removal of PSM also down regulates cash4 and (Q,R) Sax1 in the PNT. Tissue between arrowheads in B,G,M,O and Q are regions of ectopic (M) or absent gene expression (B,G,O,Q). Scale bars: (B,D,G,I,K,M,O,Q) 100 µm; (C,E,H,J,L,N,P,R) 100 µm.