Fig. 8. Misexpression of Ngn1 in the chick neural tube leads to a repression of dI3 progenitor identity. Left and right sides in A-H show the control and electroporated halves of the neural tube, respectively. (A,B) Ngn1 overexpression leads to a reduction in Isl1⁺ dI3 neurons (arrowhead in B) due to decreases in Gsh2 (C,D, arrowhead in D) and Mash1 (E,F, arrowhead in F) protein expression. (G,H) Pax2⁺ dI4 and dI6 interneurons are unaffected by Ngn1 overexpression. (I-L) Expression patterns of Gsh2 and Mash1 in Ngn1/Ngn2 double knockouts. (I,J) Gsh2 expression expands beyond the dI5/dI6 boundary in Ngn1^-/-/Ngn2^-/- embryos (arrow), whereas the dorsal boundary is unchanged. (K,L) Mash1 is not markedly expanded dorsally in Ngn1/Ngn2 deficient mice, although a few ectopic Mash1⁺ cells are found dorsal to the dI2/dI3 boundary (arrowheads). Mash1 extends ventrally in the Ngn1/Ngn2 double-mutant spinal cord, when compared with wild type (arrow). (M,N) Tlx3 is hardly changed in Ngn1/Ngn2 double knockouts, although a few Tlx3⁺ cells are found dorsal to the dI2/dI3 boundary (arrowhead).