Fig. 1. Gsh2 is expressed in the progenitors of the dI3, dI4 and dI5 neurons in the embryonic spinal cord. (A-D) A subset of Pax7⁺ cells express Gsh2. (E,F) At E10.5 and E11.5, Gsh1/Gsh2 expression encompasses dI3, dI4 and dI5 progenitor domains. (G,H) Mash1 is expressed in the same dorsal progenitor domain as Gsh1/Gsh2. (I,J) The bHLH protein Ngn1 is expressed in adjacent domains dorsal and ventral to Gsh2⁺ and Mash1⁺ progenitors. (K) Gsh2 is homogeneously expressed in all Pax3⁺ dI3 progenitors. (L) Ngn1 marks 50% of Pax3⁺ cells in the dI2 ventricular domain. (M) Ngn1 and Gsh2 are expressed in adjacent domains in the dorsal neural tube; this image is an overlay of staining for Gsh1/Gsh2 and Ngn1 of the adjacent sections shown in K and L. (N) Ventricular dividing cells, marked by BrdU, express Gsh2 in dI3 progenitors. (O) Ngn1 is expressed by some of the cells marked after a 1.5-hour pulse of BrdU. (P-S) The Gsh1/Gsh2-positive domain gives rise to dI3, dI4 and dI5 neurons. (P,Q) dI4 neurons expressing both Lhx1/Lhx5 and Lbx1 arise ventrolateral to the most dorsal Gsh2⁺ domain, whereas the most ventral Gsh2⁺ domain gives rise to Lbx1⁺ dI5 neurons that do not express Lhx1/Lhx5. (R,S) Isl1⁺ and Brn3a⁺ dI3 neurons arise from the most dorsal Gsh2⁺ progenitor domain. (T) Schematic summary of the expression of several transcription factors in alar plate progenitors.