Fig. 4. A gradient of VZ precursor differentiation is defined in the LGE by the expression of GSH2, MASH1 and DLX2. At E9.5, GSH2 (A) was expressed by precursors within the LGE (P1 precursors). (B) MASH1 was expressed in a small population of VZ precursors, and all MASH1+ cells co-expressed GSH2 in the primordial LGE (P2 precursors; C). (D) A few DLX2+ cells were present at E9.5, primarily near the pial surface of the neuroepithelium. All DLX2+ cells co-expressed MASH1 at this stage (E,F; presumptive GSH2+MASH1+DLX2-expressing P3 precursors). At E12.5, GSH2 expression appeared within the VZ (G), while MASH1 expression was relatively low in the VZ, but increased towards the SVZ (H). GSH2 and MASH1 double labeling revealed a molecular gradient from GSH2 (P1 precursors) to GSH2/MASH1 (P2 and P3 precursors) and MASH1 alone (presumptive P4 precursors) expressing precursors (I). DLX2 was also expressed in a VZ to SVZ gradient (J). MASH1 expression demonstrated a similar gradient of expression (K) and double-labeling (L), suggesting that farther from the ventricular surface precursors increasingly expressed MASH1, MASH1/DLX2 (P3 and P4 precursors) and (finally) DLX2 alone (P5 precursors). CNTFR was expressed by a subpopulation of GSH2+ cells close to the ventricular surface (M; arrow indicates example of a double-positive cell). LIFRß expression was similar to CNTFR, and very few MASH1+ cells co-expressed LIFRß (N; arrow indicates a double-positive cell). FGFR2 and MASH1 double labeling also revealed only a very small population of co-expressing cells (O; arrow indicates double-labeled cell). (P) The proposed gradient of VZ precursor differentiation and a potential role for CNTF/LIF/gp130 signaling in maintaining the P1 precursor population within the gradient (see Results and Discussion for details). Scale bar: 50 µm and 100 µm in enlarged images.