Development of boundary cap cells depends on neural tube-derived Wnt. (A, C) Illustration of a transverse section at E10.5 (A) and E12.5 (C) displaying cells contributing to the DRG in red. Green box represents caption area for subfigures B and D. respectively. (B, D) Double immunohistochemistry for Wls and β-gal expressed in Wnt1-Cre R26R mice shows that mesenchymal tissue and not cells populating the DRG express Wls. (B’, D’) Corresponding single fluorescence channels of the same sections. Dashed lines frame lineage-traced cells. (E, I) Illustration of a transverse section at E12.5 displaying BCCs in red. Green box represents caption area for subfigures F-H and J-M, respectively. (F-H) Double immunohistochemistry for Krox20 and neurofilament (NF). (F’-H’) Corresponding single fluorescence channels of the same sections. (G’) Dorsal BCCs are lost upon conditional knock-out of Wls using Wnt1-Cre. (H’) However, BCCs are rescued in conditional knockout of Wls using Sox10-Cre. (J-M) Double immunohistochemistry for Wls and β-gal expressed by the Cre reporter line R26R. J’-M’ and J”-M” are higher magnifications of the boxed areas in J-M, respectively. Dashed lines frame sensory axons. (J-J”, L-L”) Wls is expressed at the site where sensory axons enter the dorsal neural tube at the dorsal entry zone and strongly expressed in the roofplate (arrow, J, L) of control animals. (K-K”) Expression of Wls is lost in dorsal neural tube upon conditional knock-out of Wls using Wnt1-Cre, as evident in the roofplate (arrow, K) and the dorsal entry zone (K’,K”). (M-M”) Conditional ablation of Wls using Sox10-Cre does not affect expression of Wls in the dorsal neural tube in either the roofplate (arrow, M) or the dorsal entry zone (M’,M”). NT, neural tube; Dotted line show NT border; RP, roofplate; Scale bars: 25 μm; 10 μm in magnifications J’-M’. BCCs, boundary cap cells; DRG, dorsal root ganglia; E, embryonic day.