Fig. 1. Development of ßgal expression in dorsal regions of W^lacZ/+ embryos. (A) Low-power view through the trunk section of an E9.5 embryo. (B) High-power view reveals faint ßgal⁺ cells (arrow) within the dorsal midline at E9.5. (C) Low-power view through the trunk at the level of the forelimb of an E10.5 embryo. (D) High-power view of the dorsal midline reveals strong ßgal⁺ cells (filled arrow) on the dorsal midline of the NT. (E) High-power view of the ectoderm reveals strong ßgal⁺ cells (filled arrows). There are also ßgal⁺ cells in ventrolateral regions of the NT and surrounding it (open arrows in C and E). ect, ectoderm. Scale bars: 250 µm in A,C; 50 µm in B,D,E.