Fig. 6. Analysis of W^lacZ/+ embryos in the head shows that Kit⁺ cells at the dorsal midline of the midbrain-hindbrain junction give rise to melanocytes. (A) Dorsolateral view of the rostral region of a whole-mount embryo at E10.5, showing ßgal⁺ cells emanating from the dorsal aspect of the midbrain-hindbrain junction. ßgal⁺ cells emanate caudolaterally as a stream through the mesenchyme adjacent to the hindbrain, as well as to the ectoderm (asterisk). (B) Transverse section through an E10.5 embryo at the midbrain-hindbrain junction, showing ßgal⁺ cells on the dorsal midline and ectoderm. A high-power view of the same region stained for p75 and ßgal is shown in the inset; strong p75 staining is on surface of embryo. (C) Lateral and (D) dorsal views of an E11 embryo, showing increasing distribution of ßgal⁺ cells through ectoderm (asterisk). (E) Transverse section through the rostral hindbrain of an E10.5 embryo at level indicated by broken line in C, stained for ßgal (red) and Trp2 (green). The border between the mesenchyme and neural tube is indicated with a dotted line. Some ßgal⁺ cells are also present on base of roof plate (A,C, open arrow). rp, roof plate; st, stream. Scale bars: 500 µm in A,C,D; 200 µm in B; 50 µm in E.