Xenopus steel and c-kit are expressed at the right time and place to support primitive blood development. (A) Ribonuclease protection analysis of the temporal pattern of expression of Xsl-1. FGFR is included as a loading control and protects a doublet. (B-C) Expression of Xsl-1 (B) and c-kit (C) analyzed by whole-mount in situ hybridization at stages 12 and 17; cg indicates cement gland; nf, neural fold; np, neural plate. Arrows point to prospective VBI. (D) In situ hybridization of Xsl-1 and c-kit riboprobes to sagittal sections of stage 12.5 embryos. Both are expressed in the ectoderm (arrowhead), whereas c-kit is also expressed in prospective ventral mesoderm (arrow). (E) Expression of c-kit analyzed by whole-mount in situ hybridization at stages 24 and 32.