Fig. 7. msx1 lies upstream of XSlug and XSnail in the cascade leading to neural crest development. Embryos were injected in one blastomere at the two-cell stage with different combinations of HDmsx-GR and XSlug-GR (A-G) or XSnail-GR (H-N), induced at stage 12 and the expression of the neural crest markers XSlug (A,D,H,K), foxd3 (B,E,I,L) and XSnail (C,F,J,M) was analyzed at stage 18. Anterior is towards the right. The injected side detected by fluorescein staining is indicated by an arrowhead. (A-C) Embryos were injected with 500 pg of HDmsx-GR mRNA and 500 pg of XSlug-GR (ratio 1:1). Note the rescue in the expression of the neural crest markers. (D-F) Embryos were injected with 250 pg of HDmsx-GR mRNA and 750 pg of XSlug-GR (ratio 1:3). Note the rescue in the expression of the neural crest markers. (G) Summary of the expression of XSlug. The injected and uninjected side was analyzed for each embryo. Number of embryos analyzed for XSlug expression is 225. Note that the strong rescue (65%) was reached with a ratio of 1:1 for the injected mRNAs. Similar values of rescue were obtained for the other neural crest markers (72% for foxd3, total number is 225; 68% for XSnail, total number is 235). (H,I) Embryos were injected with 500 pg of HDmsx-GR mRNA and 500 pg of XSnail-GR (proportion of 1:1). Note the rescue in the expression of the neural crest markers. (K-M) Embryos were injected with 250 pg of HDmsx-GR mRNA and 750 pg of XSnail-GR (proportion of 1:3). Note the rescue in the expression of the neural crest markers. (N) Summary of the expression of XSlug. The injected and uninjected side was analyzed for each embryo. Number of embryos analyzed for XSlug expression is 215. Note that the strong rescue (67%) was reached with a ratio of 1:1 for the injected mRNAs. Similar values of rescue were obtained for the other neural crest markers (51% for foxd3, total number is 202; 62% for XSnail, total number is 215).