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Fig. 8. TheBMPpathway controls dll1 expression in the developing Xenopus epidermis. (A-D′) Embryos injected in the blastocoel at stage 9 with either BSA
or BMP4 were probed for dll1 expression at stage 12 or 25. BMP4-injected embryos showed a strong and persistent upregulation of dll1 within the epidermal
inner layer. (E-F′) Eight-cell stage embryos were injected in a ventral ectoderm precursor blastomere with GFP mRNA alone (control) or with GFP mRNA and an
mRNA encoding dominant-negative Smad5 (dnSmad5). Stage 10 embryos were sectioned and hybridised with a probe against dll1 and an antibody against GFP.
The amount of dll1 signal (red) that colocalised with GFP fluorescence (green) was lower when GFP was co-injected with dnSmad5, indicating that dnSmad5
cell-autonomously decreases dll1 expression. (G,G′) The dll1 signal (red channel fluorescence) was measured in areas of equal size within (inj) or outside (non
inj) of the injected clones in control (G) and dnSmad5-injected (G′) embryos. Signals were compared pairwise within each section, confirming the significant
decrease in dll1 signal in dnSmad5-injected cells (Wilcoxon test). The middle bar indicates the median, and the outlier bars delimit the lower and upper quartiles.
(H-J′) Embryos were injected at stage 9 with BSA (H,I,J), or with BMP4 at stage 9 (H′,I′,J′) or 11 (H′,I′,J′), then probed for dll1 2 h after injection (H-H′) or at stage
12 (I-I′) and for α-tubulin at stage 25 (J-J′). BMP4 caused ectopic dll1 activation and the loss of MCCs when injected at stage 9 but not at stage 11.
(K-V) Cryosectioned embryos were hybridised with probes against dll1 and the MCC early marker foxj1 (K-N), the ionocyte early marker foxi1e (O-R) or the SSC
early marker foxa1 (S-V) at stages 11, 12 and 14, respectively. dll1 colocalised with foxj1 at stage 11, with foxi1e at stage 12 and with foxa1 at stage 14. |
