Fig. 9. Patterns of SMAD responses reveal stepwise changes in BMP activity. (A) When nuclear Medea was detected during stage 5, it was at uniformly low levels across about 24 dorsal nuclei, and then declined across four nuclei at each edge. (B) At the beginning of stage 6, a narrow stripe of more intense nuclear Medea staining was detected at the dorsal midline. Nuclear Medea was no longer detected in dorsolateral regions, even though staining levels rose at the dorsal midline. (C) Levels of nuclear Medea peaked in dorsal midline cells during stage 7, and adjacent domains of low nuclear Medea became detectable on either side. At this stage, the entire nuclear Medea response domain was not as wide as the initial response domain during stage 5. (D) Stage 6 sog hemizygous embryos (no Sog) had a broad domain with low levels of nuclear Medea and PMAD. Levels were higher than wild-type stage 5 embryos, but did not reach the peak levels seen in wild type. (E) Heterozygous dpp embryos (1X dpp) formed a narrow dorsal midline stripe, but the levels of nuclear Medea and PMAD did not reach the peak levels seen in wild type. During stages 7 and 8, a narrower stripe was sometimes evident in the cephalic region of these embryos.

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