Fig. 2. (A) RT-PCR analysis showing that explants injected with noggin or cerberus mRNAs express six1, whereas control and bmp4-injected explants do not. H4, loading control. (B) Explants were cultured in different concentrations of Noggin, and processed for six1 expression at stage 17. The largest percentage of explants stained at high levels was observed between 1 and 5 ng/ml of Noggin. (C) BMP4 antagonizes the 1 ng/ml Noggin-induction of six1. (D) Explants were cultured as in B, and the percentage of explants with high levels of marker gene expression were plotted.