An NF-κB and Slug Regulatory Loop Active in Early Vertebrate Mesoderm
To analyze the timing of Slug activity in the early embryo, we injected one cell of two cell embryos with Slug MO (10 ng/embryo) together with RNA (650 pg/embryo) encoding the chimeric GR-Slug-GFP protein. A: In the absence of the activating drug dexamethasone, the Slug MO phenotype, i.e. suppression of Xbra expression in stage 11 embryos (A)(arrow) and suppression of Sox9 expression in stage 16 embryos (D), was unaltered. When embryos were treated with dexamethasone (20 µM) beginning at stage 8, there as an essentially complete rescue of Xbra (B,C) and Sox9 expression (E,H). Treatment of embryos with dexamethasone at stage 11 (early gastrulation) was also effective at rescuing Sox9 expression (F,H), while addition of dexamethasone at stage 13 (late gastrulation/early neurulation) produced at most a partial and inefficient rescue of Sox9 expression (G,H).