Fig. 4. Autocrine BMP pathway in ES cells. Noggin and BMP were added to reporter ES cell lines (A) BRE-luc and (B) BRE-lac2 at different concentrations to assess the reporter activity in response to activation/inhibition in vitro. The same results were obtained in BRE-lac1 ES cells (results not shown). (C) Id1 protein levels in a western blot correlated with the reporter activity in BRE-lac2 protein extracts. Equal amounts of protein (10 µg) were loaded in each lane and confirmed with Ponceau S staining; nonspecific bands are shown as loading control (l.c.). Results are presented as the mean of triplicate experiments (mean±s.d.).