Analysis of the effect of overexpression of the f mis-spliced Madh5 mRNAs on BMP4 signaling in W-20-17 osteoblast cells. (A) Schematic representation of the f mis-spliced Madh5 mRNAs and control Madh5 mRNA. The position of the endogenous ATG is indicated in the wild-type mRNA. The asterisks indicate the positions of putative in-frame ATGs in the mis-spliced mRNAs. The arrowhead indicates the 12-nucleotide insertion between exons 6 and 7. (B) Induction of alkaline phosphatase activity by BMP4 in control W-20-17 cells and W-20-17 cells expressing wild-type or mis-splice Madh5 mRNAs. Alkaline phosphatase activity was normalized to protein concentration and expressed in relative units. Error bars represent SEM.