Indian hedgehog gene is a target of the bone morphogenetic protein signaling pathway

Bone morphogenetic proteins (BMPs), a large subgroup of the transforming growth factor-beta family of growth factors, are key mediators of many fundamental processes in embryonic development. The BMP target genes mediating these effects and the mechanism of their selective regulation are poorly characterized. In this study, we used a chromatin immunoprecipitation-based gene cloning method to identify BMP target genes in a mouse embryonic carcinoma cell line. We identified the Indian hedgehog (Ihh) gene as a target of BMP signaling. Both reporter and reverses transcription-PCR assays revealed that Ihh is up-regulated in embryonic cells upon BMP treatment. The BMP response element of the Ihh promoter contains multiple GC-rich motifs known as the "Mad/Medea binding box" found in the Drosophila tinman gene and in the mouse Id1 gene. DNA binding studies revealed that Smad4 binds to these GC-rich motifs. These findings indicate that BMP stimulates Ihh expression. We also suggest expression of the Ihh gene, which contains multiple Smad binding sites, might be finely regulated by a gradient of BMP concentrations.