A Genome-Scale Analysis of the Cis-Regulatory Circuitry Underlying Hedgehog Mediated Patterning of the Mammalian Limb

Sonic hedgehog (Shh) signals via Gli transcription factors to direct digit number and identity in the vertebrate limb. We have characterized the Gli-dependent cis-regulatory network through a combination of whole genome ChIP-on-chip and transcriptional profiling of the developing mouse limb. These analyses identified approximately 5,000 high quality Gli3 binding sites, including all known Gli-dependent enhancers. Discrete binding regions exhibit a higher-order clustering, highlighting the complexity of cis-regulatory interactions. Further, Gli3 binds inertly to previously identified neural-specific Gli enhancers, demonstrating the accessibility of their cis-regulatory elements. Intersection of DNA binding data with gene expression profiles predicted 205 putative limb target genes. A subset of putative cis-regulatory regions were analyzed in transgenic embryos, establishing Blimp1 as a direct Gli target and identifying Gli-activator signaling in a direct, long-range regulation of the BMP antagonist Gremlin. In contrast, a long range silencer cassette downstream of Hand2 likely mediates Gli3 repression in the anterior limb. These studies provide the first comprehensive characterization of the transcriptional output of a Shh-patterning process in the mammalian embryo and a framework for elaborating regulatory networks in the developing limb. This SuperSeries is composed of the SubSeries listed below. Refer to individual Series