Sp8 regulatory function in the limb bud ectoderm [ChIP-seq]

Sp8 and Sp6, members of the Sp family of transcription factors, are required in a dose-dependent manner to induce Fgf8 and En1 in the limb bud ectoderm, therefore controlling proximo-distal and dorso-ventral limb development. Mouse genetics revealed that Sp8 makes a much greater contribution than Sp6 but the nature of its regulatory mechanism was unknown. Here, by combining ChIP-seq and RNA-seq genome-wide analyses we show that Sp8 predominantly functions as an activator from putative distal enhancers regulating crucial limb patterning genes and underscoring its master role in limb development. We also provide compelling evidence for Sp8 cooperating with Dlx5 for the regulation of a considerable set of its target genes. Our work supports a model in which Sp8, Sp6 and Dlx5 act conjointly to regulate target genes with a final functional outcome that depends on their relative availability. This should be considered when interpreting Sp and Dlx mutant phenotypes. Overall design: Genome-wide binding profiles for SP8 and H3K4me2 were investigated in mouse E10.5 forelimb ectoderm using ChIP-seq.