Project description: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.
Project description: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.
Project description:The physical forces that drive morphogenesis are not well characterized in vivo, especially among vertebrates. In the early limb bud, dorsal and ventral ectoderm converge to form the apical ectodermal ridge (AER), although the underlying mechanisms are unclear. By live imaging mouse embryos, we show that prospective AER progenitors intercalate at the dorsoventral boundary and that ectoderm remodels by concomitant cell division and neighbour exchange. Mesodermal expansion and ectodermal tension together generate a dorsoventrally biased stress pattern that orients ectodermal remodelling. Polarized distribution of cortical actin reflects this stress pattern in a ?-catenin- and Fgfr2-dependent manner. Intercalation of AER progenitors generates a tensile gradient that reorients resolution of multicellular rosettes on adjacent surfaces, a process facilitated by ?-catenin-dependent attachment of cortex to membrane. Therefore, feedback between tissue stress pattern and cell intercalations remodels mammalian ectoderm.
