Project description:The emergence and evolution of digits was an essential step in the success of the tetrapod lineage. Amongst the key players, Hoxd genes were functionally co-opted in the developing digital plate, where they help organize growth and patterns. To understand both the evolutionary recruitment and transcriptional regulation of this genomic locus, we analyzed its architecture and chromatin status in developing digits, combined with a deletion approach in vivo. We show that the active and inactive parts of the gene cluster adopt opposite spatial configurations, corresponding to different chromatin domains. Active genes are contacted by several regulatory islands, located within a neighboring gene desert, which contribute quantitatively or qualitatively to the global transcriptional readout. We refer to this novel type of control as a ‘regulatory archipelago’ and discuss the value of this concept to understand both the morphological flexibility of tetrapod digits and the robustness of the underlying developmental process. Distribution of histone marks and RNA Pol2 at the Hoxd locus in developing limbs and brain at E12.5
Project description:The emergence and evolution of digits was an essential step in the success of the tetrapod lineage. Amongst the key players, Hoxd genes were functionally co-opted in the developing digital plate, where they help organize growth and patterns. To understand both the evolutionary recruitment and transcriptional regulation of this genomic locus, we analyzed its architecture and chromatin status in developing digits, combined with a deletion approach in vivo. We show that the active and inactive parts of the gene cluster adopt opposite spatial configurations, corresponding to different chromatin domains. Active genes are contacted by several regulatory islands, located within a neighboring gene desert, which contribute quantitatively or qualitatively to the global transcriptional readout. We refer to this novel type of control as a ‘regulatory archipelago’ and discuss the value of this concept to understand both the morphological flexibility of tetrapod digits and the robustness of the underlying developmental process. Transcriptional activity at the Hoxd locus in developing limbs and brain at E12.5
Project description:During limb development, Hoxd genes are transcribed in two waves: Early on, when the arm and forearm are specified and subsequently, when digits form. While the latter phase is controlled by enhancers centromeric to the HoxD cluster, we show here that the early phase requires enhancers located in the opposite telomeric gene desert. The transition between the two types of regulations involves a functional switch between two distinct topological domains, as reflected by a subset of genes mapping centrally into the cluster, which initially interact with the telomeric domain and subsequently shift to establish new contacts on the opposite side. This transition between two regulatory landscapes generates an intermediate area of low Hox dose developing into the wrist, the transition between our arms and our hands. This intriguing correspondence between genomic and morphological boundaries illustrates the mechanism underlying collinear Hox gene regulation in our developing appendages. Circular Chromosome Conformation Capture (4C seq) at the HoxD locus in developing proximal and distal limbs at E9.5 and E12.5
Project description:The emergence and evolution of digits was an essential step in the success of the tetrapod lineage. Amongst the key players, Hoxd genes were functionally co-opted in the developing digital plate, where they help organize growth and patterns. To understand both the evolutionary recruitment and transcriptional regulation of this genomic locus, we analyzed its architecture and chromatin status in developing digits, combined with a deletion approach in vivo. We show that the active and inactive parts of the gene cluster adopt opposite spatial configurations, corresponding to different chromatin domains. Active genes are contacted by several regulatory islands, located within a neighboring gene desert, which contribute quantitatively or qualitatively to the global transcriptional readout. We refer to this novel type of control as a ‘regulatory archipelago’ and discuss the value of this concept to understand both the morphological flexibility of tetrapod digits and the robustness of the underlying developmental process. Chromosome Conformation Capture-on-chip analysis (4C) at the Hoxd locus in developing limbs and brain at E12.5