Fig. 6

Summary and comparison of regulatory states and minimal GRN rewiring between A. filiformis and sea urchin. a Regulatory states (left) and GRN model (right) for S. purpuratus. Regulatory states for the mesodermal territories are shown on cellular maps of cleavage (Cl), pre-hatching blastula (EBl), hatched blastula (Bl) and mesenchyme blastula (MBl). The dark green represents the skeletogenic mesoderm (SM), the light green represents the non-skeletogenic mesoderm (NSM), and the blue represents the endodermal territory. At mesenchyme blastula, the NSM is divided into precursors of pigment cells (orange) and other NSM precursors (light green). Genes expressed in each territory are listed. S. purpuratus SM-GRN architecture, modified from [2], of the genes analyzed in this study. Arrows indicate positive inputs (activation) and barred line negative inputs (repression). Dashed lines represent functional linkages inferred by perturbation data in [2] for 1 and [16] for 2. Ubq represents an inferred ubiquitous activator necessary for the expression of some of the genes downstream of the DNG. b Regulatory states (left) and potentially conserved GRN linkages (right) for A. filiformis. Regulatory states for the mesodermal territories are shown on cellular maps of pre-hatching blastula (EBl), hatched blastula (Bl), and mesenchyme blastula (MBl). The light green cells represent the mesoderm identified by the expression of pan-mesodermal genes. The dark green represents the here named SM cells expressing the skeletogenic marker genes alx1, jun, p58a, p58b, and p19; blue dots represent the expression of hesC and foxA within the mesoderm territory, while blue cells represent the endodermal territory that surrounds the mesoderm. At blastula stage, the SM is clearly separated from the rest of NSM, while the segregation of NSM and endoderm occurs at MBl stage. Genes expressed in each territory are listed. A hypothetical A. filiformis GRN including nodes and potentially conserved linkages represented as in (a) and based on the observations in this study. EM represents the minimal hypothetical positive input necessary for the hesC expression in the endomesoderm. M represents hypothetical pan-mesodermal positive input(s) necessary to drive the expression in all mesodermal cells. R represents hypothetical repressor(s) expressed in cells expressing only pan-mesodermal genes. SM represents the minimal hypothetical positive input necessary for erg to be expressed in the subset of mesodermal cells. This hypothetical model highlights the differences (nodes and linkages) based on the expression data. As discussed in the text, we parsimoniously assume that, in absence of functional data, linkages are conserved with sea urchin, but we cannot exclude alternative hypotheses