Fig. 4

Homologs of sea urchin skeletogenic genes identified in other echinoderms and expression patterns for selected candidates. Venn diagram showing the overlap of genes involved in sea urchin skeletogenesis with homologs found in other echinoderms; 494/901 are shared between four classes of echinoderms, which is a higher proportion than a set of random genes (Additional file 1: Figure S7). Whole mount in situ expression patterns in two important brittle star developmental stages for several selected candidates from different regions of overlap reveals an association with cells associated with skeleton formation. In the top right corner is depicted the currently most supported phylogeny for these four species. Schematics representing mesenchyme blastula and early gastrula stages are in the bottom right corner (in purple are shown the mesenchymal cells that will give rise to skeleton). Afi Amphiura filiformis, Pmi Patiria miniata, Ame Antedon mediterranea, Spu Strongylocentrotus prupuratus, Echi Echinoderm core (overlap of all four classes). MBl mesenchyme blastula, G gastrula