Evolutionary rewiring of gene regulatory network linkages at divergence of the echinoid subclasses

This work provides direct evidence of evolutionary rewiring of gene-regulatory circuitry accompanying divergence of two subclasses of echinoderm, the cidaroid and euechinoid sea urchins. These forms descend from a known common Paleozoic ancestor, and their embryos develop differently, offering an opportunity to probe the basic evolutionary process by which clade divergence occurs at the gene-regulatory network (GRN) level. We carried out a systematic analysis of the use of particular genes participating in embryonic skeletogenic cell specification, building on an established euechinoid developmental GRN. This study revealed that the well-known and elegantly configured regulatory circuitry that underlies skeletogenic specification in modern sea urchins is largely a novel evolutionary invention. The results dramatically display extensive regulatory changes in a specific developmental GRN, underlying an incidence of cladistic divergence at the subclass level.