Different sea urchin RAG-like genes were domesticated to carry out different functions.

The closely linked recombination activating genes ( and ) in vertebrates encode the core of the RAG recombinase that mediates the V(D)J recombination of the immunoglobulin and T-cell receptor genes. and homologues ( and ) are present in multiple invertebrate phyla, including mollusks, nemerteans, cnidarians, and sea urchins. However, the function of the invertebrates' RAGL proteins is yet unknown. The sea urchins contain multiple genes that presumably originated in a common ancestral transposon. In this study, we demonstrated that two different genes in the sea urchin ( and ) lost their mobility and, along with , were fully domesticated to carry out different functions. We found that the examined echinoid homologues have distinct expression profiles in early developmental stages and in adult tissues. Moreover, the predicted structure of the proteins suggests that while could maintain its endonuclease activity and create a heterotetramer with , the adopted a different function that does not include an interaction with DNA nor a collaboration with . By characterizing the different RAG homologues in the echinoid lineage, we hope to increase the knowledge about the evolution of these genes and shed light on their domestication processes.