AUTHOR=Yakovenko Iryna , Tobi Dror , Ner-Gaon Hadas , Oren Matan 

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

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.1066510

DOI=10.3389/fimmu.2022.1066510

ISSN=1664-3224

ABSTRACT=<p>The closely linked recombination activating genes (<italic>RAG1</italic> and <italic>RAG2</italic>) in vertebrates encode the core of the RAG recombinase that mediates the V(D)J recombination of the immunoglobulin and T-cell receptor genes. <italic>RAG1</italic> and <italic>RAG2</italic> homologues (<italic>RAG1L</italic> and <italic>RAG2L</italic>) 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 <italic>RAGL</italic> genes that presumably originated in a common ancestral transposon. In this study, we demonstrated that two different <italic>RAG1L</italic> genes in the sea urchin <italic>Paracentrutus lividus</italic> (<italic>PlRAG1La</italic> and <italic>PlRAG1Lb</italic>) lost their mobility and, along with <italic>PlRAG2L</italic>, were fully domesticated to carry out different functions. We found that the examined echinoid <italic>RAGL</italic> homologues have distinct expression profiles in early developmental stages and in adult tissues. Moreover, the predicted structure of the proteins suggests that while <italic>PlRAG1La</italic> could maintain its endonuclease activity and create a heterotetramer with <italic>PlRAG2L</italic>, the <italic>PlRAG1Lb</italic> adopted a different function that does not include an interaction with DNA nor a collaboration with <italic>PlRAG2L</italic>. 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.</p>