VDJ Recombination : Artemis and Its In Vivo Role in Hairpin Opening

Artemis is the newest player in VDJ recombination and double strand break repair. First identified in radiation-sensitive and immune-deficient patients, it was recently shown to interact with DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and have nuclease activity, becoming the most popular candidate for the opening of hairpin coding ends. Reports presented in this issue (1) and in the December issue of Molecular Cell (2) address the role of Artemis in vivo by studying the effect of its deletion on the generation of intermediates and products of VDJ recombination in mouse ES cells, MEFs, and thymocytes. In all three systems analyzed, a defect in coding joint formation was observed, which was highly dependent on the cellular background and included inefficient and partially defective opening of hairpin coding ends. In addition, Artemis-deficient ES cells and Artemis-deficient MEFs show spontaneous chromosomal abnormalities, including telomere...