Regulation of RAG expression in developing lymphocytes

Proper expression of products of the recombination-activating genes (RAGs) is essential for the development of the adaptive immune system. A major adv ance in the past year toward understanding RAG regulation is the establishm ent of green fluorescent protein (GFP)-RAG indicator mouse strains. In vivo visualization of RAG expression in single cells has helped to define the c ells that express RAGs in secondary lymphoid organs and revealed differenti al cis requirements for stage- and lineage-specific RAG expression.