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 advance in the past year toward understanding RAG regulation is the establishment of green fluorescent protein (GFP)–RAG indicator mouse strains. In vivo visualization of RAG expression in single cells has helped to define the cells that express RAGs in secondary lymphoid organs and revealed differential cis requirements for stage- and lineage-specific RAG expression.