The transcription factors encoded by the E2A gene are critical for the initiation of B cell development in the bone marrow. In the early Edition of the Proceedings of the National Academy of Sciences, Stephen Greenbaum and Yuan Zhuang report the identification of target genes regulated by E2A in lymphoid cells (PNAS, doi/10.1073/pnas. 212458899, 28 October, 2002).

Greenbaum and Zhuang combined an in vivo murine gene-tagging approach with a chromatin immunoprecipitation assay. Mice were generated carrying a dual affinity-tagged E2A knock-in allele and the resulting fusion protein was observed to have no affect on lymphoid development, but provided a powerful tool for immunoprecipitation analysis. They also observed a selective enrichment of known gene targets implicated in B cell lineage differentiation. Cloned immunoprecipitated DNA fragments identified novel E2A targets.

This is the first example of an in vivo murine gene–tagging approach to isolate target genes of an...