REVIEW

Understanding the mechanisms that regulate the de-velopment of complex mammalian organisms is one of the most fascinating problems in biology. The coordi-nated transcriptional regulation of specific sets of genes defines the framework upon which cell determination and differentiation are established. Thus, an understand-ing of tissue-specific gene transcription will significantly advance our knowledge of mammalian development. Lymphoid differentiation, the process by which com-mitted progenitor cells give rise to both the T- and B-cell lineages, has long been used as a paradigm for studies of both tissue-specific and developmentally regulated gene expression. The following two papers review different aspects of transcriptional control during T- and B-cell development, focusing on two of the best-understoo