Ikaros, an Early Lymphoid-Specific Transcription Factor and a Putative Mediator for T Cell Commitment

In a screen for transcriptional regulators that control differentiation into the T cell lineage, a complementary DNA was isolated encoding a zinc finger protein (Ikaros) related to the Drosophila gap protein Hunchback. The lkaros protein binds to and activates the enhancer of a gene encoding an early T cell differentiation antigen, CD3δ. During development, Ikaros messenger RNA was first detected in the mouse fetal liver and the embryonic thymus when hematopoietic and lymphoid progenitors initially colonize these organs; no expression was observed in the spleen or the bone marrow. The pattern of Ikaros gene expression and its ability to stimulate CD3δ transcription support the model that Ikaros functions in the specification and maturation of the T lymphocyte.