The role of the Ikaros gene in lymphocyte development and homeostasis.
The Ikaros gene, which encodes a family of hemopoietic-specific zinc finger proteins, is described as a central regulator of lymphocyte differentiation. During fetal development, it is required at the earliest stage of T cell and B cell specification. In the adult, however, lymphoid lineages rely on Ikaros at distinct phases of their development. Its activity is essential for the generation of B cell but not of T cell precursors, although the differentiation of the latter is not normal. A significant increase in CD4 thymocytes and their immediate precursors is detected, and because these cells lack markers that correlate with positive selection, a deregulation in their maturation process is suggested. Furthermore, Ikaros-null thymocytes hyperproliferate in response to T cell receptor (TCR) signaling; within days after their appearance in the thymus, clonally expanding populations are detected. Deregulated TCR-mediated responses and the fast kinetics of tumor development in these mutant thymocytes implicate Ikaros as a central tumor suppressor gene for the T cell lineage. In addition, lack of natural killer cells and selective defects in gamma delta T cells and dendritic antigen-presenting cells point to Ikaros as an essential factor for the establishment of early branchpoints of the T cell pathway. The dominant interference activity of Ikaros isoforms unable to bind DNA and their effects in lymphocyte development suggest that Ikaros works in concert with other factors. The role of Aiolos, a lymphoid-restricted and structurally related gene, in lymphoid differentiation is discussed. A model is proposed that defines Ikaros as the backbone of a complex regulatory protein network that controls cell fate decisions and regulates homeostasis in the hemo-lymphoid system. Changes in this regulatory network may reflect differentiation and proliferation adjustments made in hemo-lymphoid progenitors and precursors as they give rise to the cells of our immune system.
Georgopoulos
K
K
Cutaneous Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
Winandy
S
S
Avitahl
N
N
D000328:Adult; D000818:Animals; D002454:Cell Differentiation; D004268:DNA-Binding Proteins; D016147:Genes, Tumor Suppressor; D006410:Hematopoiesis; D006706:Homeostasis; D006801:Humans; D051740:Ikaros Transcription Factor; D008214:Lymphocytes / Q000166:cytology* / Q000276:immunology; D008954:Models, Biological; D009154:Mutation; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology; D015534:Trans-Activators / Q000235:genetics / Q000276:immunology / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics* / Q000276:immunology* / Q000502:physiology; D016335:Zinc Fingers / Q000235:genetics / Q000276:immunology / Q000502:physiology
D004268:DNA-Binding Proteins; C497239:IKZF1 protein, human; C106285:IKZF3 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D051740:Ikaros Transcription Factor