Regulation of eosinophils by the transcription factor Ikaros

Abstract Immune cell development is a tightly controlled process that enables a homeostatic level of innate and adaptive immune cells of the myeloid and lymphoid lineages, respectively. Imbalance in immune cells can lead to diseases due to immune defects or over-activation. such as immunodeficiency, allergies or autoimmunity. Ikaros is a transcription factor known to be critically important for lymphoid development, with recurrent mutations in different human diseases, but less is known about the role of Ikaros in myeloid development. Ikaros is encoded by the Ikzf1gene, and contains four DNA-binding zinc fingers (ZnF) and two ZnFs mediating protein dimerization. The four DNA-binding ZnFs (ZnF1 through ZnF4) are encoded by three exons, with the two central ZnF2 and ZnF3 encoded by exon 5 being required for binding to the core DNA recognition site. The two flanking ZnFs 1 and 4 are encoded by exon 4 and exon 6, and can modulate DNA binding by contacting the flanking DNA. Interestingly, Ikaros is highly alternatively spliced, creating multiple isoforms with different combinations of the DNA-binding ZnFs. We study the role of Ikaros in immune cell development using Ikzf1-mutant mouse models, and analysis of mice with deletions of exon 4 or exon 6 (encoding ZnF1 and ZnF4, respectively) has revealed differential phenotypes in the two mutant mouse models. Here, we describe a new role of Ikaros in regulation of eosinophils. We have found that Ikaros is required for limiting eosinophil production in bone marrow (BM), as both mutants show increased levels of BM eosinophils. Interestingly, the levels of peripheral tissue eosinophils differ between the two mutants, suggesting a second role of Ikaros in regulating migration, tissue recruitment or retention.