Cutting edge: Predominant expression of a novel Ikaros isoform in normal human hemopoiesis

Murine studies implicate Ikaros proteins as regulators of hemopoiesis, part icularly in the lymphoid lineages. High homology between murine and human I karos suggests that Ikaros expression in the two might be similar. However, initial human studies that focused on leukemia detected novel Ikaros trans cripts in patient samples. Thus, novel Ikaros splice forms and DNA nonbindi ng isoforms were linked with malignancy. We undertook an extensive analysis of normal human Ikaros expression to determine whether novel mRNAs are exp ressed as proteins and the extent to which these splice variants are unique to leukemia. Here we show that both mRNA and protein for DNA nonbinding Ik aros isoforms and splice variants previously linked to leukemia are express ed in normal human cells. However, our studies identify a new Ikaros isofor m not previously described in mouse or human. This isoform is the predomina nt Ikaros protein in normal human cells, but not in leukemia cell lines.