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

Murine studies implicate Ikaros proteins as regulators of hemopoiesis, particularly in the lymphoid lineages. High homology between murine and human Ikaros suggests that Ikaros expression in the two might be similar. However, initial human studies that focused on leukemia detected novel Ikaros transcripts in patient samples. Thus, novel Ikaros splice forms and DNA nonbinding isoforms were linked with malignancy. We undertook an extensive analysis of normal human Ikaros expression to determine whether novel mRNAs are expressed 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 Ikaros isoforms and splice variants previously linked to leukemia are expressed in normal human cells. However, our studies identify a new Ikaros isoform not previously described in mouse or human. This isoform is the predominant Ikaros protein in normal human cells, but not in leukemia cell lines.