Figure 2: Short-term radioprotection and repopulation ability is unaffected by the Ikaros mutation but severely compromised by the Ikaros DN mutation. (A) Short-term radioprotective ability of wild-type and Ikaros mutant BM. Ly5a congenic mice were lethally irradiated (9.5 Gy) and injected with 105 wild-type BM (▪), 105 Ikaros −/− BM (□), 106 Ikaros DN−/− BM (▴), or PBS alone (○). The numbers of mice injected per donor group are given in the legend, and their age was 3–4 wk. (B) Donor contribution in the myeloid lineage after transplant with wild-type and Ikaros mutant BM. Ly5a congenic mice were lethally irradiated and injected with 106 wild-type BM (gray bars), 106 Ikaros BM (left panel, hatched bars), or 6 × 106 Ikaros DN−/− BM (right panel, hatched bars). At the indicated time points after transplant, recipients were bled and assayed for donor contribution to the myeloid (Mac-1+) lineage by FACS™ analysis. A pool of four wild-type or mutant mice was used as a donor population. The experiment was repeated twice, and data shown are the analysis of one representative mouse out of eight recipients. (C) Development of lethal anemia in recipients of Ikaros DN−/− BM. 5 × 106 Ikaros DN−/− (•) or wild-type (□) BM cells were transplanted into lethally irradiated recipients, and recipient hematocrits were monitored over 5 wk. Recipients of Ikaros DN−/− BM (•) eventually died of anemia 5 wk after transplant. Numbers of mice bled were as follows: +/+ recipients, n = 12; and Ikaros DN−/− recipients, n = 28. Donors were 2–4 wk old.

Mentions: Ikaros and wild type BM cells, when given at a dose of 105 cells, radioprotected 100% of the lethally irradiated (900 rads) recipients for at least 30 d after transplant (Fig. 2 A). Animals receiving 106 Ikaros BM had almost 100% donor contribution to the myeloid (Mac-1+) lineage 7 mo after transplant (Fig. 2 B, left). Ikaros DN−/− BM cells provided at doses of 1–6 × 106 were capable of only short-term radioprotection at first (Fig. 2 A), with a steady decrease in donor contribution observed between 3.5 and 5 wk after transplant (Fig. 2 B, right). The hematocrits of Ikaros DN−/− BM recipients also decreased during this time period. 3 wk after transplant, hematocrits of Ikaros DN−/− BM recipients were <50% of wild-type BM recipients, and by day 35 they were down to one-third of wild-type values (Fig. 2 C). All recipients of Ikaros DN−/− BM died by day 35 after transplant from severe anemia.

Nichogiannopoulou A, Trevisan M, Neben S, Friedrich C, Georgopoulos K - J. Exp. Med. (1999)

Bottom Line: A progressive reduction in multipotent CFU-S(14) (colony-forming unit-spleen) progenitors and the earliest erythroid-restricted precursors (BFU-E [burst-forming unit-erythroid]) is also detected in the Ikaros mutant strains consistent with the reduction in HSCs.Nonetheless, the more mature clonogenic erythroid and myeloid precursors are less affected, indicating either the action of a compensatory mechanism to provide more progeny or a negative role of Ikaros at later stages of erythromyeloid differentiation.In Ikaros mutant mice, a decrease in expression of the tyrosine kinase receptors flk-2 and c-kit is observed in the lineage-depleted c-kit(+)Sca-1(+) population that is normally enriched for HSCs and may in part contribute to the early hemopoietic phenotypes manifested in the absence of Ikaros.

Affiliation: Cutaneous Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.

Abstract: Here we provide evidence that the Ikaros family of DNA binding factors is critical for the activity of hemopoietic stem cells (HSCs) in the mouse. Mice homozygous for an Ikaros mutation display a >30-fold reduction in long-term repopulation units, whereas mice homozygous for an Ikaros dominant negative mutation have no measurable activity. The defect in HSC activity is also illustrated by the ability of wild-type marrow to repopulate unconditioned Ikaros mutants. A progressive reduction in multipotent CFU-S(14) (colony-forming unit-spleen) progenitors and the earliest erythroid-restricted precursors (BFU-E [burst-forming unit-erythroid]) is also detected in the Ikaros mutant strains consistent with the reduction in HSCs. Nonetheless, the more mature clonogenic erythroid and myeloid precursors are less affected, indicating either the action of a compensatory mechanism to provide more progeny or a negative role of Ikaros at later stages of erythromyeloid differentiation. In Ikaros mutant mice, a decrease in expression of the tyrosine kinase receptors flk-2 and c-kit is observed in the lineage-depleted c-kit(+)Sca-1(+) population that is normally enriched for HSCs and may in part contribute to the early hemopoietic phenotypes manifested in the absence of Ikaros.