Synergistic Role of Igf2 and Dlk1 in Fetal Liver Development and Hematopoiesis in Bi-Maternal Mice

Abstract

Mouse bi-maternal embryos (BMEs) that contain two haploid sets of genomes from non-growing (ng) and fully-grown (fg) oocytes develop to embryonic day (E) 13.5. However, the ng/fg BMEs never develop beyond E13.5 because of repression of the paternally expressed imprinted genes, Igf2 and Dlk1. The present study was conducted to address the issue of whether fetal hematopoietic disorder is involved in the restricted development of BMEs. FACS analysis revealed that the livers of ng(wt)/fg BMEs contained increased numbers of immature c-kit(+)/ter119(-) hematopoietic cells, were while the numbers of mature c-kit(-)/ter119(+) hematopoietic cells were decreased. This finding was supported by histological observations. Quantitative gene expression analysis revealed that Igf2 and Dlk1 expression was repressed in the liver. To understand the role of paternally-methylated imprinted genes on chromosomes 7 and 12, particularly Igf2 and Dlk1, in fetal liver hematopoiesis, we constructed ng(Deltach7)/fg, ng(Deltach12)/fg and ng(DeltaDouble)/fg BMEs using ng oocytes harboring deletion of differentially methylated regions at distal chromosomes 7 and/or 12. The ng(Deltach7)/fg, ng(Deltach12)/fg and ng(DeltaDouble)/fg BMEs, respectively, express Igf2, Dlk1 and both, and these embryos developed to term with specific phenotypes; the ng(Deltach7)/fg and ng(Deltach12)/fg BMEs develop to term with severe growth retardation, and the ng(DeltaDouble)/fg BMEs can survive to become normal female adults. By inducing Igf2 and Dlk1 expression, the proportions of mature and immature hematopoietic cells in the livers of the ng(Deltach7)/fg, ng(Deltach12)/fg and ng(DeltaDouble)/fg BMEs were considerably restored, and particularly in the ng(DeltaDouble)/fg BMEs, hematopoiesis occurred normally with appropriate expressions of the related genes. These data suggest that inappropriate expression of Igf2 and Dlk1 is involved in impaired fetal hematopoiesis.