Inflammatory signaling regulates fetal hematopoiesis

Multiple signaling pathways contribute to blood cell formation in the fetus, but a role for innate immune/inflammatory signaling has not been described. Here we show that mouse fetuses deficient for either interferon gamma 1 (IFNg) or its receptor have decreased numbers of lymphoid progenitors and hematopoietic stem cells (HSCs) in the aorta/gonad/mesonephros region and placenta. The role of IFNg signaling was evolutionarily conserved, as morpholino knockdown of IFNg and its receptor reduced the number of hematopoietic stem and progenitor cells in the dorsal aorta and caudal hematopoietic territory of zebrafish embryos, and rag2 expressing cells in the thymus. ChIP-Seq analysis demonstrated that interferon regulatory factor 2 occupied genes in human fetal liver CD34+ hematopoietic stem/progenitor cells, and Gene Ontology analysis identified innate immunity and interferon signaling as enriched processes. Thus inflammatory signaling in the fetus, in the absence of pathogenic challenge, regulates the production of lymphoid progenitors and HSCs. Tg(Ly6a-GFP) conceptuses were generated by crossing C57BL/6 x 129S1/SVImJ F1 females with Tg(Ly6a-GFP) males. The AGM region, umbilical and vitelline arteries (A+U+V) from 100 E10.5 Tg(Ly6a-GFP) embryos were dissected, and 30,000 Ly6a-GFP+ hematopoietic cluster cells (CD31+ VEC+ ESAM+ Kit+), 130,000 Ly6a-GFP- hematopoietic cluster cells, 70,000 Ly6a-GFP+ endothelial cells (CD31+ VEC+ ESAM+ Kit-), and 300,000 Ly6a-GFP- endothelial cells sorted into TRIzol-LS (Invitrogen). The cells were lysed in TRIzol-LS and the aqueous phase was collected after adding chloroform. The aqueous phase was homogenized by 70% ethanol and RNA was isolated using Qiagen RNeasy mini kit. Four samples and two replicates for each sample.