Regulation of Gata1 Expression by HS+3.5

Abstract 3864

Precise regulation of Gata1 expression is required in order to control the balance between lymphoid/granulomonocytic (GM) and megakaryocytic-erythroid (MegE) specification, as well as to ensure correct differentiation of the MegE lineages. Transcriptional control is conferred in part by cis regulatory elements. An upstream enhancer, HS-3.5, and the erythroid first exon IE of Gata1 are necessary and sufficient to direct transgene expression in primitive but not definitive erythroid cells. Transgene expression in definitive red blood cells is restored by inclusion of an intronic DNaseI hypersensitive site, HS+3.5. Here we report the characterization of the HS+3.5 null embryonic stem cells and the HS+3.5 knockout mouse.

In vitro differentiation of HS+3.5 null ES cells resulted in reduced myeloid and megakaryocytic colony formation compared to wild type. The ΔHS+3.5 ES cells retained normal primitive erythroid colony formation. ΔHS+3.5 definitive erythroid colony progenitors displayed a decreased sensitivity to Interleukin 3 (IL3) signalling compared to wild type.

ΔHS+3.5 mice were viable and had normal blood counts and films. GM and erythroid progenitors also developed normally. However, there was a mild expansion of the E14.5 foetal liver Megakaryocytic Progenitor (MkP) compartment and an increase in Gata2 expression in both the bone marrow and foetal liver MkPs. Turning to Gata1, a decrease in Gata1 expression was observed in the following compartments: the bone marrow long term haematopoietic stem cell (LT-HSC) and the foetal liver common myeloid progenitor (CMP). The relationship between the effect of the HS+3.5 deletion on Gata1 expression and the haematopoietic phenotype will be discussed.