The secreted lymphangiogenic protein CCBE1 is essential for fetal but not postnatal erythropoiesis
Loss of CCBE1 impairs erythroblastic island formation and function
The secreted protein CCBE1 is required for lymphatic vessel growth in fish and mice, and mutations in the CCBE1 gene cause Hennekam Syndrome, a primary human lymphedema. Here we show that loss of CCBE1 also confers severe anemia in mid-gestation mouse embryos due to defective definitive erythropoiesis. Fetal liver erythroid precursors of Ccbe1 null mice exhibit reduced proliferation and increased apoptosis. Colony forming assays and hematopoietic reconstitution studies suggest that CCBE1 promotes fetal liver erythropoiesis cell non-autonomously. Consistent with these findings, Ccbe1lacZ reporter expression is not detected in hematopoietic cells and conditional deletion of Ccbe1 in hematopoietic cells does not confer anemia. The expression of the erythropoietic factors erythropoietin and stem cell factor is preserved in CCBE1-null embryos, but erythroblastic island (EBI) formation is reduced due to abnormal macrophage function. In contrast to the profound effects on fetal liver erythropoiesis, postnatal deletion of Ccbe1 does not confer anemia, even under conditions of erythropoietic stress, and EBI formation is normal in the bone marrow of adult CCBE1 knockout mice . Our findings reveal that CCBE1 plays an essential role in regulating the fetal liver erythropoietic environment and suggest that EBI formation is regulated differently in the fetal liver and bone marrow.
- Submitted October 23, 2012.
- Accepted February 9, 2013.
- Copyright © 2005 American Society of Hematology