A developmental transition in definitive erythropoiesis: erythropoietin expression is sequentially regulated by retinoic acid receptors and HNF4
- Takako Makita1,
- Gabriela Hernandez-Hoyos3,4,
- Tim Hung-Po Chen1,
- Hong Wu5,
- Ellen V. Rothenberg3, and
- Henry M. Sucov1,2,6
- Departments of 1Biochemistry and Molecular Biology and 2Cell and Neurobiology, Institute for Genetic Medicine, University of Southern California Keck School of Medicine, Los Angeles, California 90033, USA; 3Department of Biology, California Institute of Technology, Pasadena, California 91125, USA; 4Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA; 5Department of Molecular and Medical Pharmacology, Howard Hughes Medical Institute, University of California, Los Angeles School of Medicine, Los Angeles, California 90095, USA
Abstract
The cytokine erythropoietin (Epo) promotes erythropoietic progenitor cell proliferation and is required for erythropoietic differentiation. We have found that the Epo gene is a direct transcriptional target gene of retinoic acid signaling during early erythropoiesis (prior to embryonic day E12.5) in the fetal liver. Mouse embryos lacking the retinoic acid receptor gene RXRα have a morphological and histological phenotype that is comparable with embryos in which the Epo gene itself has been mutated, and flow cytometric analysis indicates that RXRα-deficient embryos are deficient in erythroid differentiation. Epo mRNA levels are reduced substantially in the fetal livers of RXRα −/−embryos at E10.25 and E11.25, and genetic analysis shows that theRXRα and Epo genes are coupled in the same pathway. We furthermore show that the Epo gene is retinoic acid inducible in embryos, and that the Epo gene enhancer contains a DR2 sequence that represents a retinoic acid receptor-binding site and a retinoic acid receptor transcriptional response element. However, unlike Epo-deficient embryos that die from anemia, the erythropoietic deficiency in RXRα −/− embryos is transient; Epo mRNA is expressed at normal levels by E12.5, and erythropoiesis and liver morphology are normal by E14.5. We show that HNF4, like RXRα a member of the nuclear receptor family, is abundantly expressed in fetal liver hepatocytes, and is competitive with retinoic acid receptors for occupancy of the Epo gene enhancer DR2 element. We propose that Epo expression is regulated during the E9.5–E11.5 phase of fetal liver erythropoiesis by RXRα and retinoic acid, and that expression then becomes dominated by HNF4 activity from E11.5 onward. This transition may be responsible for switching regulation of Epo expression from retinoic acid control to hypoxic control, as is found throughout the remainder of life.
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Footnotes
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↵6 Corresponding author.
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E-MAIL sucov{at}hsc.usc.edu; FAX (323) 442-2764.
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Article and publication are at www.genesdev.org/cgi/doi/10.1101/gad.871601.
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- Received December 6, 2000.
- Accepted February 7, 2001.
- Cold Spring Harbor Laboratory Press
