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Blood, 1 May 2005, Vol. 105, No. 9, pp. 3538-3541.
Prepublished online as a Blood First Edition Paper on January 11, 2005; DOI 10.1182/blood-2004-05-2021.
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Submitted May 28, 2004
Accepted December 26, 2004
K-Ras is essential for normal fetal liver erythropoiesis
Waleed F Khalaf, Hilary White, Mary J Wenning, Attilio Orazi, Reuben Kapur, and David A Ingram*
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA; Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, IN, USA
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA; Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
Department of Hematology/Pathology, Indiana University School of Medicine, Indianapolis, IN, USA
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA; Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA
* Corresponding author; email: dingram{at}iupui.edu.
In vitro studies suggest that Ras activation is necessary for erythroid cell development. However, genetic inactivation of the Ras isoforms, H-Ras, N-Ras, and K-Ras, in mice reportedly did not affect adult or fetal erythropoiesis though K-Ras -/- embryos were anemic. Given these discrepancies, we performed a more detailed analysis of fetal erythropoiesis in K-Ras -/- embryos. Day 13.5 K-Ras -/- embryos were pale with a marked reduction of mature erythrocytes in their fetal livers. The frequency and number of both early (erythroid burst-forming unit [BFU-E]) and late erythroid progenitors (erythroid colony forming unit [CFU-E]) were reduced in K-Ras -/- fetal livers compared to wild-type controls and displayed a delay in terminal erythroid cell maturation. Further, K-Ras -/- hematopoietic progenitors had reduced proliferation in response to erythropoietin and Kit ligand compared to control cells. Thus, these studies identify K-Ras as a unique Ras isoform, which is essential for regulating fetal erythropoiesis in vivo.

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