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Human Molecular Genetics Advance Access published online on September 9, 2005
Human Molecular Genetics, doi:10.1093/hmg/ddi337
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© The Author 2005. Published by Oxford University Press. All rights reserved
Received April 30, 2005
Revised August 3, 2005
Accepted September 6, 2005

Article

Juxtaposition of the HPFH2 enhancer is not sufficient to reactivate the {gamma}-globin gene in adult erythropoiesis

Ping Xiang 1, Hemei Han 1, Grainne Barkess 1, Ivan Olave 1, Xiangdong Fang 1, Wenxuan Yin 1, George Stamatoyannopoulos 1, and Qiliang Li 2*

1 Division of Medical Genetics, Department of Medicine, University of Washington, Seattle, WA, 98195
2 Division of Medical Genetics, Department of Medicine, University of Washington, Box 357720, Seattle, WA, 98195

* To whom correspondence should be addressed.
Qiliang Li, E-mail: li111640{at}u.washington.edu


  Abstract

Previous studies have suggested that juxtaposition of a downstream enhancer to the fetal {gamma}-globin gene results in reactivation of the {gamma} gene in adult erythrocytes of individuals with hereditary persistence of fetal hemoglobin (HPFH). To test the hypothesis in a much stricter basis, we produced {beta} locus YAC transgenic mice carrying an exact {beta} locus replicate of a deletional HPFH mutation, HPFH 2. While the {gamma}-globin gene was expressed in the HPFH 2/ {beta} locus YAC (HPFH 2/YAC) transgenic mice in the early stage of development, it was completely silenced in the adult mice. The failure of {gamma} gene reactivation by the juxtaposed HPFH 2 enhancer contradicts the results of previous studies. We speculate that the discrepant results reflect differences in the distance between the LCR and the {gamma}-globin gene characteristic of the plasmid, cosmid, or YAC constructs used for production of transgenic mice. The difference in the phenotype of the HPFH 2/YAC transgenic mice and the humans with HPFH 2 mutation suggests that in addition to juxtaposition of HPFH enhancers, the upstream region that is absent in the {beta}-YAC construct might be involved in {gamma} gene reactivation in HPFH individuals. The DNase I hypersensitive sites of the LCR were well formed and the chromatin histones were acetylated. A moderate level of pol II binding was detected in the LCR despite the fact that no transcription occurred in the globin genes of the adult HPFH 2/YAC transgenic mice. The results suggest that formation of the LCR chromatin structure in erythroid cells is independent of globin gene transcription in the locus.


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