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Blood, 15 October 2005, Vol. 106, No. 8, pp. 2680-2687. Prepublished online as a Blood First Edition Paper on June 30, 2005; DOI 10.1182/blood-2004-12-4755.
Submitted December 16, 2004
Department of Haematology, Cambridge Institute for Medical Research, Cambridge University, Cambridge, United Kingdom * Corresponding author; email: bg200{at}cam.ac.uk.
Transcriptional control has been identified as a key mechanism regulating the formation and subsequent behaviour of haematopoietic stem cells. We have used a comparative genomics approach to identify transcriptional regulatory elements of the LMO2 gene, a transcriptional cofactor originally identified through its involvement in T-cell leukaemia and subsequently shown to be critical for normal haematopoietic and endothelial development. Of the two previously characterized LMO2 promoters, the second (proximal) promoter was highly conserved in vertebrates ranging from mammals to fish. Real-time RT-PCR expression analysis identified this promoter as the predominant source of transcription in haematopoietic tissue. Transient and stable transfections indicated that the proximal promoter was active in haematopoietic progenitor and endothelial cell lines and this activity was shown to depend on three conserved Ets sites which were bound in vivo by Elf1, Fli1 and Ets1. Finally, transgenic analysis demonstrated that the LMO2 proximal promoter is sufficient for expression in endothelial cells in vivo. No haematopoietic expression was observed indicating that additional enhancers are required to mediate transcription from the proximal promoter in haematopoietic cells. Together these results suggest that the conserved proximal promoter is central to LMO2 transcription in haematopoietic and endothelial cells, where it is regulated by Ets factors.
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