The Lmo2 gene encodes a transcriptional cofactor critical for the development of 
hematopoietic stem cells. Ectopic LMO2 expression causes leukemia in T-cell 
acute lymphoblastic leukemia (T-ALL) patients and severe combined 
immunodeficiency patients undergoing retroviral gene therapy. Tightly controlled 
Lmo2 expression is therefore essential, yet no comprehensive analysis of Lmo2 
regulation has been published so far. By comparative genomics, we identified 17 
highly conserved noncoding elements, 9 of which revealed specific acetylation 
marks in chromatin-immunoprecipitation and microarray (ChIP-chip) assays 
performed across 250 kb of the Lmo2 locus in 11 cell types covering different 
stages of hematopoietic differentiation. All candidate regulatory regions were 
tested in transgenic mice. An extended LMO2 proximal promoter fragment displayed 
strong endothelial activity, while the distal promoter showed weak forebrain 
activity. Eight of the 15 distal candidate elements functioned as enhancers, 
which together recapitulated the full expression pattern of Lmo2, directing 
expression to endothelium, hematopoietic cells, tail, and forebrain. 
Interestingly, distinct combinations of specific distal regulatory elements were 
required to extend endothelial activity of the LMO2 promoter to yolk sac or 
fetal liver hematopoietic cells. Finally, Sfpi1/Pu.1, Fli1, Gata2, Tal1/Scl, and 
Lmo2 were shown to bind to and transactivate Lmo2 hematopoietic enhancers, thus 
identifying key upstream regulators and positioning Lmo2 within hematopoietic 
regulatory networks.