Single-locus analysis of retroviral integration sites in the genome of CD34⁺ HPCs. (A) The NF1/EVI2A/B locus. Distribution of MLV (red) and HIV (blue) integrations, and of the MLV integration cluster (black box) along the locus as displayed by the UCSC Genome Browser. The base position feature on the top (scale bar and chromosome number) identifies the genomic coordinates of the displayed region. H3K4me3 and Pol II tracks are those determined by ChIP sequencing in the genome of human CD34⁺/CD133⁺ HPCs.²⁴  The RefSeq Genes track shows known human protein-coding and noncoding transcripts taken from the National Center for Biotechnology Information RNA reference sequences collection. (n) indicates the total number of integration sites retrieved in the displayed region. (B) The CD34 locus. MLV and HIV integration sites and clusters are displayed on the locus as described in panel A. The upstream and downstream enhancers (orange boxes) were previously described as critical for CD34 gene expression in vivo.²⁵  (C) The LMO2 locus. MLV and HIV integration sites and clusters are displayed on the locus as described in panel A. The array of upstream enhancers (orange boxes) we reported to cooperate with the distal promoter in regulating LMO2 expression.²⁶  Translocation breakpoints associated to T-cell leukemia are indicated with green bars and were retrieved from the TICdb database of translocation breakpoints in cancer.²⁷  Integrations sites detected in peripheral blood cells of patients with adenosine deaminase–deficient SCID²⁸  are indicated in purple. A CpG island (CpG 119; green box) marking the nonhematopoietic proximal promoter is also shown.