IntroductionMolecular processes that maintain the stem cell pool and govern the proliferation and differentiation of hematopoietic stem and progenitor cells are widely investigated but incompletely understood. Identification of these genes will facilitate our understanding of hematopoiesis and may be used to improve clinical outcomes.Using differential display-polymerase chain reaction (dd-PCR), we identified a differentially expressed transcript in CD34-enriched populations, with low or absent expression in CD34-depleted populations. Sequencing of this transcript revealed significant homology to oxysterol-binding protein (OSBP). On the basis of ESTs in the GenBank database, a family of up to 8 human genes that code for OSBP-related proteins is postulated to exist. 1 These have been designated OSBP-related proteins (ORPs). A partial sequence for our OSBP-related gene was thus designated ORP-3. 1
Study design CD34 ؉ purificationUmbilical cord blood (UCB) samples were obtained after uncomplicated vaginal or cesarean delivery. Adult bone marrow (ABM) cells were obtained from cell scrapings of discarded rib and femur heads after cardiothoracic or hip-replacement surgery. All samples were donated by volunteers according to approved institutional guidelines. Mononuclear cells were prepared by density-gradient separation through Ficoll-Hypaque (Amersham Pharmacia Biotech, Uppsala, Sweden). CD34 ϩ cells were isolated using a MiniMacs bead separation kit (Miltenyi Biotec, Becton Dickinson, Sunnyvale, CA).Flow cytometric analysis of CD34 ؉ populations and fluorescence-activated cell sorting of CD34 ؉ subsets CD34 ϩ cells were labeled with anti-CD38-fluorescein isothiocyanate, anti-CD34-phycoerythrin, and anti-CD45-PECY5 (Coulter Immunotech, Fullerton, CA). CD34 ϩ purity was determined by flow cytometric analysis (FacsCalibur, Becton Dickinson) following modified ISHAGE guidelines 2 using CELLQuest software (Becton Dickinson). When required, CD34 ϩ 38 Ϫ/ dull cells were sorted using a FacsCalibur Cell Concentrator Sorting Module.
Culture of umbilical cord blood CD34 ؉ cellsIn selected experiments, isolated CD34 ϩ cells were cultured for 1 week at 37°C in a humidified atmosphere flushed with 5% CO 2 in air, at a concentration of 0.5 ϫ 10 6 cells/mL in ␣ minimum essential medium (Trace, Noble Park, Victoria, Australia) with 20% fetal bovine serum (CSL Biosciences, Parkville, Victoria, Australia), 2 mM L-glutamine, 200 U/mL penicillin-streptomycin (Sigma, St Louis, MO), 20 ng/mL recombinant human stem cell factor (Amgen, Thousand Oaks, CA), 10 ng/mL IL-1B (Endogen, Woburn, MA), 10 ng/mL IL-3, 10 ng/mL IL-6, and 10 ng/mL G-CSF (Amrad, Boronia, Victoria, Australia).
dd-PCRRNA was extracted by RNeasy total RNA isolation kit (Qiagen, Clifton Hill, Victoria, Australia) and was DNase treated (Invitrogen, Carlsbad, CA). Reverse transcription and dd-PCR were carried out as described in the RNAimage Differential Display System (GenHunter, Nashville, TN). We used ABI Prism BigDye Terminator Cycle Sequencing Ready Reaction Kit (PE Appli...