Figure 4.

Identification of a perivascular skin MPC population. A, Lung fibroblasts were isolated from explanted human lung or skin tissue via collagenase digest to form a cell suspension. Adherent cells were plated and expanded for 2 passages. At this time, flow cytometric analysis was performed on single-cell suspensions of human lung tissue to detect CD45^negative ABCG2-expressing (horizontal axis) cells. B, Representative Giemsa-stained colony-forming unit fibroblast analysis confirmed the clonogenic potential of the ABCG2-enriched populations. C–K, Lung or epidermal ear and dorsal ABCG2 MPCs targeted recombination in vivo. Recombination following administration of low-dose tamoxifen (0.5 mg) resulted in the appearance of eGFP expression, detectable by immunofluorescent staining (green). The eGFP-expressing MPCs were localized in or adjacent to SMA-positive microvessel layers (red). Scale bar: 50 mm. L, Heat map analysis of gene similarities and segregation between control skin and lung MPCs; yellow and red indicate high and low levels of expression, respectively. M–O, Probes belonging to gene ontology functional categories were selected from the whole expression data of the lung and skin MPC groups, and corresponding heat maps of expression data were constructed. A self-contained gene set test, ROAST, was employed to test for significant change in expression of sets (BMP signaling: P < 0.004; Wnt signaling: P < 0.006; angiogenesis: P < 0.01). Representative gene changes of >1.5-fold with P < 0.05 are depicted. eGFP: enhanced green fluorescent protein; FB: fibroblasts; huLung: human lung; huSkin: human skin; MC: mesenchymal cells; MPC: mesenchymal progenitor cells; SMA: smooth muscle actin; SSC-A: side-scatter.