Cell-cycle and mRNA expression analyses in EPCR⁺ HSCs. (A) E12.5 pregnant mice were exposed to BrdU for 2 hours, and embryos were subsequently analyzed for cell-cycle status. The majority of cells in the LSK/EPCR⁺ population was in the G0/G1 phase (left) and its frequency was significantly higher compared with the LSK/EPCR⁻ population (right). In contrast, roughly half of the cells in the LSK/EPCR⁻ population were in the S phase (right). (B) Fractions corresponding to each cell-cycle phase were analyzed using the BrdU-Hoechst flow cytometric approach described in panel A. The LSK/EPCR⁺ (dark gray bars) and LSK/EPCR⁻ (light gray bars) populations are shown. Error bars represent SD (n = 3). **P < .01. (C) The LSK/EPCR⁺ population contained a greater number of cells in the G0 phase than the LSK/EPCR⁻ population, as assessed by Ki67-Hoechst flow cytometry. (D) Cell-cycle–related mRNA expression profile in LSK/EPCR⁺ and LSK/EPCR⁻ cells, as assessed using a high-throughput quantitative RT-PCR system. LSK/EPCR⁺ cells expressed significantly higher levels of CDK inhibitors, such as p57 and p18, whereas LSK/EPCR⁻ cells overexpressed CDKs such as Ccnd1, Ccnd2, Cdk6, Cdk2, and Aurka. The LSK/EPCR⁺ () and LSK/EPCR⁻ () populations are shown. Error bars represent SD (n = 3). *P < .05, **P < .01.