Fig. 5

Cell cycling and proliferation are enhanced following spaceflight in neonatal CPCs. Following 30 days of culture aboard the ISS, CPCs were fixed, stained with propidium iodide, and measured using flow cytometry. The Dean–Jett–Fox model was then applied to the histogram of propidium iodide fluorescence intensity for ground-cultured and ISS-cultured CPCs a. Upon analysis b, adult CPCs exhibited a significant decrease in the percentage of cells in the G1/G0 and neonatal CPCs exhibited a significant increase in the percentage of cells in the G2/M phase. This was supported by increased expression of CDKN2A, E2F1, and PLK1, which function to regulate G1/S arrest, overcome G1/S arrests, and promote G2/M progression, respectively, in neonatal c, but not adult d, CPCs. Furthermore, increased telomerase activity, as indicated by enhanced TERT expression e, was observed in both groups. In addition to enhanced proliferation, DNA repair gene expression was induced in neonatal CPCs, as indicated by increased levels of ATM, RAD23, and RAD50 f. Adult CPCs generally exhibited increased DNA repair genes; however, only ATM expression was significantly increased g. n = 3 measurements of four pooled clones per group for cell cycling analysis; n = 3 unique clones per group for all gene expression data, except for E2F1, TERT, ATM, RAD23, and RAD50 (n = 9, three biological samples each measured in triplicate). Data are reported as the mean ± SEM, *P < 0.05, **P < 0.01, ***P < 0.001