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Purpose: To investigate the effect of EGF, IGF-1, and VEGF on ARPE19 cell proliferation and differentiation., Methods: The gene expression of RPE-specific differentiation and proliferation markers and the transcriptional and translational activity of beta-catenin signaling markers were measured by flow cytometry and RT-PCR., Results: The data showed a significant decrease in RPE65, CRALBP, and cytokeratin 18 in ARPE-19 cells stimulated with EGF and IGF-1. In addition, a significant decrease in GSK-3beta and beta-catenin was observed that was paralleled by an increase in cyclin D1 expression. Cell cycle studies revealed an increase in ARPE cells in the S-G(2)/M-phase after treatment with EGF or IGF-1. VEGF, on the other hand, led to a reduction in cyclin D1 and to an increase in GSK 3beta and beta-catenin expression which was paralleled by an increase in RPE-specific differentiation markers., Conclusions: The data demonstrate the induction of proliferation by EGF and IGF-1 and upregulation of the beta-catenin signaling pathway in ARPE-19 cells. The data suggest that activation of the beta-catenin signaling pathway may be key in activating ARPE-19 cells by different growth factors.

The cell-cycle progression of germinating embryos of maize ( Zea mays L.) was studied from 0 to 72 h after the start of imbibition using DNA flow cytometry on isolated nuclei, and analyses of thymidine kinase activity, histone biosynthesis and levels of proliferating cell nulcear antigen (PCNA). At the start of germination, 75% of the cells were in G1, but this population had decreased to 25% by 72 h. The concomitant increase of cells in S-phase did not occur continuously, but stepwise, indicating that during germination most of the cells enter S-phase as a partially synchronized population. Within the initial 60 h of embryo germination the cells passed through one S-phase; the start and duration of this period of replicative DNA synthesis was further substantiated by the analysis of S-phase-associated events, the biosynthesis of core histones and the enzyme activity of thymidine kinase, which both began to increase at about 12 h after the start of differentiation. Thymidine kinase fluctuated periodically during germination with a transient maximum at 30 h and a second peak at 72 h; histone biosynthesis was not detectable until 12 h after the start of germination. The levels of PCNA protein closely resembled the pattern of thymidine kinase during germination. Together with the cytometric data this allows a clear assignment of cell cycle events to different times of embryo differentiation. [ABSTRACT FROM AUTHOR]