Ecdysone and the cell cycle: investigations in a mosquito cell line

Abstract

Cell lines provide a tool for investigating basic biological processes that underlie the complex interactions among the tissues and organs of an intact organism. We compare the evolution of insect and mammalian populations as they progress from diploid cell strains to continuous cell lines, and review the history of the well-characterized Aedes albopictus mosquito cell line, C7-10. Like Kc and S3 cells from Drosophila melanogaster, C7-10 cells are sensitive to the insect steroid hormone, 20-hydroxyecdysone (20E), and express 20E-inducible proteins as well as the EcR and USP components of the ecdysteroid receptor. The decrease in growth associated with 20E treatment results in an accumulation of cells in the G1 phase of the cycle, and a concomitant decrease in levels of cyclin A. In contrast, 20E induces a G2 arrest in a well-studied imaginal disc cell line from the moth, Plodia interpunctella. We hypothesize that 20E-mediated events associated with molting and metamorphosis include effects on regulatory proteins that modulate the mitotic cell cycle and that differences between the 20E response in diverse insect cell lines reflect an interplay between classical receptor-mediated effects on gene expression and non-classical effects on signaling pathways similar to those recently described for the vertebrate steroid hormone, estrogen.

Fig. 1

Stages in the evolution of an established cell line from a tissue isolate. Although insects cells have not been studied as carefully as vertebrate cells, they appear not to undergo the crisis, accompanied by senescence and conversion to aneuploidy, that has been documented in mammalian cell lines.

Fig. 2

Schematic representation of the cell cycle. M, mitosis; G1, gap 1; S, synthesis; G2, gap2. Predominant cyclins (cyc) are shown in shaded ovals.