Variability of ecdysteroid‐induced cell cycle alterations in <i>Drosophila</i> Kc sublines

Abstract

The cell cycle of two lines isolated from Drosophila Kc cells was followed by flow cytofluorometry and cell counting. The first line is the 8-9K clone which grew in a medium supplemented with 5% serum; the second, named subline KcO, grew in a serum-free medium. The stationary phase is characterized by a G2 cell accumulation: 73% in the 8-9K clone and 50% in the KcO subline. When the medium was supplemented with the steroid moulting hormone 20-hydroxyecdysone, more than 90% of 8-9K cells and 65% of KcO cells were progressively arrested in G2. In the continuous presence of 20-hydroxyecdysone, most of the 8-9K cells remain G2-arrested; no massive G2 release into M was observed and only a few cells were able to divide. When treated for only 3 or 7 days, a transient release into M and proliferation occurred after hormone-free medium renewal, largely masked by G2 cell death. These results are discussed in comparison with other reports on cell cycle alteration induced by ecdysteroids.