| Abstract: | 1. 1. When checked for their responsiveness to β-ecdysone, several established lines and sublines of Drosophila melanogaster cells displayed varying behaviour: (a) most of them responded with characteristic morphological modifications accompanied by an arrest of cell multiplication; (b) in one line, the cells only stopped dividing; (c) another line reacted with immediate death of all cells; (d) one line was found to be resistant to ecdysone. 2. 2. To establish the possible genetic grounds of such a differential sensitivity to ecdysone, clones were isolated from some of the lines. All clones isolated from one of the sensitive lines displayed the same succession of morphological modifications as the original line, but each of them with its own rate. The specific sensitivity to β-ecdysone of subclones derived from the above clones was established with greater precision. Each of them responded when a certain threshold concentration of β-ecdysone (varying from 0.5×10−8 M to 5×10−8 M) was reached in the culture medium. The clones were most sensitive to ecdysone between the 3rd and the 7th month of their development. We have studied clones displaying a wide range of reactions to ecdysone, from cells sensitive to very low concentrations of the hormone, to completely resistant cells. Comparison of these genetically defined populations of cells might help towards an understanding of the different stages of ecdysone action at the cellular level. |
