[RNA and protein synthesis inDrosophila leg discs cultured in vitro]

Imaginal leg discs from late third instarDrosophila larvae were cultured in Mandaron's medium without hormone or with α-ecdysone or β-ecdysone. Incorporation of labelled precursors (tritiated uridine, tritiated leucine or tritiated proline) was studied as a function of the stage of in vitro disc development.In the absence of moulting hormone, uridine incorporation decreased as soon as the discs were explanted; leucine and proline incorporation however began to decrease only after 6 to 12 h.α- and β-ecdysone stimulated the incorporation of all three precursors; however the rate of the incorporation varied as a function of the morphological disc development.The maxima and minima of uridine incorporation preceeded in time those of proline and leucine incorporation.The peaks of incorporation were coincident with salient morphological events of development: evagination, secretion of pupal and imaginal cuticles.There were no significant differences in uridine incorporation in the presence of α-ecdysone or β-ecdysone. Leucine and proline incorporation maxima however were significantly higher in the presence of α-ecdysone than of β-ecdysone.The results show that α-ecdysone-and to a lesser extent also β-ecdysone-can induce the macromolecular syntheses required for the development of the appendage in vitro.