Ecdysteroids during the third larval instar in I(3)ecd-1ts, a temperature-sensitive mutant of Drosophila melanogaster

Abstract The temperature-sensitive l(3) ecd-1 ts mutation (A. Garen, L. Kauvar, and J. A. Lepesant (1977) . Proc. Natl. Acad. Sci USA 74, 5099–5103.) has been used in several laboratories to obtain Drosophila larvae deprived of moulting hormone. The development of mutants and controls during the third larval instar at permissive (20°C) and restrictive temperatures (29°C) was compared. Pupariation was inhibited when larvae were shifted to the restrictive temperature immediately at the second moult. The permanent larvae obtained remained active, did not leave the food, and reached a maximum weight superior to the weight of controls. Ecdysteroids were studied during the third larval instar by HPLC analysis and radioimmunoassays. A careful synchronization of the larvae at the second moult enabled the confirmation that at least one ecdysteroid peak occurs during the third larval instar, prior to the wandering stage in controls (20 or 29°C). Ecdysone was then the predominant moulting hormone, whereas 20-hydroxyecdysone was the main ecdysteroid at the time of pupariation. Low levels of ecdysteroid were measured in mutant larvae shifted to 29°C immediately at the second moult but larvae completely deprived of immunoreactive material were never observed. Nearly normal levels of ecdysteroids appeared at 27.5°C. Feeding ecd-1 larvae maintained at restrictive temperature on 20-hydroxyecdysone-yeast mixture for 16 hr triggered abortive pupariation. Ecdysteroid levels were measured after the return of the larvae to the standard medium; normal levels were restored 24 hr later. The mutant ecd-1 appears to present interesting opportunities for the detailed study of the hormonal induction of a developmental process during the third larval instar. The results of the biochemical studies performed on this mutant in other laboratories in the light of this analysis of ecdysteroids are discussed.