ECDYSTEROIDS DURING THE 3RD LARVAL INSTAR IN L(3)ECD-1TS, A TEMPERATURE-SENSITIVE MUTANT OF DROSOPHILA-MELANOGASTER

The temperature-sensitive l(3)ecd-1ts has been used in several laboratories to obtain Drosophila larvae deprived of molting hormone. The development of mutants and controls during the 3rd larval instar at permissive (20.degree. C) and restrictive temperatures (29.degree. C) was compared. Pupariation was inhibited when larvae were shifted to the restrictive temperature immediately at the 2nd molt. 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 3rd larval instar by HPLC [high-performance liquid chromatography] analysis and radioimmunoassays. A careful synchronization of the larvae at the 2nd molt enabled the confirmation that at least 1 ecdysteroid peak occurs during the 3rd larvae instar, prior to the wandering stage in controls (20.degree. or 29.degree. C). Ecdysone was then the predominant molting hormone; 20-hydroxyecdysone was the main ecdysteroid at the time of pupariation. Low levels of ecdysteroid were measured in mutant larvae shifted to 29.degree. C immediately at the 2nd molt but larvae completely deprived of immunoreactive material were never observed. Nearly normal levels of ecdysteroids appeared at 27.5.degree. C. Feeding ecd-1 larvae maintained at restrictive temperature on 20-hydroxyecdysone-yeast mixture for 16 h triggered abortive pupariation. Ecdysteroid levels were measured after the return of the larvae to the standard medium; normal levels were restored 24 h later. The mutant ecd-1 appears to present interesting opportunities for the detailed study of the hormonal induction of a developmental process during the 3rd 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.