No abstract

The Drosophila malate dehydrogenase, or malic enzyme (ME) encoded by the Men gene, is a non-mitochondrial enzyme recovered in the cytosolic fraction. By using mutation in the Men gene and deficiencies uncovering this locus, we could show that the ME activity recovered in cytosolic fractions originates exclusively from the Men gene located at map position 87D-1 on the right arm of the 3rd chromosome. We found that juvenile hormone (JH) can induce ME activity by two mechanisms. One mechanism corresponds to a direct effect of JH on the enzyme, whose activity was enhanced by a twofold factor in the absence of transcription and translation. This enhancement can be noticed 1 h after JH treatment and lasts for approx 3-4 h. The other mechanism involves the transcription of the MEN gene. In the absence of inhibitors the induction of ME activity by JH is increased by a three to fourfold factor and extends over a period of 10-16 h. Since induction of ME activity by JH and JH analogs displayed a dose-response curve, specific for each tested component, we concluded that the hormonal action could be mediated through a receptor. The use of two temperature sensitive mutations deficient in the production of ecdysteroid, ecd1 and su(f)ts67g revealed that ME response to JH requires the presence of a minimal level of the steroid hormone ecdysone, showing a complex hormonal regulatory circuit in the execution of the JH response.