Comparison of ecdysteroid production in Drosophila and Manduca: Pharmacology and cross‐species neural reactivity

Abstract

In both Manduca sexta and Drosophila melanogaster, metamorphic events are driven by ecdysteroids whose production in prothoracic gland (PGs) is stimulated periodically by neural factors. Differences in the life cycle of moths and flies have made it difficult to compare the regulation of ecdysteroid biosynthesis in these two species. As in Manduca, at least two neural factors in the larval Drosophila BVG complex were separable by molecular weight, and they stimulated increased ecdysteroid biosynthesis from the ring gland, a composite organ that includes PG cells. Drosophila neural extracts accelerated ecdysteroid biosynthesis in Manduca PGs and, conversely, partially purified Manduca PTTH preparations elevated ecdysteroid biosynthesis in Drosophila ring glands, suggesting that the two species may share structurally similar prothoracicotropic factors. Drosophila ring glands required the presence of calcium ions to respond to neural extracts, but the phosphodiesterase inhibitor MIX and cAMP analogues exerted little, if any, positive effect on production. Mean ecdysteroid production rates of BVG-ring gland complexes taken from Drosophila larvae during various phases of the wandering period were often submaximal and highly variable, suggesting that they fluctuate widely prior to pupariation. Based on available data in Drosophila and the Manduca model for the control of ecdysteroid biosynthesis, a developmental scheme for neuroendocrine control in Drosophila is proposed.

Neuronal influence on peripheral circadian oscillators in pupal Drosophila prothoracic glands

“…This suggests that physiological outputs from PG cell oscillators are under the strong influence of CRY-dependent photoreception in the brain and synaptic inputs to PG cells. Because release of ecdysteroids from PG cells depends on intracellular Ca 2+ signalling67, the lights-on signal would reduce rhythmic ecdysteroid release from PG cells and trigger the endocrine cascade underlying eclosion8. This hypothesis is consistent with Drosophila eclosion rhythms, which are known to peak at dawn35.…”

“…PG cells are considered to be circadian pacemaker cells gating eclosion timing, because when tim is over-expressed in these cells, arrhythmic eclosion occurs under conditions of constant darkness (DD)5. A reduction in the rhythmic release of ecdysteroids from PG cells, which depends on intracellular inositol 1,4,5-trisphosphate and Ca 2+ signalling, has been proposed as the mechanism of initiating the endocrine cascade required for eclosion678. Interrelations between clock gene oscillations and cellular physiological activities, however, have not been clearly characterized.…”

Prothoracicotropic Hormone Regulates Developmental Timing and Body Size in Drosophila

“…However, it eventually rises in white prepupae suggesting that an alternative mechanism for triggering metamorphosis is in place. Consistent with this idea is the observation that extracts prepared from Drosophila ventral ganglia, which should not contain the PG neurons, possess an ecdysteroidogenic activity (Henrich, 1995;Henrich et al, 1987). One likely candidate is an insulin-like peptide.…”

Calcium inhibits ovarian steroidogenesis in the blowfly Phormia regina

“…Ovary as in Lepidoptera and may differ between different groups of insects; although the cAMP pathway appears to be inhibitory in Calliphora , it has also been observed that Drosophila molting glands require the presence of external calcium ions to respond to active brain extracts (Henrich 1995). These data thus suggest that, in Diptera, calcium could have a different role in the control of steroidogenesis in (larval) molting glands and in (adult) ovaries.…”