Meeting Abstract
P2.145 Saturday, Jan. 5 Direct effects of hypoxia and nitric oxide on the secretion of ecdysone by insect prothoracic glands DELALIO, L*; DION, S; BOOTES, A; TRACKA, K; KUNDU, A; MAGUIRE, M; SMITH, WA; Northeastern University; Northeastern University; Northeastern University; Northeastern University; Northeastern University; Northeastern University; Northeastern University w.smith@neu.edu
Insect molting and metamorphosis are stimulated by ecdysone secreted by the prothoracic glands. A recent study suggests that tissue oxygenation may play a role in the timing of a molt during a given insect stage; hypoxic Manduca sexta larvae molt at a lower weight than normoxic larvae. Further, in Drosophila, the signaling gas nitric oxide (NO) appears to be required for prothoracic gland function. Knockdown of nitric oxide synthase in the prothoracic glands prolongs feeding and blocks metamorphosis. We set out to directly examine the effects of hypoxia and NO on ecdysone secretion, using glands from feeding fifth (last) larval stage M. sexta. Treatment of prothoracic glands with the NO mimetic DETA-NONOate (0.1 mM or 10 mM) did not directly stimulate ecdysone secretion. We also quantified, with the use of real-time PCR, the effects of NO on the expression of nuclear factors associated with ecdysone secretion including Manduca hormone receptor 3 (MHR3), which was decreased by NO. Hypoxia had an inhibitory effect on ecdysone secretion. Incubation of prothoracic glands for 12 hours in 2% oxygen led to a significant reduction in ecdysone secretion as compared to normoxic (20% oxygen) controls. Cellular viability was confirmed by trypan blue exclusion. Our results suggest that while oxygen and NO can modify the timing of a larval molt, and hence body size, these effects in M. sexta are not mediated by direct effects on ecdysone secretion. Rather, changes such as accelerated release of upstream stimulatory hormones, the responsiveness of the prothoracic glands to stimulation, or enhanced target tissue responsiveness to ecdysone may be responsible for observed effects on molting.
