Role of second messengers in the regulation of juvenile hormone production in insects, with particular emphasis on calcium and phosphoinositide signaling

Abstract

Juvenile hormone (JH) biosynthesis is regulated by both peptidergic and aminergic inputs. Depending upon the species and developmental stage, these signals may be either inhibitory or stimulatory (allatostatins and allatotropins). Signal transduction within corpus allatum cells occurs by way of known second messengers, including the cyclic nucleotides, Ca2+, and the phosphoinositides. We review the role of signal transduction in the regulation of JH biosynthesis in the locust, Locusta migratoria, the hornworm, Manduca sexta, and the cockroach, Diploptera punctata. Differences in signal transduction between the species reflect in part differences in the signals which regulate the corpus allatum. For example, JH biosynthesis in locusts appears to be regulated principally by allatotropic signals, whereas in the cockroach allatostatic signals appear to predominate. In M. sexta, both types of signals appear to function and are stage-dependent. This may reflect the complex nature of the juvenile hormone products in this species, whereas in locusts and cockroaches only JH III is produced. Modulation of intracellular calcium (CA2+) levels by drugs (ionophores, Ca2+ chelators and releasing agents, CA2+ channel blockers) or depolarizing agents including current injection dramatically alters JH biosynthesis, as do agents that activate the phosphoinositide pathway. Modulation of intracellular cAMP levels is associated with changes in JH production, with increases in JH biosynthesis occurring as a consequence of the stimulation of the adenylate cyclase system in locusts but with an inhibition of JH biosynthesis in cockroaches. The situation in M. sexta is more complex and appears to be both stage- and product-dependent. The effects of second messengers in the three species differ, probably as a consequence of the differences in the peptide signals that regulate JH biosynthesis and in the intrinsic state of the corpora allata (either switched on or switched off, in the absence of external signals). © 1996 Wiley-Liss, Inc.