In Heliothis virescens, reproduction is strictly dependent on juvenile hormone (JH). In females, mating induces an increase in JH titer which is correlated with elevated vitellogenin biosynthesis, and results in higher rates of egg production. Factors that may contribute to increased JH levels are (i) mating effects on JH degradation, (ii) transfer of JH in male seminal fluid, and (iii) mating-induced stimulation of JH biosynthesis. JH biosynthesis is presumably stimulated by production and/or release of stimulatory neuropeptides (allatotropins). Results from research in our laboratory and data from some recently published studies provide evidence that H. virescens allatotropins may be structurally similar or even identical to M. sexta allatotropin (Mas-AT). We have previously shown that Mas-AT-immunoreactive material is present in the H. virescens central nervous system, and also in axons projecting into the neuroendocrine corpora allata (CA).
Allatostatins presumably act on the CA by binding to membrane receptors of CA cells, thereby stimulating intracellular signal transduction pathways. The few studies that explicitly deal with signal transduction in the action of allatoactive peptides suggest that the action of allatotropin (and other neuropeptides) requires mediation via different routes and second messengers. In order to identify the second messengers involved in regulation of JH biosynthesis in H. virescens, we are currently investigating the effects on in vitro CA activity of various agonists and antagonists of components of different second messenger systems. Data from experiments in which we investigated the effects on CA activity of varying Ca2+ concentrations and of the Ca2+ ionophore A23187 in one-day-old virgin H. virescens females, indicated that an increase in intracellular Ca2+ may be correlated with stimulation of JH biosynthesis. Further experiments will address the potential involvement of the inositoltrisphosphate/diacylglycerol signaling pathway, the cyclic AMP signaling pathway, the cyclic GMP signaling pathway, of Ca2+/CaM dependent protein kinases and of protein phosphatases.
Species 1: Lepidoptera Noctuidae Heliothis virescens (tobacco budworm)
Keywords: juvenile hormone biosynthesis, signal transduction in corpora allata
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