Novel roles for the corpus allatum hormone in the cost of sexual interactions in the linden bug Pyrrhocoris apterus.

The cost of sexual interactions, usually expressed as a reduction of life-span, is a fundamental but poorly understood aspect of life. According to a widely accepted view, a rise in the "pro-aging" juvenile hormone (JH) might contribute to the decrease of life span caused by sexual interactions. We tested this hypothesis using the linden bug Pyrrhocoris apterus by removing the corpus allatum (CA), the source of JH. If JH is causally involved in the cost of sexual interactions, then the absence of CA (JH) should decrease the negative effect of sexual interactions on survival. As expected, ablating the CA significantly prolonged life-span of both virgin females and virgin males. Mated insects of both sexes lived significantly shorter than virgins. However, contrary to prediction, the decrease of life span by sexual interactions was similar in control and CA-ablated males, and was even enhanced in CA-ablated females. Another unexpected finding was that males paired with CA-ablated females lived almost as long as virgin males and significantly longer than did males paired with control females, although ablating the female CA did not cause any decrease in mating activity. On the other hand, females paired with CA-ablated males lived only slightly longer than did females paired with control males. These results highlight several important points. (1) In both genders, the negative effect of sexual interactions on insect's survival is not mediated by the insect's own CA. (2) The male CA has only minor effect on female survival, while (3) the female CA (JH) is principally responsible for the sex-induced reduction in the male survival.

Control of juvenile hormone biosynthesis in Bombyx mori: cloning of the enzymes in the mevalonate pathway and assessment of their developmental expression in the corpora allata.

We have isolated the cDNAs of all enzymes involved in the mevalonate pathway portion of the juvenile hormone (JH) biosynthetic pathway in Bombyx mori, i.e., those responsible for the formation of farnesyl diphosphate from acetyl-CoA. There is a single gene encoding each enzyme of this pathway, with the exception of farnesyl diphosphate synthase (FPPS), for which we identified three homologs. All but two of these enzymes are expressed almost exclusively in the corpora allata (CA), as indicated by quantitative RT-PCR analyses. Phosphomevalonate kinase (MevPK) was expressed in many tissues, including the CA. In day 2 4th instars, FPPS1 expression was detected primarily in the Malpighian tubules, but expression of the structurally related FPPS2 and FPPS3 occurred mainly in the CA. Since FPPS3 transcripts were 55 times less abundant than those of FPPS2, the latter is expected to play a major role in JH biosynthesis at this stage. Studies on the developmental expression of these enzymes in the CA showed that the levels of all transcripts were high during the 4th instar larvae, a stage at which in vitro JH biosynthesis was high. However, the transcripts of all the mevalonate enzymes declined to low levels and JH acid O-methyltransferase (JHAMT) transcript disappeared by day 3 when CA ceased JH production after the final larval molt. The CA did not synthesize JH during the pupal stage, coincident with the limited expression of mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate kinase and isopentenyl diphosphate isomerase, and the inactivation of the JHAMT gene. Only female CA produced JH in the adult stage, a feature associated with the re-expression of JHAMT in female but little in male adult CA. Altogether, our results point to a relationship between JH biosynthesis and expression of most JH biosynthetic enzymes in the CA.

Assessment of the role of cyclic nucleotides in allatostatin-induced inhibition of juvenile hormone biosynthesis in Diploptera punctata.

In an effort to identify the signal transduction mechanism associated with the inhibition of juvenile hormone (JH) biosynthesis by the neuropeptides allatostatins, levels of the cyclic nucleotides cAMP and cGMP were measured in corpora allata (CA) of virgin and mated Diploptera punctata females using radioimmunoassays. Treatment of isolated CA with varying concentrations of synthetic allatostatins 1, 2, 3 or 4 did not elicit significant changes in the levels of either cAMP or cGMP in any of the test glands, suggesting that these compounds do not act as second messengers for the four allatostatins tested. Simultaneous treatment of CA with allatostatin 4 and the adenylate cyclase activator forskolin did not increase the degree of inhibition of juvenile hormone biosynthesis relative to that obtained with forskolin (5 or 50 microM) alone. We interpret these results as lending further support to the suggestion that cyclic nucleotides do not play a role in the signal transduction of allatostatins 1-4 in cockroach CA.