Synaptotagmin I, a molecular target for steroid hormone signaling controlling the maturation of sexual behavior in an insect

Abstract

As in vertebrates, the insect steroid hormones, especially 20-hydroxyecdysone (20E), initiate and regulate sexual behavior by acting on the central nervous system. This 20E action is, in part, triggered by transcriptional events mediated through the binding of 20E to a heterodimer comprising the ecdysone receptor (EcR) and ultraspiracle (USP). However, to date, our knowledge about this genomic steroid pathway remains incomplete. In moths, males detect female sex pheromones, eliciting stereotyped sexual behavior. In Agrotis ipsilon males, the behavioral response and the neuronal sensitivity to sex pheromone in the olfactory center, the antennal lobe (AL), increase with age. We recently showed that 20E controlled this age-dependent olfactory plasticity via the activation of an EcR/USP-dependent pathway in the AL. Here, we cloned the gene encoding A. ipsilon synaptotagmin I (AisytI), a presynaptic vesicle protein known to act as a calcium sensor in neurotransmitter release. AisytI was expressed in the AL, where its amount increased with age, whereas its knockdown inhibited the sex pheromone-oriented flight of males. 20E administration to males induced AL AisytI expression in a dose-dependent and time-dependent manner. Moreover, A. ipsilon EcR silencing caused decreases in AL AisytI expression and the behavioral response to sex pheromone. Our results show that the synaptotagmin I gene is a target gene for the genomic steroid signaling that controls the expression of insect sexual behavior by acting on central sex pheromone processing. This study thus represents a significant advance in our understanding of the steroid actions that influence neural functions, and thereby behavioral plasticity, in various organisms. DatabaseThe nucleotide sequence of Agrotis ipsilon synaptotagmin I is available in the DDBJ/EMBL/ GenBank databases under the accession number KJ863735.

The insect HR38 nuclear receptor, a member of the NR4A subfamily, is a synchronizer of reproductive activity in a moth

“…Over these last years, growing evidence has accumulated about the involvement of 20E in the maturation of sex pheromone responses in A. ipsilon male. Indeed, it has been showed that 20E is necessary to enhance high sensitivity to sex pheromone in males during their sexual development and that this positive effect is at least in part transduced through the activation of EcR/USPdependent signalling in ALs [37], ultimately engendering the upregulation of neural plasticity-related proteins such as the synaptotagmins [38]. It is interesting to emphasise that the behavioural changes resulting from AiHR38 depletion are similar to those induced by the pharmacological inactivation of 20E/EcR/USP complex [37] or RNAi-mediated EcR silencing [38].…”

“…Indeed, it has been showed that 20E is necessary to enhance high sensitivity to sex pheromone in males during their sexual development and that this positive effect is at least in part transduced through the activation of EcR/USPdependent signalling in ALs [37], ultimately engendering the upregulation of neural plasticity-related proteins such as the synaptotagmins [38]. It is interesting to emphasise that the behavioural changes resulting from AiHR38 depletion are similar to those induced by the pharmacological inactivation of 20E/EcR/USP complex [37] or RNAi-mediated EcR silencing [38]. It is also noteworthy that the age-related expression dynamic of AL AiHR38 is positively correlated with the agedependent increase in the levels of circulating 20E and of expression of EcR and USP in ALs [37].…”

“…Indeed, the injection of 20E into young immature males, where the circulating levels of 20E is low, induced an increased responsiveness to sex pheromone and this effect was associated to the 20E inducibility of EcR and USP in ALs [37]. On the contrary, a treatment with cucurbitacin B, an antagonist of 20E/EcR/USP complex or the EcR silencing led to a decline in sex pheromone responses in old mature males [37][38][39]. In A. ipsilon, it has also been described that 15-30 min after the onset of copulation, when the formation of spermatophore is engaged, the newly mated males cease to respond behaviourally to sex pheromone.…”

Evidence for a role of oestrogen receptor‐related receptor in the regulation of male sexual behaviour in the moth Agrotis ipsilon

“…The dsRNA production and injection conditions were established by following the protocol used for the silencing of a Gprotein-coupled dopamine/ecdysteroid receptor (AipsDopEcR) and the ecdysone receptor (AiEcR) in A. ipsilon (Abrieux et al, 2013;Bozzolan et al, 2015). The dsRNAs designed against AiERR (425 bp) and bacterial LacZ (372 bp) were produced with a MEGAscriptV R T7 High Yield Transcription Kit (Ambion) according to the manufacturer's instructions.…”

Oral delivery of dsRNA by microbes: Beyond pest control

“…In addition, functional studies of genes playing distinct roles during development and adult life could be challenging since the loss of function of these GOI generally leads to lethal phenotype 22 . As shown in studies addressing the characterization of hormonal pathways for example, the same set of genes could be involved in both developmental processes and regulation of physiological state in an age-dependent manner 23,24 . In such scenario, the temperature dependent UAS/Gal80 25 or other inducible systems 21 can be used in model species.…”