Ecdysis-triggering hormone (ETH) was originally discovered and characterized as a molt termination signal in insects through its regulation of the ecdysis sequence. Here we report that ETH persists in adult Drosophila melanogaster, where it functions as an obligatory allatotropin to promote juvenile hormone (JH) production and reproduction. ETH signaling deficits lead to sharply reduced JH levels and consequent reductions of ovary size, egg production, and yolk deposition in mature oocytes. Expression of ETH and ETH receptor genes is in turn dependent on ecdysone (20E). Furthermore, 20E receptor knockdown specifically in Inka cells reduces fecundity. Our findings indicate that the canonical developmental roles of 20E, ETH, and JH during juvenile stages are repurposed to function as an endocrine network essential for reproductive success.ecdysis triggering hormone | ecdysone | juvenile hormone | fecundity | oogenesis T he life history of insects is characterized by radical morphogenetic transformations, whereby tissues are reorganized and hormones are repurposed for roles associated with stage-specific functions. During development, larvae complete each molt by shedding the cuticle under control of ecdysis triggering hormones (ETHs) targeting central peptidergic ensembles to orchestrate an innate behavioral sequence (1-3). Previous observations that Inka cells, the sole source of ETHs, persist into the adult stage (4) suggest possible reproductive functions for these peptides.We hypothesized that ETHs regulate juvenile hormone (JH) levels, based on the report of ETH receptor (ETHR) expression in the corpora allata (CA) of the silkworm, Bombyx mori (5). Evidence that ETH functions as an allatotropin in the yellow fever mosquito Aedes aegypti came from a recent study showing its activation of JH acid methyltransferase (6).JH is a sesquiterpenoid hormone with well-known morphogenetic and gonadotropic functions. In Drosophila, adult phenotypes resulting from reduction of JH levels have been characterized through induction of cell death in the CA or through enhancement of its degradation (7,8). Based on evidence from studies on Bombyx and Aedes, we investigated whether ETH functions as an allatotropin in adult Drosophila and the extent to which it may be necessary for reproductive functions.Previous studies showed that ecdysone (20E) regulates synthesis and release of ETH and expression of ETHR during larval stages of moths and mosquitoes (9-12). More recently, selftranscribing active regulatory region sequencing (STARR-Seq) data confirm that 20E induces 20E receptor (EcR) enhancer activity in promoters of both ETH and ETHR genes (13). Because circulating 20E levels are of major physiological and reproductive relevance (14), we also asked whether 20E influences ETH gene expression during the adult stage.Here we describe functional roles for 20E, ETH, and JH as a hormonal triad essential for reproductive success in Drosophila.In particular, we confirm persistence of ETH signaling throughout adulthood and demonstrate it...

Ecdysis-triggering hormone (ETH) is an integration factor in the ecdysis process of most insects, including Bombyx mori (silkworm). To understand the function of the ETH gene in silkworm, we developed an effective approach to knockdown the expression of ETH in vivo based on RNA interference (RNAi) and a binary UAS/GAL4 expression system that has been successfully used in other insect species. Two kinds of transgenic silkworm were established with this method: the effector strain with the ETH RNAi sequence under the control of UAS and the activator strain with the GAL4 coding sequence under the control of Bombyx mori cytoplasmic actin3. By crossing the two strains, double-positive transgenic silkworm was obtained, and their ETH expression was found to be dramatically lower than that of each single positive transgenic parent. Severe ecdysis deficiency proved lethal to the double-positive transgenic silkworm at the stage of pharate second instar larvae, while the single positive transgenic or wild-type silkworm had normal ecdysis. This UAS/GAL4 RNAi approach provides a way to study the function of endogenous silkworm genes at different development stages.

No abstract

Ecdysis-triggering hormone (ETH) is an integration factor in the ecdysis process of most insects, including Bombyx mori (silkworm). To understand the function of the ETH gene in silkworm, we developed an effective approach to knockdown the expression of ETH in vivo based on RNA interference (RNAi) and a binary UAS/GAL4 expression system that has been successfully used in other insect species. Two kinds of transgenic silkworm were established with this method: the effector strain with the ETH RNAi sequence under the control of UAS and the activator strain with the GAL4 coding sequence under the control of Bombyx mori cytoplasmic actin3. By crossing the two strains, double-positive transgenic silkworm was obtained, and their ETH expression was found to be dramatically lower than that of each single positive transgenic parent. Severe ecdysis deficiency proved lethal to the double-positive transgenic silkworm at the stage of pharate second instar larvae, while the single positive transgenic or wild-type silkworm had normal ecdysis. This UAS/GAL4 RNAi approach provides a way to study the function of endogenous silkworm genes at different development stages.

No abstract