The role of diuretic hormones (DHs) and their receptors in Drosophila

Functional characterization of two DH44R genes associated with starvation and desiccation in Rhopalosiphum padi (Hemiptera: Aphididae)

CRF-like diuretic hormone receptor (CRF/DHR), also known as DH44R in insects, are G-protein coupled receptors (GPCRs) that play a role in regulating osmotic balance in various insect species. These receptors have the potential to be targeted for the development of insecticides. However, our understanding of the role of DHR genes in aphids, including Rhopalosiphum padi, a major wheat pest, is currently limited. In this study, we isolated and characterized two R. padi DHRs (RpDHR1 and RpDHR2). The expression levels of RpDHR1 increased after starvation and were restored after re-feeding. The expression levels of RpDHR1 gene decreased significantly 24 h after injection of dsRNA targeting the gene. Knockdown of RpDHR1 increased aphid mortality under starvation conditions (24, 36, 48 and 60 h). Under starvation and desiccation condition, the aphid mortality decreased after knockdown of RpDHR1. This is the first study to report the role of DHR genes in the starvation and desiccation response of aphids. The results suggest that RpDHR1 is involved in the resistance of R. padi to starvation and dehydration, making it a potential target for insecticide development. Novel insecticides could be created by utilizing DHR agonists to disrupt the physiological processes of insect pests.

Cellular and molecular organization of the Drosophila foregut

The animal foregut is the first tissue to encounter ingested food, bacteria, and viruses. We characterized the adult Drosophila foregut using transcriptomics to better understand how it triages consumed items for digestion or immune response and manages resources. Cell types were assigned and validated using GFP-tagged and Gal4 reporter lines. Foregut-associated neuroendocrine cells play a major integrative role by coordinating gut activity with nutrition, the microbiome, and circadian cycles; some express clock genes. Multiple epithelial cell types comprise the proventriculus, the central foregut organ that secretes the peritrophic matrix (PM) lining the gut. Analyzing cell types synthesizing individual PM layers revealed abundant mucin production close to enterocytes, similar to the mammalian intestinal mucosa. The esophagus and salivary gland express secreted proteins likely to line the esophageal surface, some of which may generate a foregut commensal niche housing specific gut microbiome species. Overall, our results imply that the foregut coordinates dietary sensing, hormonal regulation, and immunity in a manner that has been conserved during animal evolution.

Unraveling the G protein-coupled receptor superfamily in aphids: Contractions and duplications linked to phloem feeding

The G Protein-Coupled Receptor (GPCR) superfamily is the largest and most diverse transmembrane receptor family, playing crucial roles in regulating various physiological processes. As one of the most destructive pests, aphids have been subject to previous studies, which revealed fewer GPCR superfamily members in Acyrthosiphon pisum and Aphis gossypii and the loss of multiple neuropeptide GPCRs. To elucidate the contraction patterns and evolutionary features of the aphid GPCR superfamily, we identified 97, 105, and 95 GPCR genes in Rhopalosiphum maidis, A. pisum, and A. gossypii, respectively. Comparative analysis and phylogenetic investigations with other hemipteran insects revealed a contracted GPCR superfamily in aphids. This contraction mainly occurred in biogenic amine receptors, GABA-B-R, and fz families, and several neuropeptide receptors such as ACPR, CrzR, and PTHR were completely lost. This phenomenon may be related to the parasitic nature of aphids. Additionally, several GPCRs associated with aphid feeding and water balance underwent duplication, including Lkr, NPFR, CCHa1-R, and DH-R, Type A LGRs, but the SK/CCKLR that inhibits feeding was completely lost, indicating changes in feeding genes that underpin the aphid's prolonged phloem feeding behavior. Furthermore, we observed fine-tuning in opsins, with reduced long-wavelength opsins and additional duplications of short-wavelength opsin, likely associated with daytime activity. Lastly, we found variations in the number of mthl genes in aphids. In conclusion, our investigation sheds light on the GPCR superfamily in aphids, revealing its association with diet lifestyle and laying the foundation for understanding and developing control strategies for the aphid GPCR superfamily.

The neuroendocrine and endocrine systems in insect - Historical perspective and overview

A complex cascade of events leads to the initiation and maintenance of a behavioral act in response to both internally and externally derived stimuli. These events are part of a transition of the animal into a new behavioral state, coordinated by chemicals that bias tissues and organs towards a new functional state of the animal. This form of integration is defined by the neuroendocrine (or neurosecretory) system and the endocrine system that release neurohormones or hormones, respectively. Here we describe the classical neuroendocrine and endocrine systems in insects to provide an historic perspective and overview of how neurohormones and hormones support plasticity in behavioral expression. Additionally, we describe peripheral tissues such as the midgut, epitracheal glands, and ovaries, which, whilst not necessarily being endocrine glands in the pure sense of the term, do produce and release hormones, thereby providing even more flexibility for inter-organ communication and regulation.

Structural and functional characterization of an egg-laying hormone signaling system in a lophotrochozoan - The pacific oyster (Crassostrea gigas)

The egg-laying hormones (ELHs) of gastropod mollusks were characterized more than forty years ago. Yet, they have remained little explored in other mollusks. To gain insights into the functionality of the ELH signaling system in a bivalve mollusk - the oyster Crassostrea gigas, this study investigates the processing of its ELH precursor (Cragi-ELH) by mass spectrometry. Some of the ELH mature peptides identified in this study were subsequently investigated by nuclear magnetic resonance and shown to adopt an extended alpha-helix structure in a micellar medium mimicking the plasma membrane. To further characterize the ELH signaling system in C. gigas, a G protein-coupled receptor phylogenetically related to ecdysozoan diuretic hormone DH44 and corticotropin-releasing hormone (CRH) receptors named Cragi-ELHR was also characterized functionally and shown to be specifically activated by the two predicted mature ELH peptides and their N-terminal fragments. Both Cragi-ELH and Cragi-ELHR encoding genes were mostly expressed in the visceral ganglia (VG). Cragi-ELH expression was significantly increased in the VG of both fully mature male and female oysters at the spawning stage. When the oysters were submitted to a nutritional or hyposaline stress, no change in the expression of the ligand or receptor genes was recorded, except for Cragi-ELHR only during a mild acclimation episode to brackish water. These results suggest a role of Cragi-ELH signaling in the regulation of reproduction but not in mediating the stress response in our experimental conditions.

Diuretic hormone 31 activates two G protein-coupled receptors with differential second messengers for diuresis in Drosophila suzukii

Diuretic hormones (DHs) bind to G protein-coupled receptors (GPCRs), regulating water and ion balance to maintain homeostasis in animals. Two distinct DHs are known in insects: calcitonin (CT)-like DH31 and corticotropin-releasing factor (CRF)-like DH44. In this study, we identified and characterized DH31 and two DH31 GPCR variants, DH31-Ra and DH31-Rb, from spotted-wing drosophila, Drosophila suzukii, a globally prevalent vinegar fly causing severe damage to small fruits. Both GPCRs are active, but DH31-Ra is the dominant receptor based on gene expression analyses and DH31 peptide binding affinities. A notable difference between the two variants lies in 1) the GPCR structures of their C-termini and 2) the utilization of second messengers, and the amino acid sequences of the two variants are identical. DH31-Ra contains 12 additional amino acids, providing different intracellular C-terminal configurations. DH31-Ra utilizes both cAMP and Ca2+ as second messengers, whereas DH31-Rb utilizes only cAMP; this is the first time reported for an insect CT-like DH31 peptide. DH31 stimulated fluid secretion in D. suzukii adults, and secretion increased in a dose-dependent manner. However, when the fly was injected with a mixture of DH31 and CAPA, an anti-diuretic hormone, fluid secretion was suppressed. Here, we discuss the structures of the DH31 receptors and the differential signaling pathways, including second messengers, involved in fly diuresis. These findings provide fundamental insights into the characterization of D. suzukii DH31 and DH31-Rs, and facilitate the identification of potential biological targets for D. suzukii management.