Can the mammalian organoid technology be applied to the insect gut?

Discovery of New Botanical Insecticides: Identification and Insecticidal Activity of Saponins from Clematis obscura Maxim and Insights into the Stress Response of Acyrthosiphon pisum Harris

To discover new botanical products-based insecticide candidates, 14 triterpenoid saponins (1-14) including four new ones, obscurosides A-D (1-4), were isolated from Clematis obscura Maxim as potential agrochemicals against Acyrthosiphon pisum Harris and Plutella xylostella (L.). Compounds 1-3 were characterized by a rare ribose substitution at C-3, and 4 was a bidesmoside glycosylated at the rare C-23 and C-28 positions of the oleanane aglycone. Compounds 10 (median antifeeding concentration, AFC50 = 1.10 mg/mL; half-lethal concentration, LC50 = 1.21 mg/mL) and 13 (AFC50 = 1.09 mg/mL, LC50 = 1.37 mg/mL) showed significant insecticidal activities against third larvae of P. xylostella at 72 h. All saponins displayed antifeedant activities against A. pisum with the deterrence index of 0.20-1.00 at 400 μg/mL. Compound 8 showed optimal oral toxicity (LC50 = 50.09 μg/mL) against A. pisum, followed by compounds 1, 5-7, 9, and 14 (LC50 = 90.21-179.25 μg/mL) at 72 h. The shrinkage of the cuticle and the destruction of intestinal structures of microvilli, nucleus, endoplasmic reticulum, and mitochondria were toxic symptoms of 8-treated A. pisum. The significantly declined Chitinase activity in 8-treated A. pisum with an inhibition rate of 79.1% at LC70 (70% lethal concentration) could be the main reason for its significant oral toxicities. Molecular docking revealed favorable affinities of compounds 1 and 8 with group I Chitinase OfChtI (Group I Chitinase from Ostrinia furnacalis) through conventional hydrogen bonds and alkey/π-alkey interactions by different patterns. These results will provide valuable information for the development of novel botanical pesticides for the management of insect pests, especially against A. pisum.

The untapped potential of cell culture in disentangling insect-microbial relationships

Cell culture is a powerful technique for the investigation of molecular mechanisms fundamental to health and disease in a diverse array of organisms. Cell lines offer several advantages, namely their simplistic approach and high degree of reproducibility. One field where cell culture has proven particularly useful is the study of the microbiome, where cell culture has led to the illumination of microbial influences on host immunity, nutrition, and physiology. Thus far, researchers have focused cell culture work predominantly on humans, but the growing field of insect microbiome research stands to benefit greatly from its application. Insects constitute one of Earth's most diverse and ancient life forms and, just as with humans, possess microbiomes with great significance to their health. Insects, which play critical roles in supporting food security and ecological stability, are facing increasing threats from agricultural intensification, climate change, and pesticide use. As the microbiome is closely tied to host health, gaining a more robust understanding is of increasing importance. In this review, we assert that the cultivation and utilization of insect gut cell lines in microbiome research will bridge critical knowledge gaps essential for informing insect management practices in a world under pressure.

Novel systems to study vector-pathogen interactions in malaria

Some parasitic diseases, such as malaria, require two hosts to complete their lifecycle: a human and an insect vector. Although most malaria research has focused on parasite development in the human host, the life cycle within the vector is critical for the propagation of the disease. The mosquito stage of the Plasmodium lifecycle represents a major demographic bottleneck, crucial for transmission blocking strategies. Furthermore, it is in the vector, where sexual recombination occurs generating "de novo" genetic diversity, which can favor the spread of drug resistance and hinder effective vaccine development. However, understanding of vector-parasite interactions is hampered by the lack of experimental systems that mimic the natural environment while allowing to control and standardize the complexity of the interactions. The breakthrough in stem cell technologies has provided new insights into human-pathogen interactions, but these advances have not been translated into insect models. Here, we review in vivo and in vitro systems that have been used so far to study malaria in the mosquito. We also highlight the relevance of single-cell technologies to progress understanding of these interactions with higher resolution and depth. Finally, we emphasize the necessity to develop robust and accessible ex vivo systems (tissues and organs) to enable investigation of the molecular mechanisms of parasite-vector interactions providing new targets for malaria control.

Cell penetrating peptides are versatile tools for enhancing multimodal uptake into cells from pest insects

Cell penetrating peptides (CPPs) are small peptides defined by their ability to deliver molecular cargo into cells. While the subject of frequent investigation for pharmaceutical drug delivery, little consideration has been given to the possibility of CPPs for use as insecticides or insecticide enhancers. Here, we characterize the entry of four fluorescently tagged CPPs into two insect cell lines and dissected midgut tissues in terms of both total quantity and mode of penetration. Fluorescent microscopy showed that substantial amounts of CPPs penetrate the plasma membrane via endosomal uptake in ovarian (Sf9) and midgut derived (AW1) lepidopteran cells and that this process was sensitive to selected endocytosis inhibitors. Differences in the quantity of uptake was observed between CPPs, and further differences were found in the ability CPP-1838 to efficiently penetrate membranes through passive diffusion. These findings were extended to primary midgut derived cells and dissected tissues suggesting that CPPs show a preference for goblet cells and that CPP-1838 shows far higher rates of penetration. CPP-1838 thus shows extraordinary abilities to penetrate cells efficiency in both a diffusional and endocytotic manner. From these results more sophisticated delivery methods based on the utilization of CPPs can be developed.

Immunosuppressive, antimicrobial and insecticidal activities of inhibitor cystine knot peptides produced by teratocytes of the endoparasitoid wasp Cotesia flavipes (Hymenoptera: Braconidae)

Teratocytes are specialized cells released by parasitoid wasps into their hosts. They are known for producing regulatory molecules that aid the development of immature parasitoids. We have recently reported the primary structures of cystine-rich peptides, including some containing inhibitor cystine knot (ICK) motifs, produced by teratocytes of the parasitoid Cotesia flavipes (Hymenoptera: Braconidae). ICKs are known for their stability and diverse biological functions. In this study, we produced four putative ICK peptides from the teratocytes of C. flavipes using solid-phase peptide synthesis or recombinant expression in E. coli, and investigated their functions on host immune modulation as well their potential to impair the development of two lepidopterans after ingestion of the peptides. In addition, the peptides were assayed against pathogens and human cells. The peptides did not influence total hemocyte count but suppressed cellular immunity, detectable as a reduction of hemocyte encapsulation (CftICK-I, CftICK-II, CftICK-III) and spread indexes (CftICK-IV) in the host. None of the peptides influenced the activities of prophenoloxidase and phenoloxidase in the hemolymph of larval Diatraea saccharalis (Lepidoptera: Crambidae). CftICK-I and CftICK-II with previously unknown function showed antifungal activity against Candida albicans but were non-toxic to human cells. CftICK-I, CftICK-II, and CftICK-III increased larval mortality and reduced leaf consumption of D. saccharalis, a permissive host for C. flavipes. The CftICK-III also increased larval mortality and reduced leaf consumption of Spodoptera frugiperda (Lepidoptera: Noctuidae), a non-permissive host for C. flavipes. This study highlights biological functions and biotechnological potential of ICK peptides from the teratocytes of C. flavipes.

Metabolization and sequestration of plant specialized metabolites in insect herbivores: Current and emerging approaches

Herbivorous insects encounter diverse plant specialized metabolites (PSMs) in their diet, that have deterrent, anti-nutritional, or toxic properties. Understanding how they cope with PSMs is crucial to understand their biology, population dynamics, and evolution. This review summarizes current and emerging cutting-edge methods that can be used to characterize the metabolic fate of PSMs, from ingestion to excretion or sequestration. It further emphasizes a workflow that enables not only to study PSM metabolism at different scales, but also to tackle and validate the genetic and biochemical mechanisms involved in PSM resistance by herbivores. This review thus aims at facilitating research on PSM-mediated plant-herbivore interactions.

Transcending Dimensions in Apicomplexan Research: from Two-Dimensional to Three-Dimensional In Vitro Cultures

Parasites belonging to the Apicomplexa phylum are among the most successful pathogens known in nature. They can infect a wide range of hosts, often remain undetected by the immune system, and cause acute and chronic illness. In this phylum, we can find parasites of human and veterinary health relevance, such as Toxoplasma, Plasmodium, Cryptosporidium, and Eimeria. There are still many unknowns about the biology of these pathogens due to the ethical and practical issues of performing research in their natural hosts. Animal models are often difficult or nonexistent, and as a result, there are apicomplexan life cycle stages that have not been studied. One recent alternative has been the use of three-dimensional (3D) systems such as organoids, 3D scaffolds with different matrices, microfluidic devices, organs-on-a-chip, and other tissue culture models. These 3D systems have facilitated and expanded the research of apicomplexans, allowing us to explore life stages that were previously out of reach and experimental procedures that were practically impossible to perform in animal models. Human- and animal-derived 3D systems can be obtained from different organs, allowing us to model host-pathogen interactions for diagnostic methods and vaccine development, drug testing, exploratory biology, and other applications. In this review, we summarize the most recent advances in the use of 3D systems applied to apicomplexans. We show the wide array of strategies that have been successfully used so far and apply them to explore other organisms that have been less studied.

Identification of Helicoverpa armigera promoters for biotechnological applications

Helicoverpa armigera and Helicoverpa zea are highly polyphagous major agricultural pests with a global distribution. Their control is based on insecticides, however, new, effective, and environmentally friendly control tools are required to be developed and validated. In an effort to facilitate the development of advanced biotechnological tools in these species that will take advantage of new powerful molecular biology techniques like CRISPR/Cas9, we used available transcriptomic data and literature resources, in order to identify RNA polymerase II and III promoters active in RP-HzGUT-AW1(MG), a midgut derived cell line from Helicoverpa zea. Following functional analysis in insect cell lines, four RNA polymerase II promoters from the genes HaLabial, HaTsp-2A, HaPtx-I and HaCaudal were found to exhibit high transcriptional activity in vitro. The HaTsp-2A promoter did not exhibit any activity in the non-midgut derived cell lines Sf-9 and Hi-5 despite high sequence conservation among Lepidoptera, suggesting that it may function in a gut specific manner. Furthermore, considering the utility of RNA polymerase III U6 promoters in methodologies such as RNAi and CRISPR/Cas9, we identified and evaluated four different U6 promoters of H. armigera. In vitro experiments based on luciferase and GFP reporter assays, as well as in vivo experiments targeting an essential gene of Helicoverpa, indicate that these U6 promoters are functional and can be used to experimentally silence or knockout target genes through the expression of shRNAs and sgRNAs respectively. Taking our findings together, we provide a set of promoters useful for the genetic manipulation of Helicoverpa species, that can be used in various applications in the context of agricultural biotechnology.

Mechanisms of Cell Entry by dsRNA Viruses: Insights for Efficient Delivery of dsRNA and Tools for Improved RNAi-Based Pest Control

While RNAi is often heralded as a promising new strategy for insect pest control, a major obstacle that still remains is the efficient delivery of dsRNA molecules within the cells of the targeted insects. However, it seems overlooked that dsRNA viruses already have developed efficient strategies for transport of dsRNA molecules across tissue barriers and cellular membranes. Besides protecting their dsRNA genomes in a protective shell, dsRNA viruses also display outer capsid layers that incorporate sophisticated mechanisms to disrupt the plasma membrane layer and to translocate core particles (with linear dsRNA genome fragments) within the cytoplasm. Because of the perceived efficiency of the translocation mechanism, it is well worth analyzing in detail the molecular processes that are used to achieve this feat. In this review, the mechanism of cell entry by dsRNA viruses belonging to the Reoviridae family is discussed in detail. Because of the large amount of progress in mammalian versus insect models, the mechanism of infections of reoviruses in mammals (orthoreoviruses, rotaviruses, orbiviruses) will be treated as a point of reference against which infections of reoviruses in insects (orbiviruses in midges, plant viruses in hemipterans, insect-specific cypoviruses in lepidopterans) will be compared. The goal of this discussion is to uncover the basic principles by which dsRNA viruses cross tissue barriers and translocate their cargo to the cellular cytoplasm; such knowledge subsequently can be incorporated into the design of dsRNA virus-based viral-like particles for optimal delivery of RNAi triggers in targeted insect pests.