Transcription and Post-translational Regulation of Autophagy in Insects

Understanding the role of trehalose in interactions between Wolbachia and Aedes aegypti

Mosquito-borne diseases such as chikungunya, dengue, and Zika represent a major burden on global public health. To fight against these arboviruses, vector control strategies are a priority. One existing strategy is based on the use of an endosymbiotic bacterium, Wolbachia, which reduces the transmission of arboviruses by the mosquito Aedes aegypti via a pathogen blocking effect. Wolbachia in Ae. aegypti disrupts several pathways of the host's metabolism. Trehalose is a carbohydrate circulating mainly in insect hemolymph and plays a role in numerous mechanisms as energy source or stress recovery molecule and in chitin synthesis. This study explores the importance of trehalose in the interactions between Wolbachia and Ae. aegypti, and attempts to understand the pathogen blocking effect.

Regulation of antimicrobial peptides in Hermetia illucens in response to fungal exposure

The black soldier fly (Hermetia illucens) is important for antimicrobial peptide (AMP) research due to its exposure to diverse microorganisms. However, the impact of different fungi on AMP abundance in H. illucens remains unexplored. We studied the induction of AMP expression under basal conditions and with three fungi: non-pathogenic Candida tropicalis, Saccharomyces cerevisiae, and pathogenic Beauveria bassiana, using RNA-sequencing and liquid chromatography with tandem mass spectrometry. Under naive conditions, most AMPs belonged to the lysozyme, cecropin, and defensin classes, with defensins most abundant. We demonstrate that dietary supplementation with fungi is sufficient to induce AMP expression in H. illucens. However, exposure to C. tropicalis and B. bassiana also caused downregulation of certain AMPs, suggesting that these fungi may suppress or modulate the host immune response to aid in their survival and colonization. Evidently, S. cerevisiae and B. bassiana trigger similar AMP pathways, whereas C. tropicalis elicits a distinct reaction with upregulation of defensins and cecropins. Lysozymes were upregulated by S. cerevisiae and B. bassiana, but downregulated by C. tropicalis, potentially facilitating fungal survival in the larval gut. Understanding these mechanisms opens possibilities for leveraging AMPs to combat C. tropicalis, which is implicated in human diseases.

Molecular mechanism of Serratia marcescens Bizio infection in Reticulitermes chinensis Snyder based on full-length SMRT transcriptome sequencing

Reticulitermes chinensis Snyder is an important pest in forestry and construction and is widely distributed in China. We found that Serratia marcescens Bizio strain SM1 has insecticidal activity to R. chinensis, but the pathogenic mechanism of SM1 to R. chinensis is not clear. Therefore, full-length transcriptome sequencing was performed on R. chinensis infected with SM1 and the control group. A total of 230 differentially expressed genes were identified by comparing SM1 infection group and the control group, among which 103 were downregulated and 127 were upregulated. We found downregulated genes in nine metabolic pathway categories, among which carbohydrate metabolism had the most downregulated genes, followed by energy metabolism and amino acid metabolism. We also found that some downregulated genes were related to pattern recognition receptors, cellular immunity, and humoral immunity, indicating that R. chinensis immunity was negatively affected by SM1 infection. In addition, some genes in signal transduction and genetic information processing pathways were downregulated. In this study, high-throughput full-length transcriptome analysis was used to analyse the pathogenic mechanism of SM1 to R. chinensis. The results of this study provide useful information for exploring the relationship between SM1 and R. chinensis, and provide theoretical support for the future application of SM1 and the prevention and treatment of R. chinensis.

Protein modification regulated autophagy in Bombyx mori and Drosophila melanogaster

Post-translational modifications refer to the chemical alterations of proteins following their biosynthesis, leading to changes in protein properties. These modifications, which encompass acetylation, phosphorylation, methylation, SUMOylation, ubiquitination, and others, are pivotal in a myriad of cellular functions. Macroautophagy, also known as autophagy, is a major degradation of intracellular components to cope with stress conditions and strictly regulated by nutrient depletion, insulin signaling, and energy production in mammals. Intriguingly, in insects, 20-hydroxyecdysone signaling predominantly stimulates the expression of most autophagy-related genes while concurrently inhibiting mTOR activity, thereby initiating autophagy. In this review, we will outline post-translational modification-regulated autophagy in insects, including Bombyx mori and Drosophila melanogaster, in brief. A more profound understanding of the biological significance of post-translational modifications in autophagy machinery not only unveils novel opportunities for autophagy intervention strategies but also illuminates their potential roles in development, cell differentiation, and the process of learning and memory processes in both insects and mammals.

Exploring the connection between autophagy and heat-stress tolerance in Drosophila melanogaster

Mechanisms aimed at recovering from heat-induced damages are closely associated with the ability of ectotherms to survive exposure to stressful temperatures. Autophagy, a ubiquitous stress-responsive catabolic process, has recently gained renewed attention as one of these mechanisms. By increasing the turnover of cellular structures as well as the clearance of long-lived protein and protein aggregates, the induction of autophagy has been linked to increased tolerance to a range of abiotic stressors in diverse ectothermic organisms. However, whether a link between autophagy and heat-tolerance exists in insect models remains unclear despite broad ecophysiological implications thereof. Here, we explored the putative association between autophagy and heat-tolerance using Drosophila melanogaster as a model. We hypothesized that (i) heat-stress would cause an increase of autophagy in flies' tissues, and (ii) rapamycin exposure would trigger a detectable autophagic response in adults and increase their heat-tolerance. In line with our hypothesis, we report that flies exposed to heat-stress present signs of protein aggregation and appear to trigger an autophagy-related homoeostatic response as a result. We further show that rapamycin feeding causes the systemic effect associated with target of rapamycin (TOR) inhibition, induces autophagy locally in the fly gut, and increases the heat-stress tolerance of individuals. These results argue in favour of a substantial contribution of autophagy to the heat-stress tolerance mechanisms of insects.

Autophagy Is Required to Sustain Increased Intestinal Cell Proliferation during Phenotypic Plasticity Changes in Honey Bee (Apis mellifera)

Tissue phenotypic plasticity facilitates rapid adaptation of organisms to biotic and/or abiotic pressure. The reproductive capacity of honey bee workers (Apis mellifera) is plastic and responsive to pheromones produced by broods and the queen. Egg laying workers (ELWs), which could reactivate their ovaries and lay haploid eggs upon queen lost, have been commonly discussed from many aspects. However, it remains unclear whether midgut homeostasis in ELWs is affected during plastic changes. Here, we found that the expression of nutrition- and autophagy-related genes was up-regulated in the midguts of ELWs, compared with that in nurse workers (NWs) by RNA-sequencing. Furthermore, the area and number of autophagosomes were increased, along with significantly increased cell death in the midguts of ELWs. Moreover, cell cycle progression in the midguts of ELWs was increased compared with that in NWs. Consistent with the up-regulation of nutrition-related genes, the body and midgut sizes, and the number of intestinal proliferation cells of larvae reared with royal jelly (RJ) obviously increased more than those reared without RJ in vitro. Finally, cell proliferation was dramatically suppressed in the midguts of ELWs when autophagy was inhibited. Altogether, our data suggested that autophagy was induced and required to sustain cell proliferation in ELWs' midguts, thereby revealing the critical role of autophagy played in the intestines during phenotypic plasticity changes.