Two sphingomyelin synthase homologues regulate body weight and sphingomyelin synthesis in female brown planthopper, N. lugens (Stål)

Knockdown of sphingomyelinase (NlSMase) causes ovarian malformation of brown planthopper, Nilaparvata lugens (Stål)

Sphingomyelinases (SMases) are a group of enzymes that catalyse the hydrolysis of sphingomyelins into ceramides and phosphorylcholine. They have been intensively investigated for their pathophysiological roles in mammals whereas much remains unclear about their counterparts in insects. Herein we report the cloning and functional characterization of four SMase homologue genes, designated NlSMase1-4, from brown planthopper (BPH). The phylogenetic analysis revealed that NlSMase1 and NlSMase2 were clustered into acid SMase family, and NlSMase3 and NlSMase4 with neutral SMase family. NlSMase1, NlSMase3 and NlSMase4 were highly expressed in BPH females, and NlSMaes2 in the 5th instar nymph. All four NlSMases had the lowest transcription in BPH males. NlSMase1 and NlSMase4 were highly expressed in BPH ovaries, while NlSMase2 and NlSMase3 in midgut and wings, respectively. Knocking-down of each NlSMase individual by RNA interference (RNAi) caused the ovarian malformation in BPH. The transcriptomic analysis revealed that NlSMase4 knockdown could strongly affect diacylglycerol (DAG)-related metabolisms and their downstream pathways. Further, qRT-PCR analysis of vitellogenin (Vg) genes indicates that the DAG metabolism disorder could interrupt the essential Vg accumulation for BPH oogenesis. Our study demonstrates the vital role of NlSMases in BPH reproductive development and provides new insights into the mediated mechanism of how SMases function.

Characterization of MicroRNAs Associated with Reproduction in the Brown Planthopper, Nilaparvata lugens

Insects have a robust capacity to produce offspring for propagation, and the reproductive events of female insects have been achieved at the molecular and physiological levels via regulatory gene pathways. However, the roles of MicroRNAs (miRNAs) in the reproductive development of the brown planthopper (BPH), Nilaparvata lugens, remain largely unexplored. To understand the roles of miRNAs in reproductive development, miRNAs were identified by Solexa sequencing in short-winged (SW) female adults of BPH. Small RNA libraries derived from three developmental phases (1 day, 3 days, and 5 days after emergence) were constructed and sequenced. We identified 905 miRNAs, including 263 known and 642 novel miRNAs. Among them, a total of 43 miRNAs were differentially expressed in the three developmental phases, and 14,568 putative targets for 43 differentially expressed miRNAs (DEMs) were predicted by TargetScan and miRanda. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the predicted miRNA targets illustrated the putative roles for these DEMs in reproduction. The progress events were annotated, including oogenesis, lipid biosynthetic process, and related pathways such as apoptosis, ABC transporters, and amino acid metabolism. Four highly abundant DEMs (miR-9a-5p, miR-34-5p, miR-275-3p, and miR-317-3p) were further screened, and miR-34-5p was confirmed to be involved in the regulation of reproduction. Overexpression of miR-34-5p via injecting its mimics reduced fecundity and decreased Vg expression. Moreover, target genes prediction for miR-34-5p showed they might be involved in 20E signaling cascades, apoptosis, and gonadal development, including hormone receptor 4 (HR4), caspase-1 (Cp-1), and spermatogenesis-associated protein 20 (SPATA20). These findings provide a valuable resource for future studies on the role of miRNAs in BPH reproductive development.

Bacillus symbiont drives alterations in intestinal microbiota and circulating metabolites of lepidopteran host

The symbiotic association between bacterial symbionts and insect hosts is a complicated process that is not completely understood. Herein, we used a silkworm model to study the association between symbiotic Bacillus and lepidopteran insect by investigating the changes in intestinal microbiota and hemolymph circulating metabolites of silkworm after symbiotic Bacillus subtilis treatment. Results showed that B. subtilis can generate a variety of primary and secondary metabolites, such as B vitamins and antimicrobial compounds, to provide micronutrients and enhance the pathogen resistance of their insect host. Shifts in the relative abundance of Enterococcus, Brevibacterium, Buttiauxella, Pseudomonas, Brevundimonas, and Limnobacter had significant correlations with the concentrations of differential metabolites (e.g., phospholipids and certain amino acids) in insect hemolymph. The antimicrobial compounds secreted by B. subtilis were the primary driving force for the reconstruction of intestinal microbiota. Meanwhile, the altered levels of circulating metabolites in multiple metabolic pathways were potential an adaptive mechanism of insect hosts in response to the shifts of intestinal microbiota. Our findings provided concrete evidence that bacterial intestinal symbiont can alter the physiological state of insects and highlighted the importance of the compositional alterations of intestinal microbiota as a source of variation in circulating metabolites of insect hosts. This article is protected by copyright. All rights reserved.

Neutral Ceramidase Is Required for the Reproduction of Brown Planthopper, Nilaparvata lugens (Stål)

Ceramides are bioactive sphingolipids that have been implicated in insect development; however, their role in insect reproduction remains poorly understood. Here, we report the pivotal role of neutral ceramidase (NCER) in the female reproduction of the brown planthopper (BPH), Nilaparvata lugens (Stål), a significant pest in rice cultivation in Asia. LC-MS/MS demonstrated that, among different developmental stages of BPH, the levels of ceramides were highest in 1st instar nymphs and lowest in adults. The transcription of NCER was negatively correlated with the levels of ceramides at different developmental stages of BPH, in that the transcript levels of NCER were the highest, whereas ceramides levels were the lowest in BPH adults. Knocking down NCER through RNA interference (RNAi) increased the levels of ceramides in BPH females and ovaries, which resulted in a delay in oocyte maturation, a reduction in oviposition and egg hatching rate, as well as the production of vulnerable offspring. Transmission electron microscopy (TEM) analysis and TdT-mediated dUTP Nick-End Labeling (TUNEL) assays showed mitochondrial deficiency and apoptosis in NCER-deficient oocytes. Taken together, these results suggest that NCER plays a crucial role in female reproduction in BPH, likely by regulating the levels of ceramides.

Extraction and Quantification of Sphingolipids from Hemiptera Insects by Ultra-Performance Liquid Chromatography Coupled to Tandem Mass Spectrometry

Sphingolipids are major structural components of endomembranes and have also been described as an intracellular second messenger involved in various biological functions in all eukaryotes and a few prokaryotes. Ceramides (Cer), the central molecules of sphingolipids, have been depicted in cell growth arrest, cell differentiation, and apoptosis. With the development of lipidomics, the identification of ceramides has been analyzed in many species, mostly in model insects. However, there is still a lack of research in non-model organisms. Here we describe a relatively simple and sensitive method for the extraction, identification, and quantification of ceramides in Hemiptera Insects (brown planthooper), followed by Ultra-Performance Liquid Chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). C18 is used as the separation column for quantitative detection and analysis on the triple quadruple liquid mass spectrometer. In this protocol, the standard curve method is adopted to confirm the more accurate quantification of ceramides based on the optional detection conditions.