Swevers, L. | bioRxiv Science

bioRxiv2022

Functional characterization of putative ecdysone transporters in lepidopteran pests

The insect steroid hormone ecdysone plays a critical role in insect development. Several recent studies have shown that ecdysone is transported through Organic Anion Transporting Polypeptides (OATPs) in insects such as flies and mosquitoes. However, the conservation of this mechanism across other arthropods and the role of this transporter in canonical ecdysone pathways are less well studied. Herein we functionally characterized the putative ecdysone transporter OATP74D from two major agricultural moth pests: Helicoverpa armigera (cotton bollworm) and Spodoptera frugiperda (fall armyworm). Phylogenetic analysis of OATP transporters across the superphylum Ecdysozoa revealed that Oatp74D is well represented among arthropod species and appeared only at the root of the arthropod lineage. Partial disruption of Oatp74D in S. frugiperda decreased embryo hatching rate and larval survival, suggesting that this gene is essential for development in vivo. Depletion and re-expression of OatP74D in the lepidoptera cell line RP-HzGUT-AW1(MG) confirmed the genes role in ecdysone import and demonstrated that OATP74D is essential for the transcriptional activation of ecdysone responsive genes including caspase-3, implicating this transporter in cell death pathways. Establishment of a simple and robust luciferase assay using the RP-HzGUT- AW1(MG) cell line demonstrated that both HaOATP74D and SfOATP74D are inhibited by rifampicin, a well-known organic anion transporter inhibitor. Overall, this work sheds more light on ecdysone uptake mechanisms across insect species and broadens our knowledge of the physiological roles of OATPs in the transportation of endogenous substrates. Author SummaryThe insect steroid hormone ecdysone is critical in regulating many aspects of insects life, including development and reproduction. A passive diffusion model was never functionally resolved, but was strongly supported until an organic anion transporting polypeptide was identified to mediate the transport of the hormone. The OATP74D, belonging to the Solute carrier superfamily, has been identified and functionally characterized for the first time in Drosophila melanogaster. Although phylogenetic analysis suggests that the Drosophila Oatp74D is probably conserved among several insect species, the theory for transporter mediated ecdysone uptake cannot be generalized to all insects without concrete proof. In here we provide functional evidence that the Oatp74D of two lepidopteran pest species: Helicoverpa armigera and Spodoptera frugiperda, is highly required for insect survival and development. Furthermore, we reveal that the OATP74D is necessary to regulate the expression of several ecdysone response genes, including caspase-3 which is involved in programmed cell death. In addition, we have developed a cell-based platform for screening chemical compounds against the lepidopteran orthologs of Oat74D and rifampicin was functionally shown to inhibit ecdysone uptake. Taken all together, our study reveals that Oatp74D is conserved among several arthropod species in the ecdysone pathway and given the high necessity for an effective control of these two lepidopteran species, we hypothesized that OATP74D could serve as a possible drug target in those two species.

genetics↗

bioRxiv2020

Identification of silkworm hemocyte subsets and analysis of their response to BmNPV infection based on single-cell RNA sequencing

A wide range of hemocyte types exist in insects but a full definition of the different subclasses is not yet established. The current knowledge of the classification of silkworm hemocytes mainly comes from morphology rather than specific markers, so our understanding of the detailed classification, hemocyte lineage and functions of silkworm hemocytes is very incomplete. Bombyx mori nucleopolyhedrovirus (BmNPV) is a representative member of the baculoviruses, which are a major pathogens that specifically infects silkworms and cause serious loss in sericulture industry. Here, we performed single-cell RNA sequencing (scRNA-seq) of silkworm hemocytes in BmNPV and mock-infected larvae to comprehensively identify silkworm hemocyte subsets and determined specific molecular and cellular characteristics in each hemocyte subset before and after viral infection. A total of 19 cell clusters and their potential marker genes were identified in silkworm hemocytes. Among these hemocyte clusters, clusters 0, 1, 2, 5 and 9 might be granulocytes (GR); clusters 14 and 17 were predicted as plasmatocytes (PL); cluster 18 was tentatively identified as spherulocytes (SP); and clusters 7 and 11 could possibly correspond to oenocytoids (OE). In addition, all of the hemocyte clusters were infected by BmNPV and some infected cells carried high viral-load in silkworm larvae at 3 day post infection (dpi). Interestingly, BmNPV infection can cause severe and diverse changes in gene expression in hemocytes. Cells belonging to the infection group mainly located at the early stage of the pseudotime trajectories. Furthermore, we found that BmNPV infection suppresses the immune response in the major hemocyte types. In summary, our scRNA-seq analysis revealed the diversity of silkworm hemocytes and provided a rich resource of gene expression profiles for a systems-level understanding of their functions in the uninfected condition and as a response to BmNPV.

microbiology↗