NPC1b as a novel target in controlling the cotton bollworm, Helicoverpa armigera.

BACKGROUND: Insects cannot synthesize sterols and must acquire them from food. The mechanisms underlying how insects uptake dietary sterols are largely unknown except that NPC1b, an integral membrane protein, has been shown to be responsible for dietary cholesterol uptake in Drosophila melanogaster. However, whether NPC1b orthologs in other insect species, particularly the economically important pests, function similarly remains to be determined. RESULTS: In this study, we characterized the function of NPC1b in Helicoverpa armigera, a global pest that causes severe yield losses to many important crops. Limiting dietary cholesterol uptake to insects significantly inhibited food ingestion and weight gain. Compared to the wild-type H. armigera, the CRISPR/Cas9-edited NPC1b mutant larvae were incapable of getting adequate cholesterol and died in their early life stage. Gene expression profile and in situ hybridization analyses indicated that NPC1b was mainly expressed in the midgut where dietary cholesterol was absorbed. Expression of NPC1b was also correlated with the feeding life stages and was especially upregulated during early larval instars. Protein-ligand docking and sequence similarity analyses further demonstrated that NPC1b proteins of lepidopteran insects shared a relatively conserved cholesterol binding region, NPC1b_NTD, which, however, was highly divergent from bees-derived sequences. CONCLUSION: NPC1b was crucial for dietary cholesterol uptake and growth of H. armigera, and therefore could serve as an insecticide target for the development of a novel pest-management approach to control this economically significant insect pest with little off-target effect on bees and sterol-autotrophic animals. © 2020 Society of Chemical Industry.

Phylogeny and evolution of the cholesterol transporter NPC1 in insects.

Sterols are essential nutrients for eukaryotes. Insects are obligate sterol auxotrophs and must acquire this key nutrient from their diets. The digestive tract is the organ for absorbing nutrients as well as sterols from food. In mice, the Niemann-Pick type C1 Like 1 (NPC1L1) gene is highly expressed in the intestine and is critical for cholesterol absorption. In contrast, the molecular mechanisms for the absorption of dietary sterols in insects have not been well studied. We annotated NPC1 genes in 39 insects from 10 orders using available genomic and transcriptomic information and inferred phylogenetic relationships. Insect NPC1 genes were grouped into two sister-clades, NPC1a and NPC1b, suggesting a likely duplication in the ancestor of insects. The former exhibited weaker gut-biased expression or a complete lack of tissue-biased expression, depending on the species, while the latter was highly enriched in the gut of three lepidopteran species. This result is similar to previous findings in Drosophila melanogaster. In insects, NPC1a accumulated non-synonymous substitutions at a lower rate than NPC1b. This pattern was consistent across orders, indicating that NPC1a evolved under stronger molecular constraint than NPC1b.