Abstract
The myeloid differentiation factor 2 (MD-2)-related lipid-recognition protein is involved in immune responses through recognizing bacteria lipopolysaccharide in mammals, arthropods and plants. However, the physiological roles of MD-2 in other biological processes are largely unknown. Here, we identified three homologue MD-2 genes (NlML1, NlML2 and NlML3) by searching the genome and transcriptome databases of the brown planthopper Nilaparvata lugens, a hemipteran insect species. Temporospatial analysis showed that the NlML1 gene was highly expressed in the fat body but much less so in the other tissues, while the NlML2 and NlML3 genes were highly expressed in the testis or digestive tract. RNA interference-mediated depletion of the NlML1 gene significantly downregulated the transcription of numerous integument protein genes. The NlML1 knockdown led to moulting failure and mortality at the nymph-adult transition phase, impaired egg laying and hatching, and reduced 20-hydroxyecdysone (20E) production in the nymphs. 20E could rescue the deficient moulting phenotypes derived from dsNlML1 RNAi. These novel findings indicate that NlML1 is required for nymphal moulting and female reproductive success as it plays an important role in regulating 20E synthesis, lipid and chitin metabolisms in N. lugens, thus contributing to our understanding of developmental and reproductive mechanisms in insects.
Highlights
The myeloid differentiation factor 2 (MD-2)-related lipid-recognition protein was first identified in human kidney cell lines as an extracellular binding partner of Toll-like receptor 4 (TLR4), a mammalian homologue of Drosophila Toll [1]
In vivo studies have demonstrated that MD-2- or TLR4-deficient mice are hyporesponsive to LPS, which provided further evidence that the TLR4/MD-2 receptor complex is essential for LPS recognition and LPS signalling [4,5]
As 20E treatment rescued the moulting deficits derived from dsNlML1 RNA interference (RNAi), we investigated whether 20E affects the transcript levels of differentially expressed genes (DEGs) in dsNlML1-injected nymphs
Summary
The myeloid differentiation factor 2 (MD-2)-related lipid-recognition protein was first identified in human kidney cell lines as an extracellular binding partner of Toll-like receptor 4 (TLR4), a mammalian homologue of Drosophila Toll [1]. The biological functions of MD-2 proteins have been documented in humans, mice, Arabidopsis, shrimps, and insects of the Diptera order (such as the mosquitoes Aedes aegypti and Anopheles gambiae, and the fruit fly Drosophila melanogaster) and of the Lepidoptera order (such as the silkworm Bombyx mori and the tobacco hornworm Maduca sexta) [1,2,4,11,12,13,14,15,16,17,18,19,20] Studies on these species have revealed that MD-2 proteins play important roles in host–pathogen interactions. The systematic assessment of the in vivo physiological functions of this type of lipid-recognition protein has not been sufficiently studied
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