Involvement of mind the gap in the organization of the tracheal apical extracellular matrix in Drosophila and Nilaparvata lugens.

The tracheal apical extracellular matrix (aECM) is vital for expansion of the tracheal lumen and supports the normal structure of the lumen to guarantee air entry and circulation in insects. Although it has been found that some cuticular proteins are involved in the organization of the aECM, unidentified factors still exist. Here, we found that mind the gap (Mtg), a predicted chitin-binding protein, is required for the normal formation of the apical chitin matrix of airway tubes in the model holometabolous insect Drosophila melanogaster. Similar to chitin, the Mtg protein was linearly arranged in the tracheal dorsal trunk of the tracheae in Drosophila. Decreased mtg expression in the tracheae seriously affected the viability of larvae and caused tracheal chitin spiral defects in some larvae. Analysis of mtg mutant showed that mtg was required for normal development of tracheae in embryos. Irregular taenidial folds of some mtg mutant embryos were found on either lateral view of tracheal dorsal trunk or internal view of transmission electron microscopy analysis. These abnormal tracheae were not fully filled with gas and accompanied by a reduction in tracheal width, which are characteristic phenotypes of tracheal aECM defects. Furthermore, in the hemimetabolous brown planthopper (BPH) Nilaparvata lugens, downregulation of NlCPAP1-N (a homolog of mtg) also led to the formation of abnormal tracheal chitin spirals and death. These results suggest that mtg and its homolog are involved in the proper organization of the tracheal aECMs in flies and BPH, and that this function may be conserved in insects.

Genome-Wide Screening and Functional Analysis Reveal That the Specific microRNA nlu-miR-173 Regulates Molting by Targeting Ftz-F1 in Nilaparvata lugens.

Background: Molting is a crucial physiological behavior during arthropod growth. In the past few years, molting as well as chitin biosynthesis triggered by molting, is subject to regulation by miRNAs. However, how many miRNAs are involved in insect molting at the genome-wide level remains unknown. Results: We deeply sequenced four samples obtained from nymphs at the 2nd-3rd and 4th-5th instars, and then identified 61 miRNAs conserved in the Arthropoda and 326 putative novel miRNAs in the brown planthopper Nilaparvata lugens, a fearful pest of rice. A total of 36 mature miRNAs with significant different expression levels at the genome scale during molting, including 19 conserved and 17 putative novel miRNAs were identified. After comparing the expression profiles, we found that most of the targets of 36 miRNAs showing significantly differential expression were involved in energy and hormone pathways. One of the 17 putative novel miRNAs, nlu-miR-173 was chosen for functional study. nlu-miR-173 acts in 20-hydroxyecdysone signaling through its direct target, N. lugens Ftz-F1(NlFtz-F1), a transcription factor. Furthermore, we found that the transcription of nlu-miR-173 was promoted by Broad-Complex (BR-C), suggesting that its involvement in the 20-hydroxyecdysone pathway contributes to proper molting function. Conclusion: We provided a comprehensive resource of miRNAs associated with insect molting and identified a novel miRNA as a potential target for pest control.