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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 ofmtg 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 inteal 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.