The DOMON domain protein LmKnk contributes to correct chitin content, pore canal formation and lipid deposition in the cuticle of Locusta migratoria during moulting
Funding information: German Research Foundation, Grant/Award Number: DFG grant MO1714/10-1; National Natural Science Foundation of China, Grant/Award Number: 31730074/31801749/31672364/31761133021; Project of Higher Institution Science and Technology Innovation of Shanxi Province, Grant/Award Number: 2019L0796; the Program for Top Young Academic Leaders of Higher Learning Institutions of Shanxi Province, Grant/Award Number: (TYAL) 2017
Insects prevent uncontrolled penetration of water and xenobiotics by producing an impermeable cuticle. The major component of the cuticle is chitin that adopts a crystalline structure thereby contributing to cuticle stability. Our understanding of the contribution of chitin to the cuticle barrier function is limited. Here, we studied the role of the DOMON domain protein Knickkopf (LmKnk) that is involved in chitin organization and cuticle permeability in the migratory locust Locusta migratoria. We show that LmKnk localizes to the chitin layer in the newly produced cuticle. Injection of double-stranded RNA targeting LmKnk (dsLmKnk) in locust nymphs caused failure of moulting to the next stage. Histological experiments revealed that apolysis, i.e., the detachment of the old cuticle from the body surface, was normal; however, the newly synthesized cuticle was thinner than the cuticle of the control insects. Indeed, chitin content dropped after suppression of LmKnk expression. As seen by transmission electron microscopy, crystalline chitin organization was lost in dsLmKnk-treated insects. In addition, the structure of pore canals, which are lipid transporting routes in the cuticle, was abnormal. Consistently, their content was reduced and, probably by consequence, lipid deposition on the cuticle was decreased after injection of dsLmKnk. Suppression of LmKnk transcript levels rendered L. migratoria more susceptible to each of four selected insecticides including malathion, chlorpyrifos, carbaryl and deltamethrin. Overall, our data show that LmKnk is needed for correct chitin amounts and organization, and their changes ultimately affect cuticular permeability in L. migratoria.
CONFLICT OF INTEREST
The authors declare that they have no conflicts of interest with the contents of this article.
DATA AVAILABILITY STATEMENT
The data that supports the findings of this study are available in the supplementary material of this article