title: Retroactive maintains cuticle integrity by promoting the trafficking of Knickkopf into the procuticle of Tribolium castaneum.
abstract: Molting, or the replacement of the old exoskeleton with a new cuticle, is a complex developmental process that all insects must undergo to allow unhindered growth and development. Prior to each molt, the developing new cuticle must resist the actions of potent chitinolytic enzymes that degrade the overlying old cuticle. We recently disproved the classical dogma that a physical barrier prevents chitinases from accessing the new cuticle and showed that the chitin-binding protein Knickkopf (Knk) protects the new cuticle from degradation. Here we demonstrate that, in Tribolium castaneum, the protein Retroactive (TcRtv) is an essential mediator of this protective effect of Knk. TcRtv localizes within epidermal cells and specifically confers protection to the new cuticle against chitinases by facilitating the trafficking of TcKnk into the procuticle. Down-regulation of TcRtv resulted in entrapment of TcKnk within the epidermal cells and caused molting defects and lethality in all stages of insect growth, consistent with the loss of TcKnk function. Given the ubiquity of Rtv and Knk orthologs in arthropods, we propose that this mechanism of new cuticle protection is conserved throughout the phylum.
authors: Department of Biochemistry, Kansas State University, Manhattan, Kansas, United States of America. sujatasv@ksu.edu
authors: Sujata S
authors: SS
authors: Chaudhari
authors: Yasuyuki
authors: Y
authors: Arakane
authors: Charles A
authors: CA
authors: Specht
authors: Bernard
authors: B
authors: Moussian
authors: Karl J
authors: KJ
authors: Kramer
authors: Subbaratnam
authors: S
authors: Muthukrishnan
authors: Richard W
authors: RW
authors: Beeman
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D002686:Chitin / Q000096:biosynthesis / Q000235:genetics; D002688:Chitinases / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics; D018978:Molting / Q000235:genetics / Q000502:physiology; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid; D014231:Tribolium / Q000201:enzymology / Q000235:genetics / Q000254:growth & development
chemical_list: D002352:Carrier Proteins; D029721:Drosophila Proteins; D019476:Insect Proteins; D008565:Membrane Proteins; C506753:knk protein, Drosophila; C504913:rtv protein, Drosophila; D002686:Chitin; D002688:Chitinases
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