Cuticular protein with a low complexity sequence becomes cross-linked during insect cuticle sclerotization and is required for the adult molt

• Published in: Scientific reports 2015-05, Vol.5 (1), p.10484-10484, Article 10484
• Main Authors: Mun, Seulgi, Young Noh, Mi, Dittmer, Neal T., Muthukrishnan, Subbaratnam, Kramer, Karl J., Kanost, Michael R., Arakane, Yasuyuki
• Format: Article
• Language: English
• Subjects: 14/19; 38; 38/1; 38/39; 38/89; 631/136/1660/1646; 631/337/505; 64/116; Adults; Amino Acid Sequence; Amino acids; Animals; Base Sequence; Chitin; Chitin - metabolism; Eclosion; Elytra; Epicuticle; Humanities and Social Sciences; Insect Hormones - metabolism; Insect Proteins - antagonists & inhibitors; Insect Proteins - genetics; Insect Proteins - metabolism; Insects; Laccase - metabolism; Larva - growth & development; Larva - metabolism; Maturation; Microscopy, Electron, Transmission; Molecular Sequence Data; Molting; multidisciplinary; Oxidation; Phenotype; Proteins; Pupa - growth & development; Pupa - metabolism; Quinones; Recombinant Proteins - biosynthesis; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; RNA Interference; RNA, Double-Stranded - metabolism; RNA-mediated interference; Science; Sclerotization; Structural proteins; Tribolium - growth & development; Tribolium - metabolism; Wings, Animal - metabolism; Wings, Animal - ultrastructure
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep10484

In the insect cuticle, structural proteins (CPs) and the polysaccharide chitin are the major components. It has been hypothesized that CPs are cross-linked to other CPs and possibly to chitin by quinones or quinone methides produced by the laccase2-mediated oxidation of N -acylcatechols. In this study we investigated functions of TcCP30, the third most abundant CP in protein extracts of elytra (wing covers) from Tribolium castaneum adults. The mature TcCP30 protein has a low complexity and highly polar amino acid sequence. TcCP30 is localized with chitin in horizontal laminae and vertically oriented columnar structures in rigid cuticles, but not in soft and membranous cuticles. Immunoblot analysis revealed that TcCP30 undergoes laccase2-mediated cross-linking during cuticle maturation in vivo , a process confirmed in vitro using recombinant rTcCP30. We identified TcCPR27 and TcCPR18, the two most abundant proteins in the elytra, as putative cross-linking partners of TcCP30. RNAi for the TcCP30 gene had no effect on larval and pupal growth and development. However, during adult eclosion, ~70% of the adults were unable to shed their exuvium and died. These results support the hypothesis that TcCP30 plays an integral role as a cross-linked structural protein in the formation of lightweight rigid cuticle of the beetle.