Sob gene is critical to wing development in Bombyx mori and Tribolium castaneum

A cuticular protein, BgCPLCP1, contributes to insecticide resistance by thickening the cockroach endocuticle

Overuse of insecticides has led to severe environmental problems. Insect cuticle, which consists mainly of chitin, proteins and a thin outer lipid layer, serves multiple functions. Its prominent role is as a physical barrier that impedes the penetration of xenobiotics, including insecticides. Blattella germanica (L.) is a major worldwide indoor pest that causes allergic disease and asthma. Extensive use of pyrethroid insecticides, including β-cypermethrin, has selected for the rapid and independent evolution of resistance in cockroach populations on a global scale. We demonstrated that BgCPLCP1, the first CPLCP (cuticular proteins of low complexity with a highly repetitive proline-rich region) family cuticular protein in order Blattodea, contributes to insecticide penetration resistance. Silencing BgCPLCP1 resulted in 85.0 %-85.7 % and 81.0 %-82.0 % thinner cuticle (and especially thinner endocuticle) in the insecticide-susceptible (S) and β-cypermethrin-resistant (R) strains, respectively. The thinner and more permeable cuticles resulted in 14.4 % and 20.0 % lower survival of β-cypermethrin-treated S- and R-strain cockroaches, respectively. This study advances our understanding of cuticular penetration resistance in insects and opens opportunities for the development of new efficiently and environmentally friendly insecticides targeting the CPLCP family of cuticular proteins.

Immune function analysis of LsSd, a transcription factor of the Hippo signaling pathway, in the cigarette beetle Lasioderma serricorne

The Scalloped (Sd) is a transcription factor that regulates organ size control in the Hippo-signaling pathway. Recent studies have showed that Hippo signaling also functions in the innate immune response. Although the Sd gene has been reported in many insects, their immune functions remain unexplored. In this study, the LsSd gene of Lasioderma serricorne, with a complete open reading frame that encodes a protein composed of 402 amino acids was identified. LsSd was predominantly expressed in early pupae. Tissue-specific analyses revealed that the highest concentrations of LsSd were detected in the midgut and brain. At 1–24 h after Escherichia coli infection, LsSd expression increased substantially. However, LsSd expression was downregulated 3–12 h after Staphylococcus aureus infection. RNA interference-mediated silencing of the LsSd transcript resulted in deformed, considerably smaller, and degenerated wings. Meanwhile, LsCycE, LsDiap1, and LsVg, which are involved in cell proliferation and wing development, were drastically reduced when LsSd was depleted. In a survival assay, the LsSd knockdown considerably decreased the susceptibility to S. aureus, a gram-positive bacterium. In addition, knockdown of LsSd remarkably downregulated the transcription of LsCact in response to S. aureus stimulation, while upregulating the expression of five immune-related genes. Our results provide conclusive proof for the important roles of LsSd in the immune response of L. serricorne.

The Role of Chitooligosaccharidolytic β-N-Acetylglucosamindase in the Molting and Wing Development of the Silkworm Bombyx mori

The insect glycoside hydrolase family 20 β-N-acetylhexosaminidases (HEXs) are key enzymes involved in chitin degradation. In this study, nine HEX genes in Bombyx mori were identified by genome-wide analysis. Bioinformatic analysis based on the transcriptome database indicated that each gene had a distinct expression pattern. qRT-PCR was performed to detect the expression pattern of the chitooligosaccharidolytic β-N-acetylglucosaminidase (BmChiNAG). BmChiNAG was highly expressed in chitin-rich tissues, such as the epidermis. In the wing disc and epidermis, BmChiNAG has the highest expression level during the wandering stage. CRISPR/Cas9-mediated BmChiNAG deletion was used to study the function. In the BmChiNAG-knockout line, 39.2% of female heterozygotes had small and curly wings. The ultrastructure of a cross-section showed that the lack of BmChiNAG affected the stratification of the wing membrane and the formation of the correct wing vein structure. The molting process of the homozygotes was severely hindered during the larva to pupa transition. Epidermal sections showed that the endocuticle of the pupa was not degraded in the mutant. These results indicate that BmChiNAG is involved in chitin catabolism and plays an important role in the molting and wing development of the silkworm, which highlights the potential of BmChiNAG as a pest control target.