Effects of Osiris9a on Silk Properties in Bombyx mori Determined by Transgenic Overexpression

Atomic Layer Deposition of Al2O3/TiO2 Multilayer Films on Silk for High-Efficiency UV Shielding Properties

Silk fiber, as a luxurious textile raw material, is widely used in the textile industry due to its excellent mechanical properties and wearing comfort. However, the poor (ultraviolet, UV) light stability of silk affects its further application in high-end textiles, fashionable apparel, and smart materials. Although surface modification can endow the excellent UV resistance of silk fibers, it often reduces its comfort property. Herein, a laminated ultrathin Al2O3/TiO2 coating with a total thickness of 120 nm is fabricated on the surface of silk fiber via a modified atomic layer deposition (ALD) technique. The tenacity of ALD-coated silk can maintain 61.1% of its original value after exposure to intense UV light (640 mW/cm2) under high temperature (>200 °C) for 6 h, which is far superior to other work that has been reported. This can be attributed to the synergistic effect of the reflection of UV light by the multilayer film barrier, the strong oxidizing free radicals by the Al2O3 layer in the innermost layer, and thermal shield of laminated ultrathin Al2O3/TiO2 film. ALD-coated silk fabrics can also demonstrate a multicycle laundering durability, thermal and chemical stabilities, and flame retardancy. More importantly, the wearing comfort of the modified silk has no obvious change. This method provides principle and technical guidance in high-performance and multifunctional fibers and devices.

A mutation in the Bombyx mori BmSPI51 gene results in alterations protein abundance in cocoon and unveils compensatory mechanism of silk gland proteinase inhibitors

Proteinase inhibitors constitute a significant component of Lepidoptera cocoon. BmSPI51 is the most abundant protease inhibitors in silkworm cocoons. In this study, we aimed to elucidate the biological function of BmSPI51 in both the silkworm silk gland and cocoon formation. To achieve this, we utilized CRISPR/Cas9 gene editing to target the BmSPI51 gene, resulting in premature termination of translation at the 33rd amino acid residue. The mutation of BmSPI51 did not affect the growth and development. Nevertheless, it led to a substantial decrease in the economic traits of silkworm cocoons. Proteomic analysis indicated the abundance of fibroin heavy chain (Fib-H), fibroin light chain (Fib-L), and fibrohexamerin (P25) decreased significantly in the homozygous mutants. Further analysis of cocoon proteins found that the mutants significantly increased the secretion of other protease inhibitors in order to deal with the increased environmental stress resulting from the absence of BmSPI51. Surprisingly, homozygous mutant cocoons exhibited an enhanced inhibitory ability against Saccharomyces cerevisiae compared to the WT cocoons. In conclusion, our study provides a valuable insight into the biological function of protease inhibitors and revealed their roles in cocoon formation and potential applications in biotechnology.

Identification and Functions of JHE 6 Specifically Expressed in Bombyx mori Silk Gland

Juvenile hormone esterase (JHE) is the specific enzyme that degrades juvenile hormone (JH) and regulates the JH titer in insects. JH also regulates the development of the silk gland and the synthesis and secretion of silk proteins in Bombyx mori. Here, we identified nine possible JHE family members, Bmjhe1-9. Notably, Bmjhe6 is specifically expressed in the silk gland. Using semi-quantitative, quantitative real-time RT-PCR and Western blot, it was confirmed that Bmjhe6 was specifically expressed in the middle silk gland (MSG) with high levels in the anterior region of the MSG (A-MSG). The immunofluorescence localization analysis revealed that Bmjhe6 is produced within cells, secreted into the gland lumen, and co-transported with silk proteins into the anterior silk gland (ASG). In vitro hormone induction experiments demonstrated that Bmjhe6 responds to a JH analog, increasing its expression after 12-24 h, whereas 20-hydroxyecdysone inhibited it. In addition, Bmjhe6 knockdown using dsBmjhe6 injections accelerated larval development, resulting in increased larval body and silk gland weight. This induced disordered sericin genes (Ser2, Ser3) expression, and key genes in the JH synthesis pathway (BmKr-h1 and BmMet1) were significantly upregulated along with the transcription factors (SGF-1 and Sage). These results indicate that Bmjhe6 plays an important role in silk gland growth and silk protein synthesis by modulating JH signal.

Identification and functional study of fhx-L1, a major silk component in Bombyx mori

The silkworm cocoon was composed of fibroins, sericins, protease inhibitors, and proteins of unknown function. In this study, we focused on fhx-L1 (fibrohexamerin-like1), which was the homolog of fibroin fhx (fibrohexamerin). We identified 154 fhx family genes in 44 Lepidoptera insects, and seven fhx-Ls were found in Bombyx mori. Fhx-L1 was the most abundant of these proteins in silk and was specifically expressed in the silk gland. Immunofluorescence analysis showed that fhx-L1 was secreted into the whole sericin layers, similar to sericin1 (ser1). Western blotting revealed that the fhx-L1 protein contains N-linked oligosaccharide chains. CRISPR/Cas9-mediated gene editing was used to generate a homozygous mutant of fhx-L1 (fhx-L1^KO). The cocoon of fhx-L1^KO was larger and fluffier than that of the wild-type (WT), which was attributed to the lower adhesion between silk fibers. We also found that the content of β-sheet in the mutant silk was lower than in the WT silk, which resulted in further deterioration of the mechanical properties of the fhx-L1^KO silk. Our study revealed the properties and function of fhx-L1 as a major structural component in silk. Then, our study provided a potential insight for in-depth study of silk protein function.

Analysis of histomorphometric and proteome dynamics inside the silk gland lumen of Bombyx mori revealed the dynamic change of silk protein during the molt stage

Silkworms spin different silks at different growth stages for specific purposes. The silk spun before the end of each instar is stronger than that at the beginning of each instar and cocoon silk. However, the compositional changes in silk proteins during this process are unknown. Consequently, we performed histomorphological and proteomic analyses of the silk gland to characterize changes from the instar end to the next instar beginning. The silk glands were collected on day 3 of third- and fourth-instar larvae (III-3 and IV-3) and the beginning of fourth-instar larvae (IV-0). Proteomic analysis identified 2961 proteins from all silk glands. Silk proteins P25 and Ser5 were significantly more abundant in III-3 and IV-3 than in IV-0, and many cuticular proteins and protease inhibitors increased significantly in IV-0 compared with III-3 and IV-3. This shift may cause mechanical property differences between the instar end and beginning silk. Using section staining, qPCR, and western blotting, we found for the first time that silk proteins were degraded first and then resynthesized during the molting stage. Furthermore, we revealed that fibroinase mediated the changes of silk proteins during molting. Our results provide insights into the molecular mechanisms of silk proteins dynamic regulation during molting.

BmSuc1 Affects Silk Properties by Acting on Sericin1 in Bombyx mori

BmSuc1, a novel animal-type β-fructofuranosidase (β-FFase, EC 3.2.1.26) encoding gene, was cloned and identified for the first time in the silkworm, Bombyx mori. BmSuc1 was specifically and highly expressed in the midgut and silk gland of Bombyx mori. Until now, the function of BmSuc1 in the silk gland was unclear. In this study, it was found that the expression changes of BmSuc1 in the fifth instar silk gland were consistent with the growth rate of the silk gland. Next, with the aid of the CRISPR/Cas9 system, the BmSuc1 locus was genetically mutated, and homozygous mutant silkworm strains with truncated β-FFase (BmSUC1) proteins were established. BmSuc1 mutant larvae exhibited stunted growth and decreased body weight. Interestingly, the molecular weight of part of Sericin1 (Ser1) in the silk gland of the mutant silkworms was reduced. The knockout of BmSuc1 reduced the sericin content in the silkworm cocoon shell, and the mechanical properties of the mutant line silk fibers were also negatively affected. These results reveal that BmSUC1 is involved in the synthesis of Ser1 protein in silk glands and helps to maintain the homeostasis of silk protein content in silk fibers and the mechanical properties of silk fibers, laying a foundation for the study of BmSUC1 regulation of silk protein synthesis in silk glands.

A Matrix Metalloproteinase Mediates Tracheal Development in Bombyx mori

The trachea of insects is a tubular epithelia tissue that transports oxygen and other gases. It serves as a useful model for the studying of the cellular and molecular events involved in epithelial tube formation. Almost all of the extracellular matrix can be degraded by Matrix metalloproteinases (MMPs), which is closely related to the processes of development and regeneration. The regulation of trachea by MMPs is roughly known in previous studies, but the detailed regulation mechanism and involved gene function are not fully explored. In this article, we found MMP1 expressed highly during tracheal remodeling, and knocked out it makes the tracheal branch number reduced in Bombyx mori. In trachea of transgenic BmMMP1-KO silkworm, the space expanding of taenidium and epidermal cells and the structure of apical membrane were abnormal. To explore the underlying mechanism, we detected that DE-cadherin and Integrin β1 were accumulated in trachea of transgenic BmMMP1-KO silkworm by immunohistochemistry. Moreover, 5-Bromo-2′-Deoxyuridine (BrdU) labeling showed that knockout of BmMMP1 in silkworm inhibited tracheal cell proliferation, and BmMMP1 also regulated the proliferation and migration of BmNS cells. All of the results demonstrated that BmMMP1 regulates the development of the tracheal tissue by expanding the space of tracheal cuticles and increases the number of tracheal branches by degrading DE-cadherin and Integrin β1.

Forcibly spun dragline silk fibers from web-building spider Trichonephila clavata ensure robustness irrespective of spinning speed and humidity

Web-building spiders secrete dragline silk fibers to sustain their body and use them as frameworks during web construction. They spin dragline silk fibers at various spinning speed and humidity conditions depending on their natural habitat. Here, we investigated the effect of spinning speed and humidity on the structural and mechanical properties of dragline silk fibers from web-building spider Trichonephila clavata obtained by the forcibly spinning method. We found that the crystal and morphological structures did not rely on the spinning speed and humidity. Furthermore, the mechanical strength and extensibility of the dragline silk fibers were maintained, demonstrating that dragline silk fibers ensure robustness irrespective of the spinning speed and humidity. The results obtained in the present study are helpful not only to understand the biological basis of the silk fiber formation of spiders but also contribute to consider the spinning conditions for the process of creating synthetic silk fibers.

Biofabricating a Silk Scaffold as a Functional Microbial Trap

Silk fibroin produced from silkworms has been intensively utilized as a scaffold material for a variety of biotechnological applications owing to its remarkable mechanical strength, extensibility, biocompatibility, and ease of biofunctionalization. In this research, we engineered silk as a novel trap platform capable of capturing microorganisms. Specifically, we first fabricated the silk material into a silk sponge by lyophilization, yielding a 3D scaffold with porous microstructures. The sponge stability in water was significantly improved by ethanol treatment with elevated β-sheet content and crystallinity of silk. Next, we biofunctionalized the silk sponge with a poly-specific microbial targeting molecule, ApoH (apolipoprotein H), to enable a novel silk-based microbial trap. The recombinant ApoH engineered with an additional penta-tyrosine was assembled onto the silk sponge through the horseradish peroxidase (HRP) mediated dityrosine cross-linking. Last, the ApoH-decorated silk sponge was demonstrated to be functional in capturing our model microorganism targets, E. coli and norovirus-like particles. We envision that this biofabricated silk platform, capable of trapping a variety of microbial entities, could serve as a versatile scaffold for rapid isolation and enrichment of microbial samples toward future diagnostics and therapeutics. This strategy, in turn, can expedite advancing future biodevices with functionality and sustainability.