Multicomponent nature underlies the extraordinary mechanical properties of spider dragline silk.

Dragline silk of golden orb-weaver spiders (Nephilinae) is noted for its unsurpassed toughness, combining extraordinary extensibility and tensile strength, suggesting industrial application as a sustainable biopolymer material. To pinpoint the molecular composition of dragline silk and the roles of its constituents in achieving its mechanical properties, we report a multiomics approach, combining high-quality genome sequencing and assembly, silk gland transcriptomics, and dragline silk proteomics of four Nephilinae spiders. We observed the consistent presence of the MaSp3B spidroin unique to this subfamily as well as several nonspidroin SpiCE proteins. Artificial synthesis and the combination of these components in vitro showed that the multicomponent nature of dragline silk, including MaSp3B and SpiCE, along with MaSp1 and MaSp2, is essential to realize the mechanical properties of spider dragline silk.

1000 spider silkomes: Linking sequences to silk physical properties.

Spider silks are among the toughest known materials and thus provide models for renewable, biodegradable, and sustainable biopolymers. However, the entirety of their diversity still remains elusive, and silks that exceed the performance limits of industrial fibers are constantly being found. We obtained transcriptome assemblies from 1098 species of spiders to comprehensively catalog silk gene sequences and measured the mechanical, thermal, structural, and hydration properties of the dragline silks of 446 species. The combination of these silk protein genotype-phenotype data revealed essential contributions of multicomponent structures with major ampullate spidroin 1 to 3 paralogs in high-performance dragline silks and numerous amino acid motifs contributing to each of the measured properties. We hope that our global sampling, comprehensive testing, integrated analysis, and open data will provide a solid starting point for future biomaterial designs.

Transcriptomic data during development of a two-spotted cricket Gryllus bimaculatus.

The two-spotted cricket Gryllus bimaculatus is a popular food for reptiles and other insectivorous animals, for the ease of breeding and rich nutrients. It goes through eight moulting cycles until it grows into an adult of size around 30-40 mm, but different larval instars are also used for their sizes matching the fed animals. We therefore provide a transcriptomic resource on different developmental stages of G. bimaculatus to understand the inner molecular workings of these stages contributing to varying nutrients. The raw RNA sequence data is available at NCBI Sequence Read Archive (SRA) under the BioProject PRJNA716138 and the assembled contigs are available as a supplementary data of this report.

Xanthurenic Acid Is the Main Pigment of Trichonephila clavata Gold Dragline Silk.

Spider silk is a natural fiber with remarkable strength, toughness, and elasticity that is attracting attention as a biomaterial of the future. Golden orb-weaving spiders (Trichonephila clavata) construct large, strong webs using golden threads. To characterize the pigment of golden T. clavata dragline silk, we used liquid chromatography and mass spectrometric analysis. We found that the major pigment in the golden dragline silk of T. clavata was xanthurenic acid. To investigate the possible function of the pigment, we tested the effect of xanthurenic acid on bacterial growth using gram-negative Escherichia coli and gram-positive Bacillus subtilis. We found that xanthurenic acid had a slight antibacterial effect. Furthermore, to investigate the UV tolerance of the T. clavata threads bleached of their golden color, we conducted tensile deformation tests and scanning electron microscope observations. However, in these experiments, no significant effect was observed. We therefore speculate that golden orb-weaving spiders use the pigment for other purposes, such as to attract their prey in the sunlight.

Darwin's bark spider shares a spidroin repertoire with Caerostris extrusa but achieves extraordinary silk toughness through gene expression.

Spider silk is a protein-based material whose toughness suggests possible novel applications. A particularly fascinating example of silk toughness is provided by Darwin's bark spider (Caerostris darwini) found in Madagascar. This spider produces extraordinarily tough silk, with an average toughness of 350 MJ m-1 and over 50% extensibility, and can build river-bridging webs with a size of 2.8 m2. Recent studies have suggested that specific spidroins expressed in C. darwini are responsible for the mechanical properties of its silk. Therefore, a more comprehensive investigation of spidroin sequences, silk thread protein contents and phylogenetic conservation among closely related species is required. Here, we conducted genomic, transcriptomic and proteomic analyses of C. darwini and its close relative Caerostris extrusa. A variety of spidroins and low-molecular-weight proteins were found in the dragline silk of these species; all of the genes encoding these proteins were conserved in both genomes, but their genes were more expressed in C. darwini. The potential to produce very tough silk is common in the genus Caerostris, and our results may suggest the existence of plasticity allowing silk mechanical properties to be changed by optimizing related gene expression in response to the environment.

The bagworm genome reveals a unique fibroin gene that provides high tensile strength.

Arthropod silk is known as a versatile tool, and its variability makes it an attractive biomaterial. Eumeta variegata is a bagworm moth (Lepidoptera, Psychidae) that uses silk throughout all life stages. Notably, the bagworm-specific uses of silk include larval development in a bag coated with silk and plant materials and the use of silk attachments to hang pupae. An understanding at the molecular level of bagworm silk, which enables such unique purposes, is an opportunity to expand the possibilities for artificial biomaterial design. However, very little is known about the bagworm fibroin gene and the mechanical properties of bagworm silk. Here, we report the bagworm genome, including a silk fibroin gene. The genome is approximately 700 Mbp in size, and the newly found fibroin gene has a unique repetitive motif. Furthermore, a mechanical property test demonstrates a phylogenetic relationship between the unique motif and tensile strength of bagworm silk.

Orb-weaving spider Araneus ventricosus genome elucidates the spidroin gene catalogue.

Members of the family Araneidae are common orb-weaving spiders, and they produce several types of silks throughout their behaviors and lives, from reproduction to foraging. Egg sac, prey capture thread, or dragline silk possesses characteristic mechanical properties, and its variability makes it a highly attractive material for ecological, evolutional, and industrial fields. However, the complete set of constituents of silks produced by a single species is still unclear, and novel spidroin genes as well as other proteins are still being found. Here, we present the first genome in genus Araneus together with the full set of spidroin genes with unamplified long reads and confirmed with transcriptome of the silk glands and proteome analysis of the dragline silk. The catalogue includes the first full length sequence of a paralog of major ampullate spidroin MaSp3, and several spider silk-constituting elements designated SpiCE. Family-wide phylogenomic analysis of Araneidae suggests the relatively recent acquisition of these genes, and multiple-omics analyses demonstrate that these proteins are critical components in the abdominal spidroin gland and dragline silk, contributing to the outstanding mechanical properties of silk in this group of species.

The complete mitochondrial genome of Eumeta variegata (Lepidoptera: Psychidae).

The complete mitochondrial genome of Eumeta variegate, largest bagworm moth in Japan, has been sequenced using a nanopore sequencer as a single long read. The genome has a total length of 16,601 bp, consisting of 13 protein-coding genes, 20 tRNA, 2 rRNA genes, and an AT-rich control region. The nucleotide composition was extremely AT-rich, with 42.4% A, 40.4% T, 6.67% G, and 10.6% C. This is the second report of a complete mitochondrial genome of Psychidae, and the sequence information together with a phylogenetic analysis would provide a reference data in the future studies of Lepidoptera and Psychidae.