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1. The common house spider, Parasteatoda tepidariorum, maintains silk gene expression on sub-optimal diet

   https://doi.org/10.1371/journal.pone.0237286  

   Miller, Jeremy ; Vienneau-Hathaway, Jannelle ; Dendev, Enkhbileg ; Lan, Merrina ; Ayoub, Nadia A. ( December 2020 , PLOS ONE)

   Signore, Giovanni (Ed.)

   Cobweb weaving spiders and their relatives spin multiple task-specific fiber types. The unique material properties of each silk type result from differences in amino acid sequence and structure of their component proteins, primarily spidroins (spider fibrous proteins). Amino acid content and gene expression measurements of spider silks suggest some spiders change expression patterns of individual protein components in response to environmental cues. We quantified mRNA abundance of three spidroin encoding genes involved in prey capture in the common house spider, Parasteatoda tepidariorum (Theridiidae), fed different diets. After 10 days of acclimation to the lab on a diet of mealworms, spiders were split into three groups: (1) individuals were immediately dissected, (2) spiders were fed high-energy crickets, or (3) spiders were fed low-energy flies, for 1 month. All spiders gained mass during the acclimation period and cricket-fed spiders continued to gain mass, while fly-fed spiders either maintained or lost mass. Using quantitative PCR, we found no significant differences in the absolute or relative abundance of dragline gene transcripts, major ampullate spidroin 1 ( MaSp1 ) and major ampullate spidroin 2 ( MaSp2 ), among groups. In contrast, prey-wrapping minor ampullate spidroin ( MiSp) gene transcripts were significantly less abundant in fly-fed than lab-acclimated spiders. However, when measured relative to Actin , cricket-fed spiders showed the lowest expression of MiSp . Our results suggest that house spiders are able to maintain silk production, even in the face of a low-quality diet. 

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2. Hierarchical spidroin micellar nanoparticles as the fundamental precursors of spider silks

   https://doi.org/10.1073/pnas.1810203115  

   Parent, Lucas R. ; Onofrei, David ; Xu, Dian ; Stengel, Dillan ; Roehling, John D. ; Addison, J. Bennett ; Forman, Christopher ; Amin, Samrat A. ; Cherry, Brian R. ; Yarger, Jeffery L. ; et al ( October 2018 , Proceedings of the National Academy of Sciences)

   Many natural silks produced by spiders and insects are unique materials in their exceptional toughness and tensile strength, while being lightweight and biodegradable–properties that are currently unparalleled in synthetic materials. Myriad approaches have been attempted to prepare artificial silks from recombinant spider silk spidroins but have each failed to achieve the advantageous properties of the natural material. This is because of an incomplete understanding of the in vivo spidroin-to-fiber spinning process and, particularly, because of a lack of knowledge of the true morphological nature of spidroin nanostructures in the precursor dope solution and the mechanisms by which these nanostructures transform into micrometer-scale silk fibers. Herein we determine the physical form of the natural spidroin precursor nanostructures stored within spider glands that seed the formation of their silks and reveal the fundamental structural transformations that occur during the initial stages of extrusion en route to fiber formation. Using a combination of solution phase diffusion NMR and cryogenic transmission electron microscopy (cryo-TEM), we reveal direct evidence that the concentrated spidroin proteins are stored in the silk glands of black widow spiders as complex, hierarchical nanoassemblies (∼300 nm diameter) that are composed of micellar subdomains, substructures that themselves are engaged in the initial nanoscale transformations that occur in response to shear. We find that the established micelle theory of silk fiber precursor storage is incomplete and that the first steps toward liquid crystalline organization during silk spinning involve the fibrillization of nanoscale hierarchical micelle subdomains.

    

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3. Orb weaver aggregate glue protein composition as a mechanism for rapid evolution of material properties

   https://doi.org/10.3389/fevo.2023.1099481  

   Ayoub, Nadia A. ; DuMez, Lucas ; Lazo, Cooper ; Luzaran, Maria ; Magoti, Jamal ; Morris, Sarah A. ; Baker, Richard H. ; Clarke, Thomas ; Correa-Garhwal, Sandra M. ; Hayashi, Cheryl Y. ; et al ( April 2023 , Frontiers in Ecology and Evolution)

   Introduction Orb web and cobweb weaving spiders in the superfamily Araneoidea are distinguished by their ability to make a chemically sticky aqueous glue in specialized aggregate silk glands. Aggregate glue is an environmentally responsive material that has evolved to perform optimally around the humidity at which a spider forages. Protein components and their post-translational modifications confer stickiness to the glue, but the identities of these proteins have not been described for orb web weavers. Methods Using biomechanics, gene expression data, and proteomics, we characterized the glue’s physical properties and molecular components in two congeners that live in different environments, Argiope argentata (dry southwest US) and Argiope trifasciata (humid southeast US). Results The droplets of A. argentata are less hygroscopic than those of A. trifasciata and have proportionately smaller viscoelastic protein cores, which incorporate a smaller percentage of absorbed water as humidity increases. Argiope argentata protein cores were many times stiffer and tougher than A. trifasciata protein cores. Each species’ glue included ~30 aggregate-expressed proteins, most of which were homologous between the two species, with high sequence identity. However, the relative contribution and number of gene family members of each homologous group differed. For instance, the aggregate spidroins (AgSp1 and AgSp2) accounted for nearly half of the detected glue composition in A. argentata , but only 38% in A. trifasciata . Additionally, AgSp1, which has highly negatively charged regions, was ~2X as abundant as the positively charged AgSp2 in A. argentata , but ~3X as abundant in A. trifasciata . As another example, A. argentata glue included 11 members of a newly discovered cysteine-rich gene family, versus 7 members in A. trifasciata . Discussion Cysteines form disulfide bonds that, combined with the higher potential for electrostatic interactions between AgSp1 and AgSp2, could contribute to the greater stiffness of A. argentata glue. The ability to selectively express different glue protein genes and/or to extrude their products at different rates provides a faster mechanism to evolve material properties than sequence evolution alone. 

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4. The transcriptome of Darwin’s bark spider silk glands predicts proteins contributing to dragline silk toughness

   https://doi.org/10.1038/s42003-019-0496-1  

   Garb, Jessica E. ; Haney, Robert A. ; Schwager, Evelyn E. ; Gregorič, Matjaž ; Kuntner, Matjaž ; Agnarsson, Ingi ; Blackledge, Todd A. ( July 2019 , Communications Biology)

   Darwin’s bark spider (Caerostris darwini) produces giant orb webs from dragline silk that can be twice as tough as other silks, making it the toughest biological material. This extreme toughness comes from increased extensibility relative to other draglines. We showC. darwinidragline-producing major ampullate (MA) glands highly express a novel silk gene transcript (MaSp4) encoding a protein that diverges markedly from closely related proteins and contains abundant proline, known to confer silk extensibility, in a unique GPGPQ amino acid motif. This suggestsC. darwinievolved distinct proteins that may have increased its dragline’s toughness, enabling giant webs.Caerostris darwini’sMA spinning ducts also appear unusually long, potentially facilitating alignment of silk proteins into extremely tough fibers. Thus, a suite of novel traits from the level of genes to spinning physiology to silk biomechanics are associated with the unique ecology of Darwin’s bark spider, presenting innovative designs for engineering biomaterials.

    

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5. The evolutionary history of cribellate orb-weaver capture thread spidroins

   https://doi.org/10.1186/s12862-022-02042-5  

   Correa-Garhwal, Sandra M. ; Baker, Richard H. ; Clarke, Thomas H. ; Ayoub, Nadia A. ; Hayashi, Cheryl Y. ( July 2022 , BMC Ecology and Evolution)

   Spiders have evolved two types of sticky capture threads: one with wet adhesive spun by ecribellate orb-weavers and another with dry adhesive spun by cribellate spiders. The evolutionary history of cribellate capture threads is especially poorly understood. Here, we use genomic approaches to catalog the spider-specific silk gene family (spidroins) for the cribellate orb-weaverUloborus diversus.

   We show that the cribellar spidroin, which forms the puffy fibrils of cribellate threads, has three distinct repeat units, one of which is conserved across cribellate taxa separated by ~ 250 Mya. We also propose candidates for a new silk type, paracribellar spidroins, which connect the puffy fibrils to pseudoflagelliform support lines. Moreover, we describe the complete repeat architecture for the pseudoflagelliform spidroin (Pflag), which contributes to extensibility of pseudoflagelliform axial fibers.

   Our finding that Pflag is closely related to Flag, supports homology of the support lines of cribellate and ecribellate capture threads. It further suggests an evolutionary phase following gene duplication, in which both Flag and Pflag were incorporated into the axial lines, with subsequent loss of Flag in uloborids, and increase in expression of Flag in ecribellate orb-weavers, explaining the distinct mechanical properties of the axial lines of these two groups.

    

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