The Nephila clavipes genome highlights the diversity of spider silk genes and their complex expression

Abstract

More than 380 million years of evolution have produced >46,000 extant spider species, exhibiting an incredible diversity of silks used for prey capture and reproduction [1][2][3] . Spider silks can be stronger than steel and tougher than Kevlar, yet are much lighter weight than these manmade materials 4 . Silks vary in extensibility 5 , are temperature resilient 6 , can enable electrical conduction 7 , and can inhibit bacterial growth while being nearly invisible to the human immune system 8 . Thus, novel materials derived from spider silks offer tremendous potential for medical and industrial innovation. To take advantage of their desirable properties, we must learn more about spider silk genetic structure, functional diversity, and production.A female orb-weaving spider can have up to seven morphologically differentiated types of silk glands, each believed to extrude a distinct class of silk with biophysical characteristics resulting from the expression of a unique combination of silk genes in that gland 9,10 . The silk classes of a typical 'gluey silk' orb-weaver (Araneoidea) female include (i) major ampullate silk, which exhibits great tensile strength and is employed in draglines, bridgelines, and web radii 11,12 ; (ii) minor ampullate silk, used for inelastic temporary spirals during web building 11,12 ; (iii) cement-like piriform silk that bonds fibers together and to other substrates 13,14 ; (iv) strong, yet flexible aciniform silk used for prey wrapping and egg case insulation 15 ; (v) tubuliform and cylindriform silk that constitutes the tough outer layer of egg cases 16,17 ; (vi) flagelliform silk that exhibits unparalleled extensibility and is used in the capture spiral 18,19 ; and (vii) the viscous and sticky aggregate silk that aids in prey capture [20][21][22][23][24] . Many spider species produce just a subset of these silk classes, and some produce yet other silk types, including cribellate silk 25 . Each species possesses an assortment of specialized gland types that are thought to produce distinct classes of silks to fit specific needs 9,26,27 .Spider silks are composed primarily of spidroin proteins (where a 'spidroin' is a spider fibroin [28][29][30][31] ) that, by convention, have been named and classified according to the specific silk gland in which they were first discovered. Spidroin proteins have conserved N-and C-terminal domains that flank long runs of repeated motifs 32-34 , the composition and number of which confer specific physical properties to silks 27 . Yet, despite decades of research on orb-weaver silks, there is incomplete knowledge of all the spidroins within an orb-weaver species.Adding to the sampling of sequences obtained from targeted investigations, the assembly of the velvet spider (Stegodyphus mimosarum) genome yielded 19 spidroins, the largest collection from any single species 27 . Owing to the challenges of assembling arrays of repeats, several of the S. mimosarum spidroin sequences are incomplete, without the sequences encoding N-and C-terminal domains anchored ...

Silk nano‐discs: A natural material for cancer therapy

“…However, despite years of research, it is still impossible to mimic silk's unique properties which are due to self‐assembly of the domains at nanoscale precision . Moreover, silk possesses environmental stability, ease of functionalization, favorable oxygen/water permeability, minimal antigenic response, biocompatibility, morphologic flexibility, and better mechanical properties in comparison to globular proteins, making it a viable entity in various fields of biomedical applications such as for developing sutures, controlled drug delivery, cancer therapeutics, wound healing, and so on. Although a major confusion lies regarding its degradable nature, various reports suggest that silk can be degraded by proteolytic enzymes in vivo which over the time gets absorbed slowly …”

Semi‐aquatic spider silks: transcripts, proteins, and silk fibres of the fishing spider, Dolomedes triton (Pisauridae)

“…Assembly quality assessed with BUSCO (Simão et al ., ) using Ixodes scapularis (deer tick) as a reference resulted in about 73.4% of the tick BUSCOs identified as complete in the D. triton assembly. The completeness score of the D. triton assembly is lower than previously published assemblies of Nephila clavipes 99.1% (Babb et al ., ), Argiope argentata 92.5% (Chaw et al ., ), Latrodectus hesperus 93.1%, Latrodectus geometricus 83.4%, and Steatoda grossa 90.5% (Clarke et al ., ). A likely explanation for the difference in BUSCO completeness is that the D. triton assembly included only silk gland tissues whereas the other assemblies included multiple types of tissues.…”

“…Recent proteomic studies have detected AcSp proteins in the major ampullate glands of the cob-web weaver L. hesperus but not in tubuliform glands (Chaw et al, 2015;Larracas et al, 2016). AcSp gene expression has also been detected in the aggregate, flagelliform, and minor ampullate silk glands of the orb-web weaver N. clavipes, but not the tubuliform glands (Babb et al, 2017).…”

Ontogenetic shift toward stronger, tougher silk of a web‐building, cave‐dwelling spider

“…In general, MAS is a proteinaceous fiber composed of several highly repetitive glycine and alanine sequences inducing nanoscale crystalline β‐sheet and amorphous domain formations during spinning (Hinman & Lewis, ; Simmons, Michal & Jelinski, ; Van Beek et al ., ). It may be reasonable to deduce that concurrent variations in spinning processes, silk gland duct size, or silk gene expression across body sizes, act on silk protein structures and are responsible for the mechanical property variations that we measured (Vollrath et al ., ; Pérez‐Rigueiro et al ., ; Davies, Knight & Vollrath, ; Babb et al ., ; Blamires et al ., ). However, it is also possible that differential responses of silks to external factors such as temperature, humidity or previous stress history of webs may also explain observed variation in mechanical properties.…”