Spider genomes provide insight into composition and evolution of venom and silk

Abstract

Spiders are ecologically important predators with complex venom and extraordinarily tough silk that enables capture of large prey. Here we present the assembled genome of the social velvet spider and a draft assembly of the tarantula genome that represent two major taxonomic groups of spiders. The spider genomes are large with short exons and long introns, reminiscent of mammalian genomes. Phylogenetic analyses place spiders and ticks as sister groups supporting polyphyly of the Acari. Complex sets of venom and silk genes/proteins are identified. We find that venom genes evolved by sequential duplication, and that the toxic effect of venom is most likely activated by proteases present in the venom. The set of silk genes reveals a highly dynamic gene evolution, new types of silk genes and proteins, and a novel use of aciniform silk. These insights create new opportunities for pharmacological applications of venom and biomaterial applications of silk.

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

“…4), so the previously reported transcripts could represent length polymorphisms or additional unassembled MiSp genes. Our assemblies showed multiexon splicing at the two flagelliform-type loci (FLAG-a and FLAG-b), consistent with previous reports 27 (Fig. 1).…”

“…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 .…”

“…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 .…”

“…Spidroin proteins have conserved N-and C-terminal domains that flank long runs of repeated motifs [32][33][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 on a single scaffold [10][11][12] .…”