Silk genes and silk gene expression in the spider Tengella perfuga (Zoropsidae), including a potential cribellar spidroin (CrSp)

Abstract

Most spiders spin multiple types of silk, including silks for reproduction, prey capture, and draglines. Spiders are a megadiverse group and the majority of spider silks remain uncharacterized. For example, nothing is known about the silk molecules of Tengella perfuga, a spider that spins sheet webs lined with cribellar silk. Cribellar silk is a type of adhesive capture thread composed of numerous fibrils that originate from a specialized plate-like spinning organ called the cribellum. The predominant components of spider silks are spidroins, members of a protein family synthesized in silk glands. Here, we use silk gland RNA-Seq and cDNA libraries to infer T. perfuga silks at the protein level. We show that T. perfuga spiders express 13 silk transcripts representing at least five categories of spider silk proteins (spidroins). One category is a candidate for cribellar silk and is thus named cribellar spidroin (CrSp). Studies of ontogenetic changes in web construction and spigot morphology in T. perfuga have documented that after sexual maturation, T. perfuga females continue to make capture webs but males halt web maintenance and cease spinning cribellar silk. Consistent with these observations, our candidate CrSp was expressed only in females. The other four spidroin categories correspond to paralogs of aciniform, ampullate, pyriform, and tubuliform spidroins. These spidroins are associated with egg sac and web construction. Except for the tubuliform spidroin, the spidroins from T. perfuga contain novel combinations of amino acid sequence motifs that have not been observed before in these spidroin types. Characterization of T. perfuga silk genes, particularly CrSp, expand the diversity of the spidroin family and inspire new structure/function hypotheses.

Spidroin profiling of cribellate spiders provides insight into the evolution of spider prey capture strategies

“…1 b,c). However, as mentioned in a previous study 43 , other than that, only features commonly found in spacers were observed (TT or SS), and no other noteworthy motif was found. On the other hand, Pflag had similar motifs as Flag, although the motif lengths of Pflag and Flag were different.…”

“…The cribellate spider-associated genes ( CrSp and Pflag ) were also searched based on the partial CrSp candidate sequence in T. perfuga 43 and the Flag sequence in Araneus ventricosus 48 . As a result, a full picture of the genes, including the repetitive and N/C-terminal domains of CrSp and Pflag , was obtained (Fig.…”

“…3 a and S9 ). The C-terminal regions of CrSps were classified into a group consisting of previously reported CrSp candidates in T. perfuga and S. mimosarum 43 . Although Pflags form an independent group without Flags in the phylogenetic tree (Figs.…”

“…The Octonoba spidroin catalogue including CrSp and Pflag genes was confirmed by multiple omics approaches, such as genomics, transcriptomics, and proteomics. Previously, partial spidroin genes of cribellate spiders have been found in O. varians, U. diversus (family Uloboridae), T. perfuga (family Zoropsidae), S. mimosarum (family Eresidae), and Deinopis spinosa (family Deinopidae) 43,44,55 . In O. varians, three approximately 300 aa long segments annotated as the "dragline silk spidroin 1 gene" have been reported (AY666057, AY666058, and AY666059) 55 .…”

“…However, contrary to the ecribellate spiders, there is still little molecular information about the spidroins in cribellate spiders. Regarding the CrSp gene, only partial sequences of candidate genes in Tengella perfuga (family Zoropsidae) and Stegodyphus mimosarum (family Eresidae, KFM60634.1) have been reported 43 , and the Pflag gene sequence is also only known in Deinopis spinosa (family Deinopidae) 44 .…”