Discovery of Silk Genes in the Spider Tengella perfuga
Authors:Fanny Chan , Crystal Chaw, Sandra Correa-Garhwal
Mentor:Cheryl Hayashi, Professor of Biology, University of California, Riverside
Spider silks are renowned for their impressive mechanical properties that are tailored to meet the functional demands of specific tasks via different silk types. For example, the Central American spider Tengella perfuga (Tengellidae) produces cribellate silk, a silk type that is sticky without being wet. Instead of acting like glue, cribellate silk uses atomic forces to adhere to struggling prey. Each silk type is composed of different structural proteins encoded by a family of genes called spidroins (spider fibrous protein) that are differentially expressed in silk type specific glands. The nucleotide and amino acid sequence of spidroins are linked to each silk type’s mechanical properties. Major ampullate silk, used in draglines, is known for its exceptional toughness. This silk’s tensile strength is attributed to sheet-like secondary structures that correspond to amino acid motifs, such as poly-alanine. However, the majority of spider silks remains uncharacterized at the molecular level. In fact, nothing is known about T. perfuga silk, and a cribellate silk-specific spidroin has yet to be identified. Through comparison and analysis of spidroin C-terminals, which are highly conserved across species, and spidroin repetitive regions, which are unique to each spidroin type, we will establish evolutionary relationships between tengellid and non-tengellid spidroins. We constructed three plasmid-based cDNA libraries in pZeRO-2 (Invitrogen) that corresponded to ampullate, tubuliform and small (including cribellate) silk glands. We then screened the libraries and selected clones for DNA sequencing. With BLAST, we were able to identify DNA sequences that aligned to three known spidroin paralogs: a major ampullate spidroin from the ampullate library, a tubuliform spidroin (egg case silk) and an aciniform spidroin (prey wrapping silk) from the tubuliform library. We also found two types of cDNAs that didn’t match any known spidroins, but had components that aligned with silk proteins—an indication of two new spidroin paralogs.