Researchers at the University of Notre Dame (IN, USA) used piggyBac (PB) vectors to create transgenic silkworms that produced composite silk fibers with chimeric silkworm/spider silk proteins that were integrated in an extremely stable manner. These composite fibers were (on average), tougher than the parental silkworm silk fibers, and were as tough as native dragline spider silk fibers. The thread produced by the transgenic silkworms has a relative strength and flexibility of 80% to that of native spider silk. To ensure the silkworms were been genetically modified, a gene gave the transgenic silkworms red glowing eyes was also included.

PiggyBac transposon vectors mobilize via a "cut-and-paste" mechanism, reintegrating at other sites within the genome. PB transposase specifically recognizes PB inverted terminal repeats (ITRs) that flank the transposon, binding to these sequences and catalyzing the excision of the transposon. PB then integrates at TTAA sites throughout the genome, in a relatively random fashion. For the creation of transgenic animals, the transposase is supplied cotransfected with a plasmid containing donor transposon; subsequent integration within a coding region captures the elements necessary for gene expression. The findings were published ahead of print on January 3, 2012, in the Proceedings of the National Academy of Sciences (PNAS).

“These results demonstrate that silkworms can be engineered to manufacture composite silk fibers containing stably integrated spider silk protein sequences, which significantly improve the overall mechanical properties of the parental silkworm silk fibers,” concluded lead author Prof. Malcolm Fraser, PhD, and colleagues of the department of biomedical sciences.

Commercial production of spider silk is impractical, since spiders are too cannibalistic and territorial for farming. Researchers have experimented with producing the stronger material in other organisms, including bacteria, insects, mammals, and plants, but those proteins require mechanical spinning - a task the silkworms perform naturally. The stronger fiber could find application in sutures, where some natural silkworm silk is used, as well as wound dressings, artificial ligaments, cosmetics, parachute cords, and textiles.

Related Links:
University of Notre Dame