We have a long history with the silkworm (Bombyx mori), which was native throughout Asia and thought to have been domesticated more than 5,000 years ago in China to make silk. Silkworms today are biological silk-producing machines, the products of thousands of years of careful breeding. Silk production is now a multi-billion dollar industry, with around 150,000 tons of silk created every year. But silkworms today make more than just ordinary silk.
What else do silkworms make? Thanks to some inventive genetic engineering, larvae have been made that can produce modified silk — such as silk that’s stronger than steel and fluorescent silk used in designer wedding dresses — as well as proteins for medical purposes. This is accomplished by changing the genetics of the silkworms so that they make modified silk, or medical proteins, instead of their ordinary silk.
To understand how the silkworms’ genetics are altered, a quick overview of how these critters actually produce silk is useful. The silk made by silkworms primarily consists of two proteins: fibroin and sericin. In a specific region of the silkworm’s silk gland, fibroin is created as the insoluble core of the silk. Next, sericin, which is a glue-like protein, is made and covers the fibroin. Sericin also binds two threads of silk together to make the final silk product as it emerges from the silk gland, right before it hardens upon contacting the air. Overall, the silk is 75% fibroin and 25% sericin (by weight).
To modify the silkworm’s silk, researchers make a silkworm’s silk gland produce a modified protein. They can even control what part of the silk they want to contain the new protein (e.g., the fibroin core or the sericin outer layer) by genetically targeting different regions of the silk gland. All of this is done using a vector (a small piece of DNA) that is injected into a silkworm egg, and is then incorporated into the silkworm’s silk gland as the larva grows up (via transposons).
As was mentioned, silkworms have been modified to make medically-relevant proteins. Specifically, silkworms have been made that produce interferons, antibodies, drug delivery systems, substrates for cells (such as stem cells) to be grown on in laboratories, tissue scaffolds for transplants, and more.
While they’re promising biological factories of proteins that are in demand, it still takes a lot of silkworms to make a desired amount of product. For example, researchers at the National Institute of Agrobiological Sciences, Japan, and collaborators genetically modified more than 20,000 silkworms to make enough glowing silk (using proteins from jellyfish and corals) to create an incredibly unique wedding dress. With one cocoon thread reaching 1,000 meters long, and 3,000 cocoons making 1 kilogram of silk, the number of silkworms needed for projects quickly adds up.
So if you want to wear a glowing tuxedo at your next formal affair, just be sure to start breeding the silkworms long in advance so you have more than some fluorescent tails.
For further reading:
- Tetsuya Iizuka et al.’s article “Colored Fluorescent Silk Made by Transgenic Silkworms”
- Masahiro Tomita’s article “Transgenic silkworms that weave recombinant proteins into silk cocoons”
- Pallab Ghosh’s article “GM silk worms make Spider-Man web closer to reality”
- Teisha J. Rowland’s blog post “What to Buy the Burgeoning Biologist?”
- Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre