Huge spider glue genes have proved extremely difficult to sequence, could lead to biological pest control and more – ScienceDaily

The innovative method they used could allow others to sequence more silk and glue genes, which are difficult to sequence because of their length and repetitive structure. A better understanding of these genes could bring scientists closer to the next big breakthrough in biomaterials.

Sticky solutions

Spider silk is what characterizes spider webs. For years, it has been touted as the next asset of biomaterials because of its unusual tensile strength combined with its flexibility. There are more than 45,000 known spider species, each producing between one and seven types of silk. However, despite many partial sequences, less is known about the complete genetic structure of spider silk: only about 20 complete genes were sequenced. "Twenty steps compared to what exists," says Stellwagen.

In addition, spider silk has proved difficult to produce in large quantities. Spiders convert silk stains into solid and thin fibers according to a complex process inside their body. Scientists can make the liquid, but "we can not duplicate the process of moving from liquid to solid on a large-scale industrial scale," says Stellwagen.

Spider glue, however, is a liquid both inside and outside the spider. Although the glue "presents its own challenges," explains Stellwagen, this difference could make spider glue easier to produce in a laboratory than silk.

Stellwagen considers that the control of organic pests has great potential for spider glue applications. After all, she says, "This thing has evolved to capture prey of bug."

For example, farmers could spray the glue along the barn wall to protect their livestock from biting or disease-causing insects, then rinse it without worrying about the pollution of the watercourse by dangerous pesticides. They could also use glue to protect their crops from pests. It could also be applied in areas where mosquito-borne diseases prevail. "It could also be fun to play with," says Stellwagen.

A "behemoth of a gene"

Prior to the work of Stellwagen and Renberg, funded by the Army Research Laboratory, the longest sequenced gene for silk was about 20,000 base pairs. When she started this project, Stellwagen was waiting to quickly sequence the glue genes, then move on to something else, relying on what she had learned from the sequence. Instead, it took Renberg and her two years to complete the sequence.

"It ended up being that monster of a gene that is more than twice as big as the biggest gene of silk," Stellwagen says. The day was long and difficult. She found Renberg in the lab and she said, "I think our gene is 42,000 bases long, I think we're done." And in the end, it took the risk of a state-of-the-art technique that ultimately gave the complete sequence.

Not only was the gene exceptionally long, but, like spider silk genes, it has many repeats of the same base sequence – A, T, G, and C – in the middle. Modern sequencing techniques (called "next-generation sequencing") work by generating DNA sequences for all genes in an organism, but in pieces. Then, as if to solve a puzzle, scientists must match the overlapping ends of the short sections to determine the complete sequence.

However, if your gene is repetitive, you need a single sequence, or "read", that extends from before the repetitive region beyond the end to find out how many repetitions there are there is. If your repetitive section is long, as is the case in the glue genes studied by Stellwagen and Renberg, the chances that you get the reading you need with the next generation methods is slim.

Fortunately, "third generation" sequencing techniques are now available. Third generation sequencing produces longer, but fewer readings. This is only by repeating the experience many times that you have a chance to get the readings needed to determine the number of repetitions and finally define the complete gene sequence. "It's a challenge," says Stellwagen. "You take a needle in a haystack."

But it worked. After two years spent on the computer and not having any positive results, Stellwagen and Renberg finally got the necessary readings to define the complete sequence of the gene.

Stellwagen is already thinking of the future. "Now that we have a protocol for discovering complete silk genes, what are the silks of other species like?" she asks.

"I'm super excited to finally be able to solve the problem, because it was so difficult," Stellwagen said. Although it was a much bigger challenge than expected, "We finally learned a lot and I'm happy to share it with the next person trying to solve a ridiculous gene."