Scientists Sequence Spider Glue Genes

Researchers have published the first-ever complete sequences of two genes that allow spiders to produce glue, a modified version of silk that keeps a spider’s prey stuck in its web.

Droplets of water and glue on spider silk. Image credit: Hans Braxmeier.

Spiders use a suite of remarkable silk and silk-derived materials for various applications during their life cycles, from wrapping prey and egg cases, to creating webs, lifelines, and prey capture glues.

Individual orb weaving spiders, those that construct aerial capture webs, can have up to seven different silk types, each produced within specialized glands in the abdomen.

Dragline silk forms the frame of an orb web and is famous for its toughness comparable to that of steel.

The capture spiral threads of the web are made of flagelliform silk, which is highly extensible compared to other silks.

The sticky glue that forms droplets on the capture threads is composed of modified silk protein and other compounds produced within the aggregate glands, and functions to retain prey that get caught in a spider’s silken trap.

“We see great potential for spider glue applications as organic pest control. After all, this stuff evolved to capture insect prey,” said Dr. Sarah Stellwagen, a postdoctoral researcher at the University of Maryland, Baltimore County.

“For example, farmers could spray the glue along a barn wall to protect their livestock from insects that bite or cause disease, and then could rinse it off without worrying about polluting waterways with dangerous pesticides.”

“They could use glue similarly to protect crops from pests. It could also be applied in areas where mosquito-borne illnesses are prevalent. It could also just be fun to play with.”

Dr. Stellwagen and her colleague, Dr. Rebecca Renberg of General Technical Services, LLC, sequenced and assembled two glue genes — called Aggregate Spidroin 1 (AgSp1) and Aggregate Spidroin 2 (AgSp2) — from the aggregate glands of the orb weaving spider species Argiope trifasciata.

“When we started this project, we were expecting to sequence the glue genes quickly and then move on, building on what we learned from the sequence. Instead, it took us two years just to finalize the sequence,” Dr. Stellwagen said.

The AgSp2 gene was 20,526 base pair long — about the same length as the longest known spider silk gene.

Surprisingly, AgSp1 was much bigger, organizationally distinct, and contained 42,270 base pairs.

“It ended up being this behemoth of a gene that’s more than twice as large as the previous largest silk gene,” Dr. Stellwagen said.

“It was a long, hard road to the day I found Dr. Renberg in the lab and said, ‘I think our gene is 42,000 bases long. I think we finished it.’ And in the end, it was taking a risk on a cutting-edge technique that finally yielded the complete sequence.”

Not only was the AgSp1 gene exceptionally long, but, like spider silk genes, it has many repetitions of the same sequence of bases — A, T, G, and C — in the middle.

“Now that we have a protocol for discovering full-length silk genes, what do silks from other species look like?” Dr. Stellwagen said.

“I’m super excited that I was able to finally figure out the puzzle, because it was just so hard. While it was a much bigger challenge than we expected, ultimately we learned a lot, and I am happy to put that out there for the next person who is trying to solve some ridiculous gene.”

The findings were published in the journal G3: Genes, Genomes, Genetics.

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Sarah D. Stellwagen Rebecca L. Renberg. 2019. Toward Spider Glue: Long Read Scaffolding for Extreme Length and Repetitious Silk Family Genes AgSp1 and AgSp2 with Insights into Functional Adaptation. G3: Genes, Genomes, Genetics 9 (6): 1909-1919; doi: 10.1534/g3.119.400065