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Unlocking the Secrets of Silk Gene Evolution

Hidden variations illuminated in the diversity of silk production for the first time

For thousands of years, the silkworm has cornered the market on silk production for textiles. However, convergent evolution may be spinning a new thread of opportunity for caddisflies and other arthropods. New research published in Proceedings of the National Academy of Science (PNAS) utilizes high-quality long-read sequencing to uncover the hidden variation within silk gene evolution.

“The silk industry is almost entirely dependent upon one model organism, but we know that silk properties vary across biodiversity,” explains lead author Paul Frandsen, Brigham Young University professor of plant and wildlife sciences. “So, one of the goals of our research is to harness the natural variation we observe in biodiversity to inspire better industrial products and biomaterials.”

Professor Paul Frandsen collecting insects in the river with two research assistants.
Photo by BYU Photo

Teaming up with scientists from South America and Germany, Frandsen and co-authors utilize new genome sequencing technologies to unlock the secret variations in silk as they assemble and analyze the complex gene sequence for the first time. Until now, fully resolving both copies of the particularly long silk gene with repeating patterns that line up like a chain of differently colored Lego bricks of various lengths eluded sequencing.

“Now we can actually measure the variation at the genotype level,” Frandsen said, “which will allow us to finally figure out why all of these silks behave so differently at the phenotype level, in terms of stickiness, elasticity, and strength.”

The precise analysis of silk’s gene sequence is crucial to understanding how its properties are genetically predetermined.

"While certain traits of an organism are based on individual genes, their particular characteristics can be determined by the gene variants, the so-called alleles," explains co-author Jacqueline Heckenhauer from the Senckenberg Research Institute and Natural History Museum Frankfurt. "For the first time, we were able to show that the two alleles of the silk gene differ vastly within each individual animal, both in length and in the number of repeated regions. This might have resulted in the incredibly diverse nature of the silk."

illustrated spider on a web
Photo by Ralph Holzenthal

The research team selected five species from the arthropod group for the comparison: a butterfly (Vanessa cardui), three caddisfly species (Arctopsyche grandis, Atopsyche davidsoni, Hesperophylax magnus) with different silk use and a spider (Argiope argentata). In addition, the researchers created new, high-quality reference genomes, representing the full suite of DNA in an organism, for the spider and the caddisfly Arctopsyche grandis, which will benefit future research on these species.

“We have also discovered that the variation we observe in the silk gene alleles is strikingly consistent among groups of arthropods that have been evolving independently for more than 500 million years—spiders and insects,” Frandsen said. “This may indicate that, despite independent evolutionary trajectories, there are common mechanisms for the formation and maintenance of those genes responsible for natural products such as silk."

Since genes with repetitive motifs are also known to control traits of other animals (e.g., protein that enables fish to protect themselves against frost or protein fiber keratin which is important for hair and nail formation in mammals), the researchers are interested in further exploring the patterns of allelic variation in other genes.

Parapsyche spinning silk
Photo by Riley Nelson

"In the area of comparative genomics, studying allelic variation may hold interesting insights for application-oriented research,” said Steffen Pauls, professor of general entomology at Justus Liebig University Giessen and researcher at Senckenberg and the LOEWE Centre. “For example, caddisfly larvae can produce silk that hardens and sticks underwater but remains elastic and has a very high tensile strength. This could be a helpful model for industrial production of flexible, underwater fibers."

Publication in Proceedings of the National Academy of Sciences (PNAS): Paul B. Frandsen, Scott Hotaling, Ashlyn Powell, Jacqueline Heckenhauer, Akito Y. Kawahara, Richard H. Baker, Cheryl Y. Hayashi, Blanca Ríos-Touma, Ralph Holzenthal, Steffen U. Pauls, Russell J. Stewart

"Allelic resolution of insect and spider silk genes reveals hidden genetic diversity"


Professor Paul Frandsen, PhD
Brigham Young University, College of Life Sciences
Tel. 801-422-2283

Professor Dr. Steffen Pauls
LOEWE Centre for Translational Biodiversity Genomics
Senckenberg Research Institution and Natural History Museum Frankfurt,
Department of Terrestrial Zoology
Justus-Liebig-University Giessen, Institute of Insect Biotechnology
Tel. +49 (69) 7542-1222

Dr. Jacqueline Heckenhauer
LOEWE Centre for Translational Biodiversity Genomics
Senckenberg Research Institute and Natural History Museum
Department of Terrestrial Zoology
Tel. +49 (69) 7542-1811