Epidermal threads reveal the origin of hagfish slime

• Published in: eLife Vol. 12
• Main Authors: Zeng, Yu, Plachetzki, David C, Nieders, Kristen, Campbell, Hannah, Cartee, Marissa, Pankey, M Sabrina, Guillen, Kennedy, Fudge, Douglas
• Format: Journal Article
• Language: English
• Published: England eLife Science Publications, Ltd 10.03.2023; eLife Sciences Publications, Ltd; eLife Sciences Publications Ltd
• Subjects: Analysis; Animals; Biological products; biomaterial; Cell Biology; Epidermal Cells; Epidermis; Evolutionary Biology; Goblet Cells; hagfish; Hagfishes - metabolism; morphogenesis; Mucus - metabolism; predator-prey interaction; Skin; transcriptomics; cell biology; evolutionary biology; morphogenesis; biomaterial; transcriptomics; predator-prey interaction; hagfish
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.81405

When attacked, hagfishes produce a soft, fibrous defensive slime within a fraction of a second by ejecting mucus and threads into seawater. The rapid setup and remarkable expansion of the slime make it a highly effective and unique form of defense. How this biomaterial evolved is unknown, although circumstantial evidence points to the epidermis as the origin of the thread- and mucus-producing cells in the slime glands. Here, we describe large intracellular threads within a putatively homologous cell type from hagfish epidermis. These epidermal threads averaged ~2 mm in length and ~0.5 μm in diameter. The entire hagfish body is covered by a dense layer of epidermal thread cells, with each square millimeter of skin storing a total of ~96 cm threads. Experimentally induced damage to a hagfish's skin caused the release of threads, which together with mucus, formed an adhesive epidermal slime that is more fibrous and less dilute than the defensive slime. Transcriptome analysis further suggests that epidermal threads are ancestral to the slime threads, with duplication and diversification of thread genes occurring in parallel with the evolution of slime glands. Our results support an epidermal origin of hagfish slime, which may have been driven by selection for stronger and more voluminous slime.