title: Defensive slime formation in Pacific hagfish requires Ca2+- and aquaporin-mediated swelling of released mucin vesicles.
abstract: Hagfishes defend themselves from fish predators via the rapid deployment of a fibrous slime that adheres to and clogs gills. The slime transforms from a thick glandular exudate to a fully hydrated product in a fraction of a second through a process that involves the swelling and rupture of numerous mucin vesicles. Here we demonstrate that the vesicle membrane plays an important role in regulating the swelling of mucin granules, and provide evidence that the membrane contains proteins that facilitate the movement of ions and water molecules. By exposing isolated mucin vesicles to varying combinations of inorganic ions, organic compounds and membrane channel inhibitors, we found that the majority of hagfish mucin vesicles require Ca(2+) to rupture. We also show that Ca(2+)-dependent rupture can be pharmacologically inhibited, which suggests a role for Ca(2+)-activated membrane transporters. We demonstrate that the aquaporin inhibitor mercuric chloride reduces the rate of vesicle swelling by an order of magnitude, which suggests that aquaporins facilitate the influx of water during vesicle deployment. Molecular evidence of two aquaporin homologues expressed in the slime glands further supports this idea. We propose a model of hagfish slime mucin vesicle rupture that involves Ca(2+)-activated transporters and aquaporins, and suggest that the presence of these proteins is an adaptation for increasing the speed of vesicle rupture and, consequently, the speed of the sliming response of hagfishes.
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1 Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC, Canada V0R 1B0.
authors.forename: Julia E
authors.initials: JE
authors.lastname: Herr
authors.affiliation: Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC, Canada V0R 1B0 Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, AB, Canada T6G 2R3.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Clifford
authors.affiliation: Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC, Canada V0R 1B0 Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, AB, Canada T6G 2R3.
authors.forename: Greg G
authors.initials: GG
authors.lastname: Goss
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1 Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC, Canada V0R 1B0 dfudge@uoguelph.ca.
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Fudge
mesh_terms: D000818:Animals; D051400:Aquaporin 3 / Q000235:genetics* / Q000378:metabolism; D051401:Aquaporin 4 / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D029941:Fish Proteins / Q000235:genetics* / Q000378:metabolism; D006196:Hagfishes / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009077:Mucins / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D010802:Phylogeny; D017422:Sequence Analysis, DNA
chemical_list: D051401:Aquaporin 4; D003902:Detergents; D029941:Fish Proteins; D009077:Mucins; D051400:Aquaporin 3; D017830:Octoxynol; D002118:Calcium
keywords: Holocrine secretion; Mucin; Mucus; Slime gland; Transporter