Biphasic burrowing in Atlantic hagfish (Myxine limosa).

Myxine limosa is a burrowing species of hagfish that occurs in the western North Atlantic in areas with muddy substrate and at depths generally greater than 100 meters. Burrowing of M. limosa has been observed from submersibles, but little is known about the behavior of these animals within the substrate or the biomechanical mechanisms involved.

Mechanisms of gill-clogging by hagfish slime.

Hagfishes defend themselves from gill-breathing predators by producing large volumes of fibrous slime when attacked. The slime's effectiveness comes from its ability to clog predators' gills, but the mechanisms by which hagfish slime clogs are uncertain, especially given its remarkably dilute concentration of solids. We quantified the clogging performance of hagfish slime over a range of concentrations, measured the contributions of its mucous and thread components, and measured the effect of turbulent mixing on clogging.

Epidermal threads reveal the origin of hagfish slime.

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.

Evolution of a remarkable intracellular polymer and extreme cell allometry in hagfishes.

The size of animal cells rarely scales with body size, likely due to biophysical and physiological constraints. In hagfishes, gland thread cells (GTCs) each produce a silk-like proteinaceous fiber called a slime thread. The slime threads impart strength to a hagfish's defensive slime and thus are potentially subject to selection on their function outside of the body.

From reductionism to synthesis: The case of hagfish slime.

Reductionist strategies aim to understand the mechanisms of complex systems by studying individual parts and their interactions. In this review, we discuss how reductionist approaches have shed light on the structure, function, and production of a complex biomaterial - hagfish defensive slime. Hagfish slime is an extremely dilute hydrogel-like material composed of seawater, mucus, and silk-like proteins that can deploy rapidly.

The best predictions in experimental biology are critical and persuasive.

A powerful way to evaluate scientific explanations (hypotheses) is to test the predictions that they make. In this way, predictions serve as an important bridge between abstract hypotheses and concrete experiments. Experimental biologists, however, generally receive little guidance on how to generate quality predictions.

A New Model of Hagfish Slime Mucous Vesicle Stabilization and Deployment.

Hagfishes thwart predators by releasing large volumes of gill-clogging slime, which consists of mucus and silk-like fibers. The mucous fraction originates within gland mucous cells, which release numerous vesicles that swell and rupture when ejected into seawater. Several studies have examined the function of hagfish slime mucous vesicles in vitro, but a comprehensive model of their biophysics is lacking.

Concentration effects of three common fish anesthetics on Pacific hagfish (Eptatretus stoutii).

The efficacy of three common fish anesthetics (clove oil, 2-phenoxyethanol, and tricaine methanesulfonate) was evaluated in the Pacific hagfish (Eptatretus stoutii). The overarching aim of our study was to identify the best anesthetic and concentration for the purposes of routine laboratory use of Pacific hagfish (i.e.

High concentrations of trimethylamines in slime glands inhibit skein unraveling in Pacific hagfish.

Hagfish defend themselves from fish predators by producing large volumes of gill-clogging slime when they are attacked. The slime consists of seawater and two major components that are ejected from the slime glands: mucus and threads. The threads are produced within specialized cells and packaged into intricately coiled bundles called skeins.

Concentration-independent mechanics and structure of hagfish slime.

Unlabelled: The defense mechanism of hagfish slime is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a concentrated material into a comparably "infinite" sea of water to form a dilute, sticky, cohesive elastic gel. This raises questions about the robustness of gel formation and rheological properties across a range of concentrations, which we study here for the first time. Across a nearly 100-fold change in concentration, we discover that the gel has similar viscoelastic time-dependent properties with constant power-law exponent (α=0.

Cellular mechanisms of slime gland refilling in Pacific hagfish ().

Hagfishes use their defensive slime to ward off gill-breathing predators. Slime gland refilling is a surprisingly slow process, and previous research has shown that the composition of the slime exudate changes significantly during refilling, which likely has consequences for the functionality of the slime. This study set out to expand our understanding of slime gland refilling by examining the cellular processes involved in refilling of the glands, as well as determining where in the gland the main slime cells - the gland thread cells and gland mucous cells - arise.

Emptying and refilling of slime glands in Atlantic () and Pacific () hagfishes.

Hagfishes are known for their unique defensive slime, which they use to ward off gill-breathing predators. Although much is known about the slime cells (gland thread cells and gland mucous cells), little is known about how long slime gland refilling takes, or how slime composition changes with refilling or repeated stimulation of the same gland. Slime glands can be individually electrostimulated to release slime, and this technique was used to measure slime gland refilling times for Atlantic and Pacific hagfish.

Flaccid skin protects hagfishes from shark bites.

Hagfishes defend themselves from fish predators by releasing large volumes of gill-clogging slime when they are attacked. Slime release is not anticipatory, but is only released after an attack has been initiated, raising the question of how hagfishes survive the initial attack, especially from biting predators such as sharks. We tested two hypotheses that could explain how hagfishes avoid damage from shark bites: puncture-resistant skin, and a loose and flaccid body design that makes it difficult for teeth to penetrate body musculature and viscera.

Skeletal stiffening in an amphibious fish out of water is a response to increased body weight.

Terrestrial animals must support their bodies against gravity, while aquatic animals are effectively weightless because of buoyant support from water. Given this evolutionary history of minimal gravitational loading of fishes in water, it has been hypothesized that weight-responsive musculoskeletal systems evolved during the tetrapod invasion of land and are thus absent in fishes. Amphibious fishes, however, experience increased effective weight when out of water - are these fishes responsive to gravitational loading? Contrary to the tetrapod-origin hypothesis, we found that terrestrial acclimation reversibly increased gill arch stiffness (∼60% increase) in the amphibious fish when loaded normally by gravity, but not under simulated microgravity.

Giant axonal neuropathy alters the structure of keratin intermediate filaments in human hair.

Giant axonal neuropathy (GAN) follows an autosomal recessive genetic inheritance and impedes the peripheral and central nervous system due to axonal swellings that are packed with neurofilaments. The patients display a number of phenotypes, including hypotonia, muscle weakness, decreased reflexes, ataxia, seizures, intellectual disability, pale skin and often curled hair. We used X-ray diffraction and tensile testing to determine potential changes to the structure of keratin intermediate filaments (IFs) in the hair of patients with GAN.

Hagfish Houdinis: biomechanics and behavior of squeezing through small openings.

Hagfishes are able to squeeze through small openings to gain entry to crevices, burrows, hagfish traps and carcasses, but little is known about how they do this, or what the limits of this ability are. The purpose of this study was to describe this ability, and to investigate possible mechanisms by which it is accomplished. We investigated the hypothesis that the passive movement of blood within a hagfish's flaccid subcutaneous sinus allows it to squeeze through narrow apertures that it would not be able to if it were turgid.

Identification of Wet-Spinning and Post-Spin Stretching Methods Amenable to Recombinant Spider Aciniform Silk.

Spider silks are outstanding biomaterials with mechanical properties that outperform synthetic materials. Of the six fibrillar spider silks, aciniform (or wrapping) silk is the toughest through a unique combination of strength and extensibility. In this study, a wet-spinning method for recombinant Argiope trifasciata aciniform spidroin (AcSp1) is introduced.

The Hagfish Gland Thread Cell: A Fiber-Producing Cell Involved in Predator Defense.

Fibers are ubiquitous in biology, and include tensile materials produced by specialized glands (such as silks), extracellular fibrils that reinforce exoskeletons and connective tissues (such as chitin and collagen), as well as intracellular filaments that make up the metazoan cytoskeleton (such as F-actin, microtubules, and intermediate filaments). Hagfish gland thread cells are unique in that they produce a high aspect ratio fiber from cytoskeletal building blocks within the confines of their cytoplasm. These threads are elaborately coiled into structures that readily unravel when they are ejected into seawater from the slime glands.

Morphological analysis of the hagfish heart. II. The venous pole and the pericardium.

The morphological characteristics of the venous pole and pericardium of the heart were examined in three hagfish species, Myxine glutinosa, Eptatretus stoutii, and Eptatretus cirrhatus. In these species, the atrioventricular (AV) canal is long, funnel-shaped and contains small amounts of myocardium. The AV valve is formed by two pocket-like leaflets that lack a papillary system.

Morphological analysis of the hagfish heart. I. The ventricle, the arterial connection and the ventral aorta.

We have studied the heart in three species of hagfish: Myxine glutinosa, Eptatretus stoutii, and Eptatretus cirrhatus and report about the morphology of the ventricle, the arterial connection and the ventral aorta. On the whole, the hagfish heart lacks outflow tract components, the ventricle and atrium adopt a dorso-caudal rather than a ventro-dorsal relationship, and the sinus venosus opens into the left side of the atrium. This may indicate a "defective" cardiac looping during embryogenesis.

The effects of actomyosin disruptors on the mechanical integrity of the avian crystalline lens.

Purpose: Actin and myosin within the crystalline lens maintain the structural integrity of lens fiber cells and form a hexagonal lattice cradling the posterior surface of the lens. The actomyosin network was pharmacologically disrupted to examine the effects on lenticular biomechanics and optical quality.

Methods: One lens of 7-day-old White Leghorn chickens was treated with 10 µM of a disruptor and the other with 0.

Physiology, biomechanics, and biomimetics of hagfish slime.

Hagfishes thwart attacks by fish predators by producing liters of defensive slime. The slime is produced when slime gland exudate is released into the predator's mouth, where it deploys in a fraction of a second and clogs the gills. Slime exudate is composed mainly of secretory products from two cell types, gland mucous cells and gland thread cells, which produce the mucous and fibrous components of the slime, respectively.

Spontaneous unraveling of hagfish slime thread skeins is mediated by a seawater-soluble protein adhesive.

Hagfishes are known for their ability to rapidly produce vast quantities of slime when provoked. The slime is formed via the interaction between seawater and two components released by the slime glands: mucin vesicles from gland mucous cells, which swell and rupture in seawater to form a network of mucus strands, and intermediate filament-rich threads, which are produced within gland thread cells as tightly coiled bundles called skeins. A previous study showed that the unraveling of skeins from Atlantic hagfish (Myxine glutinosa) requires both the presence of mucins and hydrodynamic mixing.