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Takes readers on a sticky scientific adventure through the three-billion-year history of slime, exploring its part in the evolution of life and its cultural and emotional significance, from its starring role in the horror genre to its subtle influence on Art Nouveau. - - Source other than the Library of Congress

Fish mucus layers are the main surface of exchange between fish and the environment, and they possess important biological and ecological functions. Fish mucus research is increasing rapidly, along with the development of high-throughput techniques, which allow the simultaneous study of numerous genes and molecules, enabling a deeper understanding of the fish mucus composition and its functions. Fish mucus plays a major role against fish infections, and research has mostly focused on the study of fish mucus bioactive molecules (e.g., antimicrobial peptides and immune-related molecules) and associated microbiota due to their potential in aquaculture and human medicine. However, external fish mucus surfaces also play important roles in social relationships between conspecifics (fish shoaling, spawning synchronisation, suitable habitat finding, or alarm signals) and in interspecific interactions such as prey-predator relationships, parasite–host interactions, and symbiosis. This article reviews the biological and ecological roles of external (gills and skin) fish mucus, discussing its importance in fish protection against pathogens and in intra and interspecific interactions. We also discuss the advances that “omics” sciences are bringing into the fish mucus research and their importance in studying the fish mucus composition and functions.

\"What kind of fish uses a slime sleeping bag? Which plants capture insects with slime? Find out the answers to these questions and more in this fascinating book about slime!\"-- Publisher's description.

Key Points Mucins are highly O -glycosylated molecules that have gel-like properties. The mucin family consists of transmembrane mucins and gel-forming mucins. The transmembrane mucins cover the apical surfaces of the enterocytes and form the glycocalyx. The gel-forming mucins are secreted from goblet cells as large multimers that form the mucus skeleton and cover all epithelial surfaces. Mucus in the small intestine forms a diffusion barrier where antimicrobial substances keep the epithelium free from microorganism. Mucus in the colon forms a dense inner mucus layer that bacteria are unable to penetrate, creating a bacteria-free zone at the epithelial surface. Some, but not all, bacteria stimulate the formation of a functional mucus system with removable mucus in the small intestine and a stratified impenetrable inner mucus layer in colon. Mucus in the intestine creates a niche for bacteria, with digestible glycans providing a stable energy source, but mucus also traps and removes bacteria. Bacteria in loose mucus are planktonic and less virulent. The small intestinal goblet cells can sample luminal material during mucus secretion and transfer the antigens to lamina propria dendritic cells, something that also happens in the colon if bacterial numbers are decreased. This communication with the immune system has tolerogenic effects. Intestinal pathogens have mechanisms that allow them to circumvent the mucus protection to reach the epithelium. These include good motility and secretion of enzymes that can degrade the otherwise protease-resistant mucins. This Review describes the unique properties of mucus and mucins, with a focus on the intestine. Mucus and mucus-producing goblet cells contribute to our innate immune defences and, in turn, are regulated by the immune system. The authors discuss the link between defective mucus production and increased susceptibility to infection and inflammatory disease. A number of mechanisms ensure that the intestine is protected from pathogens and also against our own intestinal microbiota. The outermost of these is the secreted mucus, which entraps bacteria and prevents their translocation into the tissue. Mucus contains many immunomodulatory molecules and is largely produced by the goblet cells. These cells are highly responsive to the signals they receive from the immune system and are also able to deliver antigens from the lumen to dendritic cells in the lamina propria. In this Review, we will give a basic overview of mucus, mucins and goblet cells, and explain how each of these contributes to immune regulation in the intestine.

We normally live in symbiosis with ~10¹³ bacteria present in the colon. Among the several mechanisms maintaining the bacteria/host balance, there is limited understanding of the structure, function, and properties of intestinal mucus. We now demonstrate that the mouse colonic mucus consists of two layers extending 150 μm above the epithelial cells. Proteomics revealed that both of these layers have similar protein composition, with the large gel-forming mucin Muc2 as the major structural component. The inner layer is densely packed, firmly attached to the epithelium, and devoid of bacteria. In contrast, the outer layer is movable, has an expanded volume due to proteolytic cleavages of the Muc2 mucin, and is colonized by bacteria. Muc2⁻/⁻ mice have bacteria in direct contact with the epithelial cells and far down in the crypts, explaining the inflammation and cancer development observed in these animals. These findings show that the Muc2 mucin can build a mucus barrier that separates bacteria from the colon epithelia and suggest that defects in this mucus can cause colon inflammation.

Mucosal surfaces are a main entry point for pathogens and the principal sites of defense against infection. Both bacteria and phage are associated with this mucus. Here we show that phageto-bacteria ratios were increased, relative to the adjacent environment on all mucosal surfaces sampled, ranging from cnidarians to humans. In vitro studies of tissue culture cells with and without surface mucus demonstrated that this increase in phage abundance is mucus dependent and protects the underlying epithelium from bacterial infection. Enrichment of phage in mucus occurs via binding interactions between mucin glycoproteins and Ig-like protein domains exposed on phage capsids. In particular, phage Ig-like domains bind variable glycan residues that coat the mucin glycoprotein component of mucus. Metagenomic analysis found these Ig-like proteins present in the phages sampled from many environments, particularly from locations adjacent to mucosal surfaces. Based on these observations, we present the bacteriophage adherence to mucus model that provides a ubiquitous, but non-host-derived, immunity applicable to mucosal surfaces. The model suggests that metazoan mucosal surfaces and phage coevolve to maintain phage adherence. This benefits the metazoan host by limiting mucosal bacteria, and benefits the phage through more frequent interactions with bacterial hosts. The relationships shown here suggest a symbiotic relationship between phage and metazoan hosts that provides a previously unrecognized antimicrobial defense that actively protects mucosal surfaces.

Cervicovaginal mucus (CVM) can provide a barrier that precludes HIV and other sexually transmitted virions from reaching target cells in the vaginal epithelium, thereby preventing or reducing infections. However, the barrier properties of CVM differ from woman to woman, and the causes of these variations are not yet well understood. Using high-resolution particle tracking of fluorescent HIV-1 pseudoviruses, we found that neither pH nor Nugent scores nor total lactic acid levels correlated significantly with virus trapping in unmodified CVM from diverse donors. Surprisingly, HIV-1 was generally trapped in CVM with relatively high concentrations of d -lactic acid and a Lactobacillus crispatus -dominant microbiota. In contrast, a substantial fraction of HIV-1 virions diffused rapidly through CVM with low concentrations of d -lactic acid that had a Lactobacillus iners -dominant microbiota or significant amounts of Gardnerella vaginalis , a bacterium associated with bacterial vaginosis. Our results demonstrate that the vaginal microbiota, including specific species of Lactobacillus , can alter the diffusional barrier properties of CVM against HIV and likely other sexually transmitted viruses and that these microbiota-associated changes may account in part for the elevated risks of HIV acquisition linked to bacterial vaginosis or intermediate vaginal microbiota. IMPORTANCE Variations in the vaginal microbiota, especially shifts away from Lactobacillus -dominant microbiota, are associated with differential risks of acquiring HIV or other sexually transmitted infections. However, emerging evidence suggests that Lactobacillus iners frequently colonizes women with recurring bacterial vaginosis, raising the possibility that L. iners may not be as protective as other Lactobacillus species. Our study was designed to improve understanding of how the cervicovaginal mucus barrier against HIV may vary between women along with the vaginal microbiota and led to the finding that the vaginal microbiota, including specific species of Lactobacillus , can directly alter the diffusional barrier properties of cervicovaginal mucus. This work advances our understanding of the complex barrier properties of mucus and highlights the differential protective ability of different species of Lactobacillus , with Lactobacillus crispatus and possibly other species playing a key role in protection against HIV and other sexually transmitted infections. These findings could lead to the development of novel strategies to protect women against HIV. Variations in the vaginal microbiota, especially shifts away from Lactobacillus -dominant microbiota, are associated with differential risks of acquiring HIV or other sexually transmitted infections. However, emerging evidence suggests that Lactobacillus iners frequently colonizes women with recurring bacterial vaginosis, raising the possibility that L. iners may not be as protective as other Lactobacillus species. Our study was designed to improve understanding of how the cervicovaginal mucus barrier against HIV may vary between women along with the vaginal microbiota and led to the finding that the vaginal microbiota, including specific species of Lactobacillus , can directly alter the diffusional barrier properties of cervicovaginal mucus. This work advances our understanding of the complex barrier properties of mucus and highlights the differential protective ability of different species of Lactobacillus , with Lactobacillus crispatus and possibly other species playing a key role in protection against HIV and other sexually transmitted infections. These findings could lead to the development of novel strategies to protect women against HIV.

The mechanisms by which mucus helps prevent viruses from infecting mucosal surfaces are not well understood. We engineered non-mucoadhesive nanoparticles of various sizes and used them as probes to determine the spacing between mucin fibers (pore sizes) in fresh undiluted human cervicovaginal mucus (CVM) obtained from volunteers with healthy vaginal microflora. We found that most pores in CVM have diameters significantly larger than human viruses (average pore size 340 ± 70 nm; range approximately 50-1800 nm). This mesh structure is substantially more open than the 15-100-nm spacing expected assuming mucus consists primarily of a random array of individual mucin fibers. Addition of a nonionic detergent to CVM caused the average pore size to decrease to 130 ± 50 nm. This suggests hydrophobic interactions between lipid-coated \"naked\" protein regions on mucins normally cause mucin fibers to self-condense and/or bundle with other fibers, creating mucin \"cables\" at least three times thicker than individual mucin fibers. Although the native mesh structure is not tight enough to trap most viruses, we found that herpes simplex virus (approximately 180 nm) was strongly trapped in CVM, moving at least 8,000-fold slower than non-mucoadhesive 200-nm nanoparticles. This work provides an accurate measurement of the pore structure of fresh, hydrated ex vivo CVM and demonstrates that mucoadhesion, rather than steric obstruction, may be a critical protective mechanism against a major sexually transmitted virus and perhaps other viruses.

Preterm births are a global health priority that affects 15 million babies every year worldwide. There are no effective prognostic and therapeutic strategies relating to preterm delivery, but uterine infections appear to be a major cause. The vaginal epithelium is covered by the cervicovaginal mucus, which is essential to health because of its direct involvement in reproduction and functions as a selective barrier by sheltering the beneficial lactobacilli while helping to clear pathogens. During pregnancy, the cervical canal is sealed with a cervical mucus plug that prevents the vaginal flora from ascending toward the uterine compartment, which protects the fetus from pathogens. Abnormalities of the cervical mucus plug and bacterial vaginosis are associated with a higher risk of preterm delivery. This review addresses the current understanding of the cervicovaginal mucus and the cervical mucus plug and their interactions with the microbial communities in both the physiological state and bacterial vaginosis, with a focus on gel-forming mucins. We also review the current state of knowledge of gel-forming mucins contained in mouse cervicovaginal mucus and the mouse models used to study bacterial vaginosis.

Background The mucus layer provides the first defense that keeps the epithelium free from microorganisms. However, the effect of the small intestinal mucus layer on pathogen invasion is still poorly understood, especially for swine enteric coronavirus. To better understand virus‒mucus layer‒intestinal epithelium interactions, here, we developed a porcine intestinal organoid mucus‒monolayer model under air‒liquid interface (ALI) conditions. Results We successfully established a differentiated intestinal organoid monolayer model comprising various differentiated epithelial cell types and a mucus layer under ALI conditions. Mass spectrometry analysis revealed that the mucus derived from the ALI monolayer shared a similar composition to that of the native small intestinal mucus. Importantly, our results demonstrated that the ALI monolayer exhibited lower infectivity of both TGEV and PEDV than did the submerged monolayer. To further confirm the impact of ALI mucus on coronavirus infection, mucus was collected from the ALI monolayer culture system and incubated with the viruses. These results indicated that ALI mucus treatment effectively reduced the infectivity of TGEV and PEDV. Additionally, Mucin 2 (Muc2), a major component of native small intestinal mucus, was found to be abundant in the mucus derived from the ALI monolayer, as determined by mass spectrometry analysis. Our study confirmed the potent antiviral activity of Muc2 against TGEV and PEDV infection. Considering the sialylation of Muc2 and the known sialic acid-binding activity of coronavirus, further investigations revealed that the sialic acid residues of Muc2 play a potential role in inhibiting coronavirus infection. Conclusions We established the porcine intestinal organoid mucus monolayer as a novel and valuable model for confirming the pivotal role of the small intestinal mucus layer in combating pathogen invasion. In addition, our findings highlight the significance of sialic acid modification of Muc2 in blocking coronavirus infections. This discovery opens promising avenues for the development of tailor-made drugs aimed at preventing porcine enteric coronavirus invasion.