Collagen IV of basement membranes: II. Emergence of collagen IVα345 enabled the assembly of a compact GBM as an ultrafilter in mammalian kidneys

The collagen IVα345 (Col-IVα345) scaffold, the major constituent of the glomerular basement membrane (GBM), is a critical component of the kidney glomerular filtration barrier. In Alport syndrome, affecting millions of people worldwide, over two thousand genetic variants occur in the COL4A3, COL4A4, and COL4A5 genes that encode the Col-IVα345 scaffold. Variants cause loss of scaffold, a suprastructure that tethers macromolecules, from the GBM or assembly of a defective scaffold, causing hematuria in nearly all cases, proteinuria, and often progressive kidney failure. How these variants cause proteinuria remains an enigma. In a companion paper, we found that the evolutionary emergence of the COL4A3, COL4A4, COL4A5, and COL4A6 genes coincided with kidney emergence in hagfish and shark and that the COL4A3 and COL4A4 were lost in amphibians. These findings opened an experimental window to gain insights into functionality of the Col-IVα345 scaffold. Here, using tissue staining, biochemical analysis and TEM, we characterized the scaffold chain arrangements and the morphology of the GBM of hagfish, shark, frog, and salamander. We found that α4 and α5 chains in shark GBM and α1 and α5 chains in amphibian GBM are spatially separated. Scaffolds are distinct from one another and from the mammalian Col-IVα345 scaffold, and the GBM morphologies are distinct. Our findings revealed that the evolutionary emergence of the Col-IVα345 scaffold enabled the genesis of a compact GBM that functions as an ultrafilter. Findings shed light on the conundrum, defined decades ago, whether the GBM or slit diaphragm is the primary filter.

A comparison of the growth and development of pyjama sharks (Poroderma africanum) in wild and captive populations

The pyjama shark (Poroderma africanum) is a Scyliorhinid species endemic to South Africa. Even though it is kept in captivity in many aquaria, there is a lack of research on its growth and development. In this study, we investigated the fertilization rate of eggs and the age at female sexual maturation in captive sharks and compared their growth to that of wild individuals. This is the first study to compare the growth of captive and wild catsharks as well as the first study to compare growth in male and female pyjama sharks and benefits from a much larger sample size than has previously been collected. The mean incubation rate (±standard error of the mean [SE]) was 239.46 ± 4.97 days, the mean Lt of hatchlings (±SE) was 14.65 ± 0.24 cm, and the mean Wt (±SE) was 17.19 ± 0.75 g. The observed ratio of male to female offspring (1:3.5) was also significantly different from 1:1. One female laid fertilized eggs 6.6 years after hatching and was considered sexually mature. Both in captivity and in the wild, males showed negative allometric growth and females showed isometric growth. The growth performance (Φ') was also greater in captive sharks compared to wild sharks regardless of sex. However, there was significant variation in growth between individuals of the same sex. The similar growth patterns (i.e., allometry and isometry) found in wild and captive populations are a very useful tool for informing future conservation management if the population of this shark species were to decline in the future and also prove that captive studies for this species are transferable to wild populations with regard to sexual differences. This study also provides a benchmark for further captive studies in other lesser-studied catshark species and raises interesting questions concerning sexual differences in growth for other shark species.

Emerging human-shark conflicts in the New York Bight: A call for expansive science and management

Recent spikes in interactions between humans and sharks in the New York Bight have sparked widespread reporting of possible causalities, many of which lack empirical support. Here we comment on the current state of knowledge regarding shark biology and management in New York waters emphasizing that the possible drivers of increased human-shark interactions are confounded by a lack of historical monitoring data. We outline several key research avenues that should be considered to ensure the safe and sustainable coexistence of humans, sharks, and their prey, in an era of accelerated environmental change.

Mass Spectrometry Analysis of Shark Skin Proteins

The mucus layer covering the skin of fish has several roles, including protection against pathogens and mechanical damage in which proteins play a key role. While proteins in the skin mucus layer of various common bony fish species have been explored, the proteins of shark skin mucus remain unexplored. In this pilot study, we examine the protein composition of the skin mucus in spiny dogfish sharks and chain catsharks through mass spectrometry (NanoLC-MS/MS). Overall, we identified 206 and 72 proteins in spiny dogfish (Squalus acanthias) and chain catsharks (Scyliorhinus retifer), respectively. Categorization showed that the proteins belonged to diverse biological processes and that most proteins were cellular albeit a significant minority were secreted, indicative of mucosal immune roles. The secreted proteins are reviewed in detail with emphasis on their immune potentials. Moreover, STRING protein-protein association network analysis showed that proteins of closely related shark species were more similar as compared to a more distantly related shark and a bony fish, although there were also significant overlaps. This study contributes to the growing field of molecular shark studies and provides a foundation for further research into the functional roles and potential human biomedical implications of shark skin mucus proteins.

Individual residency behaviours and seasonal long-distance movements in acoustically tagged Caribbean reef sharks in the Cayman Islands

Understanding how reef-associated sharks use coastal waters through their ontogeny is important for their effective conservation and management. This study used the horizontal movements of acoustically tagged Caribbean reef sharks (Carcharhinus perezi) to examine their use of coastal space around the Cayman Islands between 2009 and 2019. A total of 39 (59.1%) tagged sharks (male = 22, female = 17, immature = 18, mature = 21) were detected on the islands wide network of acoustic receivers. The detection data were used to calculate values of Residency Index (RI), Site-Fidelity Index (SFI) and minimum linear displacement (MLD), as well as for network analysis of individual shark movements to test for differences between demographics, seasons, and diel periods. Sharks were detected for up to 1,598 days post-tagging and some individuals showed resident behaviour but the majority of tagged individuals appear to have been one-off or only occasional transient visitors to the area. Generally, individuals showed strong site-fidelity to different areas displaying linear home ranges of < 20 km. The evidence indicates that there was no pattern of diel behaviour. Tagged sharks generally showed increased movements within and between islands during the summer (April-September), which may be related to breeding activity. Some individuals even made occasional excursions across 110 km of open water > 2,000 m deep between Grand Cayman and Little Cayman. One mature female shark showed a displacement of 148.21 km, the greatest distance reported for this species. The data shows that the distances over which some sharks moved, greatly exceeded the extent of any one of the islands' marine protected areas indicating that this species may be more mobile and dispersive than previously thought. This study provides support for the blanket protection to all sharks throughout Cayman waters, which was incorporated within the National Conservation Act in 2015.

Bioaccumulation of trace elements and hydrocarbons in chondrichthyans of the western Arabian Gulf: Environmental and human health risk assessment and implications for conservation

This is a first attempt to assess the levels of trace elements, PAHs, and TPHs in six elasmobranch species (Carcharhinus dussumieri, C. sorrah, Chiloscyllium arabicum, Gymnura poecilura, Sphyrna lewini, S. mokarran) from the Arabian Gulf. The chemical analysis showed that the concentrations of contaminants differed significantly between liver and muscle samples with both pelagic and benthic species and all families. For all species, contaminant concentrations were significantly higher in the liver than in the muscle. While muscle contaminant concentrations differed significantly with respect to species' lifestyles and families, those of liver showed no significant differences between pelagic and benthic species, neither between the four families nor between the six species. None of the analysed contaminants exceeded the internationally recognized standards in all studied species. These results enrich the knowledge on the bioaccumulation of contaminants in elasmobranchs and allow to assess the environmental status of the Arabian Gulf.

Functional diversity of sharks and rays is highly vulnerable and supported by unique species and locations worldwide

Elasmobranchs (sharks, rays and skates) are among the most threatened marine vertebrates, yet their global functional diversity remains largely unknown. Here, we use a trait dataset of >1000 species to assess elasmobranch functional diversity and compare it against other previously studied biodiversity facets (taxonomic and phylogenetic), to identify species- and spatial- conservation priorities. We show that threatened species encompass the full extent of functional space and disproportionately include functionally distinct species. Applying the conservation metric FUSE (Functionally Unique, Specialised, and Endangered) reveals that most top-ranking species differ from the top Evolutionarily Distinct and Globally Endangered (EDGE) list. Spatial analyses further show that elasmobranch functional richness is concentrated along continental shelves and around oceanic islands, with 18 distinguishable hotspots. These hotspots only marginally overlap with those of other biodiversity facets, reflecting a distinct spatial fingerprint of functional diversity. Elasmobranch biodiversity facets converge with fishing pressure along the coast of China, which emerges as a critical frontier in conservation. Meanwhile, several components of elasmobranch functional diversity fall in high seas and/or outside the global network of marine protected areas. Overall, our results highlight acute vulnerability of the world's elasmobranchs' functional diversity and reveal global priorities for elasmobranch functional biodiversity previously overlooked.

First record of the bull shark Carcharhinus leucas (Valenciennes, 1839) from the Maldivian archipelago, central Indian Ocean

Verified records of the bull shark Carcharhinus leucas are lacking in the Maldives. This study provides the first confirmed evidence of 23 sightings observed from 2013 to 2023 in the central and southern atolls of this archipelago. Most of the sightings occurred in close proximity to inhabited areas, where food waste is often discarded into the water, or in several dive sites, suggesting the presence of this species in different locations around central and southern atolls. Although further research is required to fully investigate the C. leucas population in the Maldives, this report documents and confirms its presence in this region.

Lipid-extracted muscle and liver tissues: Can they reveal mercury exposure of pelagic sharks?

Pelagic sharks are apex predators in oceanic ecosystems and tend to accumulate high amounts of mercury (Hg). The conventional method for assessing Hg exposure in sharks involves analyzing tissue samples without any chemical treatment. However, a substantial number of chemically treated tissue samples are still being preserved in laboratories or museums. It is critical to maximize the utilization of existing samples to reduce the need for additional sampling of pelagic sharks, especially endangered species. Lipid extraction is a widely employed pretreatment process for carbon isotope analysis in shark trophic ecology, while its impact on Hg quantification remains uncertain. Here, we evaluated the feasibility of using lipid-free muscle and liver tissues for investigation of Hg exposure in four endangered pelagic sharks inhabiting the eastern Pacific, including bigeye thresher (Alopias superciliosus), pelagic thresher (A. pelagicus), blue shark (Prionace glauca) and silky shark (Carcharhinus falciformis). Results showed that total Hg concentrations (THg) differed between untreated (THgbulk) and lipid-free (THglipid-free) samples for each tissue type of each species. In addition, dichloromethane-methanol extractions significantly altered the amount of Hg. This may result from the removal of lipoprotein compounds that vary between tissues and species. The THgbulk can be calculated by THglipid-free using the following formulas, THgbulk = 1.14 × THglipid-free + 0.30 and THgbulk = 0.33 × THglipid-free + 0.18, for muscle and liver tissues, respectively. These findings emphasize the applications of lipid-free tissues in THg analysis. This study may have important implications for improving evaluation of Hg exposure in endangered pelagic sharks.

Multiple interannual records of young-of-the-year identify an important area for the protection of the shortfin mako, Isurus oxyrinchus

The shortfin mako (Isurus oxyrinchus) is the second most fishery-exploited pelagic shark in the Mediterranean Sea, thus its conservation status is a cause for concern. Despite the species has been listed in fishery and trade regulations to hinder its population decline, the lack of knowledge on its distribution patterns and habitats essential for its persistence still hampers the implementation of sound conservation actions. Combining data from local expert knowledge, opportunistic catch records, and Baited Remote Underwater Videos, we show evidence of the interannual presence of young-of-the-year (YOY) I. oxyrinchus in the Pelagie Archipelago (Central Mediterranean Sea). A total of twenty-one individuals ranging 71-92.5 cm FL were incidentally caught (on average 2.3 YOY/1000 hooks) or documented on BRUVS in July and August over three consecutive years. These data coupled with questionnaires administered to longline fishers identify one specific area used by YOY in the summer months. Our study presents the most abundant record of YOY shortfin makos in the Mediterranean Sea within such a restricted time and limited area providing important information for improving the protection of this critically endangered species.

First records of the Pacific sleeper shark Somniosus cf. pacificus in the western tropical Pacific

Technological advances have enabled the expansion of ocean exploration to include the deep ocean, providing new species observations. Here, the authors present two new observations, captured by deep-sea cameras, of the sleeper shark Somniosus cf. pacificus from the Solomon Islands and Palau. This presents the first observation of S. cf. pacificus in the western Pacific tropics and extends its range about 2000 nautical miles south. The observations presented here provide much-needed information on the range of this species which can help guide future management and conservation actions.

Modeling and comparing the distributions and associations of two co-occurring catshark species off South Africa

Holohalaelurus regani and Scyliorhinus capensis are relatively small catsharks, which both occur off the continental shelf around South Africa and are often caught together as by-catch in demersal trawls. The present study used data collected during annual demersal research surveys conducted between 2009 and 2015 and is a first attempt at modeling the potential intra- and interspecific associations, by maturity stage and depth, of H. regani and S. capensis to elucidate species-specific patterns in their distributions in South African waters. Intraspecifically, both species displayed a wide overlap in distribution between maturity stages, but only H. regani displayed marked changes in distribution with maturity stage, with mature individuals found further eastwards and occupying deeper waters than immature individuals. Interspecifically, the two catsharks displayed an inverse relationship in their distribution, with an increase in the abundance of H. regani and a decrease in the abundance of S. capensis when moving from the south coast to the west coast. Some localized patches of co-occurrence were, however, evident between species and maturity stages, especially in offshore areas. Overall, our results indicated a stronger co-occurrence of mature and immature stages within each species and a rather weak co-occurrence of maturity stages between the two species. The spatial information provided in the present study provides useful information on how sharks with similar morphologies and lifestyles may partition their habitat as a mechanism for potentially reducing competition between them.

The biology and ecology of the basking shark: A review

Here we review the literature on the basking shark (Cetorhinus maximus, Gunnerus, 1765), well known as the second largest extant shark (and fish) species globally. Previous reviews were published by Kunzlik in 1988 and Sims in 2008, but in the last 15 years modern electronic and DNA sequencing technologies have resulted in considerable advances in our knowledge of the species' behaviour and ecology. Basking sharks are planktivores and under appropriate conditions spend prolonged periods at the ocean surface feeding on copepod prey that primarily make up their diet, the behaviour that gave rise to their common name. In general, they are migratory and move into higher latitude waters during the summer months, when loose surface-feeding aggregations may form at favoured sites, the best known of which at present occur at hotspots on the west coasts of Britain and Ireland. The species is found circumglobally in temperate waters, but they are also now known on occasion to migrate at depth between northern and southern hemispheres, as well as across oceans within the northern hemisphere. In the past basking shark were more abundant across much of their range, but, consequent on targeted fisheries and in some places intentional eradication, became everywhere scarce, with recent population recovery in the north-east Atlantic being the result of protective measures initiated in the 1990s. Despite their charismatic nature, some of their most fundamental biological processes including copulation, gestation and birth remain largely unknown, due to their migratory and often deep-water lifestyle. In contrast, the deployment of small-scale archival and satellite tags has revealed the details of both broadscale migratory movements and horizontal and vertical foraging behaviours. Recent genetic studies support evidence suggesting a degree of site fidelity in relation to seasonal feeding grounds, which likely explains why in the past local populations have collapsed following periods of intensive fishing. Other recent research using aerial drones and towed cameras has revealed within loose feeding aggregations elements of social behaviour that may have a courtship function as well as enhance feeding efficiency.

An integrated system to assess marine extinctions

More than 20 global marine extinctions and over 700 local extinctions have reportedly occurred during the past 500 years. However, available methods to determine how many of these species can be confidently declared true disappearances tend to be data-demanding, time-consuming, and not applicable to all taxonomic groups or scales of marine extinctions (global [G] and local [L]). We developed an integrated system to assess marine extinctions (ISAME) that can be applied to any taxonomic group at any geographic scale. We applied the ISAME method to 10 case studies to illustrate the possible ways in which the extinction status of marine species can be categorized as unverified, possibly extinct, or extinct. Of the 10 case studies we assessed, the ISAME method concludes that 6 should be categorized as unverified extinctions due to problems with species' identity and lack of reliable evidence supporting their disappearance (periwinkle-Littoraria flammea [G], houting-Coregonus oxyrinchus [G], long-spined urchin-Diadema antillarum [L], smalltooth sawfish-Pristis pectinata [L], and largetooth sawfish-P. pristis [L]). In contrast, ISAME classified the Guadalupe storm-petrel (Oceanodroma macrodactyla [G]) and the lost shark (Carcharhinus obsolerus [G]) as possibly extinct because the available evidence indicates that their extinction is plausible-while the largetooth sawfish [L] and Steller's sea cow (Hydrodamalis gigas [G]) were confirmed to be extinct. Determining whether a marine population or species is actually extinct or still extant is needed to guide conservation efforts and prevent further biodiversity losses.

Effects of gear modifications in a North Atlantic pelagic longline fishery: A multiyear study

The threat of population declines caused by pelagic longline fisheries in the Atlantic has increased the concern to find strategies that minimize the bycatch and mortality of non-target marine animals. Gear modification, such as the use of circle hooks instead of conventional J-hooks, has been identified as an effective bycatch reduction strategy in different pelagic longline fisheries around the world. This study aimed to verify the effectiveness of the use of circle hooks by quantifying catch rates, relative size selectivity, and anatomical hooking position for the most common target species (swordfish, Xiphias gladius, and blue shark, Prionace glauca), and some bycatch species (loggerhead sea turtles, Caretta caretta, and shortfin mako, Isurus oxyrinchus) caught by the Azorean longline fishing fleet. The trial was conducted for five consecutive years (2000-2004) using eight different types of hooks. In general, the blue shark catches using circle hooks were significantly higher compared to J (Mustad 9/0). The circle hooks also showed high probabilities of catching juvenile blue sharks. Conversely, the circle hooks were efficient in reducing the loggerhead sea turtle bycatch and were related to fewer catches of small sea turtle individuals. The use of circle hooks was also associated with reduced swordfish catches compared to J (Mustad 9/0), and the effect of hook types on length at capture was only significant for Circle (L. & P. 18/0-CLP18) and Ringed Tuna (RT). No significant differences were observed comparing hook type to either catch rates or size selectivity for shortfin mako. Additionally, circle hooks were more likely to lodge in the mouth than in deeper anatomical positions, when compared to J (Mustad 9/0), for the four species analysed. The present study demonstrated that the use of circle hooks could mitigate the impact of the pelagic longline fisheries in the Azores by decreasing the bycatch of sea turtles and reducing animal injuries caused by deep hooking.

First Insights into Population Structure and Genetic Diversity Versus Host Specificity in Trypanorhynch Tapeworms Using Multiplexed Shotgun Genotyping

Theory predicts relaxed host specificity and high host vagility should contribute to reduced genetic structure in parasites while strict host specificity and low host vagility should increase genetic structure. Though these predictions are intuitive, they have never been explicitly tested in a population genomic framework. Trypanorhynch tapeworms, which parasitize sharks and rays (elasmobranchs) as definitive hosts, are the only order of elasmobranch tapeworms that exhibit considerable variability in their definitive host specificity. This allows for unique combinations of host use and geographic range, making trypanorhynchs ideal candidates for studying how these traits influence population-level structure and genetic diversity. Multiplexed shotgun genotyping (MSG) data sets were generated to characterize component population structure and infrapopulation diversity for a representative of each trypanorhynch suborder: the ray-hosted Rhinoptericola megacantha (Trypanobatoida) and the shark-hosted Callitetrarhynchus gracilis (Trypanoselachoida). Adults of R. megacantha are more host-specific and less broadly distributed than adults of C. gracilis, allowing correlation between these factors and genetic structure. Replicate tapeworm specimens were sequenced from the same host individual, from multiple conspecific hosts within and across geographic regions, and from multiple definitive host species. For R. megacantha, population structure coincided with geography rather than host species. For C. gracilis, limited population structure was found, suggesting a potential link between degree of host specificity and structure. Conspecific trypanorhynchs from the same host individual were found to be as, or more, genetically divergent from one another as from conspecifics from different host individuals. For both species, high levels of homozygosity and positive FIS values were documented.

Skeletal convergence in thunniform sharks, ichthyosaurs, whales, and tunas, and its possible ecological links through the marine ecosystem evolution

Tunas, lamnid sharks, modern whales, and derived ichthyosaurs converged on the thunniform body plan, with a fusiform body, lunate caudal fin, compressed peduncle, and peduncle joint. This evolutionary convergence has been studied for a long time but little is known about whether all four clades share any skeletal characteristics. Comparisons of vertebral centrum dimensions along the body reveal that the four clades indeed share three skeletal characteristics (e.g., thick vertebral column for its length), while an additional feature is shared by cetaceans, lamnid sharks, and ichthyosaurs and two more by lamnid sharks and ichthyosaurs alone. These vertebral features are all related to the mechanics of thunniform swimming through contributions to posterior concentration of tail-stem oscillation, tail stem stabilization, peduncle joint flexibility, and caudal fin angle fixation. Quantitative identifications of these features in fossil vertebrates would allow an inference of whether they were a thunniform swimmer. Based on measurements in the literature, mosasaurs lacked these features and were probably not thunniform swimmers, whereas a Cretaceous lamniform shark had a mosaic of thunniform and non-thunniform features. The evolution of thunniform swimming appears to be linked with the evolution of prey types and, in part, niche availability through geologic time.

Development of Medical Shark Skin Forceps: Improved Grasping Power and Easy Manipulation

Background and Objectives

Important safety requirements for forceps used in surgical procedures are the ability to stably grasp fine tissue and to cause minimal tissue damage. Shark skin has the structural feature of circumpolar scales, which increase the frictional force of the scales by roughening their surface. We have developed and patented medical forceps with a shark skin pattern placed on the tip surfaces. The aim of this study was to examine the safety and efficacy of the shark skin forceps compared with existing forceps, both fundamentally and clinically.

Methods

To evaluate gripping power and usability, we compared bead transfer times for each forceps type. Grasping force and frictional force were measured quantitatively and compared among the types. To evaluate safety, we performed pathological examination of lung and urethral tissue after grasping, in an animal experiment. Subjective assessment of user experience was then performed using a questionnaire.

Results

In the dry lab assessment, transfer time was fastest using the shark skin forceps (34 s vs 61 s and 62 s, p < 0.05). Frictional force values were highest for the shark skin forceps (p < 0.05). In the animal experiment, there was no difference in pathological tissue damage to lung or ureter tissues among the forceps types after grasping. The questionnaire responses indicated advantages of the shark skin forceps in terms of ease of grasping membranes and lower degree of grasp failure.

Conclusion

Forceps with shark skin on the tips showed greater stability of tissue grasping and equivalent safety compared with existing forceps.

Plastic ingestion and trophic transfer in an endangered top predator, the longfin mako shark (Isurus paucus), from the tropical western Pacific Ocean

Plastic pollution has become a global environmental problem of major concern. However, the plastic contamination in the marine top predators, particularly in endangered species, is incompletely understood because of the limited amount of data on their presence in the digestive system and prey. This study investigated the stomach contents of an endangered but poorly known shark species, the longfin mako shark (Isurus paucus), found in the tropical western Pacific Ocean. We examined the plastics in this female specimen (1.22-m fork length) and her prey to assess the potential for trophic transfer of microplastics. Polypropylene bottle cap and lollipop packaging, longnose lancetfish (Alepisaurus ferox), and squid were found in the stomach of I. paucus, while no apparent internal injuries were noted. The microplastic fragments and granules, confirmed by laser direct infrared spectroscopy, were found in the digestive system of the intact squid ingested by I. paucus, suggesting that trophic transfer may occur between shark and prey. These results indicate that I. paucus is vulnerable to plastic ingestion and provide evidence of trophic transfer of microplastics in shark species. Our study emphasizes the need to evaluate the potential ecotoxicological consequences of increasing plastic pollution to endangered marine top predators.

Successful delivery of viviparous lantern shark from an artificial uterus and the self-production of lantern shark luciferin

Our recent success in the long-term maintenance of lantern shark embryos in artificial uterine systems has provided a novel option for the medical treatment of premature embryos for captive viviparous elasmobranchs. The remaining issue with this system is that the embryos cannot survive the abrupt change in the chemical environment from artificial uterine fluid (AUF) to seawater during delivery. To overcome this issue, the present study developed a new protocol for seawater adaptation, which is characterized by a long-term and stepwise shift from AUF to seawater prior to delivery. This protocol was employed successfully, and the specimen survived for more than seven months after delivery, the longest captive record of the species. During the experiment, we unexpectedly detected bioluminescence of the embryonic lantern shark in the artificial uterus. This observation indicates that lantern sharks can produce luciferin, a substance for bioluminescence. This contradicts the recent hypothesis that lantern sharks lack the ability to produce luciferin and use luciferin obtained from food sources.

3D relationship between hierarchical canal network and gradient mineralization of shark tooth osteodentin

Osteodentin is a dominant mineralized collagenous tissue in the teeth of many fishes, with structural and histological characteristics resembling those of bone. Osteodentin, like bone, comprises osteons as basic structural building blocks, however, it lacks the osteocytes and the lacuno-canalicular network (LCN), which are known to play critical roles in controlling the mineralization of the collagenous matrix in bone. Although numerous vascular canals exist in osteodentin, their role in tooth maturation and the matrix mineralization process remain poorly understood. Here, high resolution micro-computed tomography (micro-CT) and focused ion beam-scanning electron microscopy (FIB-SEM) were used to obtain 3D structural information of osteodentin in shark teeth at multiple scales. We observed a complex 3D network of primary canals with a diameter ranging from ∼10 µm to ∼120 µm, where the canals are surrounded by osteon-like concentric layers of lamellae, with 'interosteonal' tissue intervening between neighboring osteons. In addition, numerous hierarchically branched secondary canals extended radially from the primary canals into the interosteonal tissue, decreasing in diameter from ∼10 µm to hundreds of nanometers. Interestingly, the mineralization degree increases from the periphery of primary canals into the interosteonal tissue, suggesting that mineralization begins in the interosteonal tissue. Correspondingly, the hardness and elastic modulus of the interosteonal tissue are higher than those of the osteonal tissue. These results demonstrate that the 3D hierarchical canal network is positioned to play a critical role in controlling the gradient mineralization of osteodentin, also providing valuable insight into the formation of mineralized collagenous tissue without osteocytes and LCN. STATEMENT OF SIGNIFICANCE: Bone is a composite material with versatile mechanical properties. Osteocytes and their lacuno-canalicular network (LCN) are known to play critical roles during formation of human bone. However, the bone and osteodentin of many fishes, although lacking osteocytes and LCN, exhibit similar osteon-like structure and mechanical functions. Here, using various high resolution 3D characterization techniques, we reveal that the 3D network of primary canals and numerous hierarchically branched secondary canals correlate with the mineralization gradient and micromechanical properties of osteonal and interosteonal tissues of shark tooth osteodentin. This work significantly improves our understanding of the construction of bone-like mineralized tissue without osteocytes and LCN, and provides inspirations for the fabrication of functional materials with hierarchical structure.

Unleashing the power of shark variable single domains (VNARs): broadly neutralizing tools for combating SARS-CoV-2

The pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) generated a joint global effort to develop vaccines and other treatments that could mitigate the negative effects and the rapid spread of the virus. Single-domain antibodies derived from various sources, including cartilaginous fish, camelids, and humans, have gained attention as promising therapeutic tools against coronavirus disease 2019. Shark-derived variable new antigen receptors (VNARs) have emerged as the smallest naturally occurring antigen-binding molecules. Here, we compile and review recent published studies on VNARs with the capacity to recognize and/or neutralize SARS-CoV-2. We found a close balance between the use of natural immune libraries and synthetic VNAR libraries for the screening against SARS-CoV-2, with phage display being the preferred display technology for the selection of VNARs against this virus. In addition, we discuss potential modifications and engineering strategies employed to improve the neutralization potential of VNARs, such as exploring fusion with the Fc domain of human Immunoglobulin G (IgG) to increase avidity and therapeutic potential. This research highlights the potential of VNARs as powerful molecular tools in the fight against infectious diseases.