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At least 19 recordsLinked to original sources
PubMed1977

Haemoglobins of the shark, Heterodontus portusjacksoni. III. Amino acid sequence of the beta-chain.

The amino acid sequence of the beta-chain of the principal haemoglobin from the shark H. portusjacksoni has been determined. The chain has 141 residues, the same as that of mammalian alpha-chains and less than the 146 residues of mammalian beta-chains or the 148 residues of the alpha-chain from the tetrameric shark haemoglobin. The sequence was deduced from the sequences of peptides obtained by digestion of the globin or its cyanogen bromide fragments with trypsin, chymotrypsin, pepsin and papain. The difference in length of the beta-chain is most readily accounted for by the absence of the D helix. This small helical section is normally present in myoglobins and beta-globins but absent in alpha-chains. The deduction that it is absent from shark beta-chain is based on consideration of homology. The beta-chain shows the insertion of histidine beta2 and the deletions corresponding to residues A17 and AB1 relative to alpha-and myoglobin chains. The reactive thiol group in shark haemoglobin was shown by radioactive labelling to be residue 51 in the beta-chain, immediately preceding the E helix. The amino acid sequence of shark beta-chain shows 92 differences from human beta-chain, significantly more differences than shown by chicken or frog beta-chains, in line with its earlier time of divergence. If the tertiary structure of the shark beta-chain is the same as that of the horse then there are two changes in the alpha1beta2 contact site in oxyhaemoglobin and an additional one in deoxyhaemoglobin. When both alpha- and beta-chain contacts are considered there is a total of nine changes in residues involved in the alpha1beta2 contacts. There is no Bohr effect in shark haemoglobin, and of the residues normally involved in this effect the C-terminal histidine residue of the beta-chain is present, but the aspartyl (FG1) residue to which it is salt-linked is not, being replaced by a glutamyl residue.

Amino Acid Sequence↗
PubMed2024

Comparative genomics illuminates karyotype and sex chromosome evolution of sharks.

Chondrichthyes is an important lineage to reconstruct the evolutionary history of vertebrates. Here, we analyzed genome synteny for six chondrichthyan chromosome-level genomes. Our comparative analysis reveals a slow evolutionary rate of chromosomal changes, with infrequent but independent fusions observed in sharks, skates, and chimaeras. The chondrichthyan common ancestor had a proto-vertebrate-like karyotype, including the presence of 18 microchromosome pairs. The X chromosome is a conversed microchromosome shared by all sharks, suggesting a likely common origin of the sex chromosome at least 181 million years ago. We characterized the Y chromosomes of two sharks that are highly differentiated from the X except for a small young evolutionary stratum and a small pseudoautosomal region. We found that shark sex chromosomes lack global dosage compensation but that dosage-sensitive genes are locally compensated. Our study on shark chromosome evolution enhances our understanding of shark sex chromosomes and vertebrate chromosome evolution.

Animals↗
PubMed1978

Visual discrimination following partial telencephalic ablations in nurse sharks (Ginglymostoma cirratum).

An instrumental conditioning task was used to examine the role of the nurse shark telencephalon in black-white (BW) and horizontal-vertical stripes (HV) discrimination performance. In the first experiment, subjects initially received either bilateral anterior telencephalic control lesions or bilateral posterior telencephalic lesions aimed at destroying the central telencephalic nuclei (CN), which are known to receive direct input from the thalamic visual area. Postoperatively, the sharks were trained first on BW and then on HV. Those with anterior lesions learned both tasks as rapidly as unoperated subjects. Those with posterior lesions exhibited visual discrimination deficits related to the amount of damage to the CN and its connecting pathways. Severe damage resulted in an inability to learn either task but caused no impairments in motivation or general learning ability. In the second experiment, the sharks were first trained on BW and HV and then operated. Suction ablations were used to remove various portions of the CN. Sharks with 10% or less damage to the CN retained the preoperatively acquired discriminations almost perfectly. Those with 11-50% damage had to be retrained on both tasks. Almost total removal of the CN produced behavioral indications of blindness along with an inability to perform above the chance level on BW despite excellent retention of both discriminations over a 28-day period before surgery. It appears, however, that such sharks can still detect light. These results implicate the central telencephalic nuclei in the control of visually guided behavior in sharks.

Animals↗
PubMed2026

Genomic Tracking of Market-Derived Bull Shark Fins Back to Source Population of Origin.

International trade of shark fins remains difficult to monitor because products are rarely labelled to species and are often highly processed, resulting in severely degraded DNA. For several shark species listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), this limits external verification of source populations supplying global trade hubs. Here, we assess whether nuclear genomic approaches can be applied to market-derived bull shark (Carcharhinus leucas) fins to determine their population of origin. We analysed dried fin trimmings collected from retail vendors in Hong Kong SAR, one of the world's largest dried shark fin trade hubs, using a targeted DArTcap single nucleotide polymorphism (SNP) panel, originally developed for population genomic studies of this species. Despite substantial DNA degradation, genomic libraries were successfully obtained for most samples, yielding sufficient SNP data to perform robust provenance and sex assignment. Using a Bayesian mixed-stock analysis, most fin samples were assigned to the Indo-West Pacific (71.4%), with smaller contributions from the western Atlantic (22.6%) and eastern Pacific (3.0%). Genetic sex assignment revealed twice as many males as females, although results indicated a conservative bias towards male assignment due to the limited number of X-linked markers available in degraded samples. Our results demonstrate that genome-wide targeted approaches can be effectively applied to highly processed shark fin products to infer population sources and sex composition. This study provides proof-of-concept for integrating genomics into shark trade monitoring, highlighting its potential to improve traceability, support CITES implementation and inform conservation and fisheries management, particularly for species with well-resolved population structure.

Animals↗
PubMed1977

Partial characterization of the bile salt-dependent triacylglycerol lipase from the leopard shark pancreas.

Leopard shark triacylglycerol lipase has been characterized as a crude pancreatic preparation. The enzyme demonstrated an absolute requirement for trihydroxy bile salts for activity with natural bile salts of the shark giving a 4-fold greater stimulation of activity than pure sodium taurocholate. Bile salts also protected the enzyme from apparent inactivation by p-chloromercuribenzoate and trypsin treatment. The shark lipase demonstrated a temperature optimum of 36 degrees C and was rapidly inactivated at 50 degrees C even in the presence of bile salts. Divalent metal ions were required for activity with Ca2+ providing the greatest stimulation. At 22 degrees C, pH 8.5 and in the presence of natural bile salts, the apparent V was about 0.6 mumol fatty acid released/min per mg protein. The shark enzyme hydrolyzed over 90% of the fatty acids from trioleovylglycerol and methyl esters of pancreatic lipase-resistant fatty acids were hydrolyzed at the same rate as typical fatty acid methyl esters. Hydrolysis of triacylglycerol proceeded about ten-times faster than wax ester hydrolysis. The kinetic properties of the leopard shark enzyme were compared to other bile salt-dependent lipolytic enzymes. Pancreatic lipase activity was not detected.

Animals↗
PubMed2026

Antibody diversification in cartilaginous fishes: Mechanistic insights from the nurse shark and comparative perspectives across jawed vertebrates.

Antibody diversity in vertebrates arises through the coordinated actions of V(D)J recombination and somatic hypermutation (SHM). Cartilaginous fishes occupy a key phylogenetic position as the sister lineage to bony vertebrates and therefore provide important comparative insights into the evolution of adaptive immunity. This review focuses on the nurse shark (Ginglymostoma cirratum) as a representative model for examining antibody-diversification mechanisms in cartilaginous fishes. Shark immunoglobulin genes exhibit a multicluster organization, while immunoglobulin new antigen receptor (IgNAR), a heavy-chain-only isotype, contains a single variable domain with an extended complementarity-determining region 3 (CDR3) that can be stabilized by non-canonical disulfide bonds. These structural features, together with intracluster multi-D V(D)J recombination and distinctive SHM characterized by single and tandem substitutions and insertions/deletions, contribute to antibody diversification in sharks. By comparing cartilaginous fishes, ray-finned fishes, and mammals, this review highlights lineage-specific combinations of immunoglobulin gene organization, recombination, mutational processing, and affinity maturation. Within the heuristic framework proposed here, shark and mammalian systems are described as emphasizing "breadth-first" repertoire generation and "precision-first" affinity optimization, respectively. These terms indicate relative mechanistic emphases rather than mutually exclusive categories or sequential evolutionary stages, while ray-finned fishes exhibit a distinct combination of genomic organization and mutational features. Investigating antibody diversification in cartilaginous fishes not only advances our understanding of vertebrate immune evolution but also provides structural and mechanistic insights that may inform the development of engineered antibodies based on the IgNAR scaffold.

Antibody diversity↗
PubMed2025

Chromosome-Level Assembly and Annotation of the Grey Reef Shark (Carcharhinus amblyrhynchos) Genome.

To date less than 5% of shark species have nuclear reference genomes, despite next-generation sequencing advances. Particularly for threatened shark species, there is a lack of reliable genomes which are crucial in facilitating research and conservation applications. We assembled the first nuclear reference genome of the endangered grey reef shark (Carcharhinus amblyrhynchos) using long-read PacBio HiFi and Omni-C sequencing to reach chromosome-level contiguity (36 pseudochromosomes; 2.9 Gbp) and high completeness (94% complete BUSCOs). BRAKER3 annotated 16,505 protein-coding genes after masking repetitive elements which accounted for 59% of the genome. We identified potential X and Y sex chromosomes on pseudochromosomes 36 and 57, respectively. The quality and completeness of the draft genome of C. amblyrhynchos will enable researchers to investigate genetic variations and adaptations specific to this species as well as across other Carcharhinus spp., opening new venues for comparative genomics and advancing conservation genetic applications.

Animals↗
PubMed1978

A stochastic locomotor control model for the nurse shark, Ginglymostoma cirratum.

The locomotor behavior of the nurse shark (Ginglymostoma cirratum) is characterized by 17 variables (frequency and ratios of left, right, and total turns; their radians; straight paths (steps); distance travelled; and velocity) Within each of these variables there is an internal time dependency the structure of which was elaborated together with an improved statistical model predicting their behavior within 90% confidence limits. The model allows for the sensitive detection of subtle locomotor response to sensory stimulation as values of variables may exceed the established confidence limits within minutes after onset of the stimulus. The locomotor activity is well described by an autoregression time series model and can be predicted by only seven variables. Six of these form two independently operating clusters. The first one consists of: the number of right turns, the distance travelled and the mean velocity; the second one of: the mean size of right turns, of left turns, and of all turns. The same clustering is obtained independently by a cluster analysis of cross-sections of the seven time series. It is apparent that, among a total of 17 locomotor variables, seven behave as individually independent agents, presumably controlled by seven separate and independent centers. The output of each center can only be predicted by its own behavior. In spite of the individual of the seven variables, their internal structure is similar in important aspects which may result from control by a common command center. The shark locomotor model differs in important aspects from the previously constructed for the goldfish. The interdependence of the locomotor variables in both species may be related to the control mechanisms postulated by von Holst for the coordination of rhythmic fin movements in fishes. A locomotor control model for the nurse shark is proposed.

Animals↗
PubMed1977

Characterization of serum lipoproteins of the shark Centrophorus squamous.

1. Blood serum from the shark Centrophorus squamosus (Bonnaterre) was shown to contain VLD (very-low-density), LD (low-density) and HD (high-density) lipoproteins. 2. In shape, size and general physical properties, these lipoproteins were very similar to those described for other animals. The VLD lipoproteins were the major components of the mixture, and HD lipoproteins were present at the lowest amount. 3. In addition to the usual lipid components, the shark lipoproteins also contain substantial amounts of hydrocarbon, probably mainly squalene, and monoalkyldiacylglycerols. Only trace amounts of wax ester were detected. 4. The protein moiety of the VLD and LD lipoproteins contained a component which, in its solubility and electrophoretic properties, molecular weight and amino acid composition, resembled the B apolipoprotein of man and other mammals. This accounted for a large part of the total shark apolipoprotein. 5. There were also present smaller amounts of proteins which were soluble in 8M-urea. In their electrophoretic mobility on basic polyacrylamide gel, some of these were like the A and C apoproteins of man. 6. The electrophoretic distribution of the soluble proteins from the VLD and LD lipoproteins resembled that in higher mammals, but in the HD lipoproteins the similarity was less.

Amino Acids↗
PubMed1977

Morphology of the macula neglecta in sharks of the genus Carcharhinus.

Ears from several species of carcharhinid sharks were studied by gross dissection, light microscopy, transmission electron microscopy, and scanning electron microscopy. Structures along a possible sound transmission path to the ear are described, but main consideration is given to the structure of the macula neglecta. The macula neglecta is composed of two patches of sensory epithelium which line part of the posterior canal duct. In an adult shark the larger of these contains 224,000 sensory hair cells oriented so as to detect forces directed posteroventrolaterally in the duct. The smaller patch contains 43,000 hair cells oriented so as to detect oppositely directed forces. These receptor cells project through numerous small terminals to a total for both patches of 4,700 myelinated nerve fibers. Cytostructural variations throughout the hair cell population are also reported. Estimated acoustic properties of the tissues in this complex and the processing potential of the neural elements are interpreted as suggestive of auditory function. A mechanism based on the geometry of the receptor arrays is proposed to explain behaviorally observed instantaneous sound localization from the farfield. Evolution of the macula neglecta is reviewed, and evidence for homology of the macula neglecta and amphibian papilla is presented.

Animals↗
PubMed1979

Ultrastructure of calcified cartilage in the endoskeletal tesserae of sharks.

The tesserate pattern of endoskeletal calcification has been investigated in jaws, gill arches, vertebral arches and fins of the sharks Carcharhinus menisorrah, Triaenodon obesus and Negaprion brevirostris by techniques of light and electron microscopy. Individual tesserae develop peripherally at the boundary between cartilage and perichondrium. An inner zone, the body, is composed of calcified cartilage containing viable chondroxytes separated by basophilic contour lines which have been called Liesegang waves or rings. The outer zone of tesserae, the cap, is composed of calcified tissue which appears to be produced by perichondrial fibroblasts more directly, i.e., without first differentiating as chondroblasts. Furthermore, the cap zone is penetrated by acidophilic Sharpey fibers of collagen. It is suggested that scleroblasts of the cap zone could be classified as osteoblasts. If so, the cap could be considered a thin veneer of bone atop the calcified cartilage of the body of a tessera. By scanning electron microscopy it was observed that outer and inner surfaces of tesserae differ in appearance. Calcospherites and hydroxyapatite crystals similar to those commonly seen on the surface of bone are present on the outer surface of the tessera adjacent to the perichondrium. On the inner surface adjoining hyaline cartilage, however, calcospherites of variable size are the predominant surface feature. Transmission electron microscopy shows calcification in close association with coarse collagen fibrils on the outer side of a tessera, but such fibrils are absent from the cartilaginous matrix along the under side of tesserae. Calcified cartilage as a tissue type in the endoskeleton of sharks is a primitive vertebrate characteristic. Calcification in the tesserate pattern occurring in modern Chondrichthyes may be derived from an ancestral pattern of a continuous bed of calcified cartilage underlying a layer of perichondral bone, as theorized by Orvig ('51); or the tesserate pattern in these fish may itself be primitive.

Animals↗
PubMed1977

Fine structure of the ordinary lateral line organ. II. The lateral line canal organ of spotted shark, Mustelus manazo.

The lateral line organ of the spotted shark is characterized by its semi-cylindrical shape. Each organ (neuromast) is so closely apposed to the next that the individual neuromasts are almost continuous. The neuromast is composed of receptor cells, supporting cells and mantle cells. The receptor cells bear one kinocilium and up to 40 stereocilia. Bi-directional arrangement of the receptor cells as occurs in teleosts was demonstrated. Afferent and efferent nerve endings were found at the base of the receptor cells. The supporting cells extend from the basal lamina to the free surface. Long microvilli and a cilium-like "ciliary rod" project from the top of each supporting cell. The cell contains relatively few elements of the Golgi apparatus and little rough endoplasmic reticulum, but mitochondria and filaments are abundant. The mantle cell limits the lateral margin of the neuromast. It is distinguished from the supporting cell because of its long crescent-shaped nucleus and scarce, short microvilli. Myelinated nerve fibres are found in the subepithelial connective tissue but not in the epithelium. The fine structure of the shark lateral line organ suggests that this organ is in an intermediated step of evolution between that of lamphrey and teleost.

Animals↗
PubMed1977

Phylogeny of immunoglobulin structure and function; characterization of the cysteine-containing peptide involved in the pentamerization of shark IgM.

Nurse shark (Ginglymostoma cirratum) immunoglobulins were studied in an attempt to further define the relationship between the naturally occurring monomeric 7S and the pentameric 19S forms of extracellular IgM. A peptide containing the cysteine involved in the formation of intersubunit disulfide bonds linking 7S monomers into pentamers was isolated from the H chain of the 19S molecule and characterized. A similar peptide was also isolated from the H chain of the naturally occurring 7S molecule. These observations serve to substantiate previous claims that the two shark proteins belong to the same immunoglobulin class.

Amino Acid Sequence↗
PubMed1979

Myoglobin of the shark Heterodontus portusjacksoni: isolation and amino acid sequence.

Myoglobin isolated from red muscle of the shark H. portusjacksoni was purified by ion-exchange chromatography on sulfopropyl-Sephadex and gel-filtration. Amino acid analysis and sequence determination showed 148 amino acid residues. The amino terminal residue is acetylated as shown by mass spectrographic analysis of N-terminal peptides. There is a deletion of four residues at the amino terminal end as well as one residue in the CD interhelical area relative to other myoglobins. The complete amino acid sequence has been determined following digestion with trypsin, chymotrypsin, pepsin and staphylococcal protease. Sequences of the purified peptides were determined by the dansyl-Edman procedure. The amino acid sequence showed approximately 85 differences from mammalian, monotreme and bird myoglobins. The date of divergence of the shark H. portusjacksoni from these other orders was estimated at 450 +/- 16 million years, based on the number of amino acid differences between species and allowing for multiple mutations during the evolutionary period. This estimate agrees well with similar estimates made using alpha- and beta-globin sequences, in contrast to widely differing estimates of dates of divergence for monotremes using the same three globin chains. Compared with myoglobins from species previously studied, there are many more differences in amino acid sequences, and in many positions residues are found that are more characteristic of alpha- and beta-globins, suggesting a conservation of residues over a long period of evolutionary time. There are fewer stabilizing hydrogen bonds and salt-linkages than in other myoglobins.

Amino Acid Sequence↗
PubMed1977

Statistical comparison of the results from six analytical chemistry laboratories of the mercury content of muscle tissue of two species of sharks.

Statistical tests were carried out on the results of chemical analysis for total mercury concentrations of replicate samples of muscle tissue of school shark Galeorhinus australis (Macleay) and gummy shark Mustelus antarcticus Guenther from six independent analytical laboratories. These tests showed that one laboratory produced results 9% below the overall average of all results, another 1% below average while the other four were all 5% above average. Moreover, one laboratory had significantly lower scatter of results than the others, and the percentage scatter (standard error expressed as a percentage of the mean) in two of the laboratories tended to diminish as the magnitude of the results increased. Correction for what were concluded to be wild points indicated that the scatter for all laboratories was below 14%.

Analysis of Variance↗
PubMed1979

Shark heart mitochondria: effects of external osmolality on respiration.

Shark mitochondrial respiration was studied in media with osmolalities between 160 and 1500 milliosmoles. The respiratory control ratio, a marker for functional integrity of the isolated mitochondria, was maximal at 1000 millismoles and decreased during hypotonic or hypertonic exposure. Shark mitochondria function best at their native tonicity, a value that produces abnormal function in mammalian mitochondria.

Adenosine Diphosphate↗
PubMed1979

Local analysis or the composition of amphibian and shark teeth using laser probe mass spectrometry.

In the intention of confirming and extending previous studies on the ultrastructure of the teeth of the lower vertebrates, we have performed analyses of the amounts of various chemical elements present in the teeth of two amphibians and a shark. For this purpose we employed a laser probe mass spectrometer, with which we were able to measure profiles of the variation of amount of the different elements with depth at the different points chosen for analysis. The results are expressed as relative abundances using phosphorus as reference. Differences in the relative amounts of many elements can be observed at different sample points on a tooth, and, for a given sample point, at different depths. These differences certainly reflect ultrastructural features, although some of these may not yet have been described. Fluorine has been found to be much abundant in the teeth of a shark than in those of amphibians.

Amphibians↗
PubMed1979

Quantitative anatomical and behavioral analyses of regeneration and collateral sprouting following spinal cord transection in the nurse shark (ginglymostoma cirratum).

The spinal cord was transected at the mid-thoracic level in 32 nurse sharks. Four animals per group were sacrificed at intervals of 10, 20, 30, 40, 60 and 90 days postoperative. Two groups of fish underwent a subsequent spinla1 cord retransection at the same site at 90 days and were sacrificed 10 and 20 days later. Three sections of spinal cord were removed from each shark for histological analysis. Behaviorally, timed trials for swimming speed and a strength test for axial musculature contraction caudal to the lesion site were performed at 5 day postoperative intervals. Histological analysis showed little regeneration (9-13 percent) of two descending tracts 90 days following the lesion and no return of rostrally controlled movements caudal to the lesion. However, synaptic readjustment did occur caudal to the lesion. This phenomenon was attributed to local segmental sprouting of adjacent, intact nerve fibers. A close correlation was shown between this synaptic readjustment and the strength of uncontrollable undulatory movements seen caudal to the lesion site following spinal cord transection. The relationship of regeneration and collateral sprouting to quantitative behavioral changes is discussed.

Animals↗