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PubMed1998

Structural analysis of the nurse shark (new) antigen receptor (NAR): molecular convergence of NAR and unusual mammalian immunoglobulins.

We recently have identified an antigen receptor in sharks called NAR (new or nurse shark antigen receptor) that is secreted by splenocytes but does not associate with Ig light (L) chains. The NAR variable (V) region undergoes high levels of somatic mutation and is equally divergent from both Ig and T cell receptors (TCR). Here we show by electron microscopy that NAR V regions, unlike those of conventional Ig and TCR, do not form dimers but rather are independent, flexible domains. This unusual feature is analogous to bona fide camelid IgG in which modifications of Ig heavy chain V (VH) sequences prevent dimer formation with L chains. NAR also displays a uniquely flexible constant (C) region. Sequence analysis and modeling show that there are only two types of expressed NAR genes, each having different combinations of noncanonical cysteine (Cys) residues in the V domains that likely form disulfide bonds to stabilize the single antigen-recognition unit. In one NAR class, rearrangement events result in mature genes encoding an even number of Cys (two or four) in complementarity-determining region 3 (CDR3), which is analogous to Cys codon expression in an unusual human diversity (D) segment family. The NAR CDR3 Cys generally are encoded by preferred reading frames of rearranging D segments, providing a clear design for use of preferred reading frame in antigen receptor D regions. These unusual characteristics shared by NAR and unconventional mammalian Ig are most likely the result of convergent evolution at the molecular level.

Amino Acid Sequence↗

PubMed2003

ATP-induced reverse temperature effect in isohemoglobins from the endothermic porbeagle shark (Lamna nasus).

The evolutionary convergence of endothermic tunas and lamnid sharks is unique. Their heat exchanger-mediated endothermy represents an interesting example of the evolutionary pressure associated with this specific characteristic. To assess the implications of endothermy for gas transport and the possible contribution of hemoglobin (Hb), we investigated the effect of temperature on the oxygen equilibria of purified isohemoglobin components V and III from the porbeagle shark (Lamna nasus). In the absence of ATP the effect of temperature on oxygen affinity is normal in both Hb III (P50 = 0.9 and 2.2 torr at 10 and 26 degrees C, respectively) and Hb V (P50 = 1.5 and 2.5 torr at 10 and 26 degrees C, respectively). In the presence of this effector P50 decreases with increasing temperature in both components (P50 at 10 and 26 degrees C = 9.9 and 8.4 torr (Hb III), respectively, and 9.6 and 7.4 torr (Hb V), respectively. The reverse temperature effect in the presence of ATP will reduce the risk of oxygen loss from the arterial to the venous blood by lowering the oxygen tension gradient between the blood vessels. The mechanism behind the reverse temperature effect resembles that found in the bluefin tuna (Thunnus thynnus), an endothermic teleost, thus evidencing further convergent evolution.

Adenosine Triphosphate↗

PubMed2003

The effect of supplementing layer diets with shark cartilage or chitosan on egg components and yolk lipids.

1. An experiment was designed to evaluate the effects of the addition of shark cartilage (SC) or chitosan (CH) to layer diets on egg component weights, yolk lipids and hen plasma lipids. 2. Hy-Line laying hens (80) were used during a 56 d feeding trial. Treatments were: basal diet (BD), BD + 20 g/kg SC, BD + 30 g/kg SC, BD + 20 g/kg CH and BD + 30 g/kg CH. Eggs were analysed on d 14, 28, 42 and 56. 3. Egg weight and egg component weights were not affected by these treatments throughout the experimental period. 4. After 14d of experimental feeding, cholesterol levels were higher in eggs from birds given BD + 20 g/kg CH and BD + 30 g/kg CH than in those from birds given BD. 5. Furthermore, eggs from hens given BD + 20 g/kg SC or BD + 20 g/kg CH were higher in palmitic and stearic acids and lower in oleic acid than those from birds fed on BD. After 56 d feeding, however, palmitic and stearic acid contents in eggs from hens given any of the supplemented diets were lower than in those from hens given BD, and oleic acid in eggs from hens given BD + 20 g/kg SC, BD + 30 g/kg SC and BD + 30 g/kg CH was higher than in those from birds fed on BD. 6. Plasma cholesterol and triacylglycerol levels were not significantly affected by dietary treatment. 7. Shark cartilage or chitosan at up to 30 g/kg in layer diets did not affect egg component weights (yolk, white and shell) and total lipid contents. During the period from 42 to 56d of experimental feeding, diets containing up to 30 g/kg chitosan reduced egg yolk contents of cholesterol, palmitic and stearic acids and increased the content of oleic acid.

Animal Feed↗

PubMed2006

Occurrence of polybrominated diphenyl ethers and polychlorinated biphenyls in shark liver oil supplements.

Results are reported of a pilot survey of concentrations of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in shark liver oil supplements. Eleven brands of dietary supplements were analysed using an isotope dilution GC/MS method. Total concentrations of 10 PBDE congeners (BDE-28, -47, -49, -66, -99, -100, -153, -154, -155 and -183) ranged from 0.1 to 53 ng g-1 oil weight and total concentrations of six PCB congeners (CB-28/31, -52, -118, -153 and -180) in the samples ranged from 16 to 340 ng g-1 oil weight (undetected values are not included). Two brands of Japanese deep-sea shark liver oil contained the highest levels of PBDEs (49-53 ng g-1 oil weight) and PCBs (290-340 ng g-1 oil weight). These results indicate that PBDEs may have entered Japanese deep-sea waters.

Animals↗

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↗

PubMed1969

A specific inactivator of mammalian C'4 isolated from nurse shark (Ginglymostoma cirratum) serum.

A material which specifically inactivates mammalian C'4 was isolated from low ionic strength precipitates of nurse shark serum. The C'4 inactivator was not detected in whole serum. The conditions of its generation and its immunoelectrophoretic behavior seem to indicate that it is an enzymatically formed cleavage product of a precursor contained in whole shark serum. The inactivator was partially purified and characterized. It had an S-value of 3.3 (sucrose gradient) which was in agreement with its retardation on gel filtration, was stable between pH 5.0 and 10.0, had a half-life of 5 min at 56 degrees C, pH 7.5, was inactivated by trypsin and was nontoxic. Its powerful anticomplementary activity in vitro and in vivo was solely due to the rapid inactivation of C'4; no other complement components were affected. No cofactor requirement was observed for the equally rapid inactivation of highly purified human and guinea pig C'4. The kinetics of C'4 inactivation and TAME hydrolysis, the greater anodic mobility of inactivated human C'4, and the influence of temperature on the rate of inactivation suggest that the inactivator is an enzyme and C'4 its substrate. This conclusion was supported by the more recent detection of a split product of C'4. Intravenous administration of the C'4 inactivator could prevent lethal Forssman shock and suppress the Arthus reaction in guinea pigs; it prolonged significantly the rejection time of renal xenografts but had no detectable effect on passive cutaneous anaphylaxis. Anaphylatoxin could be generated in C'4 depleted guinea pig serum with the cobra venom factor, but not with immune precipitates. The possible relationship between C'1 esterase and the C'4 inactivator is discussed on the basis of similarities and dissimilarities.

Animals↗

PubMedDate not supplied

The unusual adrenergic-like excitatory action of acetylcholine on the ventricular cardiac muscle of the horned shark, Heterodontus portusjacksoni.

The atypical excitatory effect of acetylcholine on cardiac ventricular muscle was investigated in the horned shark, Heterodontus portusjacksoni. Electrically paced ventricular strips produced a massive 391.45% (+/-26.39%) increase in basal force of contraction in response to exogenously applied acetylcholine. The response was similar in nature to that produced by applied adrenaline, which caused a 382.52% (+/-72.47%) increase. The response to acetylcholine was blocked by the muscarinic cholinoceptor antagonist atropine and the competitive beta-adrenoceptor antagonist propranolol and was reduced by bretylium, an agent known to inhibit the release of catecholamines from adrenergic nerves. These findings strongly suggest that acetylcholine mediates a localised release of a catecholamine via muscarinic cholinoceptors in shark heart. A cholinergically controlled catecholamine store has been proposed (cholinergic-adreno complex), implying that elasmobranchs may be capable of finer control of cardiac output than has previously been suspected. This complex may represent a transitional adrenergic state between humoral and neuronal regulation. The spontaneously beating atrium showed no evidence of such an excitatory response to applied acetylcholine but produced an atropine-sensitive slowing, a response typical of other vertebrates.

Acetylcholine↗

PubMed1990

Cloning of the shark Po promoter using a genomic walking technique based on the polymerase chain reaction.

We have cloned the putative shark promoter of protein zero (Po) using a novel application of the ligation mediated single-sided polymerase chain reaction (PCR) method. This method uses linker ligation and subsequent amplifications with a linker primer and multiple specific primers to generate specificity. The method allowed us to amplify approximately 305 base pairs of shark genomic DNA sequence immediately upstream from the 5' end of our full-length Po cDNA. The Po promoter was shown to be directly linked to its first exon, contain a transcription initiation start site and sequences commonly found in eukaryotic promoters. This genomic walking technique will be useful for cloning promoters, insertion sites, and other sequences of interest without the need for constructing and screening genomic libraries.

Animals↗

PubMed1998

The complete mitochondrial DNA sequence of the shark Mustelus manazo: evaluating rooting contradictions to living bony vertebrates.

A remarkable example of a misleading mitochondrial protein tree is presented, involving ray-finned fishes, coelacanths, lungfishes, and tetrapods, with sea lampreys as an outgroup. In previous molecular phylogenetic studies on the origin of tetrapods, ray-finned fishes have been assumed as an outgroup to the tetrapod/lungfish/coelacanth clade, an assumption supported by morphological evidence. Standard methods of molecular phylogenetics applied to the protein-encoding genes of mitochondria, however, give a bizarre tree in which lamprey groups with lungfish and, therefore, ray-finned fishes are not the outgroup to a tetrapod/lungfish/coelacanth clade. All of the dozens of published phylogenetic methods, including every possible modification to maximum likelihood known to us (such as inclusion of site heterogeneity and exclusion of potentially misleading hydrophobic amino acids), fail to place the ray-finned fishes in a biologically acceptable position. A likely cause of this failure may be the use of an inappropriate outgroup. Accordingly, we have determined the complete mitochondrial DNA sequence from the shark, Mustelus manazo, which we have used as an alternative and more proximal outgroup than the lamprey. Using sharks as the outgroup, lungfish appear to be the closest living relative of tetrapods, although the possibility of a lungfish/coelacanth clade being the sister group of tetrapods cannot be excluded.

Animals↗

PubMed1999

Increased nitric oxide synthase in the vasculature of the epaulette shark brain following hypoxia.

Epaulette sharks inhabiting reef platforms are exposed to hypoxic and hyperoxic cycles. The adaptive mechanisms used to prevent neurological damage during these cycles have not been examined. Nitric oxide has a neuroprotective role in some hypoxia-tolerant species. We examined epaulette brains following a severe experimental hypoxic regimen (0.39 mgO2/l for 2 h) and compared nitric oxide synthase (NOS) expression with that in normoxic controls using NADPH-diaphorase staining. Intense NOS activity occurred in microvasculature following exposure to a severely hypoxic environment in contrast to the low levels seen in controls. We established for the first time that the epaulette shark was hypoxia-tolerant because there was no delayed phase of neuronal apoptosis. Enhanced NOS production in response to hypoxia may cause vasodilation, which would maintain the appropriate metabolic environment for continued neuronal survival during exposure to hypoxia.

Animals↗

PubMed1991

Shark attack.

Shark attacks are rare but devastating. This case had major injuries that included an open femoral fracture, massive hemorrhage, sciatic nerve laceration, and significant skin and muscle damage. The patient required 15 operative procedures, extensive physical therapy, and orthotic assistance. A review of the literature pertaining to shark bites is included.

Animals↗

PubMed2002

Electrical characterization of gel collected from shark electrosensors.

To investigate the physical mechanism of the electric sense, we present an initial electrical characterization of the glycoprotein gel that fills the electrosensitive organs of marine elasmobranchs (sharks, skates, and rays). We have collected samples of this gel, postmortem, from three shark species, and removed the majority of dissolved salts in one sample via dialysis. Here we present the results of dc conductivity measurements, low-frequency impedance spectroscopy, and electrophoresis. Electrophoresis shows a range of large protein-based molecules fitting the expectations of glycoproteins, but the gels of different species exhibit little similarity. The electrophoresis signature is unaffected by thermal cycling and measurement currents. The dc data were collected at various temperatures, and at various electric and magnetic fields, showing consistency with the properties of seawater. The impedance data collected from a dialyzed sample, however, show large values of static permittivity and a loss peak corresponding to an unusually long relaxation time, about 1 ms. The exact role of the gel is still unknown, but our results suggest its bulk properties are well matched to the sensing mechanism, as the minimum response time of an entire electric organ is on the order of 5 ms.

Animals↗

PubMed2006

Spinal deformity in a sandtiger shark, Carcharias taurus Rafinesque: a clinical-pathological study.

The present study investigated spinal deformity in a captive sandtiger shark and describes the clinical and histopathological features of the lesion. Clinically, the shark presented a marked spinal curvature in the region between the pectoral girdle and cranial dorsal fin. Radiographic studies revealed scoliosis and kyphosis of the vertebral column with a modification of the basic structure of five vertebrae. Post-mortem examination confirmed the results of radiographic studies and histological examination showed remodelling and cartilaginous proliferation of the vertebral bodies together with necrosis, haemorrhage and signs of a local chronic inflammatory response extending to the surrounding muscle. Different aetiologies are proposed and discussed but nutritional imbalance (dietary vitamin deficiency) and/or traumatic injury are considered the most likely contributing factors.

Animals↗

PubMed2007

Genetic polyandry and sexual conflict in the sandbar shark, Carcharhinus plumbeus, in the western North Atlantic and Gulf of Mexico.

To investigate patterns of polyandry in the sandbar shark (Carcharhinus plumbeus), 20 pregnant females were sampled from the western North Atlantic and Gulf of Mexico. Five species-specific microsatellite markers were used to genotype each shark and its litter. Of 20 litters, 17 (85%) were shown to have multiple sires. In multiply sired litters, the estimated minimum number of sires ranged from two to five with an average of 2.3 males per litter. Regression analysis did not demonstrate a significant relationship between female reproductive success and female body size or sire number and female body size. There was a high incidence of reproductive skew noted in litters, and two groups of males with significantly different mean reproductive success were observed. Analyses using Bateman's principles suggest that there is less direct benefit for females that acquire multiple mates than for males who bias paternity within litters. In light of past morphological and behavioural studies, these data suggest that patterns of polyandry in elasmobranchs may be determined by coercive mating, and that breeding behaviour has likely evolved in the context of sexual conflict.

Animals↗

PubMed1998

Haemorrhagic septicaemia by Aeromonas salmonicida subsp. salmonicida in a black-tip reef shark (Carcharhinus melanopterus).

One black-tip reef shark (Carcharhinus melanopterus) was found dead without previous signs of disease. Major lesions consisted in cutaneous erythema, mainly at the base of the fins, focal to diffuse inflammatory lesions in gills and intestinal wall, and discrete haemorrhages in the same organs, liver and kidneys. Microcolonies of Gram-negative rods were observed in the lamina propia of gills, underneath the intestinal mucosa and randomly distributed in the renal and hepatic parenchymas. Also, emboli containing Gram-negative rods were observed in capillaries of these organs. Aeromonas salmonicida subsp. salmonicida was isolated in pure culture from gills, liver and intestine. Specific immunostaining confirmed the relationship between the isolate and lesion-associated bacteria. No previous reports on this infection in sharks have been found in the literature.

Aeromonas↗

PubMed1980

Immunoglobulin diversity in the phylogenetically primitive shark, Heterodontus francisci. Suggested lack of structural variation between light chains isolated from different animals.

A two-step procedure employing gel filtration and anion exchange chromatography has been utilized to isolate LMW immunoglobulin from the horned shark, Heterodontus francisci. Light chains obtained by complete reduction and alkylation of the parent protein have been compared by several analytical techniques. Amino acid composition data implies a limited degree of variation in the light chains isolated from individual animals. Polyacrylamide gel electrophoresis of the CNBr digests of the light chains reveal indistinguishable banding profiles of the major peptides. Isoelectric focusing indicates limited heterogeneity in the light chain spectrotype and identity in the pI of the majority of bands detectable by staining. The suggested degree of structural similarity in the light chains of this phylogenetically primitive shark is discussed in terms of the evolutionary position of the species and current theories concerning the origins of structural diversity in immunoglobulins.

Amino Acids↗

PubMed1992

Modulation of contraction by intracellular Na+ via Na(+)-Ca2+ exchange in single shark (Squalus acanthias) ventricular myocytes.

1. The effect of direct alteration of intracellular Na+ concentration on contractile properties of whole-cell clamped shark ventricular myocytes was studied using an array of 256 photodiodes to monitor the length of the isolated myocytes. 2. In myocytes dialysed with Na(+)-free solution, the voltage dependence of Ca2+ current (ICa) and contraction were similar and bell shaped. Contractions activated at all voltages were completely suppressed by nifedipine (5 microM), and failed to show significant tonic components, suggesting dependence of the contraction on Ca2+ influx through the L-type Ca2+ channel. 3. In myocytes dialysed with 60 mM Na+, a ICa-dependent and a ICa-independent component of contraction could be identified. The Ca2+ current-dependent component was prominent in voltages between -30 to +10 mV. The ICa-independent contractions were maintained for the duration of depolarization, increased with increasing depolarization between +10 to +100 mV, and were insensitive to nifedipine. 4. In such myocytes, repolarization produced slowly decaying inward tail currents closely related to the time course of relaxation and the degree of shortening prior to repolarization. 5. With 60 mM Na+ in the pipette solution, positive clamp potentials activated decaying outward currents which correlated to the size of contraction. These outward currents appeared to be generated by the Na(+)-Ca(2+)-exchanger since they depended on the presence of intracellular Na+, and were neither suppressed by nifedipine nor by K+ channel blockers. 6. The results suggest that in shark (Squalus acanthias) ventricular myocytes, which lack functionally relevant Ca2+ release pools, both Ca2+ channel and the Na(+)-Ca2+ exchanger deliver sufficient Ca2+ to activate contraction, though the effectiveness of the latter mechanism was highly dependent on the [Na+]i.

Animals↗

PubMed2005

Transoceanic migration, spatial dynamics, and population linkages of white sharks.

The large-scale spatial dynamics and population structure of marine top predators are poorly known. We present electronic tag and photographic identification data showing a complex suite of behavioral patterns in white sharks. These include coastal return migrations and the fastest known transoceanic return migration among swimming fauna, which provide direct evidence of a link between widely separated populations in South Africa and Australia. Transoceanic return migration involved a return to the original capture location, dives to depths of 980 meters, and the tolerance of water temperatures as low as 3.4 degrees C. These findings contradict previous ideas that female white sharks do not make transoceanic migrations, and they suggest natal homing behavior.

Animal Identification Systems↗