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PubMed1989

Regulation of spermatogenesis: the shark testis model.

Spermatogenesis is a unique developmental sequence dependent on FSH and androgen. Due to the complex organization of the mammalian testis, however, mechanistic details of regulation are largely unknown. Using the dogfish shark (Squalus acanthias) in which there is a cystic mode of spermatogenesis and a topographic separation of different germ cell stages within the testis, we have obtained new information of general relevance on stage-related biochemical and morphological changes and have proposed a model in which steroids serve as parahormonal regulators of the spermatogenic progression. In addition, techniques developed for culturing staged spermatocysts (intact Sertoli/germ cell units) and isolated, staged Sertoli cells demonstrate the usefulness of this model for studying spermatogenic regulation under defined conditions in vitro.

Animals↗
PubMed2003

Calcitonin-like immunoreactivity in serum and tissues of the bonnethead shark, Sphyrna tiburo.

Calcitonin is a 32-amino acid peptide hormone that is best known for its actions in maintaining skeletal integrity and calcium homeostasis in mammals. Calcitonin also appears to function in regulating certain aspects of animal reproduction, but the nature of this role remains unclear, particularly in nonmammalian vertebrates. The present study investigated the relationship between calcitonin and reproduction in the bonnethead shark (Sphyrna tiburo), a well-studied member of the oldest living vertebrate group (i.e. elasmobranchs) known to possess a calcitonin-producing organ. Serum calcitonin concentrations were measured in 28 reproductively mature female S. tiburo using a heterologous enzyme-linked immunosorbent assay (ELISA) system. Sites of calcitonin immunoreactivity were detected in tissues of mature female and embryonic S. tiburo using immunocytochemistry. Significant increases in serum calcitonin concentrations of mature female S. tiburo occurred during early stages of gestation, a period characterized by yolk-dependency of developing embryos. Immunoreactive calcitonin was detected in the duodenum and pancreas of embryonic S. tiburo sampled during the same period. The results from this study suggest that calcitonin obtained from endogenous and/or maternal sources may function in regulating yolk digestion in embryonic S. tiburo. Therefore, the association between calcitonin and reproduction in elasmobranchs may reflect an important role for this hormone in embryonic development.

Animals↗
PubMed1976

The structure of the hypothalamic inferior lobes of the blacktip reef shark: scanning and transmission electron microscopic observations.

The inferior lobes of the shark hypothalamus were examined with light, transmission and scanning electron microscopy. The cells bordering the floor of the lateral recess appear to be typical liquor-contacting neurons. With scanning electron microscopy (SEM) the apical ends of these cells are seen to bulge into the ventricular lumen. In contrast, the roof is lined by a more typical ependymal cell characterized by numerous cilia and microvilli. In addition, SEM reveals several kinds of supraependymal cells with processes that appear to penetrate the ventricular lining. A periventricular nucleus underlies the ependymal cells. Neurons of the periventricular nucleus contain numerous lipofuchsin granules. The rest of the inferior lobe consists of many neuronal fibers. The morphology of the hypothalamic inferior lobe is discussed in relation to its possible role in feeding and aggressive behavior in both elasmobranchs and teleosts.

Animals↗
PubMed2002

Dental homologies in lamniform sharks (Chondrichthyes: Elasmobranchii).

The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.

Animals↗
PubMedDate not supplied

Exquisite specificity and peptide epitope recognition promiscuity, properties shared by antibodies from sharks to humans.

This review considers definitions of the specificity of antibodies including the development of recent concepts of recognition polyspecificity and epitope promiscuity. Using sets of homologous and unrelated peptides derived from the sequences of immunoglobulin and T cell receptor chains we offer operational definitions of cross-reactivity by investigating correlations of either identities in amino acid sequence, or in hydrophobicity/hydrophilicity profiles with degree of binding in enzyme-linked immunosorbent assays. Polyreactivity, or polyspecificity, are terms used to denote binding of a monoclonal antibody or purified antibody preparation to large complex molecules that are structurally unrelated, such as thyroglobulin and DNA. As a first approximation, there is a linear correlation between degree of sequence identity or hydrophobicity/hydrophilicity and antigenic cross-binding. However, catastrophic interchanges of amino acids can occur where changing of one amino acid out of 16 in a synthetic peptide essentially eliminates binding to certain antibodies. An operational definition of epitope promiscuity for peptides is the case where two peptides show little or no identity in amino acid sequence but bind strongly to the same antibody as shown by either direct binding or competitive inhibition. Analysis of antibodies of humans and sharks, the two most divergent species in evolution to express antibodies and the combinatorial immune response, indicates that the capacity for both exquisite specificity and epitope recognition promiscuity are essential conserved features of individual vertebrate antibodies.

Amino Acid Sequence↗
PubMed2000

The characterization of angiogenesis inhibitor from shark cartilage.

An angiogenesis inhibitor isolated from shark cartilage, SCF2, has been characterized. SCF2 was shown to have specific angiogenesis-inhibiting activity in endothelial cell culture assays. Results of structural and functional studies indicate that the inhibitor is not a typical protein. It is a heat-stable proteoglycan, which contains keratan sulfate units and peptide. Gel filtration chromatography shows that the molecular weight of the angiogenesis inhibitor is about 10 kd.

Angiogenesis Inhibitors↗
PubMed1994

Fine structure of the choroidal tapetum lucidum in the Port Jackson shark (Heterodontus phillipi).

The choroidally located tapetum lucidum of the Port Jackson shark (Heterodontus phillipi) was examined by light and electron microscopy in light-adapted specimens. In this species the tapetum consists of a single layer of overlapping cells oriented at an angle of about 30 degrees to the incoming light and situated immediately external to the choriocapillaris. These tapetal cells alternate with and are separated from one another by melanocytes which extend beyond the tapetal cells to intervene between the tapetal cells and the incoming light. The tapetal cells and the melanocytes are flattened plate-like cells with their widest dimension facing the retina. Internally the tapetal cells display a peripherally located vesicular nucleus with most organelles in a paranuclear location. The bulk of a tapetal cell is packed with regularly spaced crystals reported to be guanine. The size and spacing of these reflective crystals is commensurate with the principles of constructive interference. In light adaptation, the melanosomes of the intervening melanocytes are widely dispersed and for the most part block the passage of light to the tapetal cells. Although dark-adapted specimens were not available, it seems reasonable to assume that in dark adaptation these melanosomes will retreat to unmask the tapetum and allow it to function as a known reflective layer.

Animals↗
PubMed1987

Subcellular organization of the yolk syncytial-endoderm complex in the preimplantation yolk sac of the shark, Rhizoprionodon terraenovae.

The structure of the yolk syncytial-endoderm complex of the preimplantation yolk sac of the shark is examined by light- and transmission electron microscopy. The yolk syncytium is bounded by a membrane that is anchored to the plasmalemma of adjacent endoderm cells by desmosomes. Enlarged nuclei, rough endoplasmic reticulum, Golgi complexes, mitochondria, and other cellular organelles populate the syncytium. Microtubules and filamentous elements are also observed free in the syncytium. Yolk is present as pleomorphic droplets, the profiles of which are generally spherical but may be vesicular, especially at the periphery of large yolk droplets. Occasionally, large yolk droplets have a paracrystalline configuration. Small yolk droplets are modulated through the Golgi complex of the yolk syncytium, and it is suggested that acid hydrolases are added there. Small yolk droplets released from the maturing face of the Golgi complex are sequestered in membrane-limited packets. The membrane of the packets fuses with the membrane enveloping the yolk syncytium and the yolk droplets are released into the yolk syncytial-endoderm interspace. Subsequently, the yolk droplets are endocytosed by the endoderm. Yolk droplets disperse and fuse to form the large irregular yolk inclusions of the endoderm. Yolk metabolites are transported out of the endoderm through the yolk sac endothelium. The yolk sac endoderm thus mediates the transfer of metabolites from the yolk mass to the extraembryonic circulation.

Animals↗
PubMed1977

Ultrastructure of the different fibre types in axial muscles of the sharks Etmopterus spinax and Galeus melastomus.

Red, intermediate and white axial muscle fibres of the sharks Etmopterus spinax and Galeus melastomus were studied by electron microscopy and morphometry. The mitochondrial content is more than thirty percent in red, less than one percent in white, and up to fifteen percent in intermediate fibres. About one third of the mitochondria in red fibres are accumulated close to the sarcolemma. Red fibres contain much glycogen, present as rosettes (alpha particles). Intermediate fibres contain less glycogen (as beta particles). White fibres have scarcely any visible energy reserves. Red fibres contain slightly less (4-5%) of the sarcotubular system than the other fibre types (6-8%). In all fibre types, the terminal cisternae of the SR are regularly divided by clefts. Triads or dyads are generally positioned at the Z discs, but in Galeus white fibres two dyads may be present, one on each side of the Z disc. The morphology is discussed in relation to current views on the functions of different muscle fibre types.

Animals↗
PubMed1981

Ascending spinal systems in the nurse shark, Ginglymostoma cirratum.

The ascending spinal systems in the nurse shark were studied after spinal hemisections by use of the Nauta and Fink-Heimer techniques. The dorsal funicular fibers form a single bundle issuing fibers to the gray substance of the spinal cord, the dorsal funicular nucleus, and the vestibular complex. Some dorsal funicular fibers also appear to contribute to the spinocerebellar tract. The degenerated lateral funicular fibers are segregated into three fasciculi issuing fibers medially as they ascend through the brainstem. The largest target of these fibers is the reticular formation, but diffusely organized axons also reach 1) the gray matter of the spinal cord, 2) the dorsal motor nucleus of the vagus, 3) the nucleus "A" of the medulla oblongata, 4) the central gray substance of the brainstem, 5) the cerebellar cortex, 6) the cerebellar nucleus, 7) the nucleus intercollicularis, 8) the mesencephalic tectum, and 9) the dorsal thalamus. At the latter site the spinal input appears to partly overlap with the visual input. The results, compared with the strikingly similar findings in other classes of vertebrates, indicate that all vertebrate groups apparently have the same basic components of ascending spinal projections.

Animals↗
PubMed1994

Fine structure of the retinal pigment epithelium in the Port Jackson shark (Heterodontus phillipi).

The structure of the retinal epithelium (RPE), choriocapillaris and Bruch's membrane (complexus basalis) has been studied by light and electron microscopy in the Port Jackson shark (Heterodontus phillipi). In this elasmobranch the RPE consists of a single layer of low cuboidal cells which show basal (scleral) infolding and apical (vitreal) processes that enclose photoreceptor outer segments. Laterally these epithelial cells are joined by a series of apically located tight junctions. The RPE cells display a large vesicular nucleus, abundant smooth endoplasmic reticulum as well as numerous polysomes and mitochondria. Phagosomes are present, rough endoplasmic reticulum is scarce and myeloid bodies were not observed. Melanosomes are absent over the choroidally located tapetum lucidum, but are not abundant even in extratapetal areas. This paucity of melanosomes probably makes retinomotor movements unimportant. Bruch's membrane or complexus basalis is a pentalaminate structure. The endothelium of the choriocapillaris is thin but minimally fenestrated.

Animals↗
PubMed1977

Morphometric and autoradiographic studies on the growth of red and white axial muscle fibres in the shark Etmopterus spinax.

The axial muscle growth of the shark Etmopterus spinax has been studied by means of morphometry, slide histology and autoradiography from radioactive thymidine and amino acids. Comparisons have been made between the red and white muscles fibres. While growing from 10 to 23 cm in length, the white muscle transverse sectional (ts) area increases 5.4 times, while the red area increases 3.7 times. The mean ts area of individual white fibres increases by 2.7, and the ts area of red fibres increases by 1.6. The number of white fibres does not increase significantly, while the red fibres increase slightly in number. Red fibres incorporate amino acids faster than the white fibres, and have a higher turnover rate. The myonuclei of the red fibres (satellite cell nuclei) incorporate thymidine more often than do those of white fibres, but the frequency of the satellite cells is similar in the two fibre types. Mitoses are extremely rare in the myonuclei. The nucleocytoplasmic ratio is higher in the red than in the white fibres.

Amino Acids↗
PubMed1975

The structure of the myosatellite cells in axial muscles of the shark Geleus melastomus.

The myosatellite cells in the axial muscles of the shark Geleus melastomus is found more frequently in the red muscle fibers than in the white fibers. The total length of the cell extensions is about 100 mum. In about 20% of all cases, the extensions were present in pairs, and it is concluded that the satellite cell processes bifurcate. Processes towards the intercellular space and towards the interior of the muscle fiber are also described. The cytoplasm of the satellite cells contain glycogen, Golgi elements, lysosome-like vesicles, granular endoplasmic reticulum and microtubules. It is concluded that the morphology of the satellite cells indicates a more active function than that of a dormant reserve myoblast.

Animals↗
PubMed1986

Membrane potentials and intracellular chloride activity in the ciliary body of the shark.

We have found that membrane potential in the isolated ciliary epithelium of the shark, Squalus acanthias, is -53 mV. High extracellular potassium or ouabain (10(-5) mol X l-1) decrease the potential, and furosemide (10(-4) mol X l-1) hyperpolarizes it. There is no difference in membrane potential between the cells of the non-pigmented and pigmented layers. Intracellular chloride activity (64 mmol X l-1) was significantly higher than could be predicted from the equilibrium distribution (26 mmol X l-1) across the cell membranes. When furosemide was applied to the aqueous side of the epithelium, intracellular chloride activity decreased to 35 mmol X l-1 and approached electrochemical equilibrium. The data indicate that the ciliary epithelium possesses an active, furosemide-sensitive chloride transport mechanism which could be a Na-Cl or a 1 Na-1 K-2 Cl symport.

Animals↗
PubMed1985

Cell solute composition and potassium effects in slices of the rectal gland of the dogfish shark (Squalus acanthias).

Cell solute composition and apparent intracellular ionic concentrations (subscript i) were determined in rectal gland slices of the dogfish shark (Squalus acanthias). On aerobic incubation in elasmobranch Ringer's at 15 degrees C, the steady state values were: Ki+, 151 mM, close to its apparent electrochemical equilibrium; Cai2+, 1.7 mM; Mgi2+, 7.5 mM; Cl1-, 97 mM (maintained against its electrochemical potential gradient); the sum (Nai+ + Ki+) was about 66 meq/kg cell water lower than in the medium. Of free amino acids, only the effectively impermeable anionic taurine (32 mM) and glutamate (3.7 mM) significantly contribute to the Donnan system. Variations of the Ringer's K+ concentrations, or the presence of 0.5 mM ouabain, demonstrated the permeability of the cell membrane to na+, K+, and Cl-. Cell volume changes: 0.5 mM ouabain produced a gradual swelling and ionic changes consistent with an inhibition of the sodium pump. In high-K+ media the cells swelled massively and the membrane depolarized. A linear relationship between cell volume changes and the Nernst potential for K+ was found. These properties are consistent with a pump-and-leak system for cell volume maintenance. The K+ -induced cell swelling was found to be reversible on transfer of the tissue to regular Ringer's. The extrusion of cell water was associated with an influx of Na+ into, and an efflux of K+ from, the cells (both fluxes down-hill), as well as extrusion of Cl- against its concentration gradient.2+

Amino Acids↗
PubMed1996

Preparation of a series of sulfated tetrasaccharides from shark cartilage chondroitin sulfate D using testicular hyaluronidase and structure determination by 500 MHz 1H NMR spectroscopy.

Six tetrasaccharide fractions were isolated from shark cartilage chondroitin sulfate D by gel filtration chromatography followed by HPLC on an amine-bound silica column after exhaustive digestion with testicular hyaluronidase. Their structures were determined unambiguously by one- and two-dimensional 500 MHz 1H NMR spectroscopy in conjunction with HPLC analysis of chondroitinase AC-II digests of the tetrasaccharides. One fraction was found to contain two tetrasaccharide components. All of the seven tetrasaccharides shared the common core structure GlcA beta 1-3GalNAc beta 1-4GLcA beta 1-3GalNAc with various sulfation profiles. Four were disulfated comprising of two monosulfated disaccharide units GLcA beta 1-3GalNAc(4-sulfate) and/or GlcA beta 1-3GalNAc(6-sulfate), whereas the other three were hitherto unreported trisulfated tetrasaccharides containing a disulfated disaccharide unit GlcA(2-sulfate)beta 1-3GalNAc(6-sulfate) and a monosulfated disaccharide unit GlcA beta 1-3GalNac(4- or 6-sulfate). These sulfated tetrasaccharides were demonstrated to serve as appropriate acceptor substrates for serum alpha-N-acetylgalactosaminyltransferase, indicating their usefulness as authentic oligosaccharide substrates or probes for the glycobiology of sulfated glycosaminoglycans.

Animals↗
PubMed1986

Cyclic AMP-dependent stimulation of Na,K-ATPase in shark rectal gland.

Scatchard analysis of 3H ouabain bound to isolated rectal gland cells as a function of increasing ouabain concentrations produced a concave curvilinear plot that was resolved into two specific sites with either a high (I) or low (II) affinity for ouabain. Cyclic cAMP/theophylline (+/- furosemide, 10(-4) M) increased the amount of 3H ouabain bound to the high-affinity site I. Vanadate, a phosphate congener which promotes formation of the ouabain-binding state of the enzyme, mimicked the effects of cAMP/theophylline at low concentrations of ouabain, suggesting that cAMP/theophylline increases binding to site I by enhancing the rate of turnover of resident enzyme. Enhanced 86Rb uptake seen following cAMP/theophylline administration was primarily associated with increased flux through the high-affinity ouabain site, and this stimulation was not obliterated by the co-administration of furosemide. A model was presented which suggested the presence of two noninteracting pools of enzyme or isozymes which exhibit either a high or low affinity for ouabain. Cyclic AMP both stimulated turnover via site I, and modified the kinetics of binding of 3H ouabain to site II. The (ave) Kd of 3H ouabain for site II was increased from 3.6 microM (controls) to 0.5 microM (cAMP/theophylline) and the Hill coefficient was modified from 0.45 (controls) to 1.12 (cAMP/theophylline), suggesting a transition from a negative- to a noncooperative binding state. While furosemide reversed the effects of cAMP/theophylline on site II kinetics, it did not obliterate cAMP/theophylline effects on site I. This suggests that cAMP may alter the intrinsic turnover rate of this particular pool of Na,K-ATPase in shark rectal gland.

Animals↗
PubMed1987

Evolutionary relationships of a "primitive" shark (Heterodontus) assessed by micro-complement fixation of serum transferrin.

The evolutionary relationships of six sharks were investigated by comparing their transferrins using the micro-complement fixation method. The immunological distances observed were used to build a tree that confirms that the squaloid and galeoid species examined belong to two separate groups and that Heterodontus, a genus of hitherto uncertain position, belongs with the galeoids. The divergence time estimated from the transferrin comparisons is roughly 240 +/- 65 million years between Heterodontus and galeoids.

Animals↗