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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↗
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↗
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↗
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↗
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↗
PubMed1976

Conformation of immunoglobulin M. 2. Nanosecond fluorescence depolarization analysis of segmental flexibility in anti-epsilon-l-dimethylamino-5-naphthalenesulfonyl-L-lysine anti-immunoglobulin from horse, pig, and shark.

The rotational motions of immunoglobulin M (IgM) were investigated by the nanosecond fluorescence depolarization technique. The fluorophore epsilon-1-dimethylamino-5-naphthalenesulfonyl-L-lysine (DNS-lysine) was specifically bound in the combining sites of anti-DNS IgM antibodies from the horse, pig, and nurse shark. Fluorescence lifetime analysis showed the presence of a long lifetime component (21-27 ns) with antibodies from all three species. With the mammalian antibodies, the fluorophore appeared to be rigidly bound in the combining sites as judged by the presence of induced circular dichroism of DNS-lysine (equine antibodies) and single exponential anisotropy decay of the isolated Fabmu fragments (equine and porcine antibodies). The small amount of available purified nurse shark antibody did not allow preparation of fragments or induced circular dichroism measurements to directly determine rigidity of fluorophore binding. However, at least some of the hapten must have been rigidly bound since long rotational correlation times were measured for the shark DNS-lysine-anti-DNS complexes. When the emission anisotropy of the fluorophore-anti-DNS IgM complexes was measured as a function of time, it was found that all three antibody species exhibited restricted segmental flexibility in the nanosecond time range. Moreover, when the equine anti-DNS IgM was exposed to 1 M acetic acid for 1 h, the antibody underwent a conformational change which resulted in an increase in its overall flexibility. Comparison of the rotational correlation times of native equine IgM and of proteolytic fragments indicated that flexibility of IgM consists of either hindered rotation of the Fab'mu segment or a combination of at least two modes of motion: rotation of Fabmu and/or Fab'mu and bending of the entire (Fab')2mu region as a unit. Similar modes of flexibility also occur in native porcine IgM. In acid exposed equine IgM, the major contribution to depolarization is from independent rotation or wagging of the Fab'mu segments. Thus, acid apparently causes a conformational change in or near the Cmu2 domains. In contrast, flexibility in nurse shark IgM appears to involve only bending of (Fab')2mu as a unit. Our results suggest that segmental flexibility is an essential functional feature of all IgM antibodies and that control of this flexibility through domain interactions may play an important role in such conformationally sensitive functions as complement fixation.

Acetates↗
PubMed1976

Esterification of J chain and its effect on electrophoretic mobility in sodium dodecyl sulfate polyacrylamide gels.

Sodium dodecyl sulfate polyacrylamide gel electrophoresis yields mobilities indicative of molecular weights of approximately 27 000 for human J chain and approximately 14 000 for nurse shark J chain, in contrast to values of approximately 15 500 and approximately 12 200, respectively, obtained by other methods. The relatively high content of acidic amino acids of human J chain as compared to nurse shark J chain suggested that the greater error in the sodium dodecyl sulfate determined molecular weight for human J chain may be due to a charge anomaly. The overall net negative charge on human J chain was decreased by forming methyl esters of the carboxyl groups, resulting in a sodium dodecyl sulfate determined molecular weight of approximately 17 700. Methylated nurse shark J chain did not show a significant difference in sodium dodecyl sulfate electrophoretic mobility from the non-methylated form. These results form the basis for a possible explanation of an occasional artifact in a widely used analytical method.

Animals↗
PubMed1976

Conformation of immunoglobulin M. I. Characterization of anti-epsilon-1-dimethylamino-5-naphthalenesulfonyl-L-lysine immunoglobulin M antibodies from horse, pig, and shark.

IgM antibodies specific for the fluorophore epsiolon-1-dimethylamino-5-naphthalenesulfonyl-L-lysine(DNS-lysine) were elicited in the horse and nurse shark by immunization with a DNS-lysine streptococcal conjugate; the antibodies were purified by specific adsorption with an immunoadsorbent followed by gel filtration to select the IgM class (molecular weight 900 000). About 90% of the equine anti-DNS was IgM.DNS-Lysine, when bound in the combining sites of a population of these anti-DNS IgM antigodies from horse and nurse shark, as well as from pig, exhibited a marked fluorescence enhancement and shift of the emission spectrum to shorter wavelengths compared with emission in aqueous solution; these results indicate that the environments of the anti-DNS combining sites of this population were relatively hydrophovic. Approximately one-third of the ten possible combining sites in each of these anti-DNS IgM species bound DNS-lysine in this manner with an average intrinsic association constant (Ko) of greater than 10(6) M-1. Small differences were noted in binding behavior among the three species of antibodies. The enzymatic susceptibility of equine IgM was similar to that of human IgM. (Fab')2mu, Fab'mu, and Fabmu fragments were prepared following digestion with pepsin. These fragments could be clearly differentiated on the basis of molecular size. They bound DNS-lysine with the same affinity as intact IgM and the DNS-lysine-fragment complexes exhibited the same spectral properties as the parent IgM. It was concluded that the anti-dNs IgM antibodies from all three species, as well as the enzymatic fragments, were suitable for nanosecond depolarization studies which are reported in the accompanying paper Holowka, D.A., and Cathou, R.E. (1976), Biochemistry, the following papter in this issue.

Animals↗
PubMed1978

Comparative aspects of brain barrier systems for nonelectrolytes.

Blood-brain and blood-CSF barriers to inulin were compared in 11 vertebrate species. Twenty hours after systemic administration, [14C]inulin penetrated into the central nervous system to an equivalent extent in mudpuppy, salamander (adult and larval), red sculpin, big skate, little skate, southern stingray, and Atlantic stingray with values for RB (dpm/g brain divided by dpm/ml plasma) in the range 0.01- 0.04 and for RCSF (dpm/ml CSF divided by dpm/ml plasma) from 0.02 to 0.04. These values are similar to those reported for mammals. For dogfish, nurse shark, and lemon shark, RB ranged from 0.04 to 0.09 and RCSF from 0.08 to 0.29 and for hagfish RB=0.12, indicating that barrier systems to inulin are poorly developed in sharks and possibly absent in hagfish. Analyses of radiolabeled urea and sucrose penetration into brain and CSF revealed further differences in shark barrier function. Brain barriers to insulin in dogfish and little skate developed with age; in nurse shark there was no detectable change in the inulin ratios over the weight range, 0.2-110 kg.

Aging↗
PubMed1978

A comparison of secretory component - immunoglobulin interactions amongst different species.

1) SC from many species may be isolated by affinity chromatography to human IgA-Sepharose. 2) In some species SC may exist in two molecular forms. 3) The SC-binding sites on polymeric IgA and IgM are not identical. 4) In some species SC binds to IgM with higher affinity than to polymeric IgA while in other species SC binds best to polymeric IgA. This difference may influence the relative concentrations of these two immunoglobulin classes in the secretions of different species. 5) The SC-binding site is present on high molecular weight immunoglobulin in species as primitive as the nurse shark.

Animals↗
PubMed1975

A phylogenetic study of the role of cyclic AMP in lipid synthesis in vertebrates.

The effect of cyclic AMP on the incorporation of acetate-2-14C into sterols and fatty acid in vitro in slices of liver and intestine was examined in various representatives of the vertebrate group. In no instance was an effect on lipid synthesis noted in intestine. Cyclic AMP exerted no significant effects on hepatic lipogenesis in lower vertebrates, including the nurse shark, catfish, toad, or iguana. However, the nucleotide strongly inhibited the incorporation of acetate-2-14C into fatty acid by the chicken liver. Similar inhibition of fatty acid synthesis was also noted in rat liver, but in this mammalian species hepatic sterol synthesis was also strikingly suppressed by cyclic AMP. Interruption of the enterohepatic circuit in the rat, while enhancing rates of sterol synthesis in both liver and intestine, neither enhanced nor diminished hepatic susceptibility to suppressed sterologenesis by cyclic AMP, nor did it confer on the intestine any newfound capacity for cyclic AMP-regulated lipid synthesis.

Acetates↗
PubMed1976

The chemoattraction of neutrophils by heterologous and homologous cytotoxic sera.

Neutrophils (PMN) migrated in vitro chemotactically along concentration gradients of heterologous and homologous leukocytotoxic, complement-active sera. The heterologous systems consisted of normal, non-immune nurse shark or dog serum and human PMN; the homologous systems consisted of human or dog immune sera and human or dog PMN, respectively. Chemotaxis was induced 1) by fresh cytotoxic sera, 2) by complement alone if the cytotoxic antibodies were with the responding cells or if the cells were passively sensitized with the antibodies, and 3) by individual and combined complement components if the corresponding intermediate PMN-antibody-complement component complexes were the migrating cells. These observations represent a new mechanism of immune chemotaxis: the chemotactic stimulation is a direct consequence of a gradient-controlled immune reaction occuring at and involving the surface of the chemoattracted cell. This mechanism is distinctly different from that which depends on chemotactic factors produced or released independent of and at a distance from the responding cells.

Animals↗