Growth and derived life-history characteristics of the Brazilian electric ray Narcine brasiliensis.

The majority of batoids are listed as Threatened (20.4%) or Data Deficient (41%) by the IUCN Red List. A key challenge to assessing Data-Deficient species is obtaining estimates of key life-history characteristics. Here, a Bayesian approach was used to estimate derived life-history characteristics from a growth model applied to the Data-Deficient Brazilian electric ray Narcine brasiliensis. The age of 170 specimens (107 females, 63 males) was estimated from vertebral centra, and total length, disc width, total weight and birth size were used in a joint estimation of sex-specific length-weight models and two-dimensional von Bertalanffy growth models. Estimates of age at length zero, age at maturity, longevity and mortality at age were derived simultaneously. The Bayesian joint modelling approach was robust to small sample sizes by adding a likelihood to constrain L0 and sharing parameters, such as Brody growth coefficient between length measurements. The median growth parameter estimates were a shared L0 = 38.8 mm, female L∞ = 515 mm, 𝑘 = 0.125 and male L∞ = 387 mm, 𝑘 = 0.194. Age at maturity was estimated to be 7.40-7.49 years for females and 4.45-4.47 years for males, whereas longevity was 22.5-22.6 years for females and 14.2 years for males depending on length measurement. Age-1 natural mortality was estimated to be 0.199-0.207 for females and 0.211-0.213 for males. The derived life-history characteristics indicate N. brasiliensis is earlier maturing, but slower growing relative to other Torpediniformes. These characteristics along with the species' endemism to southern Brazil and high by-catch rates indicate that one of the IUCN Red List threatened categories may be more appropriate for the currently Data-Deficient status. The Bayesian approach used for N. brasiliensis can prove useful for utilizing limited age-growth data in other Data-Deficient batoid species to inform necessary life characteristics for conservation and management.

Evolutionary intraembryonic origin of vertebrate hematopoietic stem cells in the elasmobranch spleen.

The electric ray (Torpedo Marmorata Risso) provides an animal model for the detection of early intraembryonic hemopoietic stem cells in sea vertebrates. The spleen of this bone-marrowless vertebrate appears to be the major site of hemopoietic stem cell differentiation during development and in adulthood. Splenic development in this species was investigated and hemopoietic stem cells were detected in this organ by immunocytochemistry utilizing CD34 and CD38 antibodies. At stage I (2-cm-long embryos with external gills), the spleen contains only mesenchymal cells. At stage II (3-4 cm-long embryos with a discoidal shape and internal gills), an initial red pulp was observed in the spleen, without immunostained cells. At stage III (10-11-cm-long embryos), the spleen contained well-developed white pulp, red pulp and ellipsoids. Image analysis at stage III showed four cell populations, i.e. CD34+/CD38-, CD34+/CD38+, CD34-/CD38+, and CD34-/CD38- cells. The present findings, obtained from an elasmobranch, indicate that the CD34 and CD38 phenotypes are conserved through vertebrate evolution.

Narcine baliensis, a new species of electric ray from southeast Asia (Chondrichthyes: Torpediniformes).

A new species of numbfish, Narcine baliensis, sp. nov., is described from the tropical eastern Indian Ocean from Indonesia. It is superficially similar to N. brevilabiata and N. atzi in aspects of its color pattern, but is distinguished from both congeners in details of its color pattern, in tooth band morphology, and in proportions of its dorsal fins, among other features. Narcine baliensis, sp. nov., is unique in having a dorsal color pattern composed of large, circular, ovoid or elongate dark brown spots or blotches on dorsal disc along with more numerous small (about eye-sized or slightly greater) brownish, subcircular spots, with large blotches and small spots surrounded by a very slender creamy-white pattern, as well as in having broadly circular upper and lower tooth bands of about the same width and shape. The genus Narcine is now composed of 20 valid species, but uncertainty remains concerning the identification and morphological variation of some of its species in the tropical Indo-West Pacific region.

Real time ligand-induced motion mappings of AChBP and nAChR using X-ray single molecule tracking.

We observed the dynamic three-dimensional (3D) single molecule behaviour of acetylcholine-binding protein (AChBP) and nicotinic acetylcholine receptor (nAChR) using a single molecule tracking technique, diffracted X-ray tracking (DXT) with atomic scale and 100 µs time resolution. We found that the combined tilting and twisting motions of the proteins were enhanced upon acetylcholine (ACh) binding. We present the internal motion maps of AChBP and nAChR in the presence of either ACh or α-bungarotoxin (αBtx), with views from two rotational axes. Our findings indicate that specific motion patterns represented as biaxial angular motion maps are associated with channel function in real time and on an atomic scale.

Expression of CTL1 in myelinating structures of Torpedo marmorata.

We initially isolated CTL1 from the electric lobe of brain through functional complementation of a yeast mutant deficient in choline transport. Here, we present the first characterization of an antibody to the C-terminal of CTL1. When full length torpedo CTL1 was expressed in oocytes, a broad 60 kDa band appeared concomitant with the detection of immunoreactivity at the plasma membrane. In, the native protein was prominent throughout the CNS and along the electric nerves. CTL1 immunolabeling was particularly conspicuous in the myelin sheath surrounding the electric nerve and in central myelinated structures. The association of the presumptive choline transporter, CTL1, with myelin membranes suggests a role for this new protein in lipid production.

Ultrastructural studies on developing follicles of the spotted ray Torpedo marmorata.

Light and ultrastructural investigations on sub-adult and adult sexually mature females, demonstrates that in Torpedo marmorata folliculogenesis starts in the early embryo and that the two ovaries in the adult contain developing follicles of various sizes and morphology. Initially, the follicle is constituted by a small oocyte, surrounded by a single layer of squamous follicle cells. The organization is completed by a basal lamina and, more externally, by a theca, that at this stage is composed by a network of collagen fibers. As the oocyte growth goes on, during previtellogenesis and vitellogenesis, the organization of the basal lamina and of the oocyte nucleus does not change significantly. The basal lamina, in fact, remains acellular and constituted by fibrils intermingled in an amorphous matrix; the nucleus always shows an extended network of chromatin due to the lampbrush chromosomes, and one or two large nucleoli. By contrast, the granulosa (or follicular epithelium), the ooplasm, and the theca cells significantly change. The granulosa shows the most relevant modifications becoming multi-layered and polymorphic for the progressive appearance of intermediate and pyriform-like cells, located respectively next to the vitelline envelope, or spanning the whole granulosa. The appearance of intermediate cells follows that of intercellular bridges between small follicle cells and the oocyte so that one can postulate that, as in other vertebrates, small cells differentiate into intermediate, and then pyriform-like cells, once they have fused their plasma membrane with that of the oocyte. Regarding the ooplasm, one can observe as in previtellogenic follicles, it is characterized by the presence of intermediate vacuoles containing glycogen, while in vitellogenic follicles by an increasing number of yolk globules. The theca also undergoes significant changes: initially, it is constituted by a network of collagen fibers, but later, an outermost theca esterna containing cuboidal cells and an interna, with flattened cells, can be recognized. The role of the different constituents of the ovarian follicle in the oocyte growth is discussed.

The torpedo electrocyte: a model system to study membrane-cytoskeleton interactions at the postsynaptic membrane.

Many aspects of the organization of the electromotor synapse of electric fish resemble the nerve-muscle junction. In particular, the postsynaptic membrane in both systems share most of their proteins. As a remarquable source of cholinergic synapses, the Torpedo electrocyte model has served to identify the most important components involved in synaptic transmission such as the nicotinic acetylcholine receptor and the enzyme acetylcholinesterase, as well as proteins associated with the subsynaptic cytoskeleton and the extracellular matrix involved in the assembly of the postsynaptic membrane, namely the 43-kDa protein-rapsyn, the dystrophin/utrophin complex, agrin, and others. This review encompasses some representative experiments that helped to clarify essential aspects of the supramolecular organization and assembly of the postsynaptic apparatus of cholinergic synapses.

Developmental regulation of tyrosine phosphorylation of the nicotinic acetylcholine receptor in Torpedo electrocyte.

Tyrosine phosphorylation is thought to play a critical role in the clustering of acetylcholine receptors (AChR) at the developing neuromuscular junction. Yet, in vitro approaches have led to conflicting conclusions regarding the function of tyrosine phosphorylation of AChR beta subunit in AChR clustering. In this work, we followed in situ the time course of tyrosine phosphorylation of AChR in developing Torpedo electrocyte. We observed that tyrosine phosphorylation of the AChR beta and delta subunits occurs at a late stage of embryonic development after the accumulation of AChRs and rapsyn in the membrane and the onset of innervation. Interestingly, in the mature postsynaptic membrane, we observed two populations of AChR differing both in their phosphotyrosine content and distribution. Our data are consistent with the notion that tyrosine phosphorylation of the AChR is related to downstream events in the pathway regulating AChR accumulation rather than to initial clustering events.

Differences between embryonic and adult Torpedo acetylcholine receptor gamma subunit.

Antibodies to a synthetic peptide corresponding to residues 346-359 of the Torpedo acetylcholine receptor (AChR) gamma subunit, were employed to compare the adult and embryonic receptor. This peptide contains a consensus phosphorylation site for cAMP-dependent protein kinase (PKA). The anti-peptide antibodies discriminated between adult and embryonic AChRs, and reacted preferentially with the adult gamma form. These observed immunological differences did not seem to stem from different phosphorylation states. Our results suggest that the embryonic Torpedo AChR may have a gamma-like subunit that differs from the known adult form of this subunit, at least in the specific region that contains the phosphorylation site for PKA.

Developmental expression of the 43K and 58K postsynaptic membrane proteins and nicotinic acetylcholine receptors in Torpedo electrocytes.

The expression of the postsynaptic 43-kDa and 58-kDa proteins and actin during development of the Torpedo marmorata electric organ was compared to that of nicotinic acetylcholine receptors (AChRs). Western blot analysis demonstrates that AChRs and proteins of 43 kDa (43K protein) and 58 kDa (58K protein) are all present prior to synaptogenesis. Subsequently, levels of all 3 synaptic proteins increase dramatically during differentiation and innervation of electrocytes. In contrast, actin is present in relatively high concentrations at early times and decreases thereafter. The equimolar ratio of AChRs and the 43K protein found in the adult electric organ is established early in development. Furthermore, the AChR and 43K protein share a common postsynaptic localization in electrocytes following synapse formation. Aggregates of the AChR that form at the ventral pole of the oval-shaped electrocytes prior to innervation, however, show no detectable immunofluorescence staining with anti-43K monoclonal antibodies. Therefore, in some cases, aggregation of AChRs occurs without the 43K protein.

Torpedo electromotor system development: a quantitative analysis of synaptogenesis.

Synaptogenesis in the electric organ of Torpedo marmorato has been studied quantitatively at the ultrastructural level of observation. In addition to establishing the normal developmental time course for this event we were interested in determining whether a gradient of synaptogenesis might be present because the electric organ produces several morphologically recognizable spatiotemporal gradients during its early ontogeny. These gradients genesis of electrocyte columns, both gradients of which are operative for periods of weeks. No gradient of synaptogenesis was found, indicating this to be a synchronous process. The idea is advanced that synaptogenesis in the electric organ is modulated by extrinsic influences, many of which may originate from the target electrocytes which, by this time, have become synchronized in their development.

The developmental morphology of Torpedo marmorata: electric lobe-electromotoneuron proliferation and cell death.

Electromotoneuron proliferation and cell death have been quantitatively studied in the electric lobe of Torpedo marmorata from an embryonic body-length stage of 26-mm to adult animals. These neurons project to the electric organ and form synapses with electrocytes which possess a remarkably large postsynaptic target surface. For this reason cell death would not be predicted to occur if synaptic competition were to be hypothesized as the cause. Isolated observations at the ultrastructural level suggested, however, that cell death was indeed taking place and therefore it seemed appropriate to examine this question in detail. Our findings show first that neuron production appears to be a continuous process throughout the period studied, generating totals of over 70,000 electromotoneurons per lobe by adulthood. Second, two waves of cell death were identified, one occurring early in embryogenesis (stage 30 mm), well before the onset of synaptogenesis, and a second coincident with the onset of synaptogenesis (stages 55--74 mm). It is difficult to reconcile this latter wave with the hypothesis of synaptic competition as the postsynaptic surface at this time of development is largely devoid of synaptic contacts. We conclude that in the electromotor system of Torpedo, synaptic competition is probably not the mechanism of cell death.

[Biology and physiology of development, growth and reproduction of electric rays. Survey of research since 1965]. / Biologie et physiologie du développement, de la croissance et de la reproduction des torpilles. Un aperçu des recherches depuis 1965.

Since 1965, various works have pointed to electric rays (chiefly Torpedo marmorata and T. torpedo = T. ocellata) as an interesting material for the biological and physiological research on development (especially that of electric organs), growth and reproduction. In a review of the main published results, attention is called upon several points requiring new studies (buoyancy and its regulation during gestation time, neuroendocrine control of gestation, etc.). T. torpedo, a much abundant species in the Bay of Tunis, seems by far the most well-suited material for this, because of its annual reproductive cycle. New results concerning T. m. are also presented: gestation length, embryo retention, and weight changes of the yolk sacs. The microscopic structure of the female genital tract is illustrated.