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PubMed2006

Cerebellar efferent neurons in teleost fish.

In tetrapods, cerebellar efferent systems are mainly mediated via the cerebellar nuclei. In teleosts, the cerebellum lacks cerebellar nuclei. Instead, the cerebellar efferent neurons, termed eurydendroid cells, are arrayed within and below the ganglionic layer. Tracer injections outside of the cerebellum, which retrogradely label eurydendroid cells demonstrate that most eurydendroid cells possess two or more primary dendrites which extend broadly into the molecular layer. Some eurydendroid cells mostly situated in caudal portions of the cerebellum have only one primary dendrite. The eurydendroid cells receive inputs from the Purkinje cells and parallel fibers, but apparently do not receive inputs from the climbing fibers. Eurydendroid cells of the corpus cerebelli and medial valvula project to many brain regions, from the diencephalon to the caudal medulla. A few eurydendroid cells in the valvula project directly to the telencephalon. About half of the eurydendroid cells are aspartate immunopositive. Anti-GABA and anti-zebrin II antibodies that are known as markers for the Purkinje cells in mammals also recognize the Purkinje cells in the teleost cerebellum, but do not recognize the eurydendroid cells. These results suggest that the eurydendroid cells receive GABAergic inputs from the Purkinje cells. This relationship between the eurydendroid and Purkinje cells is similar to that between the cerebellar nuclei and Purkinje cells in mammals. The eurydendroid cells of teleost have both dissimilar as well as similar features compared to neurons of the cerebellar nuclei in tetrapods.

Afferent Pathways↗

PubMed1982

Reactivation of contraction in detergent-lysed teleost retinal cones.

Teleost retinal cones contract in the light and elongate in the dark. In the green sunfish, Lepomis cyanellus, the necklike myoid region of the cone contracts from as much as 120 micrometers (midnight dark-adapted) to 6 micrometers in fully light-adapted state. When dark-adapted fish are exposed to light (1.4 lux), cone myoids contract with a linear rate of 1.5 +/- 0.1 micrometers/min. We report here that detergent-lysed motile models of teleost retinal cones exhibit calcium- and ATP-dependent reactivated contraction, with morphology and rate comparable to that observed in vivo. For reactivation studies isolated dark-adapted retinas were lysed with nonionic detergent Brij-58 (0.1-1.0%). In reactivation medium containing 10(-5) M free calcium and 4 mM ATP, the lysed cones contracted with normal morphology at in vivo rates (1.4 +/- 1 micrometer/min). Little contraction was observed if ATP or detergent was deleted from the medium or if free calcium levels were less than 10(-8) M. Ultrastructural examination of cone models lysed with 1% Brij-58 revealed that, in spite of extensive extraction of the cytoplasmic matrix, cytoskeletal components (thin filaments, intermediate filaments, microtubules) were still present. Thus we have produced extensively extracted motile models of teleost retinal cones which undergo calcium- and ATP-dependent reactivated contraction with normal morphology at physiological rate.

Adenosine Triphosphate↗

PubMedDate not supplied

Echocardiographic and hemodynamic determinations of the ventricular filling pattern in some teleost fishes.

The current concept of ventricular filling in elasmobranch and teleost fishes is that atrial contraction is the primary, if not the exclusive, determinant of ventricular filling. Recent echocardiographic and on-line hemodynamic data for elasmobranchs, however, have demonstrated a biphasic ventricular filling pattern, characterized by an early phase that occurs during ventricular relaxation and a late phase that follows atrial systole. This study reports echocardiographic and hemodynamic analyses of ventricular filling in three teleost genera (Paralabrax, Channa, Monopterus) having markedly different heart morphologies. Both the profiles of the atrioventricular pressure gradient in Paralabrax and the ventricular inflow velocity in all three genera indicate a biphasic ventricular filling pattern. Although the relative contribution of the early and late filling phases differed among the species studied, interspecific differences in heart structure did not obscure the biphasic pattern. Also, pericardiectomy did not affect the biphasic ventricular filling pattern in Paralabrax. The presence of biphasic filling in teleosts establishes a functional similarity with the elasmobranchs and, because the biphasic ventricular filling pattern predominates in higher vertebrates, suggests that this ventricular filling mechanism may be present in the entire subphylum Vertebrata.

Animals↗

PubMed1999

The non-LTR retrotransposon Rex3 from the fish Xiphophorus is widespread among teleosts.

Rex3, the first reverse transcriptase (RT)-encoding retrotransposon isolated from the melanoma fish model Xiphophorus, is a non-long-terminal-repeat element related to the RTE family. The essential features of Rex3 are (1) an endonuclease and a reverse transcriptase, (2) 5' truncations of most of the copies, (3) a 3' tail consisting of tandem repeats of the sequence GATG, and (4) short target site sequence duplications of variable length. Compilation of Rex3 sequences from the pufferfish genome project suggested that, as observed for other members of the RTE family, no additional large open reading frame was present upstream of the endonuclease/reverse transcriptase open reading frame. There are about a thousand copies of Rex3 in the haploid genome of Xiphophorus, some of them probably resulting from recent retrotransposition events. Rex3 RNA was detected by RT-PCR in melanoma and in nontumorous tissues, as well as in melanoma-derived and embryonic cell lines. Rex3 is present in a broad panel of teleost species and was found in the promoter region and in introns of various genes. To our knowledge, Rex3 is the first autonomous retrotransposon described to date which is widespread in teleosts. This wide distribution and occasional association with coding sequences may confer on Rex3 a predisposition to play a role in genome evolution in teleosts.

Amino Acid Sequence↗

PubMed2004

Extensive expansion of the claudin gene family in the teleost fish, Fugu rubripes.

In humans, the claudin superfamily consists of 19 homologous proteins that commonly localize to tight junctions of epithelial and endothelial cells. Besides being structural tight-junction components, claudins participate in cell-cell adhesion and the paracellular transport of solutes. Here, we identify and annotate the claudin genes in the whole-genome of the teleost fish, Fugu rubripes (Fugu), and determine their phylogenetic relationships to those in mammals. Our analysis reveals extensive gene duplications in the teleost lineage, leading to 56 claudin genes in Fugu. A total of 35 Fugu claudin genes can be assigned orthology to 17 mammalian claudin genes, with the remaining 21 genes being specific to the fish lineage. Thus, a significant number of the additional Fugu genes are not the result of the proposed whole-genome duplication in the fish lineage. Expression profiling shows that most of the 56 Fugu claudin genes are expressed in a more-or-less tissue-specific fashion, or at particular developmental stages. We postulate that the expansion of the claudin gene family in teleosts allowed the acquisition of novel functions during evolution, and that fish-specific novel members of gene families such as claudins contribute to a large extent to the distinct physiology of fishes and mammals.

Animals↗

PubMed1979

H-Y antigen in the teleost.

H-Y antigen, presumably the product of mammalian testis-determining genes, has been detected in three species of teleost fish, Xiphophorus maculatus. Haplochromis burtoni, and Oryzias latipes, and in hybrids of the genus Tilapia. In X. maculatus H-Y was most readily detected in YY males, suggesting that a genetic determinant of H-Y antigen expression may exist on the teleost Y-chromosome. Although H-Y was detected in males and not in feamles in each of the species that we studied, male heterogamety has not been firmly established for H. burtoni. Thus despite the extreme phlyogenetic conservation of H-Y genes and their association with the Y-chromosome, it remains open to question whether H-Y will always be found in the heterogametic sex, and whether serologically defined H-Y antigen plays any part in the differentiation of the teleost gonad.

Animals↗

PubMed1980

Osmolality and potassium ion: their roles in initiation of sperm motility in teleosts.

Spermatozoa that are quiescent in electrolyte and nonelectrolyte solutions isotonic to seminal plasma show motility when the semen is diluted with hypotonic solution in freshwater teleosts (four species tested) and with hypertonic solution in marine teleosts (five species tested). Decrease or increase, respectively, in osmolality of the environment may be the factor initiating sperm motility in these species. The motility of chum salmon spermatozoa in a sodium chloride solution isotonic to seminal plasma is completely suppressed by approximately 10 millimoles of potassium per kilogram; topminnow spermatozoa, however, were immotile in a nonelectrolyte solution, and motility was induced by electrolytes, especially potassium. Thus ions, rather than osmolality, may be an essential determinant of sperm motility in salmonid and viviparous teleosts.

Animals↗

PubMed2004

Permeabilities of teleost and elasmobranch gill apical membranes: evidence that lipid bilayers alone do not account for barrier function.

Teleosts and elasmobranchs faced with considerable osmotic challenges living in sea water, use compensatory mechanisms to survive the loss of water (teleosts) and urea (elasmobranchs) across epithelial surfaces. We hypothesized that the gill, with a high surface area for gas exchange must have an apical membrane of exceptionally low permeability to prevent equilibration between seawater and plasma. We isolated apical membrane vesicles from the gills of Pleuronectes americanus (winter flounder) and Squalus acanthias (dogfish shark) and demonstrated approximately sixfold enrichment of the apical marker, ADPase compared to homogenate. We also isolated basolateral membranes from shark gill (enriched 2.3-fold for Na-K-ATPase) and using stopped-flow fluorometry measured membrane permeabilities to water, urea, and NH(3). Apical membrane water permeabilities were similar between species and quite low (7.4 +/- 0.7 x 10(-4) and 6.6 +/- 0.8 x 10(-4) cm/s for shark and flounder, respectively), whereas shark basolateral membranes showed twofold higher water permeability (14 +/- 2 x 10(-4) cm/s). Permeabilities to urea and NH(3) were also low in apical membranes. Because of the much lower apical to basolateral surface area we conclude that the apical membrane represents an effective barrier. However, the values we obtained were not low enough to account for low water loss (teleosts) and urea loss (elasmobranchs) measured in vivo by others. We conclude that there are other mechanisms which permit gill epithelia to serve as effective barriers. This conclusion has implications for the function of other barrier epithelia, such as the gastric mucosa, mammalian bladder, and renal thick ascending limb.

Ammonia↗

PubMed1988

Atrial natriuretic factor and salt adaptation in the teleost fish Gila atraria.

It is unknown whether atrial natriuretic factor (ANF) is a mediator of environmental salt tolerance in euryhaline teleost fish. This was investigated in anesthetized Gila atraria, a euryhaline teleost native to springs of pleistocene Lake Bonneville. Plasma levels of immunoreactive (ir) ANF [using anti-human ANF-(99-126) antibodies] in fish obtained from a "fresh water" spring were significantly lower (146 +/- 27) than those in fish obtained from a "1% NaCl" spring (347 +/- 21 pg/ml, P less than 0.01). Electron micrographs of fish atrial and ventricular cardiocytes demonstrated many perinuclear granules, which closely resembled ANF-containing secretory granules seen in mammalian atriocytes. Fish heart extract contained ANF-like material of 3 kDa, which caused a marked diuresis and natriuresis in rats. In a second study, fish from a 1% NaCl spring were kept in tanks. One-third of the fish were maintained in 1% NaCl and one-third each were either adapted to fresh- or high-salt water. After 12 days, plasma irANF levels in 1% NaCl fish were 343 +/- 55, in fresh water fish 213 +/- 20 and in high-NaCl fish 691 +/- 79 pg/ml. These values differed significantly from each other (P less than 0.01). There was a close correlation between plasma irANF levels and both environmental and internal salt concentration. These data suggest that piscine ANF is an as yet unrecognized mediator of salt tolerance in this teleost and that ANF in these animals closely resembles mammalian ANF.

Acclimatization↗

PubMed1999

Renal sulfate secretion is carbonic anhydrase dependent in a marine teleost, Pleuronectes americanus.

Though chemical assays indicate that carbonic anhydrase (CA) activity is present in marine teleost nephrons, CA inhibitors have no effect on urine pH or bicarbonate excretion, parameters typically CA dependent in almost all vertebrate groups. Because marine teleost renal sulfate secretion is associated with bicarbonate anion exchange, we investigated the effect of CA inhibition on transepithelial sulfate transport by flounder renal tubule primary monolayer cultures (PTC) and on renal sulfate secretion (QSO4) by intact flounder. Both methazolamide and ethoxzolamide (10 microM) inhibited PTC secretory flux by approximately 50%; reabsorptive sulfate flux, Na-dependent glucose transport, and transepithelial electrical resistance were unaffected. A CA inhibitor restricted to the extracellular space (10 microM polyoxyethylene-aminobenzolamide, 3.7 kDa) had no effect on PTC sulfate transport. Intravenous administration of methazolamide reduced QSO4 almost 40% and had no effect on glomerular filtration rate (GFR), urine flow rate, or Pi excretion rate. Serum pH was significantly reduced 0.2 units, whereas urine pH was unchanged. Together, the in vitro and in vivo results indicate that CA facilitates renal sulfate secretion in the seawater teleost.

Animals↗

PubMed2001

Pituitary growth hormone secretion in the turbot, a phylogenetically recent teleost, is regulated by a species-specific pattern of neuropeptides.

In mammals, growth hormone (GH) is under a dual hypothalamic control exerted by growth hormone-releasing hormone (GHRH) and somatostatin (SRIH). We investigated GH release in a pleuronectiform teleost, the turbot (Psetta maxima), using a serum-free primary culture of dispersed pituitary cells. Cells released GH for up to 12 days in culture, indicating that turbot somatotropes do not require releasing hormone for their regulation. SRIH dose-dependently inhibited GH release up to a maximal inhibitory effect of 95%. None of the potential stimulators tested induced any change in basal GH release. Also, neither forskolin, an activator of adenylate cyclase, nor phorbol ester (TPA), an activator of protein kinase C, were able to modify GH release, suggesting that spontaneous basal release already represents the maximal secretory capacity of turbot somatotropes. In contrast, forskolin and TPA were able to increase GH release in the presence of SRIH. In this condition (coincubation with SRIH), pituitary adenylate cyclase-activating polypeptide (PACAP) stimulated GH release, whereas none of the other neuropeptides tested (GHRHs; sea bream or salmon or chicken II GnRHs; TRH; CRH) had any significant effect. These data indicate that inhibitory control by SRIH may be the basic control of GH production in teleosts and lower vertebrates, while PACAP may represent the ancestral growth hormone-releasing factor in teleosts, a role taken over in higher vertebrates by GHRH.

Animals↗

PubMed2001

Adult neurogenesis and neuronal regeneration in the central nervous system of teleost fish.

In contrast to mammals, teleost fish exhibit an enormous potential to produce new neurons in the adult central nervous system and to replace damaged neurons by newly generated ones. In the gymnotiform fish Apteronotus leptorhynchus, on average, 100,000 cells, corresponding to roughly 0.2% of the total population of cells in the adult brain, are in S-phase within any 2-h period. As in all other teleosts examined thus far, many of these cells are produced in specific proliferation zones located at or near the surface of ventricular, paraventricular, and cisternal systems, or in areas that are likely derived from proliferation zones located at ventricular surfaces during embryonic development. The majority of cells born in such proliferation zones migrate within the first few weeks following their generation to specific target areas. In the cerebellum, where approximately 75% of all brain cells are born during adulthood, cells originate from the molecular layers of the corpus cerebelli and the valvula cerebelli partes lateralis and medialis, as well as from the eminentia granularis pars medialis. From these proliferation zones, the young cells migrate to the associated granule cell layers or to the eminentia granularis pars posterior, respectively. In the course of their migration, the young cells appear to be guided by radial glial fibers. Upon arrival at their target region, approximately 50% of the young cerebellar cells undergo apoptosis. The remaining cells survive for the rest of the fish's life, thus contributing to permanent brain growth. At least some cells differentiate into granule cell neurons. The potential to produce new neurons, together with the ability to guide the young cells to their target areas by radial glial fibers and to eliminate damaged cells through apoptosis, also forms the basis for the enormous regenerative capability of the central nervous system of Apteronotus, as demonstrated in the cerebellum and spinal cord. A factor involved in the cerebellar regeneration appears to be somatostatin, as the expression of this neuropeptide is up-regulated in a specific spatio-temporal fashion following mechanical lesions. Besides its involvement in neuronal regeneration adult neurogenesis in Apteronotus, and possibly teleost fish in general, appears to play a role in providing central neurons to match the growing number of sensory and motor elements in the periphery, and to establish the neural substrate to accommodate behavioral plasticity.

Aging↗

PubMed2007

Diversity of brain morphology in teleosts: brain and ecological niche.

Modern teleosts have more copies of developmental regulatory genes than other vertebrates, probably due to a whole genome duplication that occurred specifically at the base of the lineage of ray-finned fishes. The genome duplication generates duplicated genes (including their regulatory regions), and one of the duplicates might become redundant and free from selective pressures. These redundant genes might be more easily mutated during evolution. Brain morphogenesis is a process that is dependent on a large genetic program in which a subprogram for the regionalization of the brain is coupled with that for cell-proliferation control. If beneficial mutations took place in key genes within the genetic program for brain morphogenesis, it might result in the enhancement of region-specific cell proliferation and cell survival in the corresponding brain subdivisions. This mechanism might account for the appearance of various forms of teleost brains, which have been preserved under selection pressure in diverse environments. It is conceivable that variously modified brains might evolve under the conditions of natural selection so that the brains help fit the teleost species for diverse ecological niches.

Animals↗

PubMed2007

Ocular melatonin rhythms in teleost fish.

Melatonin (N-acetyl-5-methoxytryptamine) is synthesized in the pineal organ and the retina of vertebrates. In some teleost species, ocular melatonin levels can exhibit a circadian periodicity with elevated levels during the dark phase under light-dark (LD) cycles and this periodicity can persist even under constant dark (DD) cycles. However, reversed melatonin profiles and an absence of circadian ocular melatonin rhythms have also been reported. In this study, we investigated the daily rhythms of ocular melatonin in 32 teleost species under LD cycles. The melatonin profiles could be classified into three types: (1) normal profiles, with higher melatonin levels during the dark phase than the light phase; (2) reversed profiles, with higher levels during the light phase than the dark phase; (3) no significant differences in melatonin levels. We also studied whether ocular melatonin exhibits circadian rhythms under DD in selected species. Our results showed that ocular melatonin exhibited circadian rhythms in some but not all of the species examined. These results indicate that ocular melatonin rhythms in teleost fish exhibit species-specific variations as a result of the changes in the regulatory mechanisms during the course of evolution.

Animals↗

PubMed1992

Differences in optokinetic and vestibular ocular reflex performance in teleosts and their relationship to different life styles.

Horizontal eye movements in response to vestibular and optokinetic stimulation were investigated in 20 species of marine and fresh water teleosts. Most species performed spontaneous saccadic eye movements in light and in darkness. Successive saccades occurred either at irregular intervals and in different directions (few species), or in bursts of smaller saccades in one direction followed by saccades in the opposite direction (majority of species). Thus, in the latter group the lines of sight shifted cyclically from one side to the other about every 10-15 s. Eye movement responses in goldfish and toadfish were prototypical for two major functional groups. Optokinetic and vestibular nystagmus in the goldfish were much more regular and attained significantly higher gains than in the oyster toadfish. Optokinetic afternystagmus (OKAN) and per-/postrotatory nystagmus lasted about 10-12 s in the goldfish, but only 2-3 s in the oyster toadfish. Bilateral labyrinthectomy in goldfish resulted in optokinetic gains and OKAN durations that were very close to those of intact toadfish. These results indicate the presence (in goldfish) and the absence (in toadfish) of a functioning velocity storage network, respectively. Other non-ostariophysan teleosts failed to show a 'goldfish-like' response pattern as well. Ostariophysan species differed in their reflex performance as well. A 'goldfish-like' response pattern was observed in five of the seven cypriniform species and in two of the four characiform species but not in the four siluriform species. Positively correlated, combined response properties suggest that some species are better equipped for gaze stabilization at higher velocities than other species. These behavioral differences may parallel different specializations in locomotor pattern and mode of life. Absence of a functioning velocity storage network in bottom-dwelling teleosts (as in Amphibia) may be related to the sporadic, slow locomotion of these species and the resulting small requirements for continuous gaze stabilization during self-motion at higher velocities.

Animals↗

PubMed1991

Comparative cytoarchitectonic analysis of some visual pretectal nuclei in teleosts.

The posterior pretectal nucleus, which in Osteoglossum receives second order visual input and projects to the inferior lobe of the hypothalamus, was identified and characterized in species from all major groups of non-neoteleost teleosts. The hypothesis that the posterior pretectal nucleus in these species is homologous to both the pars intermedius of the superficial pretectal nucleus and nucleus glomerulosus in acanthopterygians is supported by multiple similarities in relative position and cytoarchitecture. Nucleus corticalis, which receives retinal input and projects to the posterior pretectal nucleus (or to nucleus glomerulosus), was identified in species belonging to three of the four major teleost radiations. Both the posterior pretectal nucleus and nucleus corticalis are plesiomorphic for teleosts. The presence of glomeruli in the posterior pretectal nucleus and nucleus glomerulosus in esocids and acanthopterygians, respectively, and the presence of two nuclei, the pars intermedius and nucleus glomerulosus, in acanthopterygians, as opposed to one nucleus, the posterior pretectal nucleus, are apomorphies.

Animals↗

PubMed1997

Insulin-like growth factor I in the teleost Oreochromis mossambicus, the tilapia: gene sequence, tissue expression, and cellular localization.

Using reverse transcription-PCR and molecular cloning, the complementary DNA sequence encoding preproinsulin-like growth factor I (IGF-I) of a teleost, the tilapia (Oreochromis mossambicus) was established from liver. At the amino acid level, tilapia IGF-I shows all residues necessary for the maintenance of tertiary structure and shares about 80% identity with IGF-I from other teleosts. The B and A domains of tilapia IGF-I show more than 90% homology to those of other teleosts and 86-93% to those of human. However, in contrast to salmonids, the C domain of tilapia is truncated. Reverse transcription-PCR analysis followed by Southern blotting with an internal probe specific for tilapia IGF-I indicated a transcript in liver, pancreas, gut, kidney, head kidney, gill, ovary, testis, eye, and brain. In correlation, parenchymal cells were identified as likely local production sites by the use of immunohistochemistry. IGF-I immunoreactivity was confined to D cells in pancreatic islets, gastroentero-endocrine cells, cells of renal proximal tubules, interrenal cells of the head kidney, gill chondrocytes, chloride cells of the gill epithelium, granulosa cells in the ovary, spermatocytes and Sertoli cells in testis, and neurons in retina and brain. The local production of IGF-I in multiple organs of the tilapia indicates paracrine/autocrine actions of IGF-I involved in organ-specific functions. The results further demonstrate that the primary structure of IGF-I, especially in the B and A domains, is highly conserved during phylogeny.

Amino Acid Sequence↗

PubMed1995

Change in intracellular K+ concentration caused by external osmolality change regulates sperm motility of marine and freshwater teleosts.

We previously demonstrated that osmolality isotonic to the seminal plasma suppresses sperm motility in marine and freshwater teleosts, and exposure of sperm to hypertonicity of sea water or hypotonicity of fresh water, respectively, induces the initiation of sperm motility at spawning. The motile sperm became immotile by return of osmolality to the isotonic osmolality both in a marine teleost, the puffer fish, and a freshwater teleost, the zebrafish. The initiation and termination of sperm motility could be repeated several times by changing surrounding osmolality in both species. In demembranated sperm, motility was suppressed by a K+ concentration equivalent to the seminal salt concentration in both puffer and zebrafish. Demembranated puffer sperm were reactivated when K+ concentration of the reactivating solution increased. Conversely, initiation of motility in the demembranated zebrafish sperm was induced by decreasing K+ concentration. The initiation and termination of the demembranated sperm were alternately repeated by changing K+ concentration of the reactivation solution in both species. Furthermore, intracellular K+ concentration rose when sperm motility of the puffer was initiated in hypertonic solutions. These results suggest that change in external osmolality is converted into change in intracellular K+ concentration, and that the change affects the flagellar axoneme as a signal to initiate or terminate sperm motility. The initiation and termination of motility in the demembranated puffer sperm were caused at a high pH and a low pH of the reactivating solution, respectively, suggesting the contribution of intracellular pH in the regulation of flagellar motility.

Animals↗