Xenopus Laevis Tadpoles (xenopus + laevi_tadpole)

Distribution by Scientific Domains

Selected Abstracts

Overexpression of the transcription factor Msx1 is insufficient to drive complete regeneration of refractory stage Xenopus laevis hindlimbs

Donna M. Barker
Abstract Xenopus laevis tadpoles are capable of hindlimb regeneration, although this ability declines with age. Bmp signaling is one pathway known to be necessary for successful regeneration to occur. Using an inducible transgenic line containing an activated version of the Bmp target Msx1, we assessed the ability of this transcription factor to enhance regeneration in older limbs. Despite considerable evidence correlating msx1 expression with regenerative success in vertebrate regeneration models, we show that induction of msx1 during hindlimb regeneration fails to induce complete regeneration. However, we did observe some improvement in regenerative outcome, linked to morphological changes in the early wound epithelium and a corresponding increase in proliferation in the underlying distal mesenchyme, neither of which are maintained later. Additionally, we show that Msx1 is not able to rescue limb regeneration in a Bmp signalling-deficient background, indicating that additional Bmp targets are required for regeneration in anuran limbs. Developmental Dynamics 238:1366,1378, 2009. © 2009 Wiley-Liss, Inc. [source]

Global analysis of gene expression in Xenopus hindlimbs during stage-dependent complete and incomplete regeneration

Matthew Grow
Abstract Xenopus laevis tadpoles are capable of limb regeneration after amputation, in a process that initially involves the formation of a blastema. However, Xenopus has full regenerative capacity only through premetamorphic stages. We have used the Affymetrix Xenopus laevis Genome Genechip microarray to perform a large-scale screen of gene expression in the regeneration-complete, stage 53 (st53), and regeneration-incomplete, stage 57 (st57), hindlimbs at 1 and 5 days postamputation. Through an exhaustive reannotation of the Genechip and a variety of comparative bioinformatic analyses, we have identified genes that are differentially expressed between the regeneration-complete and -incomplete stages, detected the transcriptional changes associated with the regenerating blastema, and compared these results with those of other regeneration researchers. We focus particular attention on striking transcriptional activity observed in genes associated with patterning, stress response, and inflammation. Overall, this work provides the most comprehensive views yet of a regenerating limb and different transcriptional compositions of regeneration-competent and deficient tissues. Developmental Dynamics 235:2667,2685, 2006. © 2006 Wiley-Liss, Inc. [source]

Aroclor 1254 alters morphology, survival, and gene expression in Xenopus laevis tadpoles

Anna M. Jelaso
Abstract PCBs are persistent environmental contaminants that cause a variety of adverse health effects in wildlife and humans. This article describes the use of signature gene expression patterns that link increased PCB exposure with progressive, adverse biological effects. Developing Xenopus laevis tadpoles of two age classes were exposed to the PCB mixture Aroclor 1254 for 2 days. Real-time PCR was used to quantitate mRNA expression for 11 physiologically relevant, potential bioindicator genes. Younger tadpoles (5 days postfertilization) were resistant to Aroclor 1254 and showed few changes in gross morphology, swimming behavior, survival, or gene expression. Older tadpoles (11 days postfertilization) were more susceptible to Aroclor 1254. Exposure to 25 and 50 ppm Aroclor 1254 caused alterations in gross morphology and swimming behavior and statistically significant decreases in survival. These tadpoles showed statistically significant decreases in gene expression for 9 out of the 11 genes measured. Tadpoles exposed to 10 ppm showed incipient health changes but had gene expression profiles similar to the tadpoles treated with higher doses of Aroclor 1254. Tadpoles exposed to 1 ppm did not exhibit any observable adverse health effects, yet statistically significant decreases in gene expression occurred in these tadpoles (4 out of 11 genes). After prolonged exposure, tadpoles exposed to 1 and 10 ppm Aroclor 1254 exhibited health effects similar to those exposed to higher concentrations. Therefore, changes in expression of specific genes may serve not only as molecular bioindicators of Aroclor 1254 exposure but also as predictors of impending adverse health effects. Environ. Mol. Mutagen. 40:24,35, 2002. © 2002 Wiley-Liss, Inc. [source]

Exposure to the polychlorinated biphenyl mixture Aroclor® 1254 alters melanocyte and tail muscle morphology in developing Xenopus laevis tadpoles

Marla A. Fisher
Abstract Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have damaging effects on both ecosystem and human health. Numerous studies have shown that exposure to PCBs can alter growth and development of aquatic organisms, including frogs. In this report, developing Xenopus laevis tadpoles were exposed to the PCB mixture Aroclor® 1254. Tadpoles were exposed from 5 through 9 d postfertilization to either 0, 1, 10, 50, or 100 ppm Aroclor 1254. Exposure to an acute, high concentration of Aroclor 1254 (10, 50, and 100 ppm) caused statistically significant reductions in survival and body size. In addition, tadpoles exposed to these higher concentrations showed histological abnormalities, including aberrant tail tip, myotomal, and melanocyte morphologies. Described adverse health effects associated with PCB exposure of developing frogs will serve as useful health endpoints in ongoing and future molecular-based studies that correlate health effects with changes in gene expression. [source]

ATP activates both receptor and sustentacular supporting cells in the olfactory epithelium of Xenopus laevis tadpoles

Dirk Czesnik
Abstract Nucleotides and amino acids are acknowledged categories of water-borne olfactory stimuli. In previous studies it has been shown that larvae of Xenopus laevis are able to sense amino acids. Here we report on the effect of ATP in the olfactory epithelium (OE) of Xenopus laevis tadpoles. First, ATP activates a subpopulation of cells in the OE. The ATP-sensitive subset of cells is almost perfectly disjoint from the subset of amino acid-activated cells. Both responses are not mediated by the well-described cAMP transduction pathway as the two subpopulations of cells do not overlap with a third, forskolin-activated subpopulation. We further show that, in contrast to amino acids, which act exclusively as olfactory stimuli, ATP appears to feature a second role. Surprisingly it activated a large number of sustentacular supporting cells (SCs) and, to a much lower extent, olfactory receptor neurons. The cells of the amino acid- and ATP-responding subsets featured differences in shape, size and position in the OE. The latencies to activation upon stimulus application differed markedly in these subsets. To obtain these results two technical points were important. We used a novel dextran-tetramethylrhodamine-backfilled slice preparation of the OE and we found out that an antibody to calnexin, a known molecular chaperone, also labels SCs. Our findings thus show a strong effect of ATP in the OE and we discuss some of the possible physiological functions of nucleotides in the OE. [source]

Neuronal representation of odourants in the olfactory bulb of Xenopus laevis tadpoles

Dirk Czesnik
Abstract When an odourant enters the nose, olfactory receptor neurons (ORNs) convey information about it to the olfactory bulb (OB), where this information is processed and where the first central representations of the odourant are generated. In this paper we show how odourants are represented by ensembles of OB neurons, in particular mitral cells (MCs) which are the output neurons of the OB. We were able to demonstrate for the first time that the intracellular calcium concentrations ([Ca2+]i) in the somata of these neurons undergo specific changes and that different stimuli are represented by different neuronal [Ca2+]i patterns. The similarity of patterns was assessed by cross-correlation analysis. We further show that noradrenaline (NA), which is reported to be involved in olfactory memory formation and to modulate synaptic transmission at dendrodendritic synapses in the OB, profoundly changes the representation of odourants at the level of MCs. [source]

Pigment epithelium-derived factor supports normal Müller cell development and glutamine synthetase expression after removal of the retinal pigment epithelium

GLIA, Issue 1 2001
Monica M. Jablonski
Abstract In conditions in which the retinal pigment epithelium (RPE) is dystrophic, carries a genetic mutation, or is removed physically, Müller cells undergo degenerative changes that contribute to the retinal pathology. We previously demonstrated that pigment epithelium-derived factor (PEDF), a glycoprotein secreted by the RPE cells with neuroprotective and differentiation properties, protects against photoreceptor degeneration induced by RPE removal. The purpose of the present study was to analyze the putative gliosupportive activity of PEDF on Müller cells of RPE-deprived retinas and assess whether protection of Müller cells was correlated with improved photoreceptor outer segment assembly. Eyes were dissected from Xenopus laevis tadpoles, and the RPE was removed before culturing in medium containing purified PEDF, PEDF plus anti-PEDF, or medium alone. Control eyes matured with an adherent RPE or in medium containing PEDF plus nonimmune serum. Müller cell ultrastructure was examined. Glial fibrillary acidic protein (GFAP) and glutamine synthetase were localized immunocytochemically, and the corresponding protein levels were quantified. In control retinas, Müller cells were structurally intact and formed adherens junctions with neighboring photoreceptors. In addition, they did not express GFAP, whereas glutamine synthetase expression was high. RPE removal dramatically altered the ultrastructure and biosynthetic activity of Müller cells; Müller cells failed to form adherens junctions with photoreceptors and glutamine synthetase expression was suppressed. PEDF prevented the degenerative glial response; Müller cells were ultrastructurally normal and formed junctional complexes with photoreceptors. PEDF also preserved the expression of glutamine synthetase at near-normal levels. The morphogenetic effects of PEDF were blocked by the anti-PEDF antibody. Our study documents the glioprotective effects of PEDF and suggests that maintenance of the proper Müller cell ultrastructure and expression of glutamine synthetase may be necessary to support the proper assembly of photoreceptor outer segments. GLIA 35:14,25, 2001. © 2001 Wiley-Liss, Inc. [source]

Regression of blood vessels in the ventral velum of Xenopus laevis Daudin during metamorphosis: light microscopic and transmission electron microscopic study

Structural changes of the ventral velum of Xenopus laevis tadpoles from late prometamorphosis (stage 58) to the height of metamorphic climax (stage 62) were examined by light and transmission electron microscopy. Special emphasis was given to the blood vessel regression. Early changes of velar capillaries were formation of luminal and abluminal endothelial cell processes, vacuolation, and cytoplasmic and nuclear chromatin condensation. At the height of metamorphic climax, transmission electron microscopy revealed apoptotic endothelial cells with nuclear condensation and fragmentation, intraluminal bulging of rounded endothelial cells which narrowed or even plugged the capillary, and different stages of endothelial cell detachment (,shedding') into the vessel lumen. These changes explain the ,miniaturisation' of the velar microvascular bed as well as the typical features found in resin-casts of regressing velar vessels which have been observed in a previous scanning electron microscopy study of the ventral velum. [source]

Visual deprivation increases accumulation of dense core vesicles in developing optic tectal synapses in Xenopus laevis

Jianli Li
Abstract Despite considerable progress in understanding the molecular components of synapses in the central nervous system, the ultrastructural rearrangements underlying synaptic development remain unclear. We used serial section transmission electron microscopy and three-dimensional reconstructions of the optic tectal neuropil of Xenopus laevis tadpoles to detect and quantify changes in synaptic ultrastructure over a 1-week period from stages 39 and 47, during which time the visual system of Xenopus tadpoles becomes functional. Synapse density, presynaptic maturation index, and number of synapses per axon bouton increase, whereas the number of DCVs per bouton decreases, between stages 39 and 47. The width of the synaptic cleft decreased and the diameter of postsynaptic profiles increased between stages 39 and 47 and then remained relatively unchanged after stage 47. We found no significant difference in synapse maturation between GABAergic and non-GABAergic synapses. To test the effect of visual experience on synaptogenesis, animals were deprived of visual experience for 3 days from stage 42 to 47. Visual deprivation decreased synapse maturation and the number of connections per bouton. Furthermore, visual deprivation increased the number of DCVs per bouton by more than twofold. The visual-deprivation-induced decrease in synaptic connections is specific to asymmetric non-GABAergic synapses; however, both symmetric GABAergic and asymmetric synapses show comparable increases in the number DCVs with visual deprivation. In both the control and the visually deprived animals, the number of DCVs per bouton is highly variable and does not correlate with either synapse maturation or the number of connected partners per bouton. These data suggest that synaptogenesis and DCV accumulation are regulated by visual experience and further suggest a complex spatial and temporal relation between DCV accumulation and synapse formation. J. Comp. Neurol. 518:2365,2381, 2010. © 2010 Wiley-Liss, Inc. [source]