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Robe J Denve - One of the best experts on this subject based on the ideXlab platform.

  • thyroid hormone induces dna demethylation in xenopus Tadpole brain
    Endocrinology, 2020
    Co-Authors: Samhitha Raj, Christophe J Sifuentes, Yasuhiro Kyono, Elvira Del Carmen Arellaneslicea, Arasakuma Subramani, Robe J Denve
    Abstract:

    Thyroid hormone (T3) plays pivotal roles in vertebrate development, acting via nuclear receptors (TRs) that regulate gene transcription by promoting posttranslational modifications to histones. Methylation of cytosine residues in DNA also modulates gene transcription, and our recent finding of predominant DNA demethylation in the brain of Xenopus Tadpoles at metamorphosis, a T3-dependent developmental process, caused us to hypothesize that T3 induces these changes in vivo. Treatment of pre-metamorphic Tadpoles with T3 for 24 or 48 hr increased immunoreactivity in several brain regions for the DNA demethylation intermediates 5-hydroxymethylcytosine (5-hmC) and 5-carboxylcytosine, and the methylcytosine dioxygenase ten-eleven translocation 3 (TET3). Thyroid hormone treatment induced locus-specific DNA demethylation in proximity to known T3 response elements within the DNA methyltransferase 3a and Kruppel-like factor 9 genes, analyzed by 5-hmC immunoprecipitation and methylation sensitive restriction enzyme digest. Chromatin-immunoprecipitation (ChIP) assay showed that T3 induced TET3 recruitment to these loci. Furthermore, the mRNAs for several genes encoding DNA demethylation enzymes were induced by T3 in a time-dependent manner in Tadpole brain. A TR ChIP-sequencing experiment identified putative TR binding sites at several of these genes, and we provide multiple lines of evidence to support that tet2 contains a bona fide T3 response element. Our findings show that T3 can promote DNA demethylation in developing Tadpole brain, in part by promoting TET3 recruitment to discrete genomic regions, and by inducing genes that encode DNA demethylation enzymes.

  • thyroid hormone receptor alpha is required for thyroid hormone dependent neural cell proliferation during Tadpole metamorphosis
    Frontiers in Endocrinology, 2019
    Co-Authors: Christophe J Sifuentes, Robe J Denve
    Abstract:

    Thyroid hormone (T3) plays several key roles in development of the nervous system in vertebrates, controlling diverse processes such as neurogenesis, cell migration, apoptosis, differentiation, and maturation. In anuran amphibians, the hormone exerts its actions on the Tadpole brain during metamorphosis, a developmental period dependent on T3. Thyroid hormone regulates gene transcription by binding to two nuclear receptors, TRα and TRβ. Our previous findings using pharmacological and other approaches supported that TRα plays a pivotal role in mediating T3 actions on neural cell proliferation in Xenopus Tadpole brain. Here we used Xenopus tropicalis (X. tropicalis) Tadpoles with an inactivating mutation in the gene that encodes TRα to investigate roles for TRα in mitosis and gene regulation in Tadpole brain. Gross morphological analysis showed that mutant Tadpoles had proportionally smaller brains, corrected for body size, compared with wildtype, both during prometamorphosis and at the completion of metamorphosis. This was reflected in a large reduction in phosphorylated histone 3 (pH3; a mitosis marker) immunoreactive (ir) nuclei in prometamorphic Tadpole brain, when T3-dependent cell proliferation is maximal. Treatment of wild type premetamorphic Tadpoles with T3 for 48 h induced gross morphological changes in the brain, and strongly increased pH3-ir, but had no effect in mutant Tadpoles. Thyroid hormone induction of the direct TR target genes thrb, klf9, and thibz was dysregulated in mutant Tadpoles. Analysis of gene expression by RNA sequencing in the brain of premetamorphic Tadpoles treated with or without T3 for 16 h showed that the TRα accounts for 95% of the gene regulation responses to T3.

  • leptin induces mitosis and activates the canonical wnt β catenin signaling pathway in neurogenic regions of xenopus Tadpole brain
    Frontiers in Endocrinology, 2017
    Co-Authors: Melissa Cui Ende, Christophe J Sifuentes, Robe J Denve
    Abstract:

    In addition to its well-known role as an adipostat in adult mammals, leptin has diverse physiological and developmental actions in vertebrates. Leptin has been shown to promote development of hypothalamic circuits, and to induce mitosis in different brain areas of mammals. We investigated the ontogeny of leptin mRNA, leptin actions on cell proliferation in the brain, and gene expression in the preoptic area/hypothalamus of Tadpoles of Xenopus laevis. The level of leptin mRNA was low in premetamorphic Tadpoles, but increased strongly at the beginning of metamorphosis and peaked at metamorphic climax. This increase in leptin mRNA at the onset of metamorphosis correlated with increased cell proliferation in the neurogenic zones of Tadpole brain. We found that intracerebroventricular (i.c.v.) injection of recombinant Xenopus leptin (rxLeptin) in premetamorphic Tadpoles strongly increased cell proliferation in neurogenic zones throughout the Tadpole brain. We conducted gene expression profiling of genes induced at 2 hr following i.c.v. injection of rxLeptin. This analysis identified 2322 genes induced, and 1493 genes repressed by rxLeptin. The most enriched KEGG term was the canonical Wnt/β-catenin pathway. Using electroporation-mediated gene transfer into Tadpole brain of a reporter vector responsive to the canonical Wnt/β-catenin signaling pathway, we found that i.c.v. rxLeptin injection activated Wnt/β-catenin-dependent transcriptional activity. Our findings show that leptin acts on the premetamorphic Tadpole brain to induce cell proliferation, possibly acting via the Wnt/β-catenin signaling pathway.

  • molecular mechanisms of corticosteroid synergy with thyroid hormone during Tadpole metamorphosis
    General and Comparative Endocrinology, 2010
    Co-Authors: Ronald M One, Eric D Hoopfe, Robe J Denve
    Abstract:

    Abstract Corticosteroids (CS) act synergistically with thyroid hormone (TH) to accelerate amphibian metamorphosis. Earlier studies showed that CS increase nuclear 3,5,3′-triiodothyronine (T 3 ) binding capacity in Tadpole tail, and 5′ deiodinase activity in Tadpole tissues, increasing the generation of T 3 from thyroxine (T 4 ). In the present study we investigated CS synergy with TH by analyzing expression of key genes involved in TH and CS signaling using Tadpole tail explant cultures, prometamorphic Tadpoles, and frog tissue culture cells (XTC-2 and XLT-15). Treatment of tail explants with T 3 at 100 nM, but not at 10 nM caused tail regression. Corticosterone (CORT) at three doses (100, 500 and 3400 nM) had no effect or increased tail size. T 3 at 10 nM plus CORT caused tails to regress similar to 100 nM T 3 . Thyroid hormone receptor beta (TRβ) mRNA was synergistically upregulated by T 3 plus CORT in tail explants, tail and brain in vivo , and tissue culture cells. The activating 5′ deiodinase type 2 (D2) mRNA was induced by T 3 and CORT in tail explants and tail in vivo . Thyroid hormone increased expression of glucocorticoid (GR) and mineralocorticoid receptor (MR) mRNAs. Our findings support that the synergistic actions of TH and CS in metamorphosis occur at the level of expression of genes for TRβ and D2, enhancing tissue sensitivity to TH. Concurrently, TH enhances tissue sensitivity to CS by upregulating GR and MR. Environmental stressors can modulate the timing of Tadpole metamorphosis in part by CS enhancing the response of Tadpole tissues to the actions of TH.

Debra Meloy Elmegree - One of the best experts on this subject based on the ideXlab platform.

  • local Tadpole galaxies dynamics and metallicity
    The Astrophysical Journal, 2013
    Co-Authors: Uce G Elmegree, Debra Meloy Elmegree, Sanchez J Almeida, C Munoztuno, J Mendezabreu
    Abstract:

    Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local Tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure H{alpha} velocity curves of seven local Tadpoles, representing 50% of the initial sample. Five of them show evidence for rotation ({approx}70%), and a sixth target hints at it. Often the center of rotation is spatially offset with respect to the Tadpole head (three out of five cases). The size and velocity dispersion of the heads are typical of giant H II regions, and three of them yield dynamical masses in fair agreement with their stellar masses as inferred from photometry. In four cases the velocity dispersion at the head is reduced with respect to its immediate surroundings. The oxygen metallicity estimated from [N II] {lambda}6583/H{alpha} often shows significant spatial variations across the galaxies ({approx}0.5 dex), being smallest at the head and larger elsewhere. The resulting chemical abundance gradients are opposite to the ones observed in local spirals, but agrees with disk galaxies at high redshift. We interpret the metallicity variation asmore » a sign of external gas accretion (cold-flows) onto the head of the Tadpole. The galaxies are low-metallicity outliers of the mass-metallicity relationship. In particular, two of the Tadpole heads are extremely metal poor, with a metallicity smaller than a tenth of the solar value. These two targets are also very young (ages smaller than 5 Myr). All these results combined are consistent with the local Tadpole galaxies being disks in early stages of assembling, with their star formation sustained by accretion of external metal-poor gas.« less

  • Tadpole galaxies in the hubble ultra deep field
    The Astrophysical Journal, 2010
    Co-Authors: Uce G Elmegree, Debra Meloy Elmegree
    Abstract:

    Tadpole galaxies have a head-tail shape with a large clump of star formation at the head and a diffuse tail or streak of stars off to one side. We measured the head and tail masses, ages, surface brightnesses, and sizes for 66 Tadpoles in the Hubble Ultra Deep Field (UDF) and looked at the distribution of neighbor densities and Tadpole orientations with respect to neighbors. The heads have masses of 107-108 M ☉ and photometric ages of ~0.1 Gyr for z ~ 2. The tails have slightly larger masses than the heads and comparable or slightly older ages. The most obvious interpretation of Tadpoles as young merger remnants is difficult to verify. They have no enhanced proximity to other resolved galaxies as a class, and the heads, typically <0.2 kpc in diameter, usually have no obvious double-core structure. Another possibility is ram pressure interaction between a gas-rich galaxy and a diffuse cosmological flow. Ram pressure can trigger star formation on one side of a galaxy disk, giving the Tadpole shape when viewed edge-on. Ram pressure can also strip away gas from a galaxy and put it into a tail, which then forms new stars and gravitationally drags along old stars with it. Such an effect might have already been observed in the Virgo Cluster. Another possibility is that Tadpoles are edge-on disks with large, off-center clumps. Analogous lop-sided star formation in UDF clump clusters is shown.

Donald D. Brown - One of the best experts on this subject based on the ideXlab platform.

  • transdifferentiation of Tadpole pancreatic acinar cells to duct cells mediated by notch and stromelysin 3
    Developmental Biology, 2011
    Co-Authors: Sandeep Mukhi, Donald D. Brown
    Abstract:

    The Tadpole pancreas has differentiated acinar cells but an underdeveloped ductal system. At the climax of metamorphosis thyroid hormone (TH) induces the Tadpole acinar cells to dedifferentiate to a progenitor state. After metamorphosis is complete the exocrine pancreas redifferentiates in the growing frog forming a typical vertebrate pancreas including a complex ductal system. A micro array analysis found that TH up regulates stromelysin 3 (ST3, matrix metalloproteinase 11) in the exocrine pancreas at metamorphic climax. Transgenic Tadpoles were prepared with an elastase promoter driving either the ST3 gene or the constitutively active form of Notch (IC). Expression of the transgenes was controlled by the tetracycline system. A few days after either of these transgenes is activated by doxycycline the pancreatic acinar cells turn into duct-like cells. This transdetermination occurs without cell division since both acinar and ductal markers can be visualized transiently in the same cell. We propose that remodeling of the Tadpole acinar cells is initiated when ST3 is up regulated by TH. Stromelysin-3 then cleaves and activates Notch.

  • metamorphosis is inhibited in transgenic xenopus laevis Tadpoles that overexpress type iii deiodinase
    Proceedings of the National Academy of Sciences of the United States of America, 1999
    Co-Authors: Haochu Huang, Nicholas Marsharmstrong, Donald D. Brown
    Abstract:

    One of the genes that is up-regulated by thyroid hormone (TH) during Xenopus laevis metamorphosis encodes a type III deiodinase (D3) that inactivates TH. Transgenic X. laevis Tadpoles overexpressing a GFP-D3 fusion protein were produced. These transgenic Tadpoles had high levels of deiodinase activity and were resistant to exogenous TH added 1 week after fertilization. They developed normally throughout embryogenesis and premetamorphic stages but became retarded in their development late in prometamorphosis when endogenous TH reaches its highest level. Gill and tail resorption were delayed and most of the animals arrested and died. One Tadpole completed its metamorphosis without resorbing its tail. These results demonstrate that D3 can modulate the action of TH in vivo, and document the value of the new transgenic method for functional analysis of genes involved in metamorphosis.

Shawn R Kuchta - One of the best experts on this subject based on the ideXlab platform.

  • predator mediated selection and the impact of developmental stage on viability in wood frog Tadpoles rana sylvatica
    BMC Evolutionary Biology, 2011
    Co-Authors: Ryan Calsbeek, Shawn R Kuchta
    Abstract:

    Background: Complex life histories require adaptation of a single organism for multiple ecological niches. Transitions between life stages, however, may expose individuals to an increased risk of mortality, as the process of metamorphosis typically includes developmental stages that function relatively poorly in both the pre- and postmetamorphic habitat. We studied predator-mediated selection on Tadpoles of the wood frog, Rana sylvatica ,t o identify this hypothesized period of differential predation risk and estimate its ontogenetic onset. We reared Tadpoles in replicated mesocosms in the presence of the larval odonate Anax junius, a known Tadpole predator. Results: The probability of Tadpole survival increased with increasing age and size, but declined steeply at the point in development where hind limbs began to erupt from the body wall. Selection gradient analyses indicate that natural selection favored Tadpoles with short, deep tail fins. Tadpoles resorb their tails as they progress toward metamorphosis, which may have led to the observed decrease in survivorship. Path models revealed that selection acted directly on tail morphology, rather than through its indirect influence on swimming performance. Conclusions: This is consistent with the hypothesis that tail morphology influences predation rates by reducing the probability a predator strikes the head or body.

Geoffrey R Smith - One of the best experts on this subject based on the ideXlab platform.

  • combined effects of malathion and nitrate on early growth abnormalities and mortality of wood frog rana sylvatica Tadpoles
    Ecotoxicology, 2011
    Co-Authors: S V Krishnamurthy, Geoffrey R Smith
    Abstract:

    Use of pesticides and other agro-chemicals adversely influence amphibians either directly by killing them or by inducing sublethal, chronic effects. Many studies have investigated the effect of mixtures of pesticides or fertilizers. We studied the combined effects of nitrate and malathion ([(dimethoxy phosphino thioyl] butanediotae) on the early growth, expression of abnormalities, and mortality of Wood Frog (Rana sylvatica) Tadpoles in a laboratory experiment. Tadpoles were treated with factorial combinations of 0, 8, and 16 mg NO3–N l−1 and 0, 250, 500, and 1,000 μg malathion l−1 for a period of 14 days. Feeding behaviour, total length, mean Tadpole mass, frequencies of abnormalities, and survivorship in each treatment were recorded. Malathion showed a significant negative influence on all parameters and strongly influenced the frequencies of morphological anomalies. In contrast, nitrate alone did not produce any significant effects on behavior, total length, Tadpole mass, or the frequency of abnormalities during the experiment. Malathion and nitrate had an interactive effect on Tadpole length and mass, but did not affect any other parameters. Our results suggest that exposure to malathion, even at relatively low concentrations can have serious negative consequences for Wood Frog Tadpoles. In addition, our results also indicate that there was little synergistic interaction between malathion and nitrate exposure under laboratory conditions.

  • behavioral responses of american toad and bullfrog Tadpoles to the presence of cues from the invasive fish gambusia affinis
    Biological Invasions, 2008
    Co-Authors: Geoffrey R Smith, Christopher B. Dayer, Allison Boyd, Kristen E Winter
    Abstract:

    The introduction of non-native predators is thought to have important negative effects on native prey populations. The susceptibility of native prey to non-native or introduced predators may depend on their ability to respond appropriately to the presence of these non-native predators. We conducted a laboratory based behavioral experiment to examine the response of American toad (Bufo americanus) and bullfrog (Rana catesbeiana) Tadpoles to the presence of cues from the introduced mosquitofish (Gambusia affinis), a potential Tadpole predator. Neither the American toad Tadpoles nor the bullfrog Tadpoles responded behaviorally to the presence of mosquitofish cues. If Tadpoles are unable to respond to the presence of mosquitofish cues appropriately, then their ability to avoid predation by mosquitofish may be compromised and this may contribute to the impacts of mosquitofish on some Tadpole populations.