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T Curran

Publications and source records attributed to T Curran.

At least 73 records · Page 4Linked to original sources
PubMed1996

The redox/DNA repair protein, Ref-1, is essential for early embryonic development in mice.

The DNA-binding activity of AP-1 proteins is modulated, in vitro, by a posttranslational mechanism involving reduction oxidation. This mode of regulation has been proposed to control both the transcriptional activity and the oncogenic potential of Fos and Jun. Previous studies revealed that reduction of oxidized Fos and Jun by a cellular protein, Ref-1, stimulates sequence-specific AP-1 DNA-binding activity. Ref-1, a bifunctional protein, is also capable of initiating the repair of apurinic/apyrymidinic sites in damaged DNA. The relationship between the redox and DNA repair activities of Ref-1 is intriguing; both activities have been suggested to play an important role in the cellular response to oxidative stress. To investigate the physiological function of Ref-1, we used a gene targeting strategy to generate mice lacking a functional ref-1 gene. We report here that heterozygous mutant mice develop into adulthood without any apparent abnormalities. In contrast, homozygous mutant mice, lacking a functional ref-1 gene, die during embryonic development. Detailed analysis indicates that death occurs following blastocyst formation, shortly after the time of implantation. Degeneration of the mutant embryos is clearly evident at embryonic day 5.5. These findings demonstrate that Ref-1 is essential for early embryonic development.

Animals↗
PubMed1996

Functional NMDA receptors are transiently active and support the survival of Purkinje cells in culture.

Conflicting evidence exists concerning the activity of NMDA receptors (NMDARs) in cerebellar Purkinje cells and their possible functions. To investigate the activity of NMDARS, we used whole-cell recording on immunocytochemically identified Purkinje cells in primary culture. In addition, we used mice with a disrupted NMDAR1 gene that lack functional NMDARs (NR1-/-) to assess the physiological role of NMDARs. In cultures from normal mice, NMDA-medicated currents were detected in all identified Purkinje cells at 4 d in vitro (div). After 14 d, however, NMDA responses were reduced in amplitude, whereas the responses to kainate and glutamate increased steadily in amplitude. In addition, the NMDA-induced current displayed a pronounced desensitization at these later stages; peak current declined to zero during steady application of NMDA. At 7 div, the number of surviving Purkinje cells was less in cultures treated with NMDA antagonists, and their survival was dose-dependent. Purkinje cell survival was correspondingly poorer in cultures from the NR1-/- mice than in wild-type controls, suggesting that NMDAR activity enhances the survival of Purkinje cells in vitro. The addition of moderate doses of NMDA promoted the survival of wild-type Purkinje cells in the presence of tetrodotoxin. Feeder layers of cerebellar granule cells derived from wild-type or NR1-/- mice promoted survival of Purkinje cells to a similar degree, suggesting that the NMDAR in Purkinje cells, but not in other cells, is directly involved in Purkinje cell viability. The results demonstrate that NMDARs transiently produce membrane current in Purkinje cells and may serve as one of the epigenetic factors that support the survival of Purkinje cells in vitro.

Animals↗
PubMed1996

Recessive resistance to thyroid hormone in mice lacking thyroid hormone receptor beta: evidence for tissue-specific modulation of receptor function.

The diverse functions of thyroid hormone (T3) are presumed to be mediated by two genes encoding the related receptors, TRalpha and TRbeta. However, the in vivo functions of TRalpha and TRbeta are undefined. Here, we report that targeted inactivation of the mouse TRbeta gene results in goitre and elevated levels of thyroid hormone. Also, thyroid-stimulating hormone (TSH), which is released by pituitary thyrotropes and which is normally suppressed by increased levels of thyroid hormone, was present at elevated levels in homozygous mutant (Thrb-/-) mice. These findings suggest a unique role for TRbeta that cannot be substituted by TRalpha in the T3-dependent feedback regulation of TSH transcription. Thrb-/- mice provide a recessive model for the human syndrome of resistance to thyroid hormone (RTH) that exhibits a similar endocrine disorder but which is typically caused by dominant TRbeta mutants that are transcriptional inhibitors. It is unknown whether TRalpha, TRbeta or other receptors are targets for inhibition in dominant RTH; however, the analysis of Thrb-/- mice suggests that antagonism of TRbeta-mediated pathways underlies the disorder of the pituitary-thyroid axis. Interestingly, in the brain, the absence of TRbeta may not mimic the defects often associated with dominant RTH, since no overt behavioural or neuroanatomical abnormalities were detected in Thrb-/- mice. These data define in vivo functions for TRbeta and indicate that specificity in T3 signalling is conferred by distinct receptor genes.

Amino Acid Sequence↗
PubMed1996

Developmental expression of Fos-lacZ in the brains of postnatal transgenic rats.

Previously, we reported the production and characterization of fos-lacZ transgenic mice [41] and rats [19] that can be used to monitor both constitutive and evoked expression of c-fos in vivo. When we compared the sites of spontaneous fos-lacZ expression in the brains of developing transgenic fos-lacZ mice and rats, the patterns were almost identical. However, throughout the first postnatal month, the rat striatum contained a large number of Fos-lacZ-positive cells whereas only a few positive cells were seen in the mouse. By adulthood, the number of Fos-lacZ-positive cells in the rat striatum had declined dramatically to the low basal values seen in mice. To establish whether this species difference was evident in the adult striatum, rats and mice were treated with metamphetamine. This indirect D1 agonist, triggered a pronounced induction of fos-lacZ in the rat striatum while only a modest response was observed in the mouse. These data imply: (1) there are differences in dopamine-dependent stimulus-transcription coupling between the two species. (2) Maturation of dopaminergic signalling pathways may underlie the spontaneous immediate-early gene response in the developing rat striatum.

Amphetamines↗
PubMed1996

An enhanced immune response in mice lacking the transcription factor NFAT1.

Transcription factors of the NFAT family are thought to play a major role in regulating the expression of cytokine genes and other inducible genes during the immune response. The role of NFAT1 was investigated by targeted disruption of the NFAT1 gene. Unexpectedly, cells from NFAT1 -/- mice showed increased primary responses to Leishmania major and mounted increased secondary responses to ovalbumin in vitro. In an in vivo model of allergic inflammation, the accumulation of eosinophils and levels of serum immunoglobulin E were increased in NFAT1 -/- mice. These results suggest that NFAT1 exerts a negative regulatory influence on the immune response.

Amino Acid Sequence↗
PubMed1996

Phosphorylation of c-Fos at the C-terminus enhances its transforming activity.

c-Fos is phosphorylated by MAP kinase and the 90 kDa-ribosomal S6 kinase (RSK) in vitro at serines 362 and 374 (rat) which we demonstrate are major in vivo phosphorylation sites in early G1. We have constructed c-Fos mutants with these serines changed to aspartic acid residues (FosD) to mimic phosphorylation or to alanine residues (FosA) to prevent phosphorylation. Cells expressing FosD exhibited a more extensive transformed phenotype than those expressing either FosA or wild type c-Fos (FosWT). We also observed that FosA has a reduced half-life in comparison with FosD in G1. Furthermore, we observed enhanced AP-1 transactivation activity in cells expressing FosD. These results indicate that phosphorylation of c-Fos at its extreme carboxyterminus, possibly by MAP kinase and RSK, supports the proliferative response by increasing c-Fos stability and/or by increasing its transactivation activity. Under conditions in which the MAP kinase pathway is constitutively activated, c-Fos phosphorylation probably contributes to cellular transformation. The highly conserved nature of these phosphorylation sites in other c-fos family members suggests that these may also be targets of MAP kinase and RSK.

3T3 Cells↗
PubMed1996

Ubiquitinylation of transcription factors c-Jun and c-Fos using reconstituted ubiquitinylating enzymes.

Recombinant c-Jun and c-Fos were ubiquitinylated by the ubiquitin carrier enzymes E214K, E220K, or E232K in the presence of the ubiquitin-activating enzyme, E1. Addition of ubiquitin protein ligase E3 substantially enhanced the E214K-mediated ubiquitinylation of c-Jun and c-Fos. Truncated c-Jun and c-Fos mutant proteins including wbJun and wbFos were also ubiquitinylated under the same conditions, suggesting the sites of ubiquitinylation are located within the dimerization and DNA binding domains of c-Jun and c-Fos. The E3-dependent ubiquitinylation of c-Jun was inhibited upon the heterodimerization of c-Jun with c-Fos. Further addition of E220K significantly enhanced ubiquitinylation of c-Jun in the heterodimer suggesting a regulatory role of E220K. Polyubiquitinylated c-Jun, wbFos, and wbJun, but not E220K-ubiquitinylated c-Jun, were readily degraded by the ATP-dependent 26 S multicatalytic proteases. These results suggest that the temporal control of c-Jun and c-Fos may be regulated through the ubiquitinylation pathways, and the ubiquitinylation of c-Jun and c-Fos may in turn be regulated in response to the heterodimerization between them and the cooperation between E220K and E3 mediated polyubiquitinylation.

Adenosine Triphosphate↗
PubMed1996

False recognition and the right frontal lobe: a case study.

We described a patient, BG, who exhibited a striking pattern of false recognition after an infarction of the right frontal lobe. Seven experiments document the existence of the phenomenon, explore its characteristics, and demonstrate how it can be eliminated. BG showed pathologically high false alarm rates when stimuli were visual words (experiments 1 and 4), auditory words (experiment 2), environmental sounds (experiment 3), pseudowords (experiment 5), and pictures (experiment 7). His false alarms were not merely attributable to the semantic or physical similarity of studied and non-studied items (experiments 4 and 5). However, BG's false recognitions were virtually eliminated by presenting him with categorized stimuli and testing him with new stimuli from non-studied categories (experiments 6 and 7). The results suggest that BG's false alarms may be attributable to an over-reliance on memory for general characteristics of the study episode, along with impaired memory for specific items. The damaged right frontal lobe mechanisms may normally support the monitoring and/or retrieval processes that are necessary for item-specific recognition.

Aged↗
PubMed1996

Detection of the reelin breakpoint in reeler mice.

Disruption of the reelin gene by partial deletion causes the neurological phenotype known as reeler. Here we report the cloning and sequencing of the reelin breakpoint region from the Jackson reeler strain (rl). Based on this sequence, we developed a polymerase chain reaction screen that allows the identification of mutant mice prior to the appearance of the phenotype. The assay also permits discrimination of heterozygous from wild-type mice. These findings provide a strategy for the characterization of the early anatomical and physiological consequences of the reeler mutation.

Animals↗
PubMed1996

Neuroanatomical correlates of veridical and illusory recognition memory: evidence from positron emission tomography.

Memory distortions and illusions have been thoroughly documented in psychological studies, but little is known about the neuroanatomical correlates of true and false memories. Vivid but illusory memories can be induced by asking people whether they recall or recognize words that were not previously presented, but are semantically related to other previously presented words. We used positron emission tomography to compare brain regions involved in veridical recognition of printed words that were heard several minutes earlier and illusory recognition of printed words that had not been heard earlier. Veridical and illusory recognition were each associated with blood flow increases in a left medial temporal region previously implicated in episodic memory; veridical recognition was distinguished by additional blood flow increases in a left temporoparietal region previously implicated in the retention of auditory/phonological information. This study reveals similarities and differences in the way the brain processes accurate and illusory memories.

Acoustic Stimulation↗
PubMed1996

Visual specificity effects on word stem completion: beyond transfer appropriate processing?

An important, but poorly understood, aspect of memory retrieval concerns the conditions under which priming is influenced by perceptual changes in the form of target items. According to transfer appropriate processing perspectives, perceptual specificity effects on priming require a study task that focuses attention on the perceptual, rather than semantic, features of the items. Other research suggests that perceptual specificity effects are enhanced by conditions yielding high levels of explicit memory. The present experiments manipulated encoding tasks and other variables known to influence explicit memory (repetition and retention interval) in order to gain insight into the determinants of perceptual specificity effects on visual word-stem completion. In Experiment 1 we found that perceptual specificity (letter case) effects on stem completion priming depend on perceptual encoding when subjects' awareness of the study-test relationship is limited. In Experiments 2-4 we found that perceptual specificity effects can be obtained after semantic encoding--especially when the study-test retention interval is short. Perceptual specificity effects after short retention intervals were independent of encoding task, and may reflect a form of involuntary explicit memory.

Adult↗
PubMed1996

Thyroid hormone receptor beta is essential for development of auditory function.

Congenital thyroid disorders are often associated with profound deafness, indicating a requirement for thyroid hormone (T3) and its receptors in the development of hearing. Two T3 receptor genes, Tr alpha and Tr beta are differentially expressed, although in overlapping patterns, during development. Thus, the extent to which they mediate unique or redundant functions is unclear. We demonstrate that Tr beta-deficient (Thrb-/-) mice exhibit a permanent deficit in auditory function across a wide range of frequencies, although they show no other overt neurological defects. The auditory-evoked brainstem response (ABR) in Thrb-/- mice, although greatly diminished, displayed normal waveforms, which suggested that the primary defect resides in the cochlea. Although hypothyroidism causes cochlear malformation, there was no evidence of this in Thrb-/- mice. These findings suggest that Tr beta controls the maturation of auditory function but not morphogenesis of the cochlea. Thrb-/- mice provide a model for the human endocrine disorder of resistance to thyroid hormone (RTH), which is typically associated with dominant mutations in Tr beta. However, deafness is generally absent in RTH, indicating that dominant and recessive mutations in Tr beta have different consequences on the auditory system. Our results identify Tr beta as an essential transcription factor for auditory development and indicate that distinct Tr genes serve certain unique functions.

Animals↗
PubMed1996

Fos-Jun dimerization promotes interaction of the basic region with TFIIE-34 and TFIIF.

The regulation of RNA polymerase II-mediated transcription involves both direct and indirect interactions among regulatory proteins and the general transcription factors (GTFs) that assemble at TATA-containing promoters. Here we show that the oncogenic transcription factors Fos and Jun make direct physical contacts with three proteins of the basal transcription apparatus, TFIIE-34 (TFIIE-beta), TFIIF-30 (RAP30), and TFIIF-74 (RAP74). The interactions among the activator proteins and these three GTFs were not detected with other transcription factors, including some bZIP protein family members. Both coimmunoprecipitation and protein blotting experiments demonstrated that the interactions were strongly favored by dimerization of Fos and Jun and that they involved the basic region and basic region-proximal domain of both proteins. Mutations within the DNA-binding domains of Fos and Jun abolished binding to GTFs, although the presence of DNA was not required for the association. Surprisingly, only a single basic region in the context of a protein dimer was sufficient for the interaction. Squelching of AP-1-dependent transcription in vitro by an excess of Fos-Jun dimers was relieved by the addition of TFIIE, indicating that it is a direct functional target of Fos and Jun. These results suggest that dimerization induces a conformational alteration in the basic region of Fos and Jun that promotes an association with TFIIE-34 and TFIIF, thus contributing to transcription initiation.

Animals↗
PubMed1996

Genetic analysis of thyroid hormone receptors in development and disease.

Thyroid hormone (T3) fulfills diverse functions in vertebrate development and physiology. These functions are thought to be mediated by two genes encoding the related T3 receptors. TR alpha and TR beta. The use of homologous recombination in embryonic stem cells to generate defined, single-gene mutations provides a powerful means to investigate the individual functions of TR alpha and TR beta in mice. We have shown that targeted inactivation of the TR beta gene results in goiter and elevated levels of thyroid hormone. Thyroid stimulating hormone (TSH), which is released by pituitary thyrotropes and is normally suppressed by increased levels of thyroid hormone, was present at elevated levels in homozygous mutant (Thrb-/-) mice. These findings suggest a unique role for TR beta that cannot be substituted by TR alpha in the T3-dependent feedback regulation of TSH transcription. Thrb-/- mice provide a recessive model for the human syndrome of resistance to thyroid hormone (RTH). Typically, RTH is associated with dominant mutations in TR beta. It is unknown whether TR alpha, TR beta, or other receptors are targets for inhibition in dominant RTH; however, the analysis of Thrb-/- mice suggests that antagonism of TR beta-mediated pathways underlies the disorder of the pituitary-thyroid axis. Thrb-/- mice also display defective maturation of auditory function, demonstrating that TR beta is essential for the development of hearing. Interestingly, hearing defects are generally absent in dominant RTH, indicating that in the auditory system, a dominant TR beta mutant cannot mimic the defect caused by loss of TR beta. This suggests the existence of tissue-specific mechanisms that modulate the activity of TR beta. These results define in vivo functions for TR beta and indicate that specificity in T3 signaling is conferred by distinct receptor genes.

Animals↗
PubMed1995

Spontaneous and evoked glutamate signalling influences Fos-lacZ expression and pyramidal cell death in hippocampal slice cultures from transgenic rats.

Previously, we established that a spatially and temporally predictable pattern of spontaneous cell death occurs in pyramidal hippocampal neurons maintained in organotypic slice cultures. We have begun to examine the signalling events that may be relevant to this process by analyzing the expression of cellular immediate-early genes (cIEGs). In the present studies, organotypic hippocampal cultures were generated from transgenic rats that carry a fos-lacZ fusion gene. beta-Galactosidase activity in these rats accurately recapitulates Fos expression. An association was observed between cell death, as determined by propidium iodide (PI) staining, and Fos-lacZ expression. There was a consistent rise in beta-galactosidase activity in vulnerable regions 1-2 days before the peak of spontaneous neuronal death. Long-term treatment with TTX, CNQX, or D,L-APV inhibited the spontaneous neuronal death as well as Fos-lacZ expression. Furthermore, Fos-lacZ induction and cell death could be evoked by removal of these receptor antagonists or by application of the excitotoxin, kainic acid. The association between cIEG expression and cell death, shown here and by others, suggests that these genes contribute to regulatory events involved with cell death and/or protection.

Animals↗
PubMed1995

Use of fluorescence resonance energy transfer to estimate intramolecular distances in the Msx-1 homeodomain.

We have utilized fluorescence resonance energy transfer (FRET) to investigate the spatial proximities of segments in the Msx-1 homeodomain (Msx). This strategy makes use of a single, invariant tryptophan (Trp-48) in helix III as the donor for FRET. The acceptor molecule, 5-[[[(iodoacetyl)amino]-ethyl]amino]naphthalene-1-sulfonic acid (AEDANS), was incorporated into Msx at positions 6, 10, or 27 which are within the N-terminal arm, and helices I and II since these segments have been implicated in interactions with helix III. Specific incorporation of AEDANS was achieved by using a two-step strategy consisting of site-directed mutagenesis for introducing unique cysteine residues at the selected positions followed by covalent modification of these cysteine residues with AEDANS. Using this approach, we demonstrated energy transfer between Trp-48 and the AEDANS-labeled cysteines at positions 6, 10, and 27 and estimated the distances between the Trp-48 and AEDANS pairs to be 19, 23, and 16 A, respectively. We further demonstrated that FRET provides a strategy for detecting subtle alterations in protein conformation that result from replacement of specific residues in helix III and the N-terminal arm. Together, these findings show that FRET provides a useful approach for estimating intramolecular distances and for examining the conformation of Msx. Moreover, given the fact that Trp-48 is invariant among all homeodomain sequences, we propose that FRET will provide a general approach for facilitating comparative analyses of homeodomain conformations.

Amino Acid Sequence↗