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L Lacroix

Publications and source records attributed to L Lacroix.

At least 37 records · Page 2Linked to original sources
PubMed2000

Expression of Na+/I- symporter and Pendred syndrome genes in trophoblast cells.

Placental iodide transport is critical for the fetal thyroid function, but the molecular mechanisms of this transport are not understood. The expression of two recently identified iodide transporters, namely the sodium/iodide symporter (NIS) and pendrin, the product of the gene responsible for the Pendred syndrome (PDS), was studied using real-time kinetic quantitative PCR and immunohistochemistry 1) in placental tissues collected at different gestational ages and 2) in primary cultures of villous cytotrophoblast cells (VCT) that differentiate and fuse over 2-3 days in vitro to form villous syncytiotrophoblast (VSCT) cells. Both NIS and PDS genes are expressed in placenta, albeit at low levels compared with those in thyroid tissue. NIS gene expression in placental samples from first trimester and term pregnancies was similar. In contrast, the expression of PDS gene was higher in term than in first trimester pregnancy samples. In vitro, NIS gene was expressed at a high level in VCT obtained from first trimester pregnancy, and its expression decreased by 3- to 4-fold during the differentiation of VCT in VSCT. Expression of NIS was lower (up to 30-fold) in VCT obtained in placental samples from third trimester than from first trimester pregnancy. In contrast, the expression of PDS gene was low in VCT and increased by 5- to 10-fold during VSCT formation; this was observed in cells isolated from placental samples of both first trimester and term pregnancies. Immunohistochemical analysis showed that NIS protein was present on the entire membrane of VCT, whereas pendrin was mainly located at the brush border membrane of VSCT, facing the mother. In conclusion, 1) NIS and PDS genes are differently expressed in the placenta during gestation; and 2) whereas pendrin is expressed at the brush border membrane of syncytiotrophoblast cells, NIS protein is mainly located in the cytotrophoblast layer.

Carrier Proteins↗
PubMed1999

Energetics of strand-displacement reactions in triple helices: a spectroscopic study.

DNA triple helices offer exciting new perspectives toward oligonucleotide-directed inhibition of gene expression. Purine and GT triplexes appear to be the most promising motifs for stable binding under physiological conditions compared to the pyrimidine motif, which forms at relatively low pH. There are, however, very little data available for comparison of the relative stabilities of the different classes of triplexes under identical conditions. We, therefore, designed a model system which allowed us to set up a competition between the oligonucleotides of the purine and pyrimidine motifs targeting the same Watson-Crick duplex. Several conclusions may be drawn: (i) a weak hypochromism at 260 nm is associated with purine triplex formation; (ii) delta H degree of GA, GT and TC triplex formation (at pH 7.0) was calculated as -0.1, -2.5 and -6.1 kcal/mol per base triplet, respectively. This unexpectedly low delta H degree for the purine triple helix formation implies that its delta G degree is nearly temperature-independent and it explains why these triplexes may still be observed at high temperatures. In contrast, the pyrimidine triplex is strongly favoured at lower temperatures; (iii) as a consequence, in a system where two third-strands compete for triplex formation, displacement of the GA or GT strand by a pyrimidine strand may be observed at neutral pH upon lowering the temperature. This original purine-to-pyrimidine triplex conversion shows a significant hypochromism at 260 nm and a hyperchromism at 295 nm which is similar to the duplex-to-triplex conversion in the pyrimidine motif. Further evidence for this triplex-to-triplex conversion is provided by mung bean-nuclease foot-printing assay.

Base Pairing↗
PubMed1999

Triplex formation by oligonucleotides containing 5-(1-propynyl)-2'-deoxyuridine: decreased magnesium dependence and improved intracellular gene targeting.

Oligonucleotides capable of sequence-specific triple helix formation have been proposed as DNA binding ligands useful for modulation of gene expression and for directed genome modification. However, the effectiveness of such triplex-forming oligonucleotides (TFOs) depends on their ability to bind to their target sites within cells, and this can be limited under physiologic conditions. In particular, triplex formation in the pyrimidine motif is favored by unphysiologically low pH and high magnesium concentrations. To address these limitations, a series of pyrimidine TFOs were tested for third-strand binding under a variety of conditions. Those containing 5-(1-propynyl)-2'-deoxyuridine (pdU) and 5-methyl-2'-deoxycytidine (5meC) showed superior binding characteristics at neutral pH and at low magnesium concentrations, as determined by gel mobility shift assays and thermal dissociation profiles. Over a range of Mg2+ concentrations, pdU-modified TFOs formed more stable triplexes than did TFOs containing 2'-deoxythymidine. At 1 mM Mg2+, a DeltaTm of 30 degreesC was observed for pdU- versus T-containing 15-mers (of generic sequence 5' TTTTCTTTTTTCTTTTCT 3') binding to the cognate A:T bp rich site, indicating that pdU-containing TFOs are capable of substantial binding even at physiologically low Mg2+ concentrations. In addition, the pdU-containing TFOs were superior in gene targeting experiments in mammalian cells, yielding 4-fold higher mutation frequencies in a shuttle vector-based mutagenesis assay designed to detect mutations induced by third-strand-directed psoralen adducts. These results suggest the utility of the pdU substitution in the pyrimidine motif for triplex-based gene targeting experiments.

Animals↗
PubMed1999

Two different schedules for integrating filgrastim as adjuvant therapy in the treatment of patients with advanced stage Hodgkin's lymphoma receiving MOPP/ABV hybrid chemotherapy.

PURPOSE: Management of advanced-stage Hodgkin's disease with a MOPP/ABV hybrid regimen (mechlorethamine, vincristine, procarbazine, prednisone, Adriamycin, bleomycin and vinblastine) has yielded a high complete response rate (75-85%). However, myelosuppression can limit delivery of treatment. Filgrastim has been shown to reduce chemotherapy-related neutropenia and allow for on-time administration of planned doses of chemotherapeutic agents. The objective of this study was to find the best way to integrate filgrastim with the MOPP/ABV hybrid regimen. METHODS: Enrolled in this study were 24 patients (aged 18-52 years) with newly diagnosed, histologically documented Hodgkin's disease. In schedule I, patients received filgrastim (5 microg/kg s.c. daily) beginning on day 9, 24 h after administration of ABV. In schedule II, patients received filgrastim concomitantly with procarbazine on days 2-7 (starting 24 h after day-1 MOPP administration and stopping 24 h before ABV administration) as well as after ABV beginning on day 9. Filgrastim after ABV administration was administered until two consecutive ANC readings of 10 x 10(9)/l were achieved. RESULTS: All patients were able to complete all six cycles of therapy. There was a trend to fewer dose reductions in schedule II (0.76%) as compared to schedule I (4.2%) with a P-value of 0.077 (chi-squared test). Specifically, 11.6% of MOPP courses and 5.5% of ABV courses were dose-reduced in schedule I versus 1.7% and 1.4%, respectively, in schedule II. CONCLUSION: In conclusion, filgrastim was effective in supporting the delivery of the MOPP/ABV chemotherapy. Concomitant administration of filgrastim with procarbazine (days 2-7) appears to be safe and allows the maximum dose intensity of this therapy.

Adolescent↗
PubMed1999

Expression of the Na+/I- symporter gene in human thyroid tumors: a comparison study with other thyroid-specific genes.

The expression of 4 thyroid tissue-specific genes [Na+/I- symporter (NIS), thyroid peroxidase (TPO), thyroglobulin (Tg), TSH receptor (TSH-R)] as well as of the glucose transporter type 1 (Glut1) gene was analyzed in 90 human thyroid tissues Messenger ribonucleic acids were extracted from 43 thyroid carcinomas (38 papillary and 5 follicular), 24 cold adenomas, 5 Graves' thyroid tissues, 8 toxic adenomas, and 5 hyperplastic thyroid tissues; 5 normal thyroid tissues were used as reference. A kinetic quantitative PCR method, based on the fluorescent TaqMan methodology and real-time measurement of fluorescence, was used. NIS expression was decreased in 40 of 43 thyroid carcinomas (10- to 1200-fold) and in 20 of 24 cold adenomas (2- to 700-fold); it was increased in toxic adenomas and Graves' thyroid tissues (up to 140-fold). TPO expression was decreased in thyroid carcinomas, but was normal in cold adenomas; it was increased in toxic adenomas and Graves' thyroid tissues Tg expression was decreased in thyroid carcinomas, but was normal in the other tissues. TSH-R expression was normal in most tissues studied and was decreased in only some thyroid carcinomas. In thyroid cancer tissues, a positive relationship was found between the individual levels of expression of NIS, TPO, Tg and TSH-R. No relationship was found with the age of the patient. Higher tumor stages (stages >I vs stage I) were associated with lower expression of NIS (P = 0.03) and TPO (P < 0.01). Expression of the Glut1 gene was increased in 1 of 24 adenomas and in 8 of 43 thyroid carcinomas. In 6 thyroid carcinoma patients, 131I uptake was studied in vivo; NIS expression was low in all samples; 3 patients with normal Glut-1 gene expression had 131I uptake in metastases, whereas the other 3 patients with increased Glut-1 gene expression had no detectable 131I uptake. In conclusion, this study shows 1) a reduced expression of NIS gene in most hypofunctioning benign and malignant thyroid tumors; 2) a differential regulation of the expression of thyroid-specific genes; 3) an increased expression of Glut-1 gene in some malignant tumors that may suggest a role for glucose derivative tracers to detect in vivo thyroid cancer metastases by positron emission tomography scanning.

Adenocarcinoma, Follicular↗
PubMed1998

Kinetics and thermodynamics of i-DNA formation: phosphodiester versus modified oligodeoxynucleotides.

At slightly acidic or even neutral pH, oligodeoxynucleotides that include a stretch of cytidines have been shown to form a tetrameric structure in which two parallel-stranded duplexes have their hemiprotonated C.C+base pairs face to face and fully intercalated, in a so-called i-motif. Cytosine-rich pyrimidine oligodeoxynucleotides can form an intramolecular i-motif. We have studied the ability of several DNA analogs to fold into this structure. Evidence for folding was provided by thermal denaturation. We have shown that phosphorothioate and phosphodiester oligodeoxynucleotides, but not methylphosphonate or PNA oligomers, may form the i-motif. Four different PS oligodeoxynucleotides were compared with their PO counterparts. In all cases, the melting temperature (Tm) of the phosphorothioate oligomer was equal or slightly inferior (by 2-3 degreesC) to the Tmof the natural oligodeoxynucleotide. For long oligodeoxynucleotides, a small change of pH leads to a completely different melting profile: the curves are reversible at pH 6.4 or lower, and a hysteresis is obtained at pH 6.8 or higher; cooling and heating curves were not superimposed, allowing us to determine the rate constants of association (kon) and dissociation (koff) as a function of the temperature: these rate constants give linear Arrhenius plots, in agreement with the prediction of the two-state model of association-dissociation. The activation energy Eonis strongly negative and, at neutral pH, the phosphorothioate associates and dissociates nine times faster than the phosphodiester oligodeoxynucleotide of identical sequence.

Base Sequence↗
PubMed1998

Following G-quartet formation by UV-spectroscopy.

Oligodeoxynucleotides which include stretches of guanines form a well-known tetrameric structure. We show that the recording of reversible absorbance changes at 295 nm allows to precisely monitor intramolecular guanine (G)-quartet formation and dissociation. Accurate Tm and thermodynamic values could be easily extracted from the data, whereas classical recordings at 260 nm led to a much larger uncertainty and in extreme cases, to completely inaccurate measurements. This inverted denaturation profile was observed for all G-quartet-forming oligonucleotides studied so far. This technique is very useful in all cases where intramolecular or intermolecular quadruplex formation is suspected.

DNA↗
PubMed1998

The effects of excitotoxic lesion of the medial prefrontal cortex on latent inhibition, prepulse inhibition, food hoarding, elevated plus maze, active avoidance and locomotor activity in the rat.

Latent inhibition is a measure of retarded conditioning to a previously presented nonreinforced stimulus that is impaired in schizophrenic patients and in rats treated with amphetamine. In terms of neural substrates, latent inhibition depends on the integrity of the nucleus accumbens and the inputs to this structure from the hippocampal formation and adjacent cortical areas. Since another major source of input to the nucleus accumbens is the medial prefrontal cortex, and there are numerous demonstrations that manipulations of this region can modify ventral striatal dopamine, we investigated the effects of N-methyl-D-aspartate lesion to the medial prefrontal cortex on latent inhibition, assessed in an off-baseline conditioned emotional response procedure in rats licking for water. In addition, the effects of the medial prefrontal cortex lesion were assessed on a battery of tasks potentially sensitive to medial prefrontal cortex damage, including spontaneous and amphetamine-induced activity, elevated plus maze exploration, food hoarding, prepulse inhibition, and active avoidance. The lesion decreased hoarding behaviour and increased spontaneous exploratory activity in the open field, while exerting only mild effects on amphetamine-induced activity. Prepulse inhibition, exploration of the elevated plus maze, and the acquisition of two-way active avoidance were unaffected by the lesion. Likewise, latent inhibition was left intact following the lesion, suggesting that neither the destruction of the intrinsic cells of the medial prefrontal cortex nor any potential lesion-induced changes in subcortical dopamine, affect latent inhibition.

Acoustic Stimulation↗
PubMed1998

Mutagenesis mediated by triple helix-forming oligonucleotides conjugated to psoralen: effects of linker arm length and sequence context.

Targeted mutagenesis and gene knock-out can be mediated by triple helix-forming oligonucleotides (TFO) linked to mutagenic agents, such as psoralen. However, this strategy is limited by the availability of homopurine/homopyrimidine stretches at or near the target site because such sequences are required for high-affinity triplex formation. To overcome this limitation, we have tested TFO conjugated to psoralen via linker arms of lengths varying from 2 to 86 bonds, thereby designed to deliver the psoralen at varying distances from the third strand binding site present at the 3' end of the supFG1 mutation reporter gene. Following triplex formation and UVA irradiation, mutations were detected using an SV40-based shuttle vector assay in human cells. The frequency and distribution of mutations depended on the length of the linker arm. Precise targeting was observed only for linker arms of length 2 and 6, which also yielded the highest mutation frequencies (3 and 14%, respectively). Psoralen-TFO with longer tethers yielded mutations at multiple sites, with the maximum distance from the triplex site limited by the linker length but with the distribution within that range influenced by the propensity for psoralen intercalation at A:T base-pair-rich sites. Thus, gene modification can be extended beyond the site of third strand binding but with a decrease in the precision of the targeting.

Cell Line↗
PubMed1996

Inability of RNA to form the i-motif: implications for triplex formation.

At slightly acidic or even neutral pH, oligodeoxyribonucleotides which include stretches of cytidines form a tetrameric structure involving C.C+ base pairs in a so-called i-motif. Such a structure, which is very stable at pH 6, is still detectable at neutral pH. This motif, whether intramolecular or intermolecular, was shown to act as an undesired, competing structure for triplex formation. Depending on the sequence and the experimental conditions, triple helix formation was inhibited or completely abolished. Thus, the sequence recognition repertoire of pyrimidine DNA third strands is more restricted than previously admitted; only T.A rich-oligopurine-oligopyrimidine sequences are amenable to triplex formation. On the other hand, cytosine-rich RNA oligoribonucleotides and their 2'-O-methyl derivatives were unable to form a stable autoassociated structure above pH 6. Concomitantly, they were shown to form a triplex with (C.G)-rich targets at pH 6. Thus, not only was the affinity for the duplex increased by DNA to RNA substitution, but the possibility of formation of an inactive form of the third strand was greatly reduced. Thus, i-motif formation is favored for cytosine-rich oligodeoxynucleotides, whereas triplex formation is favored for oligoribonucleotides. These properties make RNA pyrimidine oligonucleotides an attractive choice for triplex formation on a (C.G)-rich target, extending the practical sequence repertoire of pyrimidine triplexes to (C.G*C+)-rich sequences.

Base Sequence↗
PubMed1994

Translational enhancement of H-ferritin mRNA by interleukin-1 beta acts through 5' leader sequences distinct from the iron responsive element.

Interleukin-1 beta (Il-1 beta), a key cytokine in the acute phase response, elevates hepatic expression of both the heavy (H) and light (L) ferritin subunits without influencing the steady-state levels of either ferritin transcript. Transfection experiments with human hepatoma cells reveal that sequences within the 5' untranslated region (5'UTR) of H-ferritin mRNA confer translational regulation to chimaeric chloramphenicol acetyl transferase (CAT) mRNAs in response to Il-1 beta in the absence of marked changes in CAT mRNA levels. Il-1 beta dependent translational enhancement is mediated by a distinct G + C rich RNA sequence within 70 nucleotides (nt) of the start codon. The upstream Iron Responsive Element RNA stemloop does not confer increased expression to CAT mRNA in Il-1 beta stimulated hepatoma transfectants. A 38 nucleotide consensus sequence within the 5'UTRs of the mRNAs encoding the hepatic acute phase proteins alpha 1-antitrypsin (alpha 1AT), alpha 1-acid glycoprotein (AGP) and haptoglobin (Dente et al., 1985) is similar to sequences in the G + C rich H-ferritin mRNA translational regulatory element. Deletion of three nucleotides from this region of the 61 nt G + C rich element in the H-ferritin mRNA 5' leader eliminates Il-1 beta translational enhancement of the CAT reporter transcripts.

Base Sequence↗
PubMed1992

Hydroxyurea and erythropoietin therapy in sickle cell anemia.

Hydroxyurea has been shown to increase fetal hemoglobin (Hb F) production in patients with sickle cell disease and therefore has the potential to alleviate both the hemolytic and vaso-occlusive manifestations of the disease. Preliminary evidence indicates that recombinant human erythropoietin (rhEpo) may also induce Hb F. Three sickle cell anemia patients were treated with escalating doses of intravenous rhEpo and, subsequently, with daily oral hydroxyurea. After the optimal hydroxyurea dose was attained, rhEpo was added again. Two additional patients were treated with hydroxyurea alone. Treatment with rhEp, either alone or in combination with hydroxyurea, had no significant effect on the percentage of F reticulocytes or F cells. In contrast, hydroxyurea treatment was associated with a 1.5-fold to sevenfold increase in F cells and a 2.3- to 27-fold increase in the percentage of Hb F. In the three patients whose response reached a plateau, hydroxyurea treatment was associated with lessened hemolysis, decreased serum bilirubin and lactate dehydrogenase levels, and prolonged 51chromium-labeled RBC survival. Hydroxyurea treatment also resulted in decreased numbers of irreversibly sickled cells and in decreased sickling at partial oxygen saturation, increased oxygen affinity, increased total RBC cation content, and diminished potassium:chloride co-transport. All five patients treated with hydroxyurea experienced a decrease in severity and frequency of painful sickle crises. This study confirms that hydroxyurea therapy increases Hb F production and provides objective evidence of a significant reduction in hemolytic rate and intracellular polymerization. In contrast, rhEpo, either alone or in combination with hydroxyurea, offered no measurable benefit. Based on these encouraging preliminary data, large-scale, controlled clinical trials are warranted to study the safety and efficacy of hydroxyurea in the treatment of sickle cell disease.

Administration, Oral↗
PubMed1990

[Suicide and social policy in Quebec].

Starting from three documents published by organizations set up by the Québec government, the author examines how the government intends to give direction to and build a framework for social intervention in the area of suicide. The article looks at the fate that social policies could and, according to the author, should reserve for suicide. The author argues for an approach that fully recognizes the social dimension of suicide and that emphasizes primary prevention as well as government support for an autonomous community network that would have equal footing with the public network.

Health Policy↗
PubMed1981

Regulation of the expression of leghaemoglobin genes in effective and ineffective root nodules of soybean.

The expression of leghaemoglobin genes in effective and ineffective (unable to fix nitrogen) root nodules of soybean developed by Rhizobium japonicum strains 61A76, 61A24 and SM5 was measured by using a cDNA probe or a cloned leghaemoglobin sequence and in vitro translation of Lb-mRNA. Hybridization of the poly(A)-containing nodule polysomal RNA from 3-week-old nodules with a kinetically purified Lb-cDNA or with plasmid (pLbl) containing a leghaemoglobin sequence showed that Lb-mRNA is present in ineffective nodules formed by strains SM5 and 61A24 at reduced levels. Of the two major classes of electrophoretically distinguishable leghaemoglobins in soybean, LbS was not synthesized in 3-week-old strain 61A24-induced nodules while both sorts of leghaemoglobin were synthesized and accumulated in ineffective nodules formed by strain SM5 of Rhizobium. Ineffective nodules formed by strain 61A24 are green inside and do not appear to accumulate leghaemoglobin as measured by the haemochromogen assay, although low levels of apoleghaemoglobin were detected using leghaemoglobin antibodies. SM5-induced nodules were found to have about half as much as leghaemoglobin of the of effective (61A76-induced) nodules. This study demonstrates that while the appearance of leghaemoglobin is independent of nitrogenase activity in bacteroids, its synthesis is influenced to different degrees both by a mutation (SM5) and incompatibility (61A24) of Rhizobium. The primary regulation appears to be at the level of transcription or processing of mRNA since ineffective nodules contain Lb-mRNA approximately in proportion to the amount of apoleghaemoglobin present in these nodules.

Gene Expression Regulation↗