Stéphanie Guénin

The lack of a systematic validation of reference genes: a serious pitfall undervalued in reverse transcription-polymerase chain reaction (RT-PCR) analysis in plants.

Reverse transcription-polymerase chain reaction (RT-PCR) approaches have been used in a large proportion of transcriptome analyses published to date. The accuracy of the results obtained by this method strongly depends on accurate transcript normalization using stably expressed genes, known as references. Statistical algorithms have been developed recently to help validate reference genes, and most studies of gene expression in mammals, yeast and bacteria now include such validation. Surprisingly, this important approach is under-utilized in plant studies, where putative housekeeping genes tend to be used as references without any appropriate validation. Using quantitative RT-PCR, the expression stability of several genes commonly used as references was tested in various tissues of Arabidopsis thaliana and hybrid aspen (Populus tremula x Populus tremuloides). It was found that the expression of most of these genes was unstable, indicating that their use as references is inappropriate. The major impact of the use of such inappropriate references on the results obtained by RT-PCR is demonstrated in this study. Using aspen as a model, evidence is presented indicating that no gene can act as a universal reference, implying the need for a systematic validation of reference genes. For the first time, the extent to which the lack of a systematic validation of reference genes is a stumbling block to the reliability of results obtained by RT-PCR in plants is clearly shown.

Comprehensive expression profiling of the pectin methylesterase gene family during silique development in Arabidopsis thaliana

Pectin methylesterases (PME, EC. 3.1.1.11) are enzymes that demethylesterify plant cell wall pectins in muro. In Arabidopsis thaliana, putative PME proteins are thought to be encoded by a 66-member gene family. This study used real-time RT-PCR to gain an overview of the expression of the entire family at eight silique developmental stages, in flower buds and in vegetative tissue in the Arabidopsis. Only 15% of the PMEs were not expressed at any of the developmental stages studied. Among expressed PMEs, expression data could be clustered into five distinct groups: 19 PMEs highly or uniquely expressed in floral buds, 4 PMEs uniquely expressed at mid-silique developmental stages, 16 PMEs highly or uniquely expressed in silique at late developmental stages, 16 PMEs mostly ubiquitously expressed, and 1 PME with a specific expression pattern, i.e. not expressed during early silique development. Comparison of expression and phylogenetic profiles showed that, within phylogenetic group 2, all but one PME belong to the floral bud expression group. Similar results were shown for a subset of one of the phylogenetic group, which differed from others by containing most of the PMEs that do not possess any PRO part next to their catalytic part. Expression data were confirmed by two promoter:GUS transgenic plant analysis revealing a PME expressed in pollen and one in young seeds. Our results highlight the high diversity of PME expression profiles. They are discussed with regard to the role of PMEs in fruit development and cell growth.

IGF-1 activates hEAG K(+) channels through an Akt-dependent signaling pathway in breast cancer cells: role in cell proliferation.

Previous work from our laboratory has shown that human ether à go‐go (hEAG) K+ channels are crucial for breast cancer cell proliferation and cell cycle progression. In this study, we investigated the regulation of hEAG channels by an insulin‐like growth factor‐1 (IGF‐1), which is known to stimulate cell proliferation. Acute applications of IGF‐1 increased K+ current‐density and hyperpolarized MCF‐7 cells. The effects of IGF‐1 were inhibited by hEAG inhibitors. Moreover, IGF‐1 increased mRNA expression of hEAG in a time‐dependent manner in parallel with an enhancement of cell proliferation. The MCF‐7 cell proliferation induced by IGF‐1 is inhibited pharmacologically by Astemizole or Quinidine or more specifically using siRNA against hEAG channel. Either mitogen‐activated protein kinase (MAPK) or phosphatidylinositol 3‐kinase (PI3K) are known to mediate IGF‐1 cell proliferative signals through the activation of extracellular signal‐regulated kinase 1/2 (Erk 1/2) and Akt, respectively. In MCF‐7 cells, IGF‐1 rapidly stimulated Akt phosphorylation, whereas IGF‐1 had little stimulating effect on Erk 1/2 which seems to be constitutively activated. The application of wortmannin was found to block the effects of IGF‐1 on K+ current. Moreover, the inhibition of Akt phosphorylation by the application of wortmannin or by a specific reduction of Akt kinase activity reduced the hEAG mRNA levels. Taken together, our results show, for the first time, that IGF‐1 increases both the activity and the expression of hEAG channels through an Akt‐dependent pathway. Since a hEAG channel is necessary for cell proliferation, its regulation by IGF‐1 may thus play an important role in IGF‐1 signaling to promote a mitogenic effect in breast cancer cells. J. Cell. Physiol. 212:690–701, 2007.

Identification of pectin methylesterase 3 as a basic pectin methylesterase isoform involved in adventitious rooting in Arabidopsis thaliana

• Here, we focused on the biochemical characterization of the Arabidopsis thaliana pectin methylesterase 3 gene (AtPME3; At3g14310) and its role in plant development. • A combination of biochemical, gene expression, Fourier transform-infrared (FT-IR) microspectroscopy and reverse genetics approaches were used. • We showed that AtPME3 is ubiquitously expressed in A. thaliana, particularly in vascular tissues. In cell wall-enriched fractions, only the mature part of the protein was identified, suggesting that it is processed before targeting the cell wall. In all the organs tested, PME activity was reduced in the atpme3-1 mutant compared with the wild type. This was related to the disappearance of an activity band corresponding to a pI of 9.6 revealed by a zymogram. Analysis of the cell wall composition showed that the degree of methylesterification (DM) of galacturonic acids was affected in the atpme3-1 mutant. A change in the number of adventitious roots was found in the mutant, which correlated with the expression of the gene in adventitious root primordia. • Our results enable the characterization of AtPME3 as a major basic PME isoform in A. thaliana and highlight its role in adventitious rooting.

Calcium-Sensing Receptor Stimulation Induces Nonselective Cation Channel Activation in Breast Cancer Cells

The calcium-sensing receptor (CaR) is expressed in epithelial ducts of both normal human breast and breast cancer tissue, as well as in the MCF-7 cell line as assessed by immunohistochemistry and Western blot analysis. However, to date, there are no data regarding the transduction pathways of CaR in breast cancer cells. In this study, we show that a CaR agonist, spermine, and increased extracellular Ca2+ ([Ca2+]o) sequentially activate two inward currents at –80 mV. The first was highly permeable to Ca2+ and inhibited by 2-aminophenyl borate (2-APB). In contrast, the second was more sensitive to Na+ and Li+ than to Ca2+ and insensitive to 2-APB. Furthermore, intracellular dialysis with high Mg2+, flufenamic acid or amiloride perfusion was without any effect on the second current. Both currents were inhibited by La3+. Calcium imaging recordings showed that both [Ca2+]o and spermine induced an increase in intracellular calcium ([Ca2+]i) and that removal of extracellular Ca2+ or perfusion of 2-APB caused a decline in [Ca2+]i. It is well known that stimulation of CaR by an increase in [Ca2+]o or with spermine is associated with activation of phospholipase C (PLC). Inhibition of PLC reduced the [Ca2+]o-stimulated [Ca2+]i increase. Lastly, reverse-transcriptase polymerase chain reaction showed that MCF-7 cells expressed canonical transient receptor potential (TRPCs) channels. Our results suggest that, in MCF-7 cells, CaR is functionally coupled to Ca2+-permeable cationic TRPCs, for which TRPC1 and TRPC6 are the most likely candidates for the highly selective Ca2+ current. Moreover, the pharmacology of the second Na+ current excludes the involvement of the more selective Na+ transient receptor potential melastatin (TRPM4 and TRPM5) and the classical epithelial Na+ channels.

PECTIN METHYLESTERASE48 is involved in Arabidopsis pollen grain germination

Modifying homogalacturonans in the intine cell wall during maturation of the pollen grain is central for proper germination. Germination of pollen grains is a crucial step in plant reproduction. However, the molecular mechanisms involved remain unclear. We investigated the role of PECTIN METHYLESTERASE48 (PME48), an enzyme implicated in the remodeling of pectins in Arabidopsis (Arabidopsis thaliana) pollen. A combination of functional genomics, gene expression, in vivo and in vitro pollen germination, immunolabeling, and biochemical analyses was used on wild-type and Atpme48 mutant plants. We showed that AtPME48 is specifically expressed in the male gametophyte and is the second most expressed PME in dry and imbibed pollen grains. Pollen grains from homozygous mutant lines displayed a significant delay in imbibition and germination in vitro and in vivo. Moreover, numerous pollen grains showed two tips emerging instead of one in the wild type. Immunolabeling and Fourier transform infrared analyses showed that the degree of methylesterification of the homogalacturonan was higher in pme48−/− pollen grains. In contrast, the PME activity was lower in pme48−/−, partly due to a reduction of PME48 activity revealed by zymogram. Interestingly, the wild-type phenotype was restored in pme48−/− with the optimum germination medium supplemented with 2.5 mm calcium chloride, suggesting that in the wild-type pollen, the weakly methylesterified homogalacturonan is a source of Ca2+ necessary for pollen germination. Although pollen-specific PMEs are traditionally associated with pollen tube elongation, this study provides strong evidence that PME48 impacts the mechanical properties of the intine wall during maturation of the pollen grain, which, in turn, influences pollen grain germination.

MATERNAL CAFFEINE INGESTION DURING GESTATION AND LACTATION INFLUENCES RESPIRATORY ADAPTATION TO ACUTE ALVEOLAR HYPOXIA IN NEWBORN RATS AND ADENOSINE A2A AND GABAA RECEPTOR mRNA TRANSCRIPTION

Caffeine is a widely used psychostimulant freely crossing the placental barrier. At the doses usually absorbed, it acts as an antagonist of both A1 and A2A adenosine receptors. Pregnant women are generally not advised to limit their caffeine consumption and thus expose their progeny to the drug during the whole of gestation and lactation. The possibility that such caffeine exposure may have long-term consequences on brain development has led to several behavioral investigations on animal models. Despite the crucial role played by adenosine receptor systems in neonatal breathing control, few studies in vitro have been concerned with the consequences of maternal caffeine absorption on breathing, and none in the unrestrained intact animal. The present investigation analyzed the influence of caffeine exposure via placental and milk transfer on resting ventilation and on the response to moderate alveolar hypoxia of 0 to 2-day-old newborn rat (P0-P2) together with the possible underlying mechanisms. Dams absorbed caffeine (46+/-3 mg/kg/day) via drinking fluid (0.2 g/L) throughout gestation, in conditions mimicking moderate human consumption. Caffeine exposure did not significantly affect basal respiratory parameters. In contrast, it attenuated both the early increase and the secondary decrease in ventilation triggered by moderate alveolar hypoxia (11% O2 inhaled). The abolition of Fos protein expression evoked by hypoxia suggested that caffeine exposure may decrease the activity of O2-sensing peripheral chemoreceptor pathway. From real-time PCR data, those functional alterations were associated to increases in A2A adenosine receptor and alpha2 GABA(A) receptor subunit mRNAs in the medulla. This indicates that, even at moderate doses, maternal caffeine consumption may induce a series of subtle developmental alterations that may affect modulation of breathing control in the neonate in pathological situations such hypoxia.

Prenatal diazepam exposure alters respiratory control system and GABAA and adenosine receptor gene expression in newborn rats.

In experimental animals, prenatal diazepam exposure has clearly been associated with behavioral disturbances. Its impact on newborn breathing has not been documented despite potential deleterious consequences for later brain development. We addressed this issue in neonatal rats (0–2 d) born from dams, which consumed 2 mg/kg/d diazepam via drinking fluid throughout gestation. In vivo, prenatal diazepam exposure significantly altered the normoxic-breathing pattern, lowering breathing frequency (105 vs. 125 breaths/min) and increasing tidal volume (16.2 vs. 12.7 mL/kg), and the ventilatory response to hypoxia, inducing an immediate and marked decrease in tidal volume (−30%) absent in controls. In vitro, prenatal diazepam exposure significantly increased the respiratory-like frequency produced by pontomedullary and medullary preparations (+38% and +19%, respectively) and altered the respiratory-like response to application of nonoxygenated superfusate. Both in vivo and in vitro, the recovery from oxygen deprivation challenges was delayed by prenatal diazepam exposure. Finally, real-time PCR showed that prenatal diazepam exposure affected mRNA levels of α1 and α2 GABAA receptor subunits and of A1 and A2A adenosine receptors in the brainstem. These mRNA changes, which are region-specific, suggest that prenatal diazepam exposure interferes with developmental events whose impact on the respiratory system maturation deserves further studies.

Consequences of prenatal exposure to diazepam on the respiratory parameters, respiratory network activity and gene expression of alpha1 and alpha2 subunits of GABA(A) receptor in newborn rat.

Diazepam (DZP) enhances GABA action at GABA(A) receptor. Chronic prenatal administration of DZP delays the appearance of neonatal reflexes. We examined whether maternal intake of DZP might affect respiratory control system in newborn rats (0-3 day-old). This study was conducted on unrestrained animals and medulla-spinal cord preparations. In addition, the level of expression of the genes encoding for the alpha1 and alpha2 subunits of the GABA(A) receptor was assessed by quantitative real-time RT-PCR. In rats exposed to DZP, the respiratory frequency was significantly lower and the tidal volume higher than in controls with no significant alteration of the minute ventilation. The recovery from moderate hypoxia was delayed compared to controls. The respiratory-like frequency of medullary spinal cord preparation from DZP-exposed neonates was higher than in the control group. Acute applications of DZP (1 microM) to these preparations increased respiratory-like frequency in both groups, but this facilitation was attenuated following prenatal DZP exposure. The present data indicate that prenatal exposure to DZP alters both eupneic breathing and the respiratory response to hypoxia. These effects might partly be ascribed to the down-regulation of the expression of genes encoding GABA(A) receptor subunits. On the other hand, the effects of DZP exposure on reduced preparations suggested changes in the GABA(A) receptor efficiency and/or disruption of the normal development of the medullary respiratory network.

AtPME3, a ubiquitous cell wall pectin methylesterase of Arabidopsis thaliana, alters the metabolism of cruciferin seed storage proteins during post-germinative growth of seedlings

&NA; AtPME3 (At3g14310) is a ubiquitous cell wall pectin methylesterase. Atpme3‐1 loss‐of‐function mutants exhibited distinct phenotypes from the wild type (WT), and were characterized by earlier germination and reduction of root hair production. These phenotypical traits were correlated with the accumulation of a 21.5‐kDa protein in the different organs of 4‐day‐old Atpme3‐1 seedlings grown in the dark, as well as in 6‐week‐old mutant plants. Microarray analysis showed significant down‐regulation of the genes encoding several pectin‐degrading enzymes and enzymes involved in lipid and protein metabolism in the hypocotyl of 4‐day‐old dark grown mutant seedlings. Accordingly, there was a decrease in proteolytic activity of the mutant as compared with the WT. Among the genes specifying seed storage proteins, two encoding CRUCIFERINS were up‐regulated. Additional analysis by RT‐qPCR showed an overexpression of four CRUCIFERIN genes in the mutant Atpme3‐1, in which precursors of the &agr;‐ and &bgr;‐subunits of CRUCIFERIN accumulated. Together, these results provide evidence for a link between AtPME3, present in the cell wall, and CRUCIFERIN metabolism that occurs in vacuoles.