Biomedical subjects

Marc Moreau

Publications and source records attributed to Marc Moreau.

16 recordsLinked to original sources

PubMed2005

The Ca2+-induced methyltransferase xPRMT1b controls neural fate in amphibian embryo.

We have previously shown that an increase in intracellular Ca2+ is both necessary and sufficient to commit ectoderm to a neural fate in Xenopus embryos. However, the relationship between this Ca2+ increase and the expression of early neural genes has yet to be defined. Using a subtractive cDNA library between untreated and caffeine-treated animal caps, i.e., control ectoderm and ectoderm induced toward a neural fate by a release of Ca2+, we have isolated the arginine N-methyltransferase, xPRMT1b, a Ca2+-induced target gene, which plays a pivotal role in this process. First, we show in embryo and in animal cap that xPRMT1b expression is Ca2+-regulated. Second, overexpression of xPRMT1b induces the expression of early neural genes such as Zic3. Finally, in the whole embryo, antisense approach with morpholino oligonucleotide against xPRMT1b impairs neural development and in animal caps blocks the expression of neural markers induced by a release of internal Ca2+. Our results implicate an instructive role of an enzyme, an arginine methyltransferase protein, in the embryonic choice of determination between epidermal and neural fate. The results presented provide insights by which a Ca2+ increase induces neural fate.

Animals↗

PubMed2005

Evaluating MRI as a technique for visualizing the neurocentral junction.

STUDY DESIGN: Magnetic resonance imaging (MRI) of the neurocentral junction (NCJ) was correlated with gross anatomic and histologic sections acquired at the same position. OBJECTIVES: To determine the composition of the MRI of the NCJ and to explore the long-standing discrepancy between the ages of closure of the NCJ as determined by anatomic and imaging studies. SUMMARY OF BACKGROUND DATA: Disparate growth at the site of the NCJ has been implicated as a potential cause of adolescent idiopathic scoliosis since the early 1900s. Although anatomic studies have refuted this theory by maintaining that the NCJ closes before the age of 10 years, recent MRI studies have suggested that the NCJ remains open until adolescence. METHODS: One hundred fourteen porcine NCJs in various stages of development were visualized using MRI. Gross anatomic and histologic sections were acquired at the same position as MRI for correlation. RESULTS: The presence or absence of NCJ cartilage was represented by the presence or absence of a line on MRI. However, the NCJ image overestimated the width of the NCJ cartilage in the anteroposterior direction during development. As the NCJ underwent the process of closure, the NCJ image underestimated the extent of closure in the medial-lateral direction. CONCLUSIONS: Although MRI underestimated the extent of NCJ closure, MRI accurately showed whether cartilage was present or absent at the NCJ site. MRI determination of the age of NCJ closure appears reliable, and further exploration of the asymmetric growth hypothesis is required.

Aging↗

PubMed2005

Human immunodeficiency virus type 1 Tat protein induces an intracellular calcium increase in human monocytes that requires DHP receptors: involvement in TNF-alpha production.

HIV-1 Tat protein, acting at the cell membrane, stimulates the production by human monocytes of TNF-alpha, a cytokine implicated in both HIV-1 replication and pathogenesis. Here, we analyze, in primary human monocytes, the mechanisms involved in Tat-stimulated calcium mobilization and its relationship with TNF-alpha production. We show that the Tat protein induces a calcium signal by mobilizing calcium from extracellular stores. This calcium signal is totally blocked when cells are stimulated in the presence of DHP receptor inhibitors such as nimodipine or calcicludine, thus suggesting the implication of this L-type calcium channel. By using RT-PCR amplification, Western blot with antibodies directed against the alpha1D subunit, binding assays with specific agonists or antagonists, and inhibition with specific antisense oligonucleotides, we show that DHP receptors are expressed and functional in primary human monocytes. Interestingly, we demonstrate that Tat-induced calcium mobilization is tightly linked to TNF-alpha production, thus indicating that Tat-induced mobilization and TNF-alpha production are entirely mediated by DHP receptors, as shown by their total inhibition by nimodipine, calcicludine, or anti-alpha1D antisense oligonucleotides.

Calcium↗

PubMed2005

Calcium transients and neural induction in vertebrates.

Evidence indicates that a variety of different types of Ca2+ transients (i.e., standing gradients, pulses and propagating waves) may be occurring both simultaneously and sequentially during neural induction in vertebrate embryos. Transients have been observed in the dorsal marginal zone and in the presumptive neural ectoderm, suggesting that they may be generated within two distinct germ layers at separate embryological locations. It has been proposed that the Ca2+ transients might have multiple roles during the period of neural induction, ranging from: activating the expression of early neural genes; contributing to the inhibition of BMP-4 signalling; generating secretion gradients of morphogens; regulating and co-ordinating convergent extension; and establishing and reinforcing dorsoventral axis specification. Both intra- and extracellular stores (either acting separately or in combination) have been shown to generate the neuralizing Ca2+ transients via well-established release mechanisms, and transients have been shown to propagate between connected cells, suggesting an intercellular signalling dimension. Thus, good evidence is accumulating to suggest that Ca2+ might be a key central regulator in the process of neural induction.

Animals↗

PubMed2005

Repetitive pointing to remembered proprioceptive targets improves 3D hand positioning accuracy.

Repetitive pointing movements to remembered proprioceptive targets were investigated to determine whether dynamic proprioception could be used to modify the initial sensorimotor conditions associated with an active definition of the target position. Twelve blindfolded subjects used proprioception to reproduce a self-selected target position as accurately as possible. Ten repetitions for each limb were completed using overhead and scapular plane pointing tasks. A 3D optical tracking system determined hand trajectory start and endpoint positions for each repetition. These positions quantified three-dimensional pointing errors relative to the target position and the initial and preceding movement repetitions, as well as changes in movement direction and extent. Target position and cumulative start position errors were significantly greater than the corresponding preceding movement (inter-repetition) errors, and increased as the trial progressed. In contrast, hand trajectory start and endpoint inter-repetition errors decreased significantly with repeated task performance, as did movement extent, although it was consistently underestimated for each repetition. Pointing direction remained constant, except for the angle of elevation for scapular plane pointing, which consistently decreased throughout the trial. The results suggest that the initial conditions prescribed by actively defining a proprioceptive target were subsequently modified by dynamic proprioception, such that movement reproduction capability improved with repeated task performance.

Biomechanical Phenomena↗

PubMed2004

Development and initial validation of a risk score for predicting in-hospital and 1-year mortality in patients with hip fractures.

UNLABELLED: Our objectives were to better define the rates and determinants of in-hospital and 1-year mortality after hip fracture. We studied a population-based cohort of 3981 hip fracture patients. Using multivariable regression methods, we identified risk factors for mortality (older age, male sex, long-term care residence, 10 prefracture co-morbidities) and calculated a hip fracture-specific score that could accurately predict or risk-adjust in-hospital and 1-year mortality. Our methods, after further validation, may be useful for comparing outcomes across hospitals or regions. INTRODUCTION: Hip fractures in the elderly are common and associated with significant mortality and variations in outcome. The rates and determinants of mortality after hip fracture are not well defined. Our objectives were (1) to define the rate of in-hospital and 1-year mortality in hip fracture patients, (2) to describe co-morbidities at the time of fracture, and (3) to develop and validate a multivariable risk-adjustment model for mortality. MATERIALS AND METHODS: We studied a population-based cohort of 3981 hip fracture patients > or =60 years of age admitted to hospitals in a large Canadian health region from 1994 to 2000. We collected sociodemographic and prefracture co-morbidity data. Main outcomes were in-hospital and 1-year mortality. We used multivariable regression methods to first derive a risk-adjustment model for mortality in 2187 patients treated at one hospital and then validated it in 1794 patients treated at another hospital. These models were used to calculate a score that could predict or risk-adjust in-hospital and 1-year mortality after hip fracture. RESULTS AND CONCLUSIONS: The median age of the cohort was 82 years, 71% were female, and 26% had more than four prefracture co-morbidities. In-hospital mortality was 6.3%; 10.2% for men and 4.7% for women (adjusted odds ratio, 1.8; 95% CI, 1.3-2.4). Mortality at 1 year was 30.8%; 37.5% for men and 28.2% for women (adjusted p < 0.001). Older age, male sex, long-term care residence, and 10 different co-morbidities were independently associated with mortality. Risk-adjustment models based on these variables had excellent accuracy for predicting mortality in-hospital (c-statistic = 0.82) and at 1 year (c-statistic = 0.74). We conclude that 1 in 15 elderly patients with hip fracture will die during hospitalization, and almost one-third of those who survive to discharge will die within the year. The determinants of mortality were primarily older age, male sex, and prefracture co-morbidities. Our hip fracture-specific risk-adjustment tool is pragmatic and reliable, and after further validation, may be useful for comparing outcomes across different hospitals or regions.

Aged↗

PubMed2004

Dihydropyridine receptors are selective markers of Th2 cells and can be targeted to prevent Th2-dependent immunopathological disorders.

Th1 cells that produce IFN-gamma are essential in the elimination of intracellular pathogens, and Th2 cells that synthetize IL-4 control the eradication of helminths. However, highly polarized Th1 or Th2 responses may be harmful and even lethal. Thus, the development of strategies to selectively down-modulate Th1 or Th2 responses is of therapeutic importance. Herein, we demonstrate that dihydropyridine receptors (DHPR) are expressed on Th2 and not on Th1 murine cells. By using selective agonists and antagonists of DHPR, we show that DHPR are involved in TCR-dependent calcium response in Th2 cells as well as in IL-4, IL-5, and IL-10 synthesis. Nicardipine, an inhibitor of DHPR, is beneficial in experimental models of Th2-dependent pathologies in rats. It strongly inhibits the Th2-mediated autoimmune glomerulonephritis induced by injecting Brown Norway (BN) rats with heavy metals. This drug also prevents the chronic graft vs host reaction induced by injecting CD4(+) T cells from BN rats into (LEW x BN)F(1) hybrids. By contrast, treatment with nicardipine has no effect on the Th1-dependent experimental autoimmune encephalomyelitis triggered in LEW rats immunized with myelin. These data indicate that 1) DHPR are a selective marker of Th2 cells, 2) these calcium channels contribute to calcium signaling in Th2 cells, and 3) blockers of these channels are beneficial in the treatment of Th2-mediated pathologies.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed2004

Comparison of bulk enucleation methods for porcine oocytes.

Cloning of mammalian oocytes requires that the recipient oocyte is enucleated to remove all genetic material associated with the chromosomes. The procedure currently used in most species requires careful micromanipulation of oocytes treated with cytochalasin B to prevent structural damage. Although functional, this procedure requires time and limits the number of oocytes available for cloning, and our ability to understand the mechanisms of nuclear reprogramming. Therefore, this study aimed at evaluating different procedures to enucleate large pools of oocytes in a time-efficient manner. Two different approaches were tested. The first approach involved centrifugation of zona-free oocytes through a percoll gradient to separate the portion containing the chromatin from the cytoplasmic portion. The second used etoposide to prevent chromatin segregation at first metaphase and resulting in the expulsion of all chromosomes in the polar body. Using the chemical approach an average enucleation rate of 39.4 +/- 7.5% was obtained, while the centrifugation approach resulted in an average enucleation rate of 66.9 +/- 6. In terms of time efficiency, the control manipulation method takes 0.11 min and the centrifugation took an average of 0.52 min per oocyte. The MPF activity at the end of procedure was estimated through the measurement of H1 activity and as expected, the etoposide-cycloheximide treated oocytes had lower H1 activity which was restored by further incubation in the maturation medium for 5 hr while the centrifugation gave a nonsignificant intermediary result. In conclusion, the results presented suggest that both the chemical and the mechanical methods are usable alternatives to micromanipulation of oocytes to generate a large number of chromosome free cytoplasm for biochemical analysis. Mol. Reprod. Dev. 67: 70-76, 2004.

Animals↗

PubMed2004

Dynamic upper limb proprioception in multidirectional shoulder instability.

The ability of subjects with multidirectional shoulder instability to use proprioception to complete a series of upper limb repositioning tasks was investigated. Twelve subjects with multidirectional instability and 12 control subjects were blindfolded and instructed to use proprioception to reproduce a self-selected target position as accurately as possible. Subjects completed 10 repetitions for each limb using three distinct upper limb movements: overhead reaching, scapular plane pointing, and humeral external rotation with abduction. A three-dimensional video motion analysis system tracked limb position and determined spatial hand position error. Subjects with multidirectional shoulder instability showed significantly greater hand position error than control subjects. No hand position error differences were found between the symptomatic and the asymptomatic limbs of subjects in the instability group. Inter-repetition error for subjects in both groups improved significantly during the first three movement cycles. These results suggest that after movement initiation, dynamic proprioception was a factor in improving hand position accuracy in both groups, but to a lesser degree in subjects with multidirectional instability. Consequently, subjects with multidirectional instability may have a reduced capacity to use proprioception to refine and control the motor output of the upper limb.

Adult↗

PubMed2004

The choice between epidermal and neural fate: a matter of calcium.

The development of the vertebrate embryo, which includes the induction and the patterning of the three germ layers, requires signaling among cells. In vertebrates, cells of the embryonic ectoderm have a choice during gastrulation between to fates; they give rise to epidermal progenitors on the ventral side and neural progenitors on the dorsal side. It was first shown by Spemann and Mangold in 1924 that the dorsal mesoderm (also called the Spemann-Mangold Organizer) has a potent biological capacity to induce nervous system from the adjacent ectoderm. A similar observation was reported in amniotes, indicating that neural induction by the Organizer is a conserved process controlling the initial steps in vertebrates neurogenesis. Molecular studies of the last decade have led to the identification of signaling molecules which participate in these embryonic decisions. Epidermis induction occurs through a signaling cascade involving Bone Morphogenetic Proteins (BMP 2, 4, 7) and receptor-regulated Smad proteins which translocate into the nucleus to form active transcriptional complexes. These molecules mediate BMPs effect to activate epidermal-specific gene expression and to repress neural-specific gene transcription. Neural fate is revealed by factors secreted by the dorsal mesoderm (Noggin, Chordin, Follistatin, ...) which act by blocking BMP signaling. Consequently, epidermal fate is an induced fate while neural fate is interpreted as a default state of the ectoderm. This review describes the signaling pathways which act to determine the fate of the ectoderm and discuss an alternative model in which neural fate is not a default state. This new model integrates the activation of a calcium-dependent signaling pathway due to an influx of calcium through L-type calcium channels. In this model, calcium plays a central regulatory role. While calcium is required for neural determination, epidermal determination occurs when calcium-dependent signaling pathways are inactive.

Animals↗

PubMed2004

Lymphocyte calcium signaling involves dihydropyridine-sensitive L-type calcium channels: facts and controversies.

Calcium influx into lymphocytes is essential for activation, differentiation, and effector functions. While several channel- and receptor-types contribute to calcium influx, voltage-gated calcium channels (VGCC) mediate a well-characterized calcium influx pathway that is most exclusively identified in excitable cells. The role of L-type VGCCs, which belong to high-voltage activated calcium channels and are defined as dihydropyridine (DHP) receptors in excitable cells, is well documented. Interestingly, while lymphocytes do not range in the excitable cell category, the modulatory role of DHP agonists and antagonists and the identification of L-type VGCC-related molecules in B and T lymphocytes, mainly in Th2 cells, suggest these proteins are involved in the calcium response of these cells. Because the identity and the regulation of DHP receptors/channels in lymphocytes is far from being solved, we will discuss the challenging issues of demonstrating a role of L-type VGCCs in nonexcitable cells and the arguments supporting their role in lymphocytes. We will comment on the limitation of the use of DHP agonists and antagonists to ascertain a specific involvement of L-type VGCCs in lymphocyte calcium signaling. Finally, we will provide new clues on the interest of a potential use of DHP antagonists in Th2-cell-mediated pathology.

Calcium Channels, L-Type↗

PubMed2003

Calcium transients triggered by planar signals induce the expression of ZIC3 gene during neural induction in Xenopus.

In intact Xenopus embryos, an increase in intracellular Ca(2+) in the dorsal ectoderm is both necessary and sufficient to commit the ectoderm to a neural fate. However, the relationship between this Ca(2+) increase and the expression of early neural genes is as yet unknown. In intact embryos, studying the interaction between Ca(2+) signaling and gene expression during neural induction is complicated by the fact that the dorsal ectoderm receives both planar and vertical signals from the mesoderm. The experimental system may be simplified by using Keller open-face explants where vertical signals are eliminated, thus allowing the interaction between planar signals, Ca(2+) transients, and neural induction to be explored. We have imaged Ca(2+) dynamics during neural induction in open-face explants by using aequorin. Planar signals generated by the mesoderm induced localized Ca(2+) transients in groups of cells in the ectoderm. These transients resulted from the activation of L-type Ca(2+) channels. The accumulated Ca(2+) pattern correlated with the expression of the early neural precursor gene, Zic3. When the transients were blocked with pharmacological agents, the level of Zic3 expression was dramatically reduced. These data indicate that, in open-face explants, planar signals reproduce Ca(2+) -signaling patterns similar to those observed in the dorsal ectoderm of intact embryos and that the accumulated effect of the localized Ca(2+) transients over time may play a role in controlling the expression pattern of Zic3.

Aequorin↗

PubMed2003

[xMLP is an early response calcium target gene in neural determination in Xenopus laevis].

In vertebrates, neural induction occurs during gastrulation when ectodermal cells choose between two fates, neural and epidermal. In Xenopus, neural induction has been regarded as a default pathway as it occurs, in dorsal ectoderm, when ventralizing signals (mainly Bone Morphogenesis Proteins, BMPs, potent epidermal inducers) are inhibited by dorsalizing signals, including factors such as noggin, chordin, and follistatin. However, our previous studies demonstrated that an instructive signal triggered by the activation of L-type voltage-sensitive calcium channels, resulting in a transient increase in intracellular free calcium, appears to be a necessary and sufficient requirement to induce the competent ectoderm toward the neural pathway. Here we further explore the relationship between the Ca2+ transient signals observed and the expression of early neural genes. We have performed a subtractive approach to identify the genes which are transcribed early after the calcium signal and involved in neural determination. We have analyzed a candidate gene (xMLP) which encodes a MARCKS-like protein, a substrate for PKC. We show that this gene is activated by a calcium transient signals and induced by noggin overexpression. xMLP is expressed at the right time in presumptive neural territories. The putative role of xMLP in the process of neural induction is discussed.

Animals↗

PubMed2003

[Luminous plant and animals or the expression of aequorin and "chameleon" probes: a new light in calcium signaling].

Calcium ion is a universal second messenger in numerous cell physiological processes. The paper describes the structure and the activation mechanisms of the bioluminescent (aequorin) and fluorescent based GFP calcium sensitive probes (Cameleon) and the data obtained with such probes in genetically transformed animal and vegetal organisms. The importance of these in vivo Ca2+ imaging molecules in the understanding of calcium signalling is discussed.

Aequorin↗

PubMed2002

The effects of exposure to intense, 24 h light on the development of scoliosis in young chickens.

The aetiology of adolescent 5 coliosis remains unknown and hindering research is the absence of an appropriate animal model. It is now well-established that pinealectomy in young chickens results in the development of scoliosis that has many of the characteristics seen in patients with adolescent idiopathic scoliosis but the mechanism underlying this phenomenon remains elusive. The principle product of the pineal gland is melatonin and so many studies have focused on studying the effects of reduced levels of this hormone. The results have been mixed and the role of melatonin remains unclear. As melatonin production is inhibited by light, it was hypothesised that providing the chickens with an environment consisting of intense, continuous light would reduce serum melatonin levels and avoid any of the potential artifacts involved with the pinealectomy surgery. Consequently, pinealectomised and normal chickens were exposed to very intense light for complete 24 h in each day. At the end of 22 days in this environment serum melatonin levels had been reduced to very low levels in all chickens. Most importantly, 15% of the normal chickens had developed scoliosis and the number of pinealectomised chickens that developed scoliosis increased from 50% to 80%. The results showed that a method for reducing serum melatonin without pinealectomy has been established and which can be used in further experiments. Furthermore, the results also showed that reduced levels of serum melatonin has significant effects on the development of scoliosis. The indication is that there is a threshold level of serum melatonin below which scoliosis may develop probably in conjunction with some other factor which has yet to be identified.

Adolescent↗

PubMed2002

Assessment of the validity of observing three-dimensional images of the spine using polarising, synchronised techniques.

Three-dimensional imaging is an emerging technique in radiology. It might be used to help view the spine and assist in improving evaluation of scoliosis. These images are currently computer generated and although very effective are actually optical iflusions. Questions remain as to the reliability and validity of these images which are important considerations when treatment regimens are being developed and surgery contemplated. Using a constructed three-diemnsional image of a box, this study assessed the inter- and intra-reliability of viewing a specific point on this box and also the inter-reliability of identifying the coordinates of this same point. There was good reliability for viewing a single point in the X and Z axes which formed the plane of the computer but there was a 10X decrease in reliability along the Y-axis (depth). This pattern was repeated when considering the relationship between observers to identify the actual coordinates of the same point.

Artifacts↗