Simultaneous near ultraviolet and visible excitation confocal microscopy of calcium transients in Xenopus oocytes.
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Animals↗
Biomedical subjects
S Girard
Publications and source records attributed to S Girard.
Acceleration of intracellular calcium waves in Xenopus oocytes by calcium influx.
Many cell membrane receptors stimulate the phosphoinositide (PI) cycle, which produces complex intracellular calcium signals that regulate diverse processes such as secretion and transcription. A major messenger of this cycle, inositol 1,4,5-triphosphate (IP3), stimulates its receptor channel on the endoplasmic reticulum to release calcium into the cytosol. Activation of the PI cycle also induces calcium influx, which refills the intracellular calcium stores. Confocal microscopy was used to show that receptor-activated calcium influx, enhanced by hyperpolarization, modulates the frequency and velocity of IP3-dependent calcium waves in Xenopus laevis oocytes. These results demonstrate that transmembrane voltage and calcium influx pathways may regulate spatial and temporal patterns of IP3-dependent calcium release.
Acetylcholine↗
Calcium wave propagation by calcium-induced calcium release: an unusual excitable system.
We discuss in detail the behaviour of a model, proposed by Goldbeter et al. (1990. Proc. natn. Acad. Sci. 87, 1461-1465), for intracellular calcium wave propagation by calcium-induced calcium release, focusing our attention on excitability and the propagation of waves in one spatial dimension. The model with no diffusion behaves like a generic excitable system, and threshold behaviour, excitability and oscillations can be understood within this general framework. However, when diffusion is included, the model no longer behaves like a generic excitable system; the fast and slow variables are not distinct and previous results on excitable systems do not necessarily apply. We consider a piecewise linear simplification of the model, and construct travelling pulse and periodic plane wave solutions to the simplified model. The analogous behaviour in the full model is studied numerically. Goldbeter's model for calcium-induced calcium release is an excitable system of a type not previously studied in detail.
Animals↗
Intracellular waves observed by confocal microscopy from Xenopus oocytes.
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Animals↗
Two-dimensional model of calcium waves reproduces the patterns observed in Xenopus oocytes.
Biological excitability enables the rapid transmission of physiological signals over distance. Using confocal fluorescence microscopy, we previously reported circular, planar, and spiral waves of Ca2+ in Xenopus laevis oocytes that annihilated one another upon collision. We present experimental evidence that the excitable process underlying wave propagation depends on Ca2+ diffusion and does not require oscillations in inositol (1,4,5)trisphosphate (IP3) concentration. Extending an existing ordinary differential equation (ODE) model of Ca2+ oscillations to two spatial dimensions, we develop a partial differential equation (PDE) model of Ca2+ excitability. The model assumes that cytosolic Ca2+ couples neighboring Ca2+ release sites. This simple PDE model qualitatively reproduces our experimental observations.
Animals↗
Subcellular patterns of calcium release determined by G protein-specific residues of muscarinic receptors.
Calcium release from intracellular stores is a point of convergence for a variety of receptors involved in cell signaling. Consequently, the mechanism(s) by which cells differentiate between individual receptor signals is central to transmembrane communication. There are significant differences in timing and magnitude of Ca2+ release stimulated by the m2 and m3 muscarinic acetylcholine receptors. The m2 receptors couple to a pertussis toxin-sensitive G protein to activate phosphatidyl inositol hydrolysis weakly and to stimulate small, delayed and oscillatory chloride currents. In contrast, m3 receptors potently activate phosphatidyl inositol hydrolysis and stimulate large, rapid and transient chloride currents by a pertussis toxin-insensitive G protein pathway. Using confocal microscopy, we now show that the m2- and m3-coupled Ca2+ release pathways can also be spatially distinguished. At submaximal acetylcholine concentrations, both receptors stimulated pulses of Ca2+ release from discrete foci in random, periodic and frequently bursting patterns of activity. But maximal stimulation of m2 receptors increased the number of focal release sites, whereas m3 receptors invariably evoked a Ca2+ wave propagating rapidly just beneath the plasma membrane surface. Analysis of pertussis toxin sensitivity and hybrid m2-m3 muscarinic acetylcholine receptors confirmed that these Ca2+ release patterns represent distinct cell signalling pathways.
Acetylcholine↗
Spiral calcium wave propagation and annihilation in Xenopus laevis oocytes.
Intracellular calcium (Ca2+) is a ubiquitous second messenger. Information is encoded in the magnitude, frequency, and spatial organization of changes in the concentration of cytosolic free Ca2+. Regenerative spiral waves of release of free Ca2+ were observed by confocal microscopy in Xenopus laevis oocytes expressing muscarinic acetylcholine receptor subtypes. This pattern of Ca2+ activity is characteristic of an intracellular milieu that behaves as a regenerative excitable medium. The minimal critical radius for propagation of focal Ca2+ waves (10.4 micrometers) and the effective diffusion constant for the excitation signal (2.3 x 10(-6) square centimeters per second) were estimated from measurements of velocity and curvature of circular wavefronts expanding from foci. By modeling Ca2+ release with cellular automata, the absolute refractory period for Ca2+ stores (4.7 seconds) was determined. Other phenomena expected of an excitable medium, such as wave propagation of undiminished amplitude and annihilation of colliding wavefronts, were observed.
Animals↗
[The placenta and trisomies 13, 18, 21].
In 30 cases of trisomies 13, 18 and 21, the placenta showed different lesions of hypotrophy, immaturity, hydrops, trophoblastic recurrences or cysts and mineralisation of the trophoblastic basal lamina. These are non specific lesions and can be observed in a variety of conditions, but their association is striking in most cases of trisomies. Different pathological patterns may thus evoke a trisomy, though that diagnosis can only be ascertained by chromosome analysis.
Chromosomes, Human, Pair 13↗
[Chorionic villi sampling. Results with the first 500 samples].
531 chorionic villi forceps biopsies were carried out, to look for genetic diseases. Sampling was impossible in 24 cases (4.5%). The following indications were chosen: maternal age over 38 years: 361 cases; parental chromosome abnormality: 28 cases; previous history of chromosome abnormality: 21 cases; X-linked disease: 77 cases; metabolic disease: 32 cases; hemoglobinopathy: 7 cases; blood group determination: 5 cases. An elective abortion was carried out in 44 cases (8.7%), whereas 465 pregnancies were not interrupted. Full term has been reached in 327 pregnancies. The rate of miscarriage in this group is 3.9% (13 miscarriages out of 327 pregnancies followed). The results obtained at the Saint-Vincent-de-Paul Hospital show that the cytogenetic technique is reliable, and that the low risk of sampling allows its application in the diagnosis of chromosome anomalies.
Adult↗
Enhancing the sensitivity of DNA detection and recovery from agarose gels.
By inserting nitrocellulose strips into agarose gels alongside the electrophoresed lanes and passing an electric current perpendicularly in the direction of the strips, highly efficient transfer of DNA bands onto the membrane in the form of concentrated dots is achieved. DNA detection limits by this technique are enhanced, at least three times as visualized by ethidium bromide fluorescence and at least twice more by radiolabeling.
Chromatography, High Pressure Liquid↗
Agyria--pachygyria and Miller-Dieker syndrome: clinical, genetic and chromosome studies.
Twelve cases of lissencephaly are reported. A high resolution chromosome study was performed on each in order to detect small chromosomal anomalies, undetectable with routine techniques. Only one case was shown to have an unbalanced karyotype with a microdeletion of the short arm of chromosome 17 (del 17p). This child also had symptoms of the Miller-Dieker syndrome, consisting of lissencephaly, characteristic facies, pre- and post-natal growth retardation and other birth defects. As proposed by Dobyns, it seems justifiable to classify lissencephalies into four different groups, according to other clinical manifestations and results of chromosome studies.
Cerebral Cortex↗
Lethal acrodysgenital dwarfism: a severe lethal condition resembling Smith-Lemli-Opitz syndrome.
We report eight cases of a lethal association of failure to thrive, facial dysmorphism, ambiguous genitalia, syndactyly, postaxial polydactyly, and internal developmental anomalies (Hirschsprung's disease, cardiac and renal malformation). This syndrome is likely to be autosomal recessive and resembles Smith-Lemli-Opitz (SLO) syndrome. However, the lethality, the common occurrence of polydactyly, and the sexual ambiguity distinguishes this condition from SLO syndrome. A review of published reports supports the separate classification of this syndrome for which we propose the name lethal acrodysgenital dwarfism.
Abnormalities, Multiple↗
[Zellweger syndrome: apropos of prenatal diagnosis using trophoblast biopsy].
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Adult↗
Interstitial dup(1p) and severe intrauterine growth retardation.
An 1,860 g baby girl was born spontaneously after a 38 weeks pregnancy with important foetal hypotrophy and died at 6 weeks of life. She had an inverted duplication of a small part of the short arm of chromosome 1p:46, XX, inv dup(1) (pter p31::p11p13::p31 ter). This observation is compared to three others reported in the literature with intrachromosomal duplication of 1p.
Chromosome Aberrations↗
Experience with first trimester prenatal diagnosis of Menkes disease.
We have performed 28 first trimester diagnoses for Menkes disease in 27 high risk pregnancies by direct copper measurement on chorionic villi (c.v.) Two male fetuses were found to be affected because of significantly increased copper content. In one male fetus a slightly increased copper content was observed indicating an exogenous copper contamination of the sample. This view was supported by normal results observed after abortion. Three out of 15 diagnostic c.v. samples with a female karyotype showed increased copper levels. In two of these cases, part of the copper content might have been released from the cannulae used for these particular biopsies. Histochemical visualization of copper accumulation in fixed chorionic villi of two affected fetuses and one female fetus was observed. [64Cu]-uptake studies have been performed on 11 diagnostic and 10 control c.v. samples. As the control samples in some cases were found to incorporate more [64Cu] than the corresponding diagnostic sample, this method cannot at present be used for diagnosis. Compiled results on newborn females gave evidence that two carriers expressed the paternal X-chromosome, and two carriers expressed the maternal X-chromosome in in chorionic villi.
Adult↗
De novo inv del(4) in an infant with the Wolf-Hirschhorn syndrome.
An infant was found to have a de novo complex rearrangement of one chromosome 4. Her karyotype was interpreted as 46,XX,inv del(4)(pter::p16.3::q31.2----p15.2::q31.2----qter). Clinically she showed the features of the Wolf-Hirschhorn syndrome.
Chromosome Aberrations↗
[Sampling, culturing and karyotyping of chorionic villi].
The authors report on 69 samples of chorionic villi taken from patients who were undergoing therapeutic termination of pregnancy. These samples were taken using small forceps which were guided by ultrasound. The reliability and the chances of culturing these villi in order to work out the caryotype of the fetus and to study the enzymes is discussed.
Chorionic Villi↗
Paternal age and Down's syndrome diagnosed prenatally: no association in French data.
An investigation of a paternal age effect independent of maternal age was undertaken for 118 trisomy 21 cases diagnosed prenatally in 6656 amniocenteses. The mean of the difference delta in paternal age of Down's syndrome cases compared to those with normal genotypes after controlling for maternal age was +0.46 with a 95 per cent confidence interval of -0.84 to +1.76. This revealed no evidence for a paternal age effect. Multiple applications of the Mantel-Haenszel test revealed no statistically significant evidence for a paternal age effect independent of maternal age. These results are in agreement with those of Hook and Cross (1982b) but not with claims of Stene et al. (1981), of a strong paternal age effect detected in studies on prenatal diagnosis. The hypothesis suggested by Hook and Cross (1982a) that there is a rather weak paternal age effect independent of maternal age in most if not all populations cannot be excluded. If temporal or geographic factors account for the differences in studies on paternal age effect, extrapolation to other time periods or populations cannot be done.
Adolescent↗