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Biomedical subjects

C Dehay

Publications and source records attributed to C Dehay.

At least 19 recordsLinked to original sources
PubMed2002

Hispano-Indian admixture in Paraguay studied by analysis of HLA-DRB1 polymorphism.

The genetic polymorphism of the Paraguayan population results from the admixture between South American Indians named Guaranis and Spaniards. In order to evaluate the genetic predominance in the Paraguayan population, we typed 50 healthy Paraguayans for HLA-DRB1 by molecular biology and compared their HLA-DRB1 polymorphism to that of the Guaranis and of two Spanish populations. Six significant differences of alleles frequencies were observed between Paraguayans and Guaranis--DRB1*01, 06 (13, 14), 15, 16, 07--whereas only one difference was observed with the Spaniards (DRB1*14). The DRB1*14 frequency was higher in Paraguayan than in the Spanish populations essentially due to the presence of DRB1*1402 related alleles (1402,06,13). These alleles are extremely rare in the Spanish populations whereas frequent in the Guaranis from Brazil and in South American Indian tribes living in the lymitrophe regions of Paraguay (Toba, Wichi and Terena). Thus, the presence of the DRB1*1402 related alleles (6%) in the Paraguayan population constitutes the major Indian contribution to the HLA-DR polymorphism of the Paraguayan population. The genetic distances between Paraguayans and the two Spanish populations were closer (.494 and .415) than that between Paraguayans and Guaranis (.958). Altogether these results suggest the predominance of the Spanish genetic in the Paraguayan population. Historical events are discussed to explain this predominance.

Alleles↗
PubMed2001

An efficient system for conditional gene expression in embryonic stem cells and in their in vitro and in vivo differentiated derivatives.

We have developed a universally applicable system for conditional gene expression in embryonic stem (ES) cells that relies on tamoxifen-dependent Cre recombinase-loxP site-mediated recombination and bicistronic gene-trap expression vectors that allow transgene expression from endogenous cellular promoters. Two vectors were introduced into the genome of recipient ES cells, successively: (i) a bicistronic gene-trap vector encoding the beta-galactosidase/neo(R) fusion protein and the Cre-ER(T2) (Cre recombinase fused to a mutated ligand-binding domain of the human estrogen receptor) and (ii) a bicistronic gene-trap vector encoding the hygro(R) protein and the human alkaline phosphatase (hAP), the expression of which is prevented by tandemly repeated stop-of-transcription sequences flanked by loxP sites. In selected clones, hAP expression was shown to be regulated accurately by 4'hydroxy-tamoxifen. Strict hormone-dependent expression of hAP was achieved (i) in vitro in undifferentiated ES cells and embryoid bodies, (ii) in vivo in virtually all the tissues of the 10-day-old chimeric fetus (after injection of 4'hydroxy-tamoxifen to foster mothers), and (iii) ex vivo in primary embryonic fibroblasts isolated from chimeric fetuses. Therefore, this approach can be applied to drive conditional expression of virtually any transgene in a large variety of cell types, both in vitro and in vivo.

Alkaline Phosphatase↗
PubMed2001

Cell-cycle kinetics of neocortical precursors are influenced by embryonic thalamic axons.

Thalamic afferents are known to exert a control over the differentiation of cortical areas at late stages of development. Here, we show that thalamic afferents also influence early stages of corticogenesis at the level of the ventricular zone. Using an in vitro approach, we show that embryonic day 14 mouse thalamic axons release a diffusable factor that promotes the proliferation of cortical precursors over a restricted developmental window. The thalamic mitogenic effect on cortical precursors (1) shortens the total cell-cycle duration via a reduction of the G(1) phase; (2) facilitates the G(1)/S transition leading to an increase in proliferative divisions; (3) is significantly reduced by antibodies directed against bFGF; and (4) influences the proliferation of both glial and neuronal precursors and does not preclude the action of signals that induce differentiation in these two lineages. We have related these in vitro findings to the in vivo condition: the organotypic culture of cortical explants in which anatomical thalamocortical innervation is preserved shows significantly increased proliferation rates compared with cortical explants devoid of subcortical afferents. These results are in line with a number of studies at subcortical levels showing the control of neurogenesis via afferent fibers in both vertebrates and invertebrates. Specifically, they indicate the mechanisms whereby embryonic thalamic afferents contribute to the known early regionalization of the ventricular zone, which plays a major role in the specification of neocortical areas.

Animals↗
PubMed2001

Pre- and post-mitotic events contribute to the progressive acquisition of area-specific connectional fate in the neocortex.

The adult primary motor cortex (area 6) is characterized by a stronger projection to the spinal cord than the primary somatosensory cortex (area 3). Here we have explored the progressive and regressive phenomena that determine these areal differences in the number of corticospinal neurons (CSNs). CSNs were birthdated with [(3)H]thymidine and subsequently retrogradely labeled from the spinal cord. The time window of CSN production is identical in both areas. The probability that a cohort of neuroblasts project to the spinal cord is indicated by the percentage of [(3)H]thymidine-positive neurons that can be back-labeled from the spinal cord. In the neonate this fate index is significantly higher in area 6 compared with area 3, indicating that early regionalization of cell fate contributes to areal differences in CSN number. In neonatal reeler mice, an increase in CSN number was accompanied by an increased fate index, showing that the integrity of the post-mitotic environment is required for the specification of the appropriate number of neurons expressing a given connectional phenotype. Postnatal development in reeler and normal is characterized by an area-specific elimination of CSN axons, which reduces areal differences in CSN number. These results show a progressive acquisition of CSN fate in the neocortex and indicate that both early regionalization and late environmental signals contribute to determining areal differences of connectional phenotype.

Animals↗
PubMed2000

Binocular competition does not regulate retinogeniculate arbor size in fetal monkey.

Binocular interactions play a prominent role in shaping the axonal arbors of geniculocortical fibers and the arbors of Y cells in the retinogeniculate pathway of the fetal cat. Fiber interactions between the two eyes have also been suggested to regulate the formation of retinal projections to the dorsal lateral geniculate nucleus (dlgn) of the fetal monkey, but whether this reflects structural refinements of retinal arbors has not been established. To address this issue, we quantified the morphologic properties of individual fibers in two macaque monkeys at embryonic day (E) 110 and E121 that had an eye removed at E69 and E61, respectively. Fibers were labeled by DiI crystals into the fixed optic tract and were visualized by confocal microscopy. Three measurements were made: the number of branch points within the axon terminal arbor, the total arborization length, and the incidence of axonal side branches on the preterminal axon within the confines of the geniculate. There were no significant differences with respect to these parameters between the prenatal enucleates and normal monkeys of comparable age. This was the case for retinal fibers innervating the magnocellular and the parvocellular segments of the dlgn. The arbors stemming from the remaining eye were widely distributed in the dlgn, with some terminating in territories normally innervated by the other (enucleated) eye. These results lend support to the hypothesis that the expanded projection from the remaining eye to the lateral geniculate nucleus of the prenatally enucleated monkey is due to the maintenance of a contingent of retinal fibers normally eliminated by ganglion cell death.

Animals↗
PubMed2000

A linkage disequilibrium map of the MHC region based on the analysis of 14 loci haplotypes in 50 French families.

A sample of 100 individuals from 50 French families of known pedigrees were typed for 14 loci of the HLA region (DPB1, DQB1, DQA1, DRB1, DRB3, 4, 5, C4B, C4A, Bf, C2, TNFa, TNFb, B, Cw, A). Linkage disequilibrium in each pair of loci was investigated by an exact test using a Markov chain algorithm. The results indicate no disequilibrium between DPB1 and the other loci, whereas the other class II genes are all significantly linked to each other. Linkage disequilibrium is also detected between some pairs of class I and class II-class I loci despite the long physical distance separating the loci (e.g. A-B, Cw-DRB1). On the other hand, some contiguous loci of the class III region are found to be in equilibrium with each other. Several hypotheses including selection, but also unequal allelic diversity at different MHC loci are discussed to explain this complex pattern of linkage disequilibrium.

Chromosome Mapping↗
PubMed1999

Prenatal development of retinogeniculate axons in the macaque monkey during segregation of binocular inputs.

In the fetal monkey the projections from the two eyes are initially completely intermingled within the dorsal lateral geniculate nucleus (DLGN) before separating into eye-specific layers (). To assess the cellular basis of this developmental process, we examined the morphological properties of individual retinogeniculate axons in prenatal monkeys of known gestational ages. The period studied spanned the time from when binocular overlap has been reported to be maximum, circa embryonic (E) day 77 through E112, when the segregation process is already largely completed in the caudal portion of the nucleus. Retinogeniculate fibers were labeled by making small deposits of DiI crystals into the fixed optic tract. After adequate time was allowed for diffusion of the tracer, fibers were visualized by confocal microscopy, and morphometric measures were made from photomontages. This revealed that retinogeniculate fibers in the embryonic monkey undergo continuous growth and elaboration during binocular overlap and subsequent segregation. Importantly, very few side-branches were found along the preterminal axon throughout the developmental period studied. Thus, restructuring of retinogeniculate fibers does not underlie the formation of eye-restricted projections in the primate. Rather, the results support the hypothesis that binocular segregation in the embryonic monkey is caused by the loss of retinal fibers that initially innervate inappropriate territories ().

Animals↗
PubMed1998

Neurogenesis and commitment of corticospinal neurons in reeler.

In the homozygous (but not the heterozygous) reeler mutant, disruption of neuron migration leads to a major perturbation of the cortical environment that in turn could modify (1) the specification of neuronal fate and (2) the proliferation dynamics of cortical precursors. To investigate these issues, tritiated thymidine injections during cortical neurogenesis were coupled with postnatal injections of a retrograde tracer in the spinal cord to accurately measure the neurogenesis of corticospinal neurons in the heterozygous and homozygous mutant. The homozygous reeler shows (1) strict conservation of area-specific timetables of corticospinal neuron generation; (2) neurons with the appropriate birthdates show an enhanced probability of projecting to the spinal cord; (3) during early stages of corticogenesis, there is a reduced rate of neuron production followed at later stages by an increased rate of neuron production; and (4) these changes in the rate of neuron production were shown to be at least partially attributable to changes in the proportions of differentiative divisions. Taken together, our results show that in the developing cortex, the neurogenesis and specification of a given neuronal phenotype are partially controlled by the postmigratory compartment. On the other hand, neither areal identity nor the chronology of production of layer-specific neuronal phenotype seems to depend on the integrity of the cellular environment.

Afferent Pathways↗
PubMed1998

Area-specific laminar distribution of cortical feedback neurons projecting to cat area 17: quantitative analysis in the adult and during ontogeny.

Corticocortical pathways can be classified as feedback and feedforward, in part according to the laminar distribution of the parent cell bodies. Here, we have developed exhaustive sampling procedures to determine unambiguously this laminar distribution. This shows that individual extrastriate areas in the adult cat have highly stereotyped proportions of supragranular layer neurons with respect to the total population of neurons back-projecting to area 17. During development, these adult laminar patterns emerge from an initially uniform radial distribution through a process of selective reorganization, which is highly specific to each area. Injections of fluorescent retrograde tracers were made in area 17. In areas 19, 20, posteromedial lateral suprasylvian area, and anteromedial lateral suprasylvian area, we defined a projection zone as the region containing retrogradely labeled neurons. In the neonate, counts of labeled neurons throughout the projection zones show constant percentages of 40% in the supragranular layers. During development, there is an area-specific reduction in the percentage of supragranular labeled neurons generating the laminar distributions characteristic of each area. Numbers of labeled neurons were estimated at different eccentricities of the projection zone. This finding indicates that during development there is a relative decrease in the numbers of labeled neurons of the periphery of the projection zone in the supragranular layers but not in the infragranular layers. This decrease is accompanied by a relative decrease in the dimensions of the supragranular projection zone with respect to the infragranular projection zone. These findings suggest that each extrastriate area precisely adjusts the proportions of supragranular layer neurons back-projecting to striate cortex in part by developmental changes in the divergence-convergence values of individual neurons. This shaping of corticocortical connectivity occurs relatively late in postnatal development and could, therefore, be under epigenetic control.

Animals↗
PubMed1997

Regulation of neuroblast cell-cycle kinetics plays a crucial role in the generation of unique features of neocortical areas.

Cortical neurons are generated in the germinal zones lining the ventricles before migrating predominantly radially. To investigate regional differences in the cell-cycle kinetics of neuroblasts, pulse [3H]-thymidine injections were made throughout corticogenesis, and labeled neuron counts were compared in areas 3, 6, 17, and 18a in the adult mouse. The relationship between height in the cortex and intensity of autoradiographic signal distinguishes first generation and subsequent generations of neurons. This provides the mitotic history of defined sets of neurons and is a powerful tool for analyzing areal differences in cell-cycle kinetics. The infragranular laminar labeling indices of different generations show significant differences in areas 3 and 6. The labeling index of first generation neurons shows that the rate of neuron production is higher in area 3 than in area 6. This increased generation rate in area 3 was accompanied by two major changes. First, computation of the labeling index of the subsequent generation neurons (which reflects percentages of precursors in S-phase at the moment of the pulse) indicates a shorter cell cycle in area 3. Second, the total population of labeled neurons contains a higher proportion of first generation neurons in area 3, implying a higher leaving fraction in this area. Computer simulations of these areal differences of cell-cycle kinetics generate neuron numbers that are in close agreement with published data. Altogether these findings reveal an early regionalization of the ventricular zone that serves to generate unique features of future cortical areas.

Aging↗
PubMed1997

The timetable of laminar neurogenesis contributes to the specification of cortical areas in mouse isocortex.

In the primate visual cortex, the birthdate of neurons in homologous layers differ on either side of the 17-18 border suggesting that there might be different timetables of laminar histogenesis in these two areas (Dehay et al. [1993] Nature 366:464-466 and Kennedy et al. [1996] Soc. Neurosci. Abst. 22:525). Because of the potential importance of these findings for understanding mechanisms that generate areal identity, we have developed an experimental approach that makes it possible to accurately compute the timetable of laminar histogenesis from birthdating experiments. Here we report the results of an exhaustive examination of the tempo of layer production in five cortical areas of the mouse. Tritiated thymidine pulse injections were made during embryonic development and labeled neurons were examined in three frontoparietal areas (areas 3, 4, and 6) and two occipital areas (areas 17 and 18a) of the adult cortex. The correlation between the radial distribution of neurons and the intensities of labeling enabled us to reliably identify first generation neurons (i.e., those neurons that quit the cell-cycle in the first round of mitosis after injection). For each cortical layer, the percentage of first generation neurons with respect to the total number of neurons defined a laminar labeling index. Changes of the laminar labeling index over time determined the timetable of layer formation. The onset and duration of layer formation was identical in the two occipital areas. This finding contrasted with the frontoparietal areas where there were important differences in the timing of infragranular and granular layer formation and noticeably production of layers VIa, V, and IV occurs earlier in area 3 than in area 6. The timing of laminar production of areas 17 and 18a resembles more that of area 3 than that of area 6. With respect to areas 3 and 6, area 4 shows an intermediate but significantly different timetable of layer production. These marked areal differences in the timetable of laminar histogenesis contrasted with the relative homogeneity within areas so that we have been able to demonstrate that the interareal differences are not merely the expression of known neurogenic gradients. These results suggest that in the mouse frontoparietal isocortex, neighbouring regions of the ventricular zone that will give rise to distinct areas follow distinct programs of layer production. These areal differences occur before thalamic innervation and suggest an early regionalisation of laminar histogenesis.

Animals↗
PubMed1997

The T3R alpha gene encoding a thyroid hormone receptor is essential for post-natal development and thyroid hormone production.

The diverse functions of thyroid hormones are thought to be mediated by two nuclear receptors, T3R alpha1 and T3R beta, encoded by the genes T3R alpha and T3R beta respectively. The T3R alpha gene also produces a non-ligand-binding protein T3R alpha2. The in vivo functions of these receptors are still unclear. We describe here the homozygous inactivation of the T3R alpha gene which abrogates the production of both T3R alpha1 and T3R alpha2 isoforms and that leads to death in mice within 5 weeks after birth. After 2 weeks of life, the homozygous mice become progressively hypothyroidic and exhibit a growth arrest. Small intestine and bones showed a strongly delayed maturation. In contrast to the negative regulatory function of the T3R beta gene on thyroid hormone production, our data show that the T3R alpha gene products are involved in up-regulation of thyroid hormone production at weaning time. Thus, thyroid hormone production might be balanced through a positive T3R alpha and a negative T3R beta pathway. The abnormal phenotypes observed on the homozygous mutant mice strongly suggest that the T3R alpha gene is essential for the transformation of a mother-dependent pup to an 'adult' mouse. These data define crucial in vivo functions for thyroid hormones through a T3R alpha pathway during post-natal development.

Acetylcholine↗
PubMed1996

Phenotypic characterisation of respecified visual cortex subsequent to prenatal enucleation in the monkey: development of acetylcholinesterase and cytochrome oxidase patterns.

Prenatal bilateral enucleation induces cortex, which normally would have become striate cortex, to follow a default developmental pathway and to take on the cytoarchitectonic appearance of extrastriate cortex (default extrastriate cortex, Dehay et al. [1996] J. Comp. Neurol. 367:70-89). We have investigated if this manipulation influences the cortical expression of acetylcholinesterase (AChE) and cytochrome oxidase (CO). Early enucleation (before embryonic day 81; E81) had only minor effects on the distribution of AChE and CO in the striate cortex. In animals that underwent operation, the striate cortex CO blobs were significantly more closely spaced on the operculum compared with the calcarine. After early enucleation, there was a periodic distribution of CO dense patches in default extrastriate cortex. These CO patches had a center-to-center spacing that was considerably smaller than that of CO stripes in normal area V2, but was somewhat larger than that of the CO blobs in striate cortex. Although the CO stripes characteristic of normal area V2 could not be detected, there were some high-frequency CO patches, similar to those found in default extrastriate cortex. Early enucleation caused a failure to form the transient AChE bands running perpendicular to the striate border, which are normally present in the fetus and early neonate. Late enucleation did not alter AChE expression in extrastriate cortex. The relatively minor effects of early enucleation in the reduced striate cortex contrast with the changes in expression of these enzymes in extrastriate cortex, which accompany large shifts in the location of the striate border. This suggests a massive reorganisation of cortical phenotype in extrastriate cortex.

Acetylcholinesterase↗
PubMed1996

Role of directed growth and target selection in the formation of cortical pathways: prenatal development of the projection of area V2 to area V4 in the monkey.

In experiments combining retrograde tracers and histochemistry, we have looked at the prenatal development of the cortical pathway linking areas V2 and V4. Transient expression of acetylcholinesterase in fetal area V2 reveals the separate compartments that project to V4 (temporal directed pathway) and V5 (parietal directed pathway). During early stages of pathway formation, V2 neurons projecting to area V4 are clustered in the appropriate compartments. During the phase of rapid axonal growth, there is a selective increase of connections originating from the appropriate compartments leading to a strongly clustered organization at the peak of connectivity. During this phase, injections involving the white matter also showed clustering, but this was somewhat reduced in comparison to that of gray matter injections. The growth phase is followed by an elimination phase during which there is a tendency for a preferential loss of intercluster connections, which may sharpen the early formed pattern. These results demonstrate the primary role of axonal guidance and target recognition mechanisms followed by a limited extent of selective elimination during the formation of functional cortical pathways in the primate isocortex. Compared to previous findings, these results suggest that the developmental restriction of callosal connections is not a universal model of cortical development. In the present report, the directed growth and early specification of feed-forward connections contrast with the prolonged remodelling of monkey feedback projections, suggesting two distinct developmental strategies of pathway formation in the monkey.

Acetylcholinesterase↗
PubMed1996

Contribution of thalamic input to the specification of cytoarchitectonic cortical fields in the primate: effects of bilateral enucleation in the fetal monkey on the boundaries, dimensions, and gyrification of striate and extrastriate cortex.

Bilateral enucleation was performed at different fetal ages during corticogenesis, and the brains were prepared for histological examination. Early-enucleated fetuses (operated prior to embryonic day 77) showed morphological changes at the level of the thalamus and the cortex. In the thalamus, there was a loss of lamination and a decrease in size of the lateral geniculate nucleus. There was a decrease in the size of the inferior pulvinar, but there was no change in the lateral pulvinar. The border of striate cortex was as sharp in the enucleates as it was in the normal monkeys. In three of the four early enucleates, we observed an interdigitation of striate and extrastriate cortex. In three of the early enucleates, we observed a small island of nonstriate cortex near the striate border that was surrounded entirely by striate cortex. Enucleation led to an age-related reduction of striate cortex. This reduction was greater in the operculum than in the calcarine fissure. The reduction of striate cortex was accompanied by an increase in the dimensions of extrastriate visual cortex, so that the overall dimensions of the neocortex remained invariant. The extrastriate cortex in the enucleated animals presented a uniform cytoarchitecture and was indistinguishable from area 18 in the normal animal. There were changes in the gyral pattern that were restricted mainly to the cortex on the operculum. A deepening of minor dimples as well as the induction of a variable number of supplementary sulci led to an increase in the convolution of the occipital lobe. These results are discussed with respect to the specification of cortical areas. They demonstrate that the reduction in striate cortex was not accompanied by an equivalent reduction in the neocortex; rather, there was a border shift, and a large volume of cortex that was destined to become striate cortex appears to be cytoarchitectonically normal extrastriate cortex.

Aging↗
PubMed1995

In vitro differentiation of embryonic stem cells into glial cells and functional neurons.

Mouse embryonic stem cells were induced to differentiate in culture with retinoic acid. Putative precursors of neurons and glial cells (nestin-positive cells) were clearly identified as early as three days after the onset of differentiation. At day 6, neuron-like cells could be clearly identified, either as isolated cells or as cellular networks. Some of these cells were positive for astrocyte- or oligodendrocyte-specific antigens (GFAP or O4 antigens, respectively). Other cells were positive for neuron-specific antigens (cytoskeleton proteins MAP2, MAP5 and NF200, as well as synaptophysin). Some neuronal-like cells were also positive for acetylcholinesterase activity or glutamic acid decarboxylase expression, indicating that ES cells could differentiate into GABAergic and possibly cholinergic neurons. Electrophysiological analyses performed in voltage clamp conditions showed that cell membranes contained voltage-dependent channels. Overshooting action potentials could be triggered by current injection. Taken together, these data provide evidence that embryonic stem cells can differentiate first into neuron-glia progenitors, and later into glial cells and functional neurons, in vitro. This technique provides an unique system to study early steps of neuronal differentiation in vitro.

Animals↗
PubMed1994

Developmental changes in the distribution of acetylcholinesterase in the extrastriate visual cortex of the monkey.

In the fetal and neonatal monkey, periodically organized regions of high activity of acetylcholinesterase were found in the visual cortical area V2 (Area 18). The acetylcholinesterase bands, like the thin and thick stripes of cytochrome oxidase, were found to run orthogonal to the area 17/18 border. During neonatal development these bands progressively narrow and finally disappear shortly after four months of age.

Acetylcholinesterase↗