PubMed Health⌕ Search

Biomedical subjects

Franck Girard

Publications and source records attributed to Franck Girard.

9 recordsLinked to original sources
PubMed2006

Chromatin immunoprecipitation reveals a novel role for the Drosophila SoxNeuro transcription factor in axonal patterning.

In all metazoans, the expression of group B HMG domain Sox transcription factors is associated with the earliest stages of CNS development. In Drosophila, SoxNeuro (SoxN) is involved in dorso-ventral patterning of the neuroectoderm, and in the formation and segregation of neuroblasts. In this report, we show that SoxN expression persists in a subset of neurons and glial cells of the ventral nerve cord at embryonic stages 15/16. In an attempt to address SoxN function in late stages of CNS development, we have used a chromatin immunoprecipitation approach to isolate genomic regions bound in vivo by SoxN. We identified several genes involved in the regulation of axon scaffolding as potential direct target genes of SoxN, including beat1a, semaphorin2a, fasciclin2, longitudinal lacking and tailup/islet. We present genetic evidence for a direct involvement of SoxN in axonal patterning. Indeed, overexpressing a transcriptionally hyperactive mutated SoxN protein in neurons results in specific defects in axon scaffolding, which are also observed in transheterozygous combinations of SoxN null mutation and mutations in its target genes.

Animals↗
PubMed2005

SUMO represses transcriptional activity of the Drosophila SoxNeuro and human Sox3 central nervous system-specific transcription factors.

Sry high mobility group (HMG) box (Sox) transcription factors are involved in the development of central nervous system (CNS) in all metazoans. Little is known on the molecular mechanisms that regulate their transcriptional activity. Covalent posttranslational modification by small ubiquitin-like modifier (SUMO) regulates several nuclear events, including the transcriptional activity of transcription factors. Here, we demonstrate that SoxNeuro, an HMG box-containing transcription factor involved in neuroblast formation in Drosophila, is a substrate for SUMO modification. SUMOylation assays in HeLa cells and Drosophila S2 cells reveal that lysine 439 is the major SUMO acceptor site. The sequence in SoxNeuro targeted for SUMOylation, IKSE, is part of a small inhibitory domain, able to repress in cis the activity of two adjacent transcriptional activation domains. Our data show that SUMO modification represses SoxNeuro transcriptional activity in transfected cells. Overexpression in Drosophila embryos of a SoxN form that cannot be targeted for SUMOylation strongly impairs the development of the CNS, suggesting that SUMO modification of SoxN is crucial for regulating its activity in vivo. Finally, we present evidence that SUMO modification of group B1 Sox factors was conserved during evolution, because Sox3, the human counterpart of SoxN, is also negatively regulated through SUMO modification.

Amino Acid Motifs↗
PubMed2005

Functional analysis of the chicken delta1-crystallin enhancer activity in Drosophila reveals remarkable evolutionary conservation between chicken and fly.

Functional conservation of enhancers among evolutionarily diverged organisms is a powerful way to identify basic regulatory circuits and key developmental regulators. This is especially applicable to Crystallin genes. Despite unexpected heterogeneity and diversity in their DNA sequences, many studies have revealed that most of the Crystallin genes are regulated by a relatively small set of developmentally important transcription factors. The chicken delta1-crystallin is one of the best-characterized Crystallin genes. Its lens-specific regulation is governed by a 30 bp long DC5 fragment present in the third intron of the gene. DC5 contains PAX6 and SOX2 binding sites, and its activity depends on the cooperative binding of these two transcription factors. To test the idea that Pax6 and Sox2, together with the DC5 enhancer, could form a basic regulatory circuit functional in distantly related animals, we introduced the DC5 fragment into Drosophila and studied its activation pattern and regulation. The results show that the DC5 enhancer is not only active in the compound eye but, remarkably, is specifically active in those cells responsible for Crystallin secretion in Drosophila, i.e. the cone cells. However, regulation of the DC5 enhancer is carried out not by Pax6, but by Pax2 (D-Pax2; shaven--FlyBase) in combination with the Sox2 homologue SoxN. Both proteins (D-PAX2 and SOXN) bind cooperatively to the DC5 fragment and activate the enhancer synergistically. As PAX6 and PAX2 proteins derive from the same ancestor, we propose that during evolution Pax6 function in vertebrate lens development was retained by Pax2 in Drosophila.

Animals↗
PubMed2004

When more means less: a paradox BOLD response in human visual cortex.

The predictions of the 'Linear Transfer Model' (LTM) have been tested only by modulating the frequency of the action potentials while keeping the size of the activated neuronal population constant. The LTM states that the blood oxygenation level-dependent contrast (BOLD) signal is directly proportional to the neuronal activity averaged over milliseconds or seconds. We examined the influence on the BOLD response, of manipulating the size of the activated neuronal population while maintaining the electrical discharge activity constant. We performed functional MR measurements on 30 awake, healthy adult volunteers (15 male and 15 female) using a flashed and reversing checkerboard. These stimuli induced the same vascular response and the same increase in the electrical discharge activity but varied in the size of the neuronal population being activated. The BOLD response measured by the extent of activation and the BOLD signal amplitude, was larger for the flashed than to the reversing checkerboard. An assessment of the local deoxyhemoglobin (HbR) concentration indicated that the neuronal activity was lower during the flashed checkerboard than the reversing checkerboard. Because the checkerboard associated with the lower neuronal activity yielded the larger number of activated voxels and the larger BOLD signal, our results run contrary to the predictions of the 'Linear Transfer Model' and for this reason we refer to them as paradoxical. Stimuli defined by luminance contrast or a chromatic contrast yielded identical results. We conclude that the 'LTM' may apply to stimuli that modulate the electrical discharge activity but not to stimuli that modulate the size of the activated neuronal population.

Adolescent↗
PubMed2004

How much luxury is there in 'luxury perfusion'? An analysis of the BOLD response in the visual areas V1 and V2.

We re-analyzed the functional magnetic resonance imaging data from a study involving awake, adult, human volunteers in order to examine the influence of vascular density on the blood oxygenation level-dependent (BOLD) response. We employed a flashed and reversing stimulus paradigm where the latter stimulated twice the number of receptive fields and with it doubled the neuronal metabolic load (CMRO2) compared to the former stimulus. The blood flow increase to these stimuli was identical, so that differences in the BOLD response are due to differences in the oxygen extraction fraction. By comparing the BOLD response in human striate cortex (V1) and its neighbor, extra-striate area V2 to the two stimuli, we were able to determine the influence of the higher vascular density of striate cortex on the BOLD response. In striate cortex, the extent of activation, as measured by the number of activated voxels, was larger for the flashed than for the reversing stimulus. In extra-striate area V2, no such difference in the extent of activation was noted. Gauging the local concentration of HbR using deltaR2*, we found it to be significantly lower for the flashed than for the reversing checkerboard. We estimated the HbR concentration in extra-striate area V2 to be double that of striate cortex independent of the stimulus presented. A frequency distribution of the deltaR2* values for the flashed and reversing checkerboard revealed a shift consistent with an increase in the HbR concentration between areas V1 and V2. The metabolically most demanding stimulus, the reversing checkerboard was associated with the highest HbR concentration and with the largest number of voxels with a negative BOLD response.

Adult↗
PubMed2004

What the little differences between men and women tells us about the BOLD response.

We analyzed the functional MRI signal of 15 men and 15 women. All had been presented with a flashed and a reversing, radial checkerboard stimulus. We investigated both positive and negative blood oxygenation level-dependent (BOLD) responses. The extent of activation and the change in the neuronal activity were examined. The former, by counting the number of activated voxels, the latter by using deltaR2* as an indicator of the change in the local deoxyhemoglobin (HbR) concentration. We examined both the positive and the negative BOLD response. Positive BOLD response: The flashed checkerboard gave rise to a larger number of activated voxels than for the reversing checkerboard. The mean number of activated pixels did not differ between men and women. The peak deltaR2* was significantly larger to the flashed than the reversing checkerboard, but did not reveal a gender-related difference. We noted an attenuation of the BOLD signal amplitude with time. This attenuation was larger in women than in men. Negative BOLD response: The attenuation was also larger for the flashed than the reversing stimulus and more pronounced in the chromatic contrast compared to the luminance contrast stimulus. The extent of activation was larger for the flashed than the reversing checkerboard, but did not differ between the sexes. The deltaR2* for the chromatic contrast checkerboard was larger in men than in women. No other significant differences were found. We conclude that the difference in the extent of activation between men and women is the result of our ability to detect activated pixels using statistical methods and not the result of a difference in the processing between the sexes.

Cerebrovascular Circulation↗
PubMed2003

Genome-wide identification of in vivo Drosophila Engrailed-binding DNA fragments and related target genes.

Chromatin immunoprecipitation after UV crosslinking of DNA/protein interactions was used to construct a library enriched in genomic sequences that bind to the Engrailed transcription factor in Drosophila embryos. Sequencing of the clones led to the identification of 203 Engrailed-binding fragments localized in intergenic or intronic regions. Genes lying near these fragments, which are considered as potential Engrailed target genes, are involved in different developmental pathways, such as anteroposterior patterning, muscle development, tracheal pathfinding or axon guidance. We validated this approach by in vitro and in vivo tests performed on a subset of Engrailed potential targets involved in these various pathways. Finally, we present strong evidence showing that an immunoprecipitated genomic DNA fragment corresponds to a promoter region involved in the direct regulation of frizzled2 expression by engrailed in vivo.

Animals↗
PubMed2002

19F-magnetic resonance spectroscopy and chemical shift imaging for schizophrenic patients using haloperidol decanoate.

Haloperidol decanoate is widely used in the maintenance treatment of schizophrenia and other psychotic disorders, but knowledge concerning its pharmacokinetics at the injected region is very limited. Because the chemical structure of haloperidol contains fluorine, in vivo 19F-magnetic resonance (MR) spectroscopy (repetition time (TR) = 1 s) and chemical shift imaging (CSI; TR = 1 s, pixel size = 15 x 15 mm) were performed in schizophrenic patients who were treated with haloperidol decanoate (three men and one woman) to measure its diachronic change at the injection point and visualize its local distribution after intramuscular injection. 19F signals (T1 time = 365 ms) were obtained at the haloperidol decanoate-injected region. The decrease rate of the signal-to-noise ratio (SNR) by 19F-MR spectroscopy seemed large in comparison with that of the plasma haloperidol concentration. The distribution was clearly visualized by 19F-CSI for a few days after the injection, but after 1 week could no longer be seen. Although the slow-release characteristics of depot neuroleptics have been explained by the slow diffusion of esterified neuroleptics from the oil vehicle, this result may suggest that there are other mechanisms involved in maintaining the plasma haloperidol concentration. In vivo 19F-MR spectroscopy and CSI are potentially applicable for the pharmacokinetic analysis of haloperidol and other drugs containing fluorine in their structure.

Adult↗