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Biomedical subjects

S Vincent

Publications and source records attributed to S Vincent.

At least 19 recordsLinked to original sources
PubMed1999

Inhibition of RhoGAP activity is sufficient for the induction of Rho-mediated actin reorganization.

It is generally believed that the induction of actin cytoskeleton rearrangements by extracellular stimuli results from the activation of guanine nucleotide exchange factors for the Rho GTPases. Here, we present evidence that the inactivation of RhoGAP (GTPase activating protein) activity is an equally effective means of promoting Rho-mediated cellular processes. We observed that exposure of cultured fibroblasts to sodium fluoride (NaF) results in a rapid and potent stimulation of actin stress fiber formation. This effect is mediated by the Rho GTPase and is associated with the inactivation of cellular RhoGAP activity. Specifically, NaF promotes formation of a high-affinity complex between Rho and the two cellular p190 RhoGAPs in vivo, apparently sequestering limiting amounts of RhoGAP activity, thereby resulting in Rho activation. p190 RhoGAP activity was found to account for approximately 60% of the total RhoGAP activity detected in whole cell extracts, indicating that relatively small changes in cellular RhoGAP activity can have potent effects on Rho activation. We also found that sub-effective concentrations of NaF combined with sub-effective concentrations of the Rho pathway activator, lysophosphatidic acid, which stimulates guanine nucleotide exchange activity on the Rho GTPase, results in the rapid induction of actin stress fibers. Together, these results suggest that the Rho GTPase is regulated by a fine balance of nucleotide exchange and RhoGAP activities, and that inactivation of RhoGAP activity may be a physiologically important regulatory mechanism for activating the Rho GTPase.

3T3 Cells↗
PubMed1999

Nonstructural C protein is required for efficient measles virus replication in human peripheral blood cells.

The P gene of measles virus (MV) encodes the phosphoprotein, a component of the virus ribonucleoprotein complex, and two nonstructural proteins, C and V, with unknown functions. Growth of recombinant MV, defective in C or V expression, was explored in human peripheral blood mononuclear cells (PBMC). The production of infectious recombinant MV V- was comparable to that of parental MV tag in simian Vero fibroblasts and in PBMC. In contrast, MV C- progeny was strongly reduced in PBMC but not in Vero cells. Consistently, the expression of both hemagglutinin and fusion proteins, as well as that of nucleoprotein mRNA, was lower in MV C--infected PBMC. Thus, efficient replication of MV in natural host cells requires the expression of the nonstructural C protein. The immunosuppression that accompanies MV infection is associated with a decrease in the in vitro lymphoproliferative response to mitogens. MV C- was as potent as MV tag or MV V- in inhibiting the phytohemagglutinin-induced proliferation of PBMC, indicating that neither the C protein nor the V protein is directly involved in this effect.

Animals↗
PubMed1999

[Angiogenesis and neuropathology].

Angiogenesis is crucial for both tissue development and tissue function and is an integral part of central nervous system embryogenesis and tumor growth. Angiogenesis is extremely active during development, then remains stable during adulthood and decreases gradually during aging. Physiological processes and inflammation can transiently stimulate angiogenesis in adults. Angiogenesis is modulated by a host signaling pathways, growth factors, growth factor receptors, and membrane proteins associated with these receptors or transcription factors. In disorders affecting the central nervous systems, as in those arising elsewhere in the body, angiogenesis can become inadequate, excessive, or qualitatively abnormal (dysplasia). These abnormalities can result in cerebral trophic disorders and in secondary remodeling. A few examples are given to illustrate various types of primary angiogenesis disorders responsible for cerebral lesions and of secondary angiogenesis disorders caused by an underlying cerebral disorder.

Adult↗
PubMed1998

Myoblast city, the Drosophila homolog of DOCK180/CED-5, is required in a Rac signaling pathway utilized for multiple developmental processes.

The Rac and Cdc42 GTPases share several regulators and effectors, yet perform distinct biological functions. The factors determining such specificity in vivo have not been identified. In a mutational screen in Drosophila to identify Rac-specific signaling components, we isolated 11 alleles of myoblast city (mbc). mbc mutant embryos exhibit defects in dorsal closure, myogenesis, and neural development. DOCK180, the mammalian homolog of Mbc, associates with Rac, but not Cdc42, in a nucleotide-independent manner. These results suggest that Mbc is a specific upstream regulator of Rac activity that mediates several morphogenetic processes in Drosophila embryogenesis.

Animals↗
PubMed1998

A novel AP180-related protein in vesicles that concentrate at acetylcholine receptor clusters.

Monoclonal antibodies were generated to vesicular membranes of clathrin coated vesicles enriched for acetylcholinesterase (AChE). One of these, C172, recognizes vesicles which accumulate in muscle cells around nuclei associated with acetylcholine receptor AChR clusters. Immunoblots of muscle extracts and brain purified clathrin coated vesicles show that C172 recognizes a 100 kd band in muscle, but a 180 kd band in brain. Western blots of purified AP180 protein stained with the two antibodies AP180.1 and C172 displayed the same staining pattern. Tryptic digests probed with peptide antibodies (PS26 and PS27) generated to known sequences of AP180 were used to map the epitope for C172 within the brain AP180 sequence. On immunoblots of digested AP180, all AP180 antibodies and C172 recognized a 100 kd tryptic fragment, however only C172 recognized a smaller 60 kd. Our results suggest that the C172 epitope is located within amino acids 305-598 of the AP180 sequence. Confocal fluorescence microscopy of myoblasts and myotubes stained with the C172 antibody gives a punctate immunofluorescence pattern. Myoblasts stained with C172 revealed a polarized distribution of vesicles distinct from that observed when cells are stained with gamma adaptin antibody which is known to localize to trans Golgi network. Myotubes stained with C172 antibody reveal a linear array of vesicular staining. Quantitative analysis of C172 reactive vesicles revealed a significant increase in number of vesicles present around the nuclei associated with the acetylcholine receptor clusters. These vesicles did not colocalize with the Golgi cisternae. These results indicate that a protein with homology to the neuron-specific coated vesicle protein AP180, is present in muscle cells associated with vesicles showing significant concentration around postsynaptic nuclei present in close proximity to AChR clusters.

Adaptor Proteins, Vesicular Transport↗
PubMed1998

Evidence for distinct mechanisms of transition state stabilization of GTPases by fluoride.

GTPase-activating proteins (GAPs) function by stabilizing the GTPase transition state. This has been most clearly demonstrated by the formation of a high-affinity complex between various GAPs and GDP-bound GTPases in the presence of aluminum tetrafluoride, which can mimic the gamma-phosphate of GTP. Herein, we report that p190 RhoGAP forms a high-affinity complex with Rho GTPases in the presence of fluoride ions, suggesting that p190 also functions to stabilize the GTPase transition state. However, this Rho-p190 complex does not require aluminum ions or even guanine nucleotide, indicating a distinct role for fluoride that is not consistent with the gamma-phosphate-mimicking hypothesis. These results indicate that it is necessary to reconsider the assumed role of fluoride in stabilizing a variety of other GTPase-GAP interactions where the requirement for aluminum or guanine nucleotide has not yet been addressed.

3T3 Cells↗
PubMed1998

Wegener's granulomatosis presenting as oral lesions: a case report.

Wegener's granulomatosis will classically present as a triad of respiratory, kidney, and vascular involvement. The disease may run a course of rapidly progressive or mild and indolent and escape diagnosis for some time. The clinician must be aware of the possibility of Wegener's granulomatosis presenting initially with intraoral lesions. Prompt biopsies and blood studies along with the proper referrals will give the patient their best chance at a remission with the least systemic damage. We present a case of Wegener's granulomatosis that presented with oral lesions before other signs and symptoms.

Diagnosis, Differential↗
PubMed1998

The Drosophila protein Dof is specifically required for FGF signaling.

Receptor tyrosine kinases (RTKs) transmit signals to the cell nucleus via the MAP kinase (MAPK) cascade, using specific molecules to link the activated receptors to the MAPK cascade activator, Ras. We have identified a component of the FGF receptor (FGFR) signal transduction pathway, Downstream of FGFR (Dof). Dof is an intracellular protein that is essential for signal transmission by the FGFR and acts downstream of the receptor and upstream of Ras. Unlike other signaling molecules that act downstream of RTKs, Dof is not expressed ubiquitously but is present exclusively in cells that express FGFRs. Dof is needed in these cells for activation of the MAPK cascade via FGF signaling, but not for activation via other RTK ligands. Dof therefore appears to be committed exclusively to FGFR-mediated signal transduction.

Amino Acid Sequence↗
PubMed1998

Mechanical performance of clinically available, neonatal, high-frequency, oscillatory-type ventilators.

OBJECTIVE: To perform a functional evaluation of five different high-frequency, oscillatory-type ventilators that are currently being marketed for neonatal high-frequency oscillation. DESIGN: Observational animal study. SETTING: Laboratory. SUBJECTS: New Zealand White male rabbits. INTERVENTIONS: Oscillator waveforms and delivered volumes were measured plethysmographically for the following ventilators: the SensorMedics 3100 A; the Dräger Baby Log 8000; the Metran Humming V; the Infant Star; and the Infant Star 950. The independent variables which were adjusted included frequency (5 to 15 Hz), amplitude (25% to 100%), mean airway pressure (5 to 25 cm H2O) and lung injury. MEASUREMENTS AND MAIN RESULTS: At 15 Hz, the volume delivered at the 100% amplitude setting varied from 2.1 to 8.8 mL. Generally, the delivered volume decreased with increasing frequency, and with increased percentage of amplitude. Volume delivery was relatively unaffected by mean airway pressure but decreased with lung injury. Waveforms ranged from pure sinusoidal to a complex square wave. The handling of inspiration/expiration time ratios was ventilator specific. The SensorMedics inspiration/ expiration ratio is user selected over a range from 1:2.3 (30% inspiratory time) to 1:1 (50% inspiratory time) and once selected it is consistent over its entire range of operating frequencies. The Drager ratio is machine determined and varied from 1:2.5 at 5 Hz to 1:1 at 15 Hz. Inspiratory time of the Infant Star is machine set at 18 msecs such that the inspiration/expiration ratio is 1:10.1 at 5 Hz and 1:2.7 at 15 Hz. The Humming V has a fixed inspiration/expiration ratio of 1:1. The relationship of the mean airway pressure displayed on the ventilator to the alveolar occlusion pressure varied considerably among devices. The displayed mean pressure could either overestimate (SensorMedics at 33% inspiratory time or Infant Star), approximate (Humming V), or underestimate (Dräger) the mean lung distending pressure measured during a brief occlusion maneuver. CONCLUSIONS: The findings demonstrate large variations in machine performance. The ventilators also differed profoundly in complexity of operation and versatility as neonatal ventilators.

Animals↗
PubMed1998

Stage-specific expression of the Kit receptor and its ligand (KL) during male gametogenesis in the mouse: a Kit-KL interaction critical for meiosis.

The Kit receptor and its ligand KL, which together constitute an essential effector at various stages of embryonic development, are both present during adult gametogenesis. In the testis, KL is expressed in Sertoli cells, and Kit in germ cells, starting at the premeiotic stages. A series of observations indicated previously a role in spermatogonia survival, without excluding a possible function at later stages. We identified a complex pattern of expression of the two components in the adult murine testis, suggestive of a role in the meiotic progression of spermatocytes. At stages VII-VIII of the cycle of the seminiferous epithelium, the time when spermatocytes enter meiosis, the membrane-associated form of KL extends on the Sertoli cell from the peripheral to the adluminal compartment of the tubule. We also found that the receptor is present on the surface of germ cells up to the pachytene stage. The availability of differentiated Sertoli cell lines, which express the KL protein and support part of the maturation of germ cells in coculture, allowed us to ask whether, in the in vitro reconstructed system, transit of spermatocytes through meiosis requires the Kit-KL interaction. Addition of a blocking monoclonal antibody against the Kit receptor (ACK2) inhibited extensively the appearance of haploid cells and the expression of a haploid-phase-specific gene (Prm1). Recognition of the supporting Sertoli cell by germ cells was not affected, indicating a requirement for the activity of the receptor for either entering or completing meiosis. Involvement of the membrane-associated form of the ligand was suggested by the observation that addition of the soluble form of KL was equally inhibitory.

Animals↗
PubMed1998

The transcription factors KNIRPS and KNIRPS RELATED control cell migration and branch morphogenesis during Drosophila tracheal development.

Cell migration during embryonic tracheal system development in Drosophila requires DPP and EGF signaling to generate the archetypal branching pattern. We show that two genes encoding the transcription factors KNIRPS and KNIRPS RELATED possess multiple and redundant functions during tracheal development. knirps/knirps related activity is necessary to mediate DPP signaling which is required for tracheal cell migration and formation of the dorsal and ventral branches. Ectopic knirps or knirps related expression in lateral tracheal cells respecifies their anteroposterior to a dorsoventral migration behavior, similar to that observed in the case of ectopic DPP expression. In dorsal tracheal cells knirps/knirps related activity represses the transcription factor SPALT; this repression is essential for secondary and terminal branch formation. However, in cells of the dorsal trunk, spalt expression is required for normal anteroposterior cell migration and morphogenesis. spalt expression is maintained by the EGF receptor pathway and, hence, some of the opposing activities of the EGF and DPP signaling pathways are mediated by spalt and knirps/knirps related. Furthermore, we provide evidence that the border between cells acquiring dorsal branch and dorsal trunk identity is established by the direct interaction of KNIRPS with a spalt cis-regulatory element.

Animals↗
PubMed1998

[Guidelines for the evaluation of internal quality control of smears for screening of uterine cancer in France in the structures of Pathologic Anatomy and Cytology. French Association for Quality Assurance in Pathologic Anatomy and Cytology (AFAQAP)--Commission for cervical smears].

A national organized mass-screening effective programme is the only way to reduce the risk of cervical cancer, if properly organized and correlated with a system of Quality Assurance. Since 1900, an Association for Quality Assurance was created by the French pathologists, named "AFAQAP". These pathologists thus demonstrated their interest in this kind of action that should be effective if women and clinicians are also implied. The pathologists have concluded the first part of their programme with these French guidelines for internal quality control of pap smears.

Female↗
PubMed1997

Antimicrobial protection of the mouse testis: synthesis of defensins of the cryptdin family.

We report the synthesis by mouse testicular cells of antibiotic peptides related to the defensins secreted by the Paneth cells of the intestinal epithelium. A Sertoli cell-derived line (15P-1), Sertoli cells in primary cultures, and explanted testicular tissue in culture medium were observed to release protease-sensitive material with a broad-spectrum antibacterial activity. The activity of 15P-1 culture medium was increased 10- to 50-fold in the presence of fractions enriched in round spermatids and of nerve growth factor. Two series of results suggest that this activity may correspond to the release by testicular cells of defensin peptides, and specifically, of peptides of the cryptdin family first identified in the Paneth cells of intestinal crypts. First, a characteristic nucleotide sequence corresponding to the conserved first exon of the mouse cryptdin and cryptdin-related (CRS) genes was evidenced in the RNA of 15P-1 cells and of the testis. Second, immunohistochemical analysis demonstrated the presence of cryptdins of the cryp-1, -2, -3, -6 group in 15P-1 cells, and identified two distinct localizations in the testis. Inside the seminiferous tubule, these cryptdins were found accumulated in Sertoli cells at stages corresponding to the maturation of spermatids. In the interstitial space, Leydig cells also contained immunoreactive cryptdins.

Animals↗