PubMed Health⌕ Search

Biomedical subjects

C Robin

Publications and source records attributed to C Robin.

At least 19 recordsLinked to original sources
PubMed2006

Positional cloning of a cyromazine resistance gene in Drosophila melanogaster.

Cyromazine is an effective insecticide used to control dipteran insects. Its precise mode of action is yet to be determined, although it has been suggested that it interferes with the hormone system, sclerotization of the cuticle, or nucleic acid metabolism. To understand the way in which cyromazine acts, we have positionally cloned a cyromazine resistance gene from Drosophila melanogaster. Six cyromazine resistance alleles had previously been generated by ethyl methanasulphonate treatment. Two of these failed to complement each other and here we identify them as having independent non-sense mutations in CG32743, which is an ortholog of Smg1 of worms and mammals and encodes a phosphatidylinositol kinase-like kinase (PIKK). RNAi experiments confirm that cyromazine resistance can be achieved by knocking down CG32743. These are the first cyromazine resistant mutations identified at the nucleotide level. In mammals Smg1 phosphorylates P53 in response to DNA damage. This finding supports the hypothesis that cyromazine interferes with nucleic acid metabolism.

Alleles↗
PubMed2006

Dynamic of the genetic structure of bacterial and fungal communities at different developmental stages of Medicago truncatula Gaertn. cv. Jemalong line J5.

The genetic structure of bacterial and fungal communities was characterized in the rhizosphere of Medicago truncatula Gaertn. cv. Jemalong line J5 at five developmental stages (three vegetative and two reproductive stages), and in three compartments (bulk soil, rhizosphere soil and root tissues). The genetic structure of microbial communities was determined by cultivation-independent methods using directly extracted DNA that was characterized by automated ribosomal intergenic spacer analysis (ARISA). Principal component analyses (PCA) indicate that, for all developmental stages, the genetic structure of microbial communities differed significantly by compartment, with a major shift in the community in root tissues corresponding to the most intimate compartment with the plant. Differences were also recorded during plant development, the most significant being observed during the transition between vegetative and reproductive stages. Throughout this period, plants were shown to establish the highest level of symbiotic association (mycorrhization, nodulation) with arbuscular mycorrhizal fungi and Rhizobia. During the reproductive stages, the dynamics of the genetic structure differed between bacterial and fungal communities. At the last reproductive stage, the genetic structure of bacterial communities became close to that recorded during the first vegetative stages, suggesting a resilience phenomenon, whereas the genetic structure of fungal communities remained different from the vegetative stages and also from the early reproductive stages, suggesting a persistence of the rhizosphere effect.

Bacteria↗
PubMed2004

Influence of maize mucilage on the diversity and activity of the denitrifying community.

In order to understand the effect of the maize rhizosphere on denitrification, the diversity and the activity of the denitrifying community were studied in soil amended with maize mucilage. Diversity of the denitrifying community was investigated by polymerase chain reaction (PCR) amplification of total community DNA extracted from soils using gene fragments, encoding the nitrate reductase (narG) and the nitrous oxide reductase (nosZ), as molecular markers. To assess the underlying diversity, PCR products were cloned and 10 gene libraries were obtained for each targeted gene. Libraries containing 738 and 713 narG and nosZ clones, respectively, were screened by restriction fragment analysis, and grouped based on their RFLP (restriction fragment length polymorphism) patterns. In all, 117 and 171 different clone families have been identified for narG and nosZ and representatives of RFLP families containing at least two clones were sequenced. Rarefaction curves of both genes did not reach a clear saturation, indicating that analysis of an increasing number of clones would have revealed further diversity. Recovered NarG sequences were related to NarG from Actinomycetales and from Proteobacteria but most of them are not related to NarG from known bacteria. In contrast, most of the NosZ sequences were related to NosZ from alpha, beta, and gammaProteobacteria. Denitrifying activity was monitored by incubating the control and amended soils anaerobically in presence of acetylene. The N2O production rates revealed denitrifying activity to be greater in amended soil than in control soil. Altogether, our results revealed that mucilage addition to the soil results in a strong impact on the activity of the denitrifying community and minor changes on its diversity.

Actinomycetales↗
PubMed2003

Developmental origins of hematopoietic stem cells.

Hematopoietic stem cells (HSCs) are at the foundation of the hematopoietic hierarchy and give rise to all blood lineages in the adult organism. A thorough understanding of the molecular, cellular, and developmental biology of HSCs is of fundamental importance, but is also clinically relevant for the advancement of cell replacement therapies and transplantation protocols in blood-related genetic disease and leukemias. While the major anatomical sites of hematopoiesis change during ontogeny, it was long believed that the developmental origin of the adult mammalian hematopoietic system was the yolk sac. However, current studies have shown that the first adult-type HSCs are autonomously generated in the intrabody portion of the mouse embryo, the aorta-gonads-mesonephros (AGM) region, and sublocalize to the dorsal aorta. HSCs are also found in the other large embryonic vessels, the vitelline and umbilical arteries. The intraluminal hematopoietic clusters along these vessels, together with the role of the Runx1 transcription factor in cluster and HSC formation and the HSC/endothelial/mesenchymal Runxl expression pattern, strongly suggest a vascular endothelial/mesenchymal origin for the first HSCs. Moreover, a transgenic mouse line expressing the GFP marker under the control of the Sca-1 transcriptional regulatory elements (GFP expression marks all HSCs) shows a clear localization of GFP-expressing cells to the endothelial cell layer of the dorsal aorta. Thus, highly enriched GFP-positive AGM HSCs will serve as a basis for the future examination of the cellular and molecular factors involved in the induction and expansion of adult HSCs.

Animals↗
PubMed2002

Weibull parameters of composite resin bond strengths to porcelain and noble alloy using the Rocatec system.

OBJECTIVE: The aim of the study was to determine the Weibull distribution parameters S(0) and m of the tensile bond strength of a composite resin sandwiched between a noble metal alloy and a feldspathic porcelain using the Rocatec system. METHODS: Specimens were prepared either as Au-Pt-Pd alloy cylinders alone or as alloy cylinders and a feldspathic porcelain. Surface treatments included 110 microm Al(2)O(3) sandblasting (Rocatec Pre), tribochemical silica coating (Rocatec Plus) and silane application (ESPE-Sil) prior to composite bonding. The tensile bond strengths of ceramic-resin-ceramic and metal-resin-metal specimens were determined before and after thermocycling at 5-60 degrees C for 1000 cycles. Statistical analyses were conducted using two parameter Weibull distributions determined by the characteristic strength (S(0)) at the 63% probability of failure, the Weibull modulus (m) and the 95% confidence intervals. RESULTS: With respect to the control group (no Rocatec) (7.5MPa), the Rocatec system significantly augmented the characteristic tensile bond strength S(0) of metal (17-18MPa) and porcelain (20-28MPa) groups. Thermocycling had no effect on the tensile bond strength of the metal samples and increased (not significant) the bond of the porcelain group. The Weibull modulus m for all groups ranged from 2.8 to 3.7. SIGNIFICANCE: This study confirmed the efficacy of the Rocatec system for bonding composite resin to metal or ceramic substrates. However, the variability of the strength of the bond is shown in the low Weibull modulus values obtained. This reflect the difficulties in controlling flaw formation and warrants research for future improvement.

Composite Resins↗
PubMed2002

Successful transduction of human multipotent, lymphoid (T, B, NK) and myeloid, and transplantable CD34+CD38low cord blood cells using a murine oncoretroviral vector.

Hematopoietic stem cells (HSC) are subject to great interest because of their medical importance and their biological properties. Therefore, the possibility of genetically modifying human HSC is a major concern in several inherited pathologies. In this study, we aimed to demonstrate that a murine oncoretroviral vector can transduce multipotential cord blood (CB) stem cells. Sorted CB CD34(+)CD38(low) cells were transduced with a Moloney-based MFG retroviral vector containing the coding sequence of the murine CD2 (mCD2). CD34(+)mCD2(+) cells were sorted by flow cytometry and cultured either in bulk or at one cell per well in culture conditions that allow differentiation along lymphoid (T, B, and NK) and myeloid (M) lineages. Phenotypic analysis of cells generated in culture showed that CD34(+)mCD2(+) cells could give rise to all lymphoid and myeloid progeny, indicating that the MFG/mCD2 vector had transduced progenitors of all tested lineages. Moreover, clonal cultures of 660 CD34(+)mCD2(+) cells showed that approximately 5% of these cells were able to generate both myeloid and lymphoid (B + NK) progenies; for 25% of them, this included the production of lymphoid T cells. We also demonstrate that transduced CD34(+)CD38(low) CB cells with lymphoid and myeloid potentials were capable of engraftment into the bone marrow (BM) of nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice during several months. These results show that MFG retroviral vectors can transduce multipotent (T, B, NK, M) human hematopoietic progenitors with in vivo repopulating activity.

Animals↗
PubMed2001

Different expression of CD41 on human lymphoid and myeloid progenitors from adults and neonates.

The glycoprotein (Gp) IIb/IIIa integrin, also called CD41, is the platelet receptor for fibrinogen and several other extracellular matrix molecules. Recent evidence suggests that its expression is much wider in the hematopoietic system than was previously thought. To investigate the precise expression of the CD41 antigen during megakaryocyte (MK) differentiation, CD34(+) cells from cord blood and mobilized blood cells from adults were grown for 6 days in the presence of stem cell factor and thrombopoietin. Two different pathways of differentiation were observed: one in the adult and one in the neonate cells. In the neonate samples, early MK differentiation proceeded from CD34(+)CD41(-) through a CD34(-)CD41(+)CD42(-) stage of differentiation to more mature cells. In contrast, in the adult samples, CD41 and CD42 were co-expressed on a CD34(+) cell. The rare CD34(+)CD41(+)CD42(-) cell subset in neonates was not committed to MK differentiation but contained cells with all myeloid and lymphoid potentialities along with long-term culture initiating cells (LTC-ICs) and nonobese diabetic/severe combined immune-deficient repopulating cells. In the adult samples, the CD34(+)CD41(+)CD42(-) subset was enriched in MK progenitors, but also contained erythroid progenitors, rare myeloid progenitors, and some LTC-ICs. All together, these results demonstrate that the CD41 antigen is expressed at a low level on primitive hematopoietic cells with a myeloid and lymphoid potential and that its expression is ontogenically regulated, leading to marked differences in the surface antigenic properties of differentiating megakaryocytic cells from neonates and adults. (Blood. 2001;97:2023-2030)

Adult↗
PubMed2001

Peopling the past: new perspectives on the ancient Maya.

The new direction in Maya archaeology is toward achieving a greater understanding of people and their roles and their relations in the past. To answer emerging humanistic questions about ancient people's lives Mayanists are increasingly making use of new and existing scientific methods from archaeology and other disciplines. Maya archaeology is bridging the divide between the humanities and sciences to answer questions about ancient people previously considered beyond the realm of archaeological knowledge.

Archaeology↗
PubMed2001

The human embryo, but not its yolk sac, generates lympho-myeloid stem cells: mapping multipotent hematopoietic cell fate in intraembryonic mesoderm.

We have traced emerging hematopoietic cells along human early ontogeny by culturing embryonic tissue rudiments in the presence of stromal cells that promote myeloid and B cell differentiation, and by assaying T cell potential in the NOD-SCID mouse thymus. Hematogenous potential was present inside the embryo as early as day 19 of development in the absence of detectable CD34+ hematopoietic cells, and spanned both lymphoid and myeloid lineages from day 24 in the splanchnopleural mesoderm and derived aorta where CD34+ progenitors appear at day 27. By contrast, hematopoietic cells arising in the third week yolk sac, as well as their progeny at later stages, were restricted to myelopoiesis and therefore are unlikely to contribute to definitive hematopoiesis in man.

Antigens, CD34↗
PubMed1999

Identification of lymphomyeloid primitive progenitor cells in fresh human cord blood and in the marrow of nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice transplanted with human CD34(+) cord blood cells.

Transplantation of genetically marked donor cells in mice have unambiguously identified individual clones with full differentiative potential in all lymphoid and myeloid pathways. Such evidence has been lacking in humans because of limitations inherent to clonal stem cell assays. In this work, we used single cell cultures to show that human cord blood (CB) contains totipotent CD34(+) cells capable of T, B, natural killer, and granulocytic cell differentiation. Single CD34(+) CD19(-)Thy1(+) (or CD38(-)) cells from fresh CB were first induced to proliferate and their progeny separately studied in mouse fetal thymic organotypic cultures (FTOCs) and cocultures on murine stromal feeder layers. 10% of the clones individually analyzed produced CD19(+), CD56(+), and CD15(+) cells in stromal cocultures and CD4(+)CD8(+) T cells in FTOCs, identifying totipotent progenitor cells. Furthermore, we showed that totipotent clones with similar lymphomyeloid potential are detected in the bone marrow of nonobese diabetic severe combined immunodeficient (NOD-SCID) mice transplanted 4 mo earlier with human CB CD34(+) cells. These results provide the first direct demonstration that human CB contains totipotent lymphomyeloid progenitors and transplantable CD34(+) cells with the ability to reconstitute, in the marrow of recipient mice, the hierarchy of hematopoietic compartments, including a compartment of functional totipotent cells. These experimental approaches can now be exploited to analyze mechanisms controlling the decisions of such primitive human progenitors and to design conditions for their ampification that can be helpful for therapeutic purposes.

Animals↗
PubMed1999

Identification of human T-lymphoid progenitor cells in CD34+ CD38low and CD34+ CD38+ subsets of human cord blood and bone marrow cells using NOD-SCID fetal thymus organ cultures.

In contrast to myeloid and B-lymphoid differentiation, which take place in the marrow environment, development of T cells requires the presence of thymic stromal cells. We demonstrate in this study that human CD34+, CD34+ CD38+ and CD34+ CD38(low) cells from both cord blood and adult bone marrow reproducibly develop into CD4+ CD8+ T cells when introduced into NOD-SCID embryonic thymuses and further cultured in organotypic cultures. Such human/mouse FTOC fetal thymic organ culture) thus represents a reproducible and sensitive system to assess the T-cell potential of human primitive progenitor cells. The frequency of T-cell progenitors among cord-blood-derived CD34+ cells was estimated to be 1/500. Furthermore, the differentiation steps classically observed in human thymus were reproduced in NOD-SCID FTOC initiated with cord blood and human marrow CD34+ cells: immature human CD41(low) CD8- sCD3- TCR alphabeta- CD5+ CD1a+ T cells were mixed with CD4+ CD8+ cells and more mature CD4+ CD8- TCR alphabeta+ cells. However, in FTOC initiated with bone marrow T progenitors, <10% double-positive cells were observed, whereas this proportion increased to 50% when cord blood CD34+ cells were used, and most CD4+ cells were immature T cells. These differences may be explained by a lower frequency of T-cell progenitors in adult samples, but may also suggest differences in the thymic signals required by bone marrow versus cord blood T progenitors. Finally, since cytokine-stimulated CD34+ CD38(low) cells retained their ability to generate T cells, these FTOC assays will be of value to monitor, when combined with other biological assays, the influence of different expansion protocols on the potential of human stem cells.

ADP-ribosyl Cyclase↗
PubMed1998

NK cells differentiated from bone marrow, cord blood and peripheral blood stem cells exhibit similar phenotype and functions.

In the present study, we investigated the differentiation of human NK cells from bone marrow, cord blood and mobilized peripheral blood purified CD34+ stem cells using a potent culture system. Elutriated CD34+ stem cells were grown for several weeks in medium supplemented with stem cell factor (SCF) and IL-15 in the presence or absence of a murine stromal cell line (MS-5). Our data indicate that IL-15 induced the proliferation and maturation of highly positive CD56+ NK cells in both types of culture, although murine stromal cells slightly increased the proliferation of NK cells. NK cells differentiated in the presence of MS-5 were mostly CD56+ CD7 and a small subset expressed CD16. These in vitro differentiated CD56+ NK cells displayed cytolytic activity against the HLA class I- target K562. The CD56+ CD16+ subset also lysed NK-resistant Daudi cells. Neither of these NK subsets were shown to express Fas ligand. Total CD56+ cells expressed high amounts of transforming growth factor-beta and granulocyte-macrophage colony-stimulating factor, but no IFN-gamma. Investigation of NK receptor expression showed that most CD56+ cells expressed membrane CD94 and NKG2-A mRNA. PCR analysis revealed that p58 was also expressed in these cells. The role of CD94 in NK cell-mediated cytotoxicity was assessed on human HLA-B7-transfected murine L cells. While a low cytotoxic activity towards HLA-B7 cells was observed, the HLA-DR4 control cells were killed with high efficiency. These studies demonstrate that cytolytic and cytokine-producing NK cells may be derived from adult and fetal precursors by IL-15 and that these cells express a CD94 receptor which may influence their lytic potential.

ADP-ribosyl Cyclase↗
PubMed1996

Duplication and divergence of the genes of the alpha-esterase cluster of Drosophila melanogaster.

The alpha-esterase cluster of D. melanogaster contains 11 esterase genes dispersed over 60 kb. Embedded in the cluster are two unrelated open reading frames that have sequence similarity with genes encoding ubiquitin-conjugating enzyme and tropomyosin. The esterase amino acid sequences show 37-66% identity with one another and all but one have all the motifs characteristic of functional members of the carboxyl/cholinesterase multigene family. The exception has several frameshift mutations and appears to be a pseudogene. Patterns of amino acid differences among cluster members in relation to generic models of carboxyl/cholinesterase protein structure are broadly similar to those among other carboxyl/cholinesterases sequenced to date. However the alpha-esterases differ from most other members of the family in: their lack of a signal peptide; the lack of conservation in cysteines involved in disulfide bridges; and in four indels, two of which occur in or adjacent to regions that align with proposed substrate-binding sites of other carboxyl/cholinesterases. Phylogenetic analyses clearly identify three simple gene duplication events within the cluster. The most recent event involved the pseudogene which is located in an intron of another esterase gene. However, relative rate tests suggest that the pseudogene remained functional after the duplication event and has become inactive relatively recently. The distribution of indels also suggests a deeper node in the gene phylogeny that separates six genes at the two ends of the cluster from a block of five in the middle.

Amino Acid Sequence↗
PubMed1996

[Spontaneous spinal epidural hematoma: 2 cases].

The authors report on two cases of spontaneous spinal epidural hematomas with atypical subacute clinical presentation and good recovery after surgical treatment. Etiologies, physiopathology, early diagnosis and treatment are considered through a brief review of the literature.

Adult↗
PubMed1995

[Progressive lupus dementia. 2 cases with or without antiphospholipid antibodies].

Two cases of lupus dementia presented many points of particular interest: 1) the progressive installation of intellectual deterioration, inaugural for the first observation; 2) the diagnostic difficulties of neurolupus with the ARA criteria; 3) the appearance of cerebral magnetic resonance imaging with confluent hypersignals of the periventricular white matter on T2-weighted images; 4) the patholophysiological hypotheses: vascular disease? immunologic disease?; 5) the clinical improvement and SPECT amelioration for the second patient with corticosteroids.

Antibodies, Antiphospholipid↗