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J Riou

Publications and source records attributed to J Riou.

At least 19 recordsLinked to original sources
PubMed2001

Hb Mont Saint Aignan [beta128(H6)Ala-->Pro]: a new unstable variant leading to chronic microcytic anemia.

Hb Mont Saint-Aignan [beta128(H6)Ala-->Pro] is a mildly unstable variant, associated with hemolytic anemia, marked microcytosis and increased alpha/beta biosynthetic ratio (1.55 versus 1.1 +/- 0.1 in the control). The abnormal chain was isolated by selective precipitation with isopropanol and the structural modification determined by protein chemistry methods (reversed phase high performance liquid chromatography and mass spectrometry). Possible mechanisms underlying the beta(+)-thalassemia-like expression of this variant are discussed.

Adult↗
PubMed2001

Abnormal hemoglobins: laboratory methods.

Laboratory methods allowing the detection and characterization of hemoglobin variants are reviewed. Protein chemistry techniques such as isoelectrofocusing, electrophoreses under various experimental conditions, cation exchange and reversed phase high performance liquid chromatography, are the most frequently used for the detection of variants. When associated with a few additional data they may lead to a presumptive diagnosis. DNA studies are also developed in many laboratories. Final identification of a variant may be achieved either by molecular biology techniques or by protein sequence analysis in which mass spectrometry now occupies a key position.

Chemistry Techniques, Analytical↗
PubMed2000

Cellular uptake and interaction with purified membranes of rebeccamycin derivatives.

Rebeccamycin is an antitumor antibiotic possessing a DNA-intercalating indolocarbazole chromophore linked to a glycosyl residue. The carbohydrate moiety of rebeccamycin and related synthetic analogues, such as the potent antitumor drug NB-506 (6-N-formylamino-12,13-dihydro-1, 11-dihydroxy-13-(beta-D-glucopyranosyl)-5H-indolo[2,3-a]pyrrolo- [3,4-c]carbazole-5,7-(6H)-dione), is a key element for both DNA-binding and inhibition of DNA topoisomerase I. In this study, we have investigated the cellular uptake of rebeccamycin derivatives and their interaction with purified membranes. The transport of radiolabeled [3H]dechlorinated rebeccamycin was studied using the human leukemia HL60 and melanoma B16 cell lines as well as two murine leukemia cell lines sensitive (P388) or resistant (P388CPT5) to camptothecin. In all cases, the uptake is rapid but limited to about 6% of the drug molecules. In HL60 cells, the uptake entered a steady-state phase of intracellular accumulation of about 0.26+/-0.05 pmol/10(6) cells, which persisted to at least 90 min. The efflux of exchangeable radiolabeled molecules was relatively weak. Fluorescence studies were performed to compare the interaction of a rebeccamycin derivative and its aglycone with membranes purified from HL60 cells. The glycosylated drug molecules bound to the cell membranes can be extracted upon washing with buffer or by adding an excess of DNA. In contrast, the indolocarbazole drug lacking the carbohydrate domain remains tightly bound to the membranes with very little or no exchange upon the addition of DNA. The membrane transport and binding properties of indolocarbazole drugs related to rebeccamycin are reminiscent to those of other DNA-intercalating antitumor agents. The uptake most likely occurs via a passive diffusion through the plasma membranes and the glycosyl residue of the drug plays an essential role for the translocation of the drug from the membranes to the internal cell components, such as DNA.

Aminoglycosides↗
PubMed2000

Role of frizzled 7 in the regulation of convergent extension movements during gastrulation in Xenopus laevis.

Wnt signalling plays a crucial role in the control of morphogenetic movements. We describe the expression and functional analyses of frizzled 7 (Xfz7) during gastrulation in Xenopus. Low levels of Xfz7 transcripts are expressed maternally during cleavage stages; its zygotic expression strongly increases at the beginning of gastrulation and is predominantly localized to the presumptive neuroectoderm and deep cells of the involuting mesoderm. Overexpression of Xfz7 in the dorsal equatorial region affects the movements of convergent extension and delays mesodermal involution. It alters the correct localization, but not the expression, of mesodermal and neural markers. These effects can be rescued by extra-Xfz7, which is a secreted form of the receptor that also weakly inhibits convergent extension when overexpressed. This suggests that the wild-type and truncated receptors have opposing effects when coexpressed and that overexpression of Xfz7 causes an increased signalling activity. Consistent with this, Xfz7 biochemically and functionally interacts with Xwnt11. In addition, Dishevelled, but not (&bgr;)-catenin, synergizes with Xfz7 to affect convergent extension. Furthermore, overexpression of Xfz7 and Xwnt11 also affects convergent extension in activin-treated animal caps, and this can be efficiently reversed by coexpression of Cdc42(T17N), a dominant negative mutant of the small GTPase Cdc42 known as a key regulator of actin cytoskeleton. Conversely, Cdc42(G12V), a constitutively active mutant, rescues the effects of extra-Xfz7 on convergent extension in a dose-dependent manner. That both gain-of-function and loss-of-function of both frizzled and dishevelled produce the same phenotype has been well described in Drosophila tissue polarity. Therefore, our results suggest an endogenous role of Xfz7 in the regulation of convergent extension during gastrulation.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Signaling specificities of fibroblast growth factor receptors in early Xenopus embryo.

Formation of mesoderm and posterior structures in early Xenopus embryos is dependent on fibroblast growth factor (FGF) signaling. Although several FGF receptors (FGFRs) are expressed in the early embryo, their respective role in these processes remains poorly understood. We provide evidence that FGFR-1 and FGFR-4 signals elicit distinct responses both in naive and neuralized ectodermal cells. We show that naive ectodermal cells expressing a constitutively active chimeric torso-FGFR-1 (t-R1) are converted into mesoderm in a Ras-dependent manner, while those expressing torso-FGFR-4 (t-R4) differentiate into epidermis without significant activation of Erk-1. In neuralized ectoderm, expression of t-R4 causes the up-regulation of the midbrain markers En-2 and Wnt-1, but not of the hindbrain nor the spinal cord markers Krox20 and Hoxb9. Mutation of tyr(776) in the phospholipase C-(gamma) binding consensus sequence YLDL of t-R4 completely abolishes En-2 and Wnt-1 induction. In contrast to t-R4, platelet derived growth factor (PDGF)-dependent FGFR-1 activation in neuralized ectodermal cells expressing a chimeric PDGFR-FGFR-1 receptor results in the expression of Krox20 and Hoxb9. A similar effect is observed when an inducible form of oncogenic Raf is expressed, therefore implicating FGFR-1 and Raf in the transduction of FGF-caudalizing signals in neural tissue. Our results suggest that FGFR-1 and FGFR-4 transduce distinct signals in embryonic cells, and mainly differ in their ability to activate the Ras/MAPK pathway.

Animals↗
PubMed2000

Hb Ernz [beta123(H1)Thr-->Asn] and Hb Renert [beta133(H11)Val-->Ala]: two new neutral variants revealed by reversed phase high performance liquid chromatography analysis.

Analysis of globin chains by reversed phase high performance liquid chromatography, used as an additional tool for characterizing hemoglobin variants, has led to the discovery of a new class of variants that display only differences in hydrophobicity. Two such variants are here described. Hb Ernz was found in a man of Italian origin who was polycythemic, and in two of his three daughters who were hematologically normal. Hb Renert, a slightly unstable variant, was found in a man from Cape Verde who also carried Hb S and presented with chronic hemolysis. The structural abnormalities were characterized by protein structure methods involving reversed phase high performance liquid chromatographic separations of globins and peptides, followed by mass spectrometry studies (electrospray, ion trap, tandem mass spectrometry).

Chromatography, High Pressure Liquid↗
PubMed2000

Two new Ggamma chain variants: Hb F-clamart [gamma17(A14)Lys-->Asn] and Hb F-Ouled Rabah [gamma19(B1)Asn-->Lys].

Two new fetal hemoglobin variants affecting the Ggamma chain are reported. Hb F-Clamart was found during investigation of a French newborn who presented with a mild microcytemia. The second variant was found during neonatal screening for hemoglobinopathies of 30,000 babies from a population-at-risk living in the Paris region. It was named Hb F-Ouled Rabah because its structural modification and ethnic distribution is similar to that of Hb D-Ouled Rabah [beta19(B1)Asn-->Lys]. Hb F-Ouled Rabah is clinically silent and occurs at a frequency of ca. 0.1% in newborns originating from Maghreb. Structural characterization of both variants was done by protein chemistry methods, including amino acids analysis and mass spectrometry.

Africa, Northern↗
PubMed2000

Two new variants with the same substitution at position beta122: Hb Bushey [beta122(GH5)Phe-->Leu] and Hb Casablanca [beta65(E9)lys-->Met; beta122(GH5)Phe-->Leu].

Hb Bushey, found in a Chinese baby and his father, is a new variant with a point mutation leading to the substitution Phe-->Leu at position beta122. Hb Casablanca, found in a family from Morocco, is a further example of a hemoglobin variant that carries two abnormalities in the same chain; the first is identical to that of Hb Bushey and the second to that of Hb J-Antakya [beta65 (E9)Lys-->Met]. Structural abnormalities of both Hbs were determined by protein chemistry methods including electrospray and tandem mass spectrometry. Their stability and oxygen binding properties were found to be identical to those of Hb A. Various mechanisms that may lead to two point mutations in the same chain are reviewed briefly.

2,3-Diphosphoglycerate↗
PubMed1999

Two hemoglobin variants with an alteration of the oxygen-linked chloride binding: Hb Antananarivo [alpha1(NA1)Val-->Gly] and Hb Barbizon [beta144(HC1)Lys-->Met].

We here report two new, clinically silent, hemoglobin variants in which the structural modification disturbs the oxygen-linked chloride binding. Hb Antananarivo [alpha1(NA1)Val-->Gly] was found during a systematic hematological study in a 24-year-old woman, who originates from Madagascar. Hb Barbizon [beta144 (HC1)Lys-Met] was found in several members of a French family. The oxygen binding properties of Hb Barbizon were similar to those of Hb Antananarivo showing, in vitro, a decreased chloride effect as compared to Hb A. In Hb Barbizon, the replacement of lysine beta144 by a methionine residue decreased from 4 to 2 the excess positive charges in the central cavity, thus leading to a reduction of about half of the chloride effect. For Hb Antananarivo, the mechanism is unclear since there is no difference in the number of positive charges in the central cavity but alterations are likely at the alpha1alpha2 interface.

Adult↗
PubMed1999

The association of Hb Khartoum [beta124(H2)Pro-->Arg] with gamma+-thalassemia is responsible for hemolytic disease in the newborn of a Sudanese family.

The unstable Hb Khartoum with a Pro-->Arg replacement at position beta124 was identified by isoelectrofocusing, high performance liquid chromatography, and peptide mapping in a mother and two male children of a Sudanese family. All three were heterozygous for the abnormal hemoglobin; the father and a third male child did not carry the mutation. The mother was also homozygous for two putative gamma+-thalassemia point mutations, one affecting both Agamma and Ggamma genes at IVS-II-115 (A-->G), and one affecting the Ggamma gene at the 3' untranslated region (-A) at position -6 from the polyadenylation site. The father had normal gamma genes. All three children were heterozygous for both the gamma+-thalassemia mutations. The two older children, who were compound heterozygotes for Hb Khartoum/gamma+-thalassemia, presented at birth with severe neonatal jaundice which necessitated exchange blood transfusions. Other causes of neonatal jaundice were excluded. The third male child, who did not carry the Hb Khartoum anomaly but was heterozygous for gamma+-thalassemia, did not develop neonatal jaundice. It is concluded that the instability of Hb Khartoum in combination with gamma+-thalassemia is responsible for neonatal hemolytic anemia in this family.

Adult↗