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L Schreiber

Publications and source records attributed to L Schreiber.

At least 37 records · Page 2Linked to original sources
PubMed2000

omega-Hydroxylation of epoxy- and hydroxy-fatty acids by CYP94A1: possible involvement in plant defence.

The C(18) fatty acid derivatives 9,10-epoxystearic acid and 9,10-dihydroxystearic acid were hydroxylated on the terminal methyl by microsomes of yeast expressing CYP94A1 cloned from Vicia sativa. The reactions did not occur in incubations of microsomes from yeast transformed with a void plasmid or in the absence of NADPH. After incubation of a synthetic racemic mixture of 9,10-epoxystearic acid, the chirality of the residual epoxide was shifted to 66:34 in favour of the 9S,10R enantiomer. Both the 9S,10R and 9R,10S enantiomers were incubated separately. We determined respective K(m) and V(max) values of 1.2+/-0.1 microM and 19.2+/-0.3 nmol/min per nmol of cytochrome P450 for the 9R,10S enantiomer and of 5.9+/-0.1 microM and 20.2+/-1.0 nmol/min per nmol of cytochrome P450 for the 9S,10R enantiomer. This demonstrated that CYP94A1 is enantioselective for the 9R,10S, which is preferentially formed in V. sativa microsomes. Cutin analysis of V. sativa seedlings revealed that it is mainly constituted of derivatives of palmitic acid, a C(16) fatty acid. Our results suggest that CYP94A1 might play a minor role in cutin synthesis and could be involved in plant defence. Indeed, 18-hydroxy-9,10-epoxystearic acid and 9,10,18-trihydroxystearic acid have been described as potential messengers in plant-pathogen interactions.

Cloning, Molecular↗
PubMed1999

Production in vitro by the cytochrome P450 CYP94A1 of major C18 cutin monomers and potential messengers in plant-pathogen interactions: enantioselectivity studies.

The major C(18) cutin monomers are 18-hydroxy-9,10-epoxystearic and 9,10,18-trihydroxystearic acids. These compounds are also known messengers in plant-pathogen interactions. We have previously shown that their common precursor 9,10-epoxystearic acid was formed by the epoxidation of oleic acid in Vicia sativa microsomes (Pinot, Salaün, Bosch, Lesot, Mioskowski and Durst (1992) Biochem. Biophys. Res. Commun. 184, 183-193). Here we determine the chirality of the epoxide produced as (9R,10S) and (9S,10R) in the ratio 90:10 respectively. We further show that microsomes from yeast expressing the cytochrome P450 CYP94A1 are capable of hydroxylating the methyl terminus of 9,10-epoxystearic and 9,10-dihydroxystearic acids in the presence of NADPH to form the corresponding 18-hydroxy derivatives. The reactions were not catalysed by microsomes from yeast transformed with a void plasmid or in absence of NADPH. After incubation of a synthetic racemic mixture of 9,10-epoxystearic acid with microsomes of yeast expressing CYP94A1, the chirality of the residual epoxide was shifted to 66:34 in favour of the (9S,10R) enantiomer. Both enantiomers were incubated separately and V(max)/K(m) values of 16 and 3.42 ml/min per nmol of P450 for (9R, 10S) and (9S,10R) respectively were determined, demonstrating that CYP94A1 is enantioselective for the (9R,10S) enantiomer, which is preferentially formed in V. sativa microsomes. Compared with the epoxide, the diol 9,10-dihydroxystearic acid was a much poorer substrate for the omega-hydroxylase, with a measured V(max)/K(m) of 0.33 ml/min per nmol of P450. Our results indicate that the activity of CYP94A1 is strongly influenced by the stereochemistry of the 9, 10-epoxide and the nature of substituents on carbons 9 and 10, with V(max)/K(m) values for epoxide>>oleic acid>diol.

Chromatography, High Pressure Liquid↗
PubMed1999

Chemical analysis and immunolocalisation of lignin and suberin in endodermal and hypodermal/rhizodermal cell walls of developing maize (Zea mays L.) primary roots.

The composition of suberin and lignin in endodermal cell walls (ECWs) and in rhizodermal/hypodermal cell walls (RHCWs) of developing primary maize (Zea mays L.) roots was analysed after depolymerisation of enzymatically isolated cell wall material. Absolute suberin amounts related to root length significantly increased from primary ECWs (Casparian strips) to secondary ECWs (suberin lamella). During further maturation of the endodermis, reaching the final tertiary developmental state characterised by the deposition of lignified secondary cell walls (u-shaped cell wall deposits), suberin amounts remained constant. Absolute amounts of lignin related to root length constantly increased throughout the change from primary to tertiary ECWs. The suberin of Casparian strips contained high amounts of carboxylic and 2-hydroxy acids, and differed substantially from the suberin of secondary and tertiary ECWs, which was dominated by high contents of omega-hydroxycarboxylic and 1,omega-dicarboxylic acids. Furthermore, the chain-length distribution of suberin monomers in primary ECWs ranged from C(16) to C(24), whereas in secondary and tertiary ECWs a shift towards higher chain lengths (C(16) to C(28)) was observed. The lignin composition of Casparian strips (primary ECWs) showed a high syringyl content and was similar to lignin in secondary cell walls of the tertiary ECWs, whereas lignin in secondary ECWs contained higher amounts of p-hydroxyphenyl units. The suberin and lignin compositions of RHCWs rarely changed with increasing root age. However, compared to the suberin in ECWs, where C(16) and C(18) were the most prominent chain lengths, the suberin of RHCWs was dominated by the higher chain lengths (C(24) and C(26)). The composition of RHCW lignin was similar to that of secondary-ECW lignin. Using lignin-specific antibodies, lignin epitopes were indeed found to be located in the Casparian strip. Surprisingly, the mature suberin layers of tertiary ECWs contained comparable amounts of lignin-like epitopes.

Cell Wall↗
PubMed1999

Fourier transform infrared-spectroscopic characterisation of isolated endodermal cell walls from plant roots: chemical nature in relation to anatomical development

The chemical nature of enzymatically isolated endodermal cell walls from Cicer arietinum L., Clivia miniata Reg. and Iris germanica L. was studied by FTIR (Fourier transform infrared) spectroscopy. Observed frequencies were assigned to functional groups present in the cell wall and relative amounts of the biopolymers suberin and lignin, cell wall carbohydrates and proteins were determined. Infrared absorption spectra indicated structural characteristics for the three different developmental states of the isolated endodermal cell wall: primary endodermis with Casparian strips (state I), secondary endodermis with suberin lamellae (state II), and tertiary endodermis with U-shaped cell wall depositions (state III). The data obtained from this study are compared with previous results obtained by chemical degradation of isolated endodermal cell walls and subsequent determination of monomeric degradation products by gas chromatography and mass spectrometry. It is concluded that FTIR spectroscopy represents a direct and nondestructive method suitable for the rapid investigation of isolated plant cell walls. Furthermore, the observation that the suberin-assigned absorption bands disappeared after transesterification of the samples with BF(3)-methanol confirmed that suberin is completely degraded by this treatment.

Journal Article↗
PubMed1999

Antenatal sonographic diagnosis of epignathus at 15 weeks of pregnancy.

Epignathus is a rare, benign, congenital teratoma of the hard palate. Most of these teratomas are unidirectional and protrude through the mouth. Hence, the prognosis depends on the size of the tumor and the degree of face distortion and airway obstruction that it causes. However, some epignathi protrude bidirectionally, involving and destroying the brain tissue, resulting in a poor prognosis. This report presents a case of ultrasonographic detection of a bidirectional epignathus at 15 weeks of pregnancy.

Abortion, Induced↗
PubMed1999

Do placentae of term singleton pregnancies obtained by assisted reproductive technologies differ from those of spontaneously conceived pregnancies?

The study was conducted to investigate the association of placental morphological and histopathological features with term, singleton pregnancies obtained by assisted reproductive technologies (ART). The study group comprised 45 consecutive women with a singleton pregnancy, obtained by ART, who delivered at term. For each subject in the study group, the consecutive, matched-for-age-and-parity woman, with a term singleton, spontaneously conceived pregnancy served as the controls. The placentae of both groups were subject to a detailed morphological and histopathological investigation by one pathologist, who was blinded to specimen origin. Pregnancy complications, fetal weight and perinatal outcome were similar in both groups. No differences in morphological or histopathological features of the placenta were observed between the groups. Nevertheless, the placentae of the study group showed a borderline, significantly higher placental weight and placental:fetal weight ratio, and placental thickness was significantly higher. Abnormal umbilical cord insertion was significantly more prevalent in the study group. Neither the specific ART method employed, nor the infertility factor affected the results, suggesting that multiple embryo transfers and/or ovulation induction protocols may account for these differences.

Adult↗
PubMed1997

p94fer facilitates cellular recovery of gamma irradiated pre-T cells.

p94fer is a ubiquitous, nuclear and cytoplasmic tyrosine kinase, whose accumulation has been demonstrated in all mammalian cell lines analysed. In the present work, the p94fer expression profile was determined in cell lines which were not tested before. While being present in several hematopoietic and non hematopoietic cell lines including thymic stromal cells, the p94fer kinase could not be detected in pre-T and T cell lines. p94fer was also absent in pre-B line, but accumulated in these cells upon their induced development to antibody producing cells. This is in agreement with the absence of p94fer in primary thymic and splenic T lymphocytes and its induced accumulation in stimulated B cells. Relatively high p94fer levels were detected in primary thymic and splenic stromal cells. Ectopic expression of p94fer in pre-T cells slightly affected their cell cycle profile but it did not affect their apoptotic death which was induced by ionizing radiation. However, p94fer facilitated dramatically, the cellular recovery of gamma irradiated pre-T cells which have escaped the apoptotic death. The enhanced recovery of the irradiated, p94fer expressing pre-T cells, resulted most probably from their increased survival, rather than from a prominent change in their proliferation rate. The absence of p94fer from pre-B and pre-T cells, may thus contribute to the relative sensitivity of these cells to ionizing radiation and to their dependence on the functioning of other nuclear tyrosine kinasese.

3T3 Cells↗
PubMed1997

Cadmium leads to stimulated expression of the lipid transfer protein genes in barley: implications for the involvement of lipid transfer proteins in wax assembly.

In order to investigate the nature of genes expressed in leaf epidermal cells of higher plants, we have identified the nucleotide sequence of a cDNA designated ltp 7a2b encoding a novel nonspecific lipid transfer protein of barley (Hordeum vulgare L. cv. Gerbel). The cDNA of 755 basepairs contains an open reading frame of 366 nucleotides coding for a 12.3-kDa polypeptide. The first 29 amino acids constitute the putative signal peptide, characteristic for targeting to the secretory pathway. Analysis of mRNA levels by Northern blotting indicated that ltp 7a2b is preferentially expressed in the leaf epidermis. Levels of mRNA decreased during ageing of leaf tissue. Expression of ltp 7a2b was stimulated by a factor of 2 - 3 when the seedlings were grown in the presence of cadmium (10 - 1600 microM). Concomitantly, the primary leaves of Cd-exposed seedlings contained elevated levels of abscisic acid and thicker was layer of the cuticle. At 100 microM Cd in the hydroponic medium, the was cover was increased by 50%. The increase in abscisic acid content, ltp 7a2b mRNA and was coverage was either not seen, or seen much less, in Ni- and Zn-stressed seedlings. The data add circumstantial evidence to the recently proposed hypothesis that nonspecific lipid transfer proteins function in transfer of cutin and/or wax monomers from the site of synthesis in the cell to the cuticle.

Amino Acid Sequence↗
PubMed1996

Induction of apoptosis and p53 expression in immature thymocytes by direct interaction with thymic epithelial cells.

Apoptosis of normal thymocytes was shown to be triggered by several mechanisms (e.g. glucocorticoids, gamma-irradiation). In the present study the authors report on thymocyte apoptosis that is induced by thymic epithelial cells. The thymocytes undergo a massive apoptotic death within 24 h of cocultivation with thymic epithelial cell monolayers derived from primary cultures (PTEC) or from a thymic epithelial cell line (TEC). Non-thymic monolayers were inactive. Apoptosis induction in this experimental model requires direct contact between the thymocytes and the thymic epithelial monolayer and can be blocked by anti-CD2 and anti-LFA-1 antibodies. The immature CD3-/+dull CD4+CD8+ thymocytes were the cells which undergo apoptosis. The fact that the authors are dealing with a massive apoptotic process of immature cells in the absence of exogenous antigen suggests that it involves the nonselected thymocytes. The apoptotic pathway selected by thymocytes following their culturing on TEC involves p53 expression. Indeed it was found that TEC-induced apoptosis, led to the accumulation of p53 protein that preceded the step of DNA fragmentation in freshly isolated thymocytes as well as in a glucocorticoid resistant thymoma cell line. Since glucocorticoid-induced thymocyte apoptosis is p53-independent, glucocorticoids are conceivably not involved in TEC-induced thymocyte death. The in vitro experimental model presented here may reflect the physiological sequence of events leading to thymocyte death in the thymus.

Animals↗
PubMed1995

Disseminated Nocardia transvalensis infection resembling pulmonary infarction in a liver transplant recipient.

Infections due to Nocardia transvalensis are extremely rare: only four disseminated infections with this pathogen have been reported, three of which ended fatally. This is the first report of a liver transplant recipient with Nocardia transvalensis infection. The patient had disseminated infection with pulmonary involvement, which presented as pulmonary infarction. Despite a ten-day delay in the administration of correct therapy, he responded rapidly to trimethoprim-sulfamethoxazole. The pitfalls of differentiating nocardial infection from pulmonary thromboembolism in solid organ transplant recipients and the diagnostic considerations unique to liver transplant recipients are discussed.

Bacteremia↗
PubMed1995

The role of thymocytes in regulating thymic epithelial cell growth and function.

The basic tenet underlying the present work and supported by recent studies is that there is a dialogue between developing thymocytes and thymic stromal cells. One direction in this dialogue, i.e. thymic stromal cell role in shaping thymocyte maturation, has been extensively studied. The other direction, thymocyte effect on stromal cell development and function, started to emerge only recently on the basis of in vivo observations in SCID and knockout mice. An in vitro approach to the analysis of this interaction may add substantial insight into the process, as demonstrated by the present work. We made use of a culture system of either murine thymic epithelial cells (TEC line) cultured alone or cocultured with thymocytes. Unstimulated thymocytes or their supernatant caused 40-80% inhibition of TEC cell proliferation, as measured by 3H-thymidine incorporation. Cell cycle analysis by flow cytometry indicated that this inhibition can be attributed to reduction in G2/M phase cell number pari passu with an increase in Go/G1 cell number. This inhibitory effect was found to be partially mediated by TGF-beta produced by thymocytes. On the other hand, thymocytes augmented IL-6 production by TEC cells in coculture, an effect which could not be reproduced by thymocyte culture supernatant and was not inhibited by thymocyte pretreatment with formaldehyde or emetine. Furthermore, antibodies against thymocyte adhesion molecules (CD2, LFA-1) blocked the thymocyte-induced IL-6 secretion. IL-6 was found to be an autocrine growth factor of TEC in culture, since a combination of anti IL-6 and anti IL-6 receptor antibodies caused 70% inhibition of TEC proliferation and addition of exogenous recombinant IL-6 doubled the rate of proliferation. These results suggest that thymocytes regulate thymic epithelial cell growth by a complex set of inhibitory and enhancing signals mediated through either soluble factors or direct contact. The ultimate effect is dependent on the balance between different signals and may be different in different microenvironmental settings in vivo. In coculture in vitro the dominant effect was growth inhibition of the epithelial cells by thymocytes.

Animals↗
PubMed1995

Hemoglobin switching in humans is accompanied by changes in the ratio of the transcription factors, GATA-1 and SP1.

BACKGROUND: Understanding the mechanism of developmental regulation of hemoglobin switching has scientific as well as clinical relevance because of the influence of fetal hemoglobin (HbF) production in adulthood on the clinical manifestation of thalassemia and sickle cell anemia. We have previously found that the normal developmental patterns of globin gene expression are recapitulated in an experimental system of primary cultures that support differentiation of erythroid progenitors. We further found that high activities of the transcriptional activators, GATA-1 and SP1, are associated with normal adult erythroid differentiation. MATERIALS AND METHODS: In the present work, we have studied, the activities of GATA-1 and SP1 during differentiation of cultured erythroid progenitors derived from cord blood and from fetal livers, as well as from beta zero-thalassemia patients. RESULTS: The results showed high GATA-1 binding activity and very low SP1 activity in the fetal liver cultures. This pattern was in contrast to cultures derived from normal adult peripheral blood, in which both GATA-1 and SP1 activities were high. Cord blood cultures showed an additive combination of "adult" and "fetal" patterns. The progenitors derived from a beta zero-thalassemia patient with high HbF production showed "fetal" pattern. On the other hand, in cultures of 2 beta zero-thalassemia patients without high HbF, "adult" pattern was observed. CONCLUSIONS: In the present work, we show that human fetal and adult erythroid progenitors are distinct in their transcription factors, and that the commitment to fetal or adult program occurs at a very early differentiation stage. Our studies also demonstrate that under anemic stress, recruitment of fetal progenitors may occur in adulthood.

Adult↗
PubMed1994

Ischemia-induced brain iron delocalization: effect of iron chelators.

Tissue damage in cerebral ischemia may be produced by acidosis-induced delocalization of intracellular iron which acts as a catalyst in oxidative reactions. Acidosis was induced either by homogenization and incubation of rat cortical homogenates in acidified buffers or by submitting hyperglycemic rats to complete ischemia, a procedure that leads to intracellular lactic acidosis. The level of low molecular weight species (LMWS) iron was measured after filtration of tissue homogenates through a 10,000 Mr ultrafiltration membrane. When cortical tissue was homogenized in buffer pH 7, the level of LMWS iron was equal to 0.21 microgram/g. It was significantly enhanced by acidification of the homogenization medium, reaching 0.34 microgram/g at pH 6 and 0.75 microgram/g at pH 5. When the tissue was homogenized in water, the LMWS iron level reached 0.17 microgram/g in normoglycemic rats and 0.38 microgram/g (p < .05) in hyperglycemic rats. Both aerobic incubation of homogenates for 1 h at 37 degrees C and inclusion of EDTA in the homogenization medium led to further increases in the iron level. In order to demonstrate the deleterious role of iron in brain ischemia, the effect of treatment with bipyridyl, an iron-chelating agent, was assessed by measuring regional brain edema by the specific gravity method, 24 h following induction of thrombotic brain infarction. The treatment significantly attenuated the development of brain edema, reducing the water content of the infarcted area by about 2.5%. Taken together, these results support the hypothesis that a significant component of brain ischemic injury involves an iron-dependent mechanism.

2,2'-Dipyridyl↗
PubMed1994

Toxic epidermal necrolysis associated with Klebsiella pneumoniae sepsis.

Toxic epidermal necrolysis (TEN) is a rare condition in childhood usually attributed to drugs. We describe a 4-month-old infant who developed typical clinical and histologic findings of TEN concomitantly with Klebsiella pneumoniae sepsis. We emphasize that in cases of acute, severe exfoliative disease in infants, apart from staphylococcal infection, gram-negative bacterial sepsis must also be considered.

Bacteremia↗
PubMed1992

Effect of acidosis and anoxia on iron delocalization from brain homogenates.

Cortical homogenates were prepared from rat brain in Krebs-Ringer phosphate media adjusted to pH 7, 6 or 5 and incubated for 1 hr under aerotic or anaerobic conditions in the presence of dipyridyl, an iron chelator. Low molecular weight species (LMWS) iron was measured spectrophotometrically after passing of the homogenates through a 10,000-Mr ultrafiltration membrane. Following aerobic incubation, LMWS iron reached 1.24 micrograms/g tissue at pH 7, and increased 1.7-fold at pH 6 and 3.1-fold at pH 5. Anoxia enhanced significantly the amount of ultrafiltrable iron at the three pH values, the LMWS iron level being increased by 190% at pH 7, by 113% at pH 6, and by 77% at pH 5. Addition of the ultrafiltrates to brain membranes caused significant rises in the production of lipid peroxides assessed by the thiobarbituric acid test, indicating that LMWS iron was in a form capable for catalysing oxygen-derived free radical-mediated lipid peroxidation. It was concluded that decompartmentalization of intracellular iron may be an important factor in the initiation of peroxidative damage to ischemic cells.

2,2'-Dipyridyl↗