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Biomedical subjects

B Lambert

Publications and source records attributed to B Lambert.

At least 19 recordsLinked to original sources
PubMed1992

Visual dysfunction without retinitis in patients with acquired immunodeficiency syndrome.

Patients with human immunodeficiency virus infection may have noninfectious and infectious retinopathies, as well as clinical symptoms consistent with optic nerve dysfunction. Noninfectious acquired immunodeficiency syndrome-related retinopathy is seen in most patients with AIDS. Morphologic studies have shown that the number of retrobulbar optic nerve fibers in patients with AIDS is decreased compared to the number of optic nerve fibers in normal control eyes. To determine whether these patients had a visual dysfunction consistent with damage to the macula and optic nerve, 78 subjects (156 eyes) were studied using color-vision and contrast-sensitivity testing. The Farnsworth-Munsell 100-Hue color-vision test was performed on all subjects and age-corrected color-vision scores for all groups were compared. A significant decrease in color discrimination was found in the patients with AIDS (P less than .001). Contrast-sensitivity testing disclosed a deficit of contrast threshold in patients with AIDS at four of five spatial frequencies and in patients with AIDS-related complex at three of the five spatial frequencies examined. This study demonstrated a functional visual deficit in eyes without retinitis consistent with dysfunction of the macula or optic nerve in patients with AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Induction of 6-thioguanine-resistant mutants in human diploid fibroblasts in vitro with ethylene oxide.

Human diploid fibroblasts (strain VH-10) were exposed to the direct-acting alkylating agent, ethylene oxide (EtO), in vitro, and the frequency of HPRT mutants was evaluated by selection in medium containing 6-thioguanine. A dose-dependent increase of the mutant frequency was found in the dose range of 2.5-10 mMh of EtO. The EtO-induced mutant frequency increased 5-19 times the background frequency at low or moderately toxic doses, which indicates that EtO is a strong mutagen in human fibroblasts in vitro. The mutagenic potency was 9.8 x 10(-6) per mMh.

Alkylating Agents↗
PubMed1992

Mutations causing defective splicing in the human hprt gene.

Ten intron mutations and one exon mutation giving rise to defective splicing in the human gene for hypoxanthine phosphoribosyl transferase (hprt) in T-lymphocytes have been characterized. The splicing mutants were detected by PCR amplification of hprt cDNA and direct sequencing. Nine of the mutants showed skipping of whole exons or parts of exons in the cDNA, one mutant had an inclusion of an intron sequence into the cDNA, and one mutant showed both inclusion of an intron sequence and skipping of exons as well as a normal cDNA. Genomic PCR and direct sequencing of the splice sites involved showed one deletion of three base pairs and 10 different single base alterations to be responsible for these splice alterations. One mutation in the last base pair of exon 6 causing skipping of the entire exon 6 was found, whereas an identical mutation in the last base pair of exon 2 caused no aberrant splicing. It was also found that a deletion mutation in the pyrimidine rich stretch of the acceptor site of intron 7 caused skipping of the entire exon 8, whereas a base substitution in the last base of intron 7 caused exclusion of only the first 21 base pairs of exon 8 as a result of the activation of a cryptic acceptor site in exon 8. The results show that many different types of mutations at several different sites can cause splicing errors in the hprt gene and that the sequence differences between the splice sites influence the possible spectrum of mutations in each site.

Base Sequence↗
PubMed1992

Mutation analysis and prenatal diagnosis in a Lesch-Nyhan family showing non-random X-inactivation interfering with carrier detection tests.

A nonsense mutation at the CpG-site in the codon for Arg(169) in the gene for hypoxanthine phosphoribosyltransferase (hprt) was identified by genomic polymerase chain reaction (PCR) and DNA sequencing in cultured fibroblasts from two brothers with Lesch Nyhan's syndrome. The recurrence of mutation at this CpG-site in several unrelated Lesch-Nyhan families suggests that deamination of 5-methylcytosine is a possible mechanism for mutagenesis. The level of hprt-mRNA in the fibroblasts of the patients was similar to that in healthy controls, whereas hprt-enzyme activity was not detectable. The mutation in this family was also identified in five female relatives and prenatally in a male fetus. Unexpectedly, results from hair follicle analyses and fibroblast selection studies in 8-azaguanine and 6-thioguanine medium showed a non-carrier phenotype in three of the female heterozygotes, whereas X-inactivation mosaicism was demonstrated in one heterozygote. A possible explanation for the apparent non-random X-inactivation in this family is the co-existence of the hprt mutation with an undefined X-linked lethal mutation. This observation is of practical relevance for carrier detection in other Lesch-Nyhan families.

Base Sequence↗
PubMed1992

Strand specificity for mutations induced by (+)-anti BPDE in the hprt gene in human T-lymphocytes.

Mutations in the hprt gene in T-lymphocyte clones isolated from primary cultures treated with the (+)-anti enantiomer of 7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE) in vitro, and from untreated control cultures, were characterized using polymerase chain reaction and direct sequencing of hprt cDNA and genomic fragments. The spectrum of BPDE-induced mutations was very specific and clearly different from the background spectrum, which comprised many different types of mutations. Of the BPDE-induced mutations, 20/22 were transversions of GC base pairs and 18/22 were GC greater than TA transversions, which is in agreement with what has been found in other mammalian systems. While no particular 'hotspot' was observed for BPDE in the hprt gene, a sequence context specificity was detected. Ten of the 14 BPDE-induced mutations in the coding region were located in the sequence context AGG, and 2 in AG dinucleotides, which indicates that such sequences are sensitive to BPDE mutagenesis. Nine of the 22 BPDE-induced mutations and 2/12 background point mutations caused mRNA splicing errors. Six of the BPDE-induced splicing errors were caused by GC greater than TA transversions in the AG dinucleotide of different splice acceptor sites, which indicates that these sites may be frequent targets of BPDE mutagenesis. All mutated GC base pairs in the BPDE-induced spectrum were oriented so that the guanine was located on the non-transcribed strand. Assuming that the premutagenic lesion in these cases was covalent binding of BPDE to guanine and that BPDE bound randomly to both strands, the strand specificity of the BPDE-induced mutations indicates that preferential excision repair of BPDE adducts on the transcribed strand occurs in the hprt gene in human T-cells.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1992

Autocrine biological effects of glycosyl inositol phosphate produced by reconstituted pig thyroid follicles: role of pertussis toxin sensitive G proteins.

We examine the autocrine activity of glycosyl inositol phosphate (InP-gly) on thyroid metabolism. The cAMP accumulation promoted by thyrotropin (TSH) or forskolin was modulated by InP-gly, stimulated by the lowest tested concentration (10(-8) M) and progressively inhibited by higher concentrations. Iodide uptake and iodine organification were decreased in a concentration-dependent manner by InP-gly alone, or in the presence of TSH. The IAP component of pertussis toxin blocked the inhibitory action of InP-gly on cAMP accumulation by reconstituted thyroid follicles (RTF), suggesting the participation of Gi protein. But the same treatment with IAP was without effect on iodine metabolism, suggesting that there is a second target for InP-gly, more distal than Gi protein, or coupled to another G protein which is insensitive to the toxin.

Animals↗
PubMed1992

Missense mutations and evolutionary conserved amino acids at the human hypoxanthine phosphoribosyl-transferase locus.

Molecular characterization of in vivo mutation at the human hypoxanthine phosphoribosyltransferase (hprt) locus has revealed a broad spectrum of mutation, both with regard to germ-line mutation in Lesch-Nyhan and gout patients, and somatic mutation in 6-thioguanine resistant T-lymphocytes from healthy individuals. The pattern of missense mutation shows a non-random distribution with a preferential location to codons for amino acids which are identical in human and the two parasites Schistosoma mansoni and Plasmodium falciparum. Although these 'evolutionary conserved' amino acids account for only 32% of the amino acids in the human hprt protein, they are involved in 76% of the missense mutations at the hprt locus in human T-lymphocytes, 67% in Lesch-Nyhan patients (with severe hprt-deficiency), but only 43% in gout patients (with partial hprt deficiency). This observation supports the notion that evolutionary conserved amino acids constitute functionally important sites in the hprt enzyme, and missense mutations affecting these amino acids will often lead to complete loss of enzyme activity. Substitutions of 'non-conserved' amino acids cause less severe hprt-deficiency (as seen in the gout patients), or may even escape clinical diagnosis. These considerations are important for the understanding of structure-activity relationships in the hprt protein, possible differences between hprt mutational spectra in germ-line and somatic cells, and the mutational spectra induced by specific exogeneous mutagens.

Amino Acid Sequence↗
PubMed1992

Novel Bacillus thuringiensis insecticidal crystal protein with a silent activity against coleopteran larvae.

A novel Bacillus thuringiensis crystal protein with a silent activity against the Colorado potato beetle is described. The crystal proteins are produced as bipyramidal crystals. These crystals contain a protein of 129 kDa with a trypsin-resistant core fragment of 72 kDa. Neither a spore-crystal mixture nor in vitro-solubilized crystals are toxic to any of several Lepidoptera and Coleoptera species tested. In contrast, a trypsin-treated solution containing the 72-kDa tryptic core fragment of the protoxin is highly toxic to Colorado potato beetle larvae. The crystal protein-encoding gene was cloned and sequenced. The inferred amino acid sequence of the putative toxic fragment has 37, 32, and 33% homology to the CryIIIA, CryIIIB, and CryIIID toxins, respectively. Interestingly, the 501 C-terminal amino acids show 41 to 48% amino acid identity with corresponding C-terminal amino acid sequences of other crystal proteins. Because of the toxicity of the fragment to the Colorado potato beetle and because of the distinct similarities of the toxic fragment with the other CryIII proteins, this gene was given a new subclass name (cryIIIC) within the CryIII class of coleopteran-active crystal proteins. CryIIIC represents the first example of a crystal protein with a silent activity towards coleopteran insect larvae. Natural CryIIIC crystals are not toxic. Toxicity is revealed only after an in vitro solubilization and activation step.

Amino Acid Sequence↗
PubMed1991

The effect of glycosyl inositol-phosphate on cAMP production in isolated rat fat-cells is transduced by a pertussis toxin sensitive G-protein.

In fat-cells, insulin increases synergistically the inhibitory effects of adenosine and prostaglandin E2 on adenylyl cyclase activity. When the endogenous production of these feedback inhibitors is suppressed, insulin is no more active in conditions where glycosyl inositol-phosphate which is a putative mediator of its action, is always efficient. Moreover, glycosyl inositol-phosphate signal is transduced by a G protein sensitive to IAP intoxication.

Adenosine↗
PubMed1991

Expression of the hypoxanthine phosphoribosyl transferase gene in resting and growth-stimulated human lymphocytes.

Expression of the hypoxanthine phosphoribosyl transferase (hprt) gene was studied in resting and growth stimulated human lymphocytes by determinations of hprt-RNA and enzyme activity levels in cell extracts. Hprt-RNA was determined by quantitative solution hybridization and enzyme activity by measuring the rate of conversion of [14C]hypoxanthine to inosine 5'-monophosphate. In resting Go-lymphocytes, the hprt activity (5 nmol/h per 10(6) cells) was twice as high as in human fibroblasts, whereas the hprt-RNA level was very low (0.3 pg per 10(6) cells, or approx. one mRNA molecule per cell). Both RNA and enzyme activity remained at these levels in cells that were incubated in the presence of cycloheximide (CHX, 20 micrograms/ml) for up to 48 h, which suggests that hprt gene expression in resting lymphocytes depends mainly on a stable protein with a half-life of more than 48 h. In phytohemagglutinin (PHA) stimulated lymphocytes, the hprt-RNA levels increased 10-20-fold, while the enzyme activity increased 5-fold. The addition of hydroxyurea (0.01 M) to the culture medium did not prevent the increase of hrpt-RNA, whereas the increase of both RNA and enzyme activity was abrogated in the presence of CHX. Thus, the induction of hprt expression in growth stimulated lymphocytes requires new protein synthesis, and is not coupled to DNA replication. In long-term lymphocyte cultures, both hprt-RNA and enzyme activities showed high steady-state levels. After removal of PHA and growth factors from the culture medium the hprt-RNA levels decreased by over 80% within 24 h, while the enzyme activity was unaffected. Inhibition of transcription by actinomycin D (5 micrograms/ml) caused a rapid decay of the hprt-RNA, with an estimated half-time of 5.1 h. When CHX was added to actinomycin D inhibited cells, the rate of hprt-RNA breakdown was reduced. The hprt enzyme activity declined by approx. 50% during 24 in the presence of CHX. Thus, the enhanced expression of hprt-RNA in proliferating lymphocytes depends on continuous growth stimulation and seems to be associated with a high transcriptional activity and turnover of the RNA. In contrast, the enzyme activity is relatively stable, and less sensitive to alterations of growth conditions.

Cells, Cultured↗
PubMed1991

The fragile X mutation does not have any major effect on the expression of the hypoxanthine phosphoribosyltransferase (HPRT) locus in human fibroblasts.

The possible influence of the fragile X mutation at Xq27 on the expression of the neighbouring gene (at Xq26) for hypoxanthine phosphoribosyl transferase (HPRT) was studied by determination of the levels of HPRT-RNA and HPRT enzyme activity in fibroblast cell cultures from 7 fragile X patients. These levels were lower (although not statistically significantly lower) than in normal fibroblast cultures. Hence, these data do not support the notion of a major effect of the fragile X mutation on the expression of the HPRT gene.

Cells, Cultured↗
PubMed1991

Escherichia coli Fpg protein and UvrABC endonuclease repair DNA damage induced by methylene blue plus visible light in vivo and in vitro.

pBR322 plasmid DNA was treated with methylene blue plus visible light (MB-light) and tested for transformation efficiency in Escherichia coli mutants defective in either formamidopyrimidine-DNA glycosylase (Fpg protein) and/or UvrABC endonuclease. The survival of pBR322 DNA treated with MB-light was not significantly reduced when transformed into either fpg-1 or uvrA single mutants compared with that in the wild-type strain. In contrast, the survival of MB-light-treated pBR322 DNA was greatly reduced in the fpg-1 uvrA double mutant. The synergistic effect of these two mutations was not observed in transformation experiments using pBR322 DNA treated with methyl methanesulfonate, UV light at 254 nm, or ionizing radiation. In vitro experiments showed that MB-light-treated pBR322 DNA is a substrate for the Fpg protein and UvrABC endonuclease. The number of sites sensitive to cleavage by either Fpg protein or UvrABC endonuclease was 10-fold greater than the number of apurinic-apyrimidinic sites indicated as Nfo protein (endonuclease IR)-sensitive sites. Seven Fpg protein-sensitive sites per PBR322 molecule were required to produce a lethal hit when transformed into the uvrA fpg-1 mutant. These results suggest that MB-light induces DNA base modifications which are lethal and that these modifications are repaired by Fpg protein and UvrABC endonuclease in vivo and in vitro. Therefore, one of the physiological functions of Fpg protein might be to repair DNA base damage induced by photosensitizers and light.

Bacterial Proteins↗