The protein product of the het-s heterokaryon incompatibility gene of the fungus Podospora anserina behaves as a prion analog

The het-s locus of Podospora anserina is a heterokaryon incompatibility locus. The coexpression of the antagonistic het-s and het-S alleles triggers a lethal reaction that prevents the formation of viable heterokaryons. Strains that contain the het-s allele can display two different phenotypes, [Het-s] or [Het-s*], according to their reactivity in incompatibility. The detection in these phenotypically distinct strains of a protein expressed from the het-s gene indicates that the difference in reactivity depends on a posttranslational difference between two forms of the polypeptide encoded by the het-s gene. This posttranslational modification does not affect the electrophoretic mobility of the protein in SDS/PAGE. Several results suggest a similarity of behavior between the protein encoded by the het-s gene and prions. The [Het-s] character can propagate in [Het-s*] strains as an infectious agent, producing a [Het-s*] --> [Het-s] transition, independently of protein synthesis. Expression of the [Het-s] character requires a functional het-s gene. The protein present in [Het-s] strains is more resistant to proteinase K than that present in [Het-s*] mycelium. Furthermore, overexpression of the het-s gene increases the frequency of the transition from [Het-s*] to [Het-s]. We propose that this transition is the consequence of a self-propagating conformational modification of the protein mediated by the formation of complexes between the two different forms of the polypeptide.

Ontogeny of the D1 dopamine receptor in the rat striatonigral system: an immunohistochemical study

Antibodies were raised against a recombinant protein to analyse the pre- and postnatal ontogeny of the neurons expressing the D1 dopamine receptor in the striatum by immunohistochemistry. We report that D1 immunoreactivity is detectable from gestational day (G) 15 and is distributed homogeneously throughout the striatum from G15 to G18. From G19-20 to postnatal day (P) 3, D1 immunoreactivity becomes heterogeneous and predominates in cell bodies of the patch compartment while very limited immunoreactivity is detectable in the matricial compartment. The differential intensity between patches and matrix reaches its peak around P0. From P2, the pattern of D1 immunoreactivity progressively assumes the homogeneous distribution characteristic of the adult striatum. The expression of D1 mRNA in striatal neurons, as investigated by in situ hybridization, displays a similar pattern during this period. Substance P mRNA is also preferentially expressed in the patch compartment during the same period. D1 immunoreactivity appears at G17 in the substantia nigra as clusters of fibres and increases subsequently until reaching its adult form during the first postnatal week. These results demonstrate that the two compartments of the developing striatum display differential transcriptional and translational activity for the D1 gene and consequently two different and successive patterns of expression of D1 protein: patch neurons first express D1 receptor intensely while matrix neurons express it later and in smaller amounts so that D1 receptor appears transiently during the perinatal period as a marker of the patch compartment.

[Contribution of gene amplification in the biological diagnosis of toxoplasmosis]

Biological diagnosis of toxoplasmosis is generally based on indirect arguments (serology). In cases of immaturity or of immune depression, however, evidence of the parasite has to be obtained. This involves time-consuming or relatively insensitive culture techniques. Molecular biology, and more particularly the polymerase chain reaction gene amplification technique, makes it possible to identify an extremely small quantity of parasites in a complex biological fluid in a few hours. We summarized our experience with an original technique using toxoplasma ribosomal DNA as the target. Its use in the amniotic fluid provides a distinct improvement in antenatal diagnosis and is fast becoming the technique of reference. Difficult cases have been solved by its application in ophthalmology. Finally, in immunodepressed patients, especially in cases of acquired immunodeficiency syndrome, assessment is currently ongoing. The results obtained so far, especially in the analysis of the cerebral spinal fluid, are encouraging.

Detection of Toxoplasma gondii in aqueous humour by the polymerase chain reaction

Ocular toxoplasmosis is the most frequent infectious cause of chorioretinal inflammation in immunocompetent patients. Nowadays, the biological diagnosis of ocular toxoplasmosis requires serological tests and anterior chamber puncture to detect the local production of specific antibodies. A new technique is described to detect Toxoplasma in aqueous humour by a polymerase chain reaction in which the target is a specific ribosomal DNA segment. Sixty eight patients (71 eyes) were included; 59 (83%) eyes were suspected of having ocular toxoplasmosis. Of these 59 eyes, 15 (25.4%) had characteristic fundus lesions with obvious intraocular inflammation signs and 44 (75%) had retinal scar of ocular toxoplasmosis without clinically detectable inflammation. Twelve (17%) eyes had uveitis of non-Toxoplasma origin and constituted the control group. The parasite was present in aqueous humour in 20 (33.8%) cases. No false positives were detected. The sensitivity of the test is reduced by the low numbers of the sample. The combination of this technique with Witmer-Desmonts coefficient increases the probability of making a biological diagnosis of ocular toxoplasmosis. The physiopathological value of this technique is emphasised and the presence of tachyzoites in the anterior chamber is suggested. This should be a very promising technique for the diagnosis of ocular toxoplasmosis.

Retinoic acid decreases retinoic acid and triiodothyronine nuclear receptor expression in the liver of hyperthyroidic rats

Retinoic acid (RA) and triiodothyronine (T3) exert many of their actions by binding to specific nuclear receptors (respectively, RA receptor (RAR) and T3) receptor (TR) belonging to a 'superfamily' of receptors. Some heterologous regulation of these receptors has been shown, and in particular regulation of the maximum binding capacity of TR by either retinol or RA. Now, using hyperthyroidic rats as a model, the effect of RA on binding capacity and on the mRNA levels of TR and RAR was investigated. The results show that the benefit of vitamin A treatment for the hyperthyroidic state, which has been described for a long time, could be the result of a down-heteroregulation of TR by RA, the active metabolite of retinol.

Contribution of a new PCR assay to the prenatal diagnosis of congenital toxoplasmosis

A polymerase chain reaction (PCR) assay has been developed for the detection of Toxoplasma gondii. The target sequence (88 bp) is part of a rDNA repetitive gene. A signal can be observed with only one parasite. It is directly and rapidly detected by electrophoresis and ethidium bromide staining. We report a prospective study of 80 documented cases of toxoplasmic seroconversions during pregnancy. The PCR assay of the amniotic fluids was compared with the current standard methods for diagnosis of fetal infection. Seventy specimens gave no PCR signal, and were negative according to prenatal tests and postnatal examinations. The presence of T. gondii was detected in ten specimens by PCR analysis. Four were confirmed by isolation of the parasite from the amniotic fluid; four by biological study of the fetal blood. For the remaining two, infection was diagnosed after birth. Together with ultrasonographic and biological data, this technique permits prenatal diagnosis within 1 day.

Polymorphism of class I alcohol dehydrogenase in French, Vietnamese and Niger populations: genotyping by PCR amplification and RFLP analysis on dried blood spots

The polymorphism of human alcohol dehydrogenase (ADH) can contribute to the explanation of the important ethnic differences towards alcohol metabolism. Its assessment at the genomic DNA level with a procedure, excluding labelled probes, consisting of PCR (Polymerase chain reaction) amplification on dried blood spots and analysis of allele-specific RFLP (Restriction fragment length polymorphism) profiles, is well adapted to extensive studies in population samples. It can emphasize the importance of ADH as a genetic marker of population. Three ethnic groups (French Caucasians, Vietnamese Orientals, Black Africans from Niger) were studied. ADH2 and ADH3 genotypes were in equilibrium according to the Hardy-Weinberg law. Important differences were noted in the distribution of ADH2 and ADH3 alleles.

Use of polymerase chain reaction to detect Toxoplasma

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c-erb-A mRNA content and triiodothyronine nuclear receptor binding capacity in rat liver according to vitamin A status

Vitamin A is required for normal growth and development and synergistically acts with thyroid hormones in these processes. Effects of retinol dietary intake (0, 5, 50 U retinol/g food) on the triiodothyronine (T3) nuclear receptor were examined in rat liver. Properties of this receptor have been investigated by an in vitro binding method. The amount of c-erb-A mRNA has been deduced by reverse transcription and amplification methods (PCR). Results show that both retinol deficiency and excess leads to a reduced amount of c-erb-A mRNA and to a decreased T3 binding capacity, suggesting that retinol, or retinoic acid which is its natural metabolite, contributes to the regulation of the T3 nuclear receptor properties.

Glutathione S-transferase class mu in French alcoholic cirrhotic patients

The lack of glutathione S-transferase mu (GST mu) was examined in 45 healthy French Caucasians and 45 alcoholic cirrhotic French Caucasians: microsamples of blood were taken and DNA amplified by the polymerase chain reaction. We have concluded that there is no relationship between this genotype and the development of alcoholic cirrhosis in these heavy consumers of ethanol.

Improved methods for genotype determination of human alcohol dehydrogenase (ADH) at ADH 2 and ADH 3 loci by using polymerase chain reaction-directed mutagenesis

The human gene for producing alcohol dehydrogenase (ADH; EC 1.1.1.1) is polymorphic at ADH 2 and ADH 3 loci. Until now, the study of this polymorphism required liver biopsy or allele-specific radioactive probes. We have used directed mutagenesis by the polymerase chain reaction (PCR) to amplify and analyze the genotype of ADH 2 and ADH 3 loci. Thus, we could determine easily and unambiguously the complete genotype at these two loci by using a microsample of blood and restriction fragment length polymorphism after DNA amplification by PCR.

Improved methods for genotype determination of human alcohol dehydrogenase (ADH) at ADH 2 and ADH 3 loci by using polymerase chain reaction-directed mutagenesis

The human gene for producing alcohol dehydrogenase (ADH; EC 1.1.1.1) is polymorphic at ADH 2 and ADH 3 loci. Until now, the study of this polymorphism required liver biopsy or allele-specific radioactive probes. We have used directed mutagenesis by the polymerase chain reaction (PCR) to amplify and analyze the genotype of ADH 2 and ADH 3 loci. Thus, we could determine easily and unambiguously the complete genotype at these two loci by using a microsample of blood and restriction fragment length polymorphism after DNA amplification by PCR.

repa, a repetitive and dispersed DNA sequence of the filamentous fungus Podospora anserina

The sequences of homologous DNA regions of two wild-type strains of the fungus Podospora anserina, revealed in one strain the presence of a 349bp insertion leading to a RFLP. This DNA sequence is repeated in the genome and some of its locations are different in various wild-type strains. This DNA element exhibits structural similarities with the yeast solo delta, sigma or tau elements.

Genotyping study of alcohol dehydrogenase class I polymorphism in French patients with alcoholic cirrhosis. The French Group for Research on Alcohol and Liver

Comparison of alcohol dehydrogenase polymorphism at the loci ADH2 and ADH3 is made in France between 46 alcoholic cirrhotic patients and 39 controls, by genotyping technique using polymerase chain reaction on blood microsample collected on blotting paper. The genotype distributions are similar, with low frequency of the ADH2(2) allele. Polymorphism at the ADH3 locus is not a genetic factor for alcoholic cirrhosis in France.

Immunological comparison of individual ribosomal proteins in six species of the genus Podospora

The ribosomal proteins of six species belonging to the genus Podospora have been compared by electrophoretical and immunological methods. The important variability in the electrophoretical properties is similar to other lower eukaryotes but we could specify the extent of the variability of the r-proteins by the analysis of immunological relationships between individual proteins. Radioimmuno-detection of ribosomal proteins blotted on nitrocellulose sheets after separation on two-dimensional gels, was used to determine common antigenic sites on the r-proteins of the different species. These sites may be present on proteins that do or do not have identical electrophoretical mobilities. Furthermore, the proteins which co-migrate do not necessarily cross-react.

DNA-dependent RNA polymerase III from the fungus Podospora comata. Purification, subunit structure and comparison with the homologous enzyme of a related species

DNA-dependent RNA polymerase III has been purified to homogeneity from the filamentous fungus Podospora comata. The enzyme was extracted at low ionic strength, separated from the polymerases I and II by DEAE-Sephadex chromatography and purified by heparin-Sepharose and phosphocellulose chromatography; 0.1-0.2 mg highly purified homogeneous enzyme with a specific activity of 220 units/mg could be obtained from 2 kg wet mycelium. The subunit composition of the enzyme was determined after sodium dodecyl sulphate/polyacrylamide gel electrophoresis; thirteen putative subunits of molecular weight 174000 (a), 129000 b), 87000 (c), 50000 (d), 39000 (e), 23500 (f), 21000 (g), 19000 (h), 17000 (i), 16500 (j), 13500 (k), 11000 (l) and 10000 (m) were identified. All of the polypeptide components of the enzyme are present in about integral stoichiometric amounts as judged by dye binding. The presence of subunit Mr = 87000 in a molar ratio 1:1 is necessary to obtain very active enzyme. Thirteen homologous subunits were observed in a preparation of RNA polymerase III from Podospora anserina, which is a related species. Only subunit i is different in the two species.

Genetics of ribosomal components in Podospora spp. as revealed by interspecific hybridization

The ribosomal proteins of several species within the genus Podospora have been analyzed by two-dimensional polyacrylamide gel electrophoresis. Differences in the migration of four proteins of the large subunit have been found between the two hybridizable species Podospora anserina and P. comata. Haploid offspring of this interspecific cross show all possible combinations of ribosomal proteins from both species. Therefore, the homologous proteins are functionally interchangeable. Moreover, the sizes of the different classes of offspring show that the genes encoding the four ribosomal proteins L2, L13, L16, and L20 are not clustered.

A new mutant form of the ribosomal protein L21 in the fungus Podospora anserina: identification of the structural gene for this protein

A muation in the cyR1 gene of the fungus Podospora anserina confers resistance to cycloheximide and leads to an alteration of the 60S ribosomal protein L21 (Bégueret et al. 1977). Nine revertants of this mutant were isolated and the properties of these strains were analyzed. It was found that one revertant strain contains a new mutant form of L21. It is proposed that cyR1 gene is the structural gene for protein L21 and that the alteration of this protein is responsible for the resistance to cycloheximide in vivo.

Altered ribosomal proteins in mutants of the fungus Podospora anserina

In the fungus Podospora anserina, a double mutant strain which combines two ribosomal mutations exhibits a marked sensitivity to NH4+ acetate. Mutations which suppress this phenotype were isolated. Two mutants were found to have an electrophoretically altered ribosomal protein. In one mutant, protein S15 from the small subunit has a reduced charge; in the other, the 60 S protein L16 is shorter than the homologous wild type protein. Both mutant and wild type proteins are present in heterokaryotic strains combining mutant and wild type nuclei. We therefore propose that the alteration of S15 and L16 results from mutations in the structural genes for these proteins.

Isolation and partial characterization of the multiple forms of deoxyribonucleic acid-dependent ribonucleic acid polymerase in the fungus Podospora anserina

Three DNA-dependent RNA polymerases have been isolated and partially purified from the mycelium of the fungus Podospora anserina. Separated by DEAE-Sephadex chromatography, they have been designated RNA polymerases I, II, and III according to their order of elution. Their catalytic properties and alpha-amanitin sensitivity are in agreement with those of the homologous enzymes found in other eukaryotic organisms. The three enzymes exhibit rather sharp monophasic ammonium sulfate dependence with optima which are, respectively, 0.035 M, 0.050 M, and 0.075 M. Enzyme I has the largest Mn2+/Mg2+ activity ratio, shows a marked preference for native DNA, and is insensitive to alpha-amanitin. Enzyme III uses poly(dA-dT) in preference to native DNA as template and is only partially sensitive to alpha-amanitin. Enzyme II is sensitive to alpha-amanitin, but high concentrations of the toxin are required for inhibition compared to other eukaryotic class II enzymes. Three similar RNA polymerases with comparable levels of activity were found in the temperature-dependent VR strain when cellular incompatibility, leading to a rapid cessation of RNA synthesis, was induced.

Ribosomal proteins in the fungus Podospora anserina: evidence for an electrophoretically altered 60S protein in a cycloheximide resistant mutant

Proteins of cytoplasmic ribosomes of the Podospora anserina were analyzed by two dimensional gel electrophoresis. The numbers of proteins were estimated to be 28 in the small subunit and 41 in the large subunit. The L21 protein of the large subunit was found to migrate differently in a cycloheximide resistant mutant.