Incompatibility in Podospora anserina: Comparative Properties of the Antagonistic Cytoplasmic Factors of a Nonallelic System

In the fungus Podospora anserina, the interaction between the nonallelic incompatible R and V genes has two consequences: a lytic reaction due to the synthesis of specific proteolytic enzymes, and a quenching in protein and ribonucleic acid synthesis. The incompatibility reaction when vegetative or sexual R and V cells fuse is asymmetric: it is induced only in the R protoplasm. The cessation in ribonucleic acid and protein synthesis was investigated in heterokaryotic strains carrying the antagonistic R and V genes and their "neutral" r and v alleles. Asymmetry between R and V genes lies in the fact that the strains homozygous for the R genes are the only strains that cannot grow. From these results it is postulated that the V-gene product is a diffusible cytoplasmic factor and that the R-gene product, which is nonautonomous, is a ribosomal component.     

Short- and Long-Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive-Induced Seizures

Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment.     

Comparison of different cationic probes for electron microscopic visualization of bacterial polyanionic capsular material

We have isolated from the ovine rumen eight bacterial strains belonging to the speciesButyrivibrio fibrisolvens. DNA hybridization studies showed that the eight strains could be divided into four homology groups, of which none was closely related to the type strain ATCC 19171. Measurement of cross-hybridization between selected pairs of bacterial strains showed that DNA types which produced low, but significant, cross-hybridization on dot-blots were able to form heteroduplexes with between 8.4% and 32.9% of the efficiency of homoduplex formation. Thermal denaturation of the same heteroduplexes resulted in Tm values 6.4–7.5°C lower than those of the homologous duplexes formed under the same conditions. In some cases, hybridization between strains was below the level of reliable measurement. Similar experiments with ten recently isolated strains ofBacteroides ruminicola sub-sp.brevis revealed a similar degree of genetic divergence between isolates.     

Hormonal regulation of inositol 1,4,5-trisphosphate receptor in rat liver

Inositol 1,4,5-trisphosphate (IP3) is a second messenger which induces Ca2+ release from an intracellular store. We have investigated the properties of the [32P]IP3 binding sites in rat liver. Two specific [32P]IP3 receptors with KD of 2.3 and 88 nM and respective capacities of 33 fmol/mg protein and 195 fmol/mg protein have been detected in a crude membrane fraction prepared from rat liver homogenate. The pretreatment of the liver with IP3-dependent hormones increased two-fold the capacity of the high affinity site. This effect was partly reversed by dibutyryl cyclic AMP. Permeabilized hepatocytes also displayed two [32P]IP3 binding sites with KD of 1.5 and 84 nM and respective capacities of 8 and 300 fmol/10(6) cells. We have measured the [32P]IP3 binding and the IP3-induced 45Ca2+ release in the same batch of permeabilized hepatocytes. In a low Mg2+ medium, the EC50 for 45Ca2+ release was in close correlation with the KD for the low affinity site. These data suggest that an equilibrium between two states of the IP3 receptor is regulated by hormone action and the low affinity state is responsible for the intracellular Ca2+ release.