Regulation of S-adenosylmethionine decarboxylase activity in rat liver and prostate

Two methods were used for the quantitation of S-adenosylmethionine decarboxylase protein. The first involved titrating the active site of the enzyme by reduction of the Schiff base between 3H-decarboxylated S-adenosylmethionine and the pyruvate prosthetic group with sodium cyanoborohydride. The second method was radioimmunoassay with rabbit antiserum which was used to determine the total immunoreactive enzyme protein. It was found that the increased S-adenosylmethionine decarboxylase activity produced in rat prostate by treatment with alpha-difluoromethylornithine and in both prostate and liver by methylglyoxal bis(guanylhydrazone) were due entirely to increases in the amount of enzyme protein. The ratio of enzyme activity to protein (measured by either method) remained constant in rats treated with the drugs. Treatment with 2% alpha-difluoromethylornithine in the drinking water for 3 days increased prostatic S-adenosylmethionine decarboxylase protein by 5-fold. A substantial part, but not all, of this increase could be accounted for by a slowing of the rate of degradation of the enzyme. The half-life for loss of activity and titratable protein after inhibition of protein synthesis by cycloheximide was increased from 35 to 108 min by treatment with alpha-difluoromethylornithine. However, the half-life for loss of immunoreactive protein which was considerably longer was only increased from 139 to 213 min. The molecular weight of the S-adenosylmethionine decarboxylase subunit determined by immunoblotting was 32,000, and no smaller immunoreactive fragments were detected. These results indicate that spermidine depletion produced by alpha-difluoromethylornithine affects the degradation of S-adenosylmethionine decarboxylase at an early step involving the loss of the active site without substantial breakdown of the protein.     

Analysis of the heterochromatin of <Emphasis Type="Italic">Cebus</Emphasis> (Primates,Platyrrhini) by micro-FISH and banding pattern comparisons

The karyotype of the neotropical primate genus Cebus (Platyrrhini: Cebidae), considered the most ancestral one, shows the greatest amount of heterochromatin described among Platyrrhini genera. Banding techniques and restriction enzyme digestion have previously revealed great variability of quantity and composition of heterochromatin in this genus. In this context, we use fluorescence in situ hybridization (FISH) to analyse this genomic region and discuss its possible role in the diversification of Cebus. We used a heterochromatin probe for chromosome 11 of Cebus libidinosus (11qHe+ CLI probe), obtained by chromosome microdissection. Twenty-six specimens belonging to the families Atelidae, Cebidae, Callitrichidae and Pithecidae (Platyrrhini) were studied. Fourteen out of 26 specimens were Cebus (Cebidae) individuals of C. libidinosus, C. xanthosternos, C. apella, C. nigritus, C. albifrons, C. kaapori and C. olivaceus. In Cebus specimens, we found 6 to 22 positive signals located in interstitial and telomeric positions along the different species. No hybridization signal was observed among the remaining Ceboidea species, thus reinforcing the idea of a Cebus-specific heterochromatin composed of a complex system of repetitive sequences.     

The role of refuge areas in the phenology of Rhopalosiphum padi in low rainfall cropping areas of South Australia

Extensive surveys of possible aphid habitats in South Australia indicated that irrigated perennial grass pastures in the Mount Lofty Ranges and Lower Murray Valley were summer refuges for Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Large numbers of aphids build up in these pastures each year during autumn (April and May) with numbers peaking in May. The size of the May peak was related to the number of aphids surviving the summer. The proportions of alates were highest in May and August/September. Both peaks coincided with a photoperiod of between 11.2 and 11.5 h, and partial correlations suggested that aphid density, photoperiod and temperature were all significant determinants of alate production.     

Effet de la farnesylacetone sur les syntheses proteiques de l'ovaire chez le crabe Carcinus maenas

Summary

We have analysed in vitro the effect of farnesylacetone, a substance produced by the androgenic gland of Crustacea, in a concentration of 20 ng/ml, on the protein synthesis in the ovary of Carcinus maenas. In winter, the farneslyacetone seems to be ineffective; the incorporation of labelled precursor per mass unity is then related to the weight of the sample. In summer, an activation of protein synthesis can be observed. These results do not depend on ovary maturation and concern all the proteins of the gonad.     

Further evidence for cortical control over replication of the macronucleus and basal bodies in Stentor

This paper presents further evidence that the cortex controls macronuclear replication and basal body production during the cell cycle of Stentor. At the onset of cell division, basal body production occurs on the ventral side of the cell to form an oral primordium; this structure develops slowly into the oral apparatus destined for the posterior daughter cell. Meanwhile, a series of morphological changes in the macronucleus (coalescence, elongation, nodulation) doubles the number of nodes in preparation for division. When a cell undergoing oral development is grafted to a morphostatic cell of equal size, oral development is usually induced in the morphostatic component and the two members of the graft complex eventually become synchronized with respect to macronuclear morphology. However, primordium induction and nuclear synchronization usually do not occur when the 2 members of the graft complex are separated by cortical discontinuities which heal gradually, even though the graft components demonstrably share a common endoplasm throughout the experiment. These results suggest that the cell surface may control the replication of organelles such as the macronucleus and basal bodies which are normally kept “in step” with the cell cycle in such a way that they are not lost or reproduced too frequently.