Inhibition of egg development and implantation in rats after post-coital administration of the progesterone antagonist RU 486

RU 486 was administered to rats on Day 1 or Days 1 + 2 of pregnancy. Endometrial sensitivity (i.e. decidualization in response to oil instillation) was delayed by 2.5 mg/kg injected s.c. on Day 1, and almost half of the animals also exhibited a delay in implantation of 1-2 days. Higher doses (5 or 10 mg/kg) administered on Days 1 + 2 reduced the number of implantations to zero in all animals. Apparently normal morulae were found up to the evening of Day 4 in the oviduct and/or the uterus of most animals. However, on the morning of Day 5, ova were detected in only 25% of the animals and all were in the uterus: none was at the blastocyst stage and they appeared to be degenerated or compacted morulae. Egg survival and rate of egg recovery from the uterus was not improved by early ovariectomy, showing that this antiprogestagen acts on these events independently of the presence of circulating oestrogens.     

Cytogenetic study of F1 hybrids betweenCrepis dinarica andCrepis froelichiana (Asteraceae)

Crepis dinarica andC. froelichiana are two closely related species of theC. praemorsa complex. Even though they exhibit the same chromosome number (2n = 8) and similar idiogram shape, they differ widely in quantity and distribution of heterochromatin bands. The hybrids between these two species comprise three morphological types. Parental genomes were distinguished in hybrids by Giemsa differential staining (C-banding). Although meiosis presents only a few abnormalities (about 2.4%), the percentage of aborted pollen grains is very high (90%).     

Hemagglutination Inhibition with Arboviruses: Relationship Between Titers and Source of Erythrocytes

Antigens for Grand Arbaud, Hazara, and California arboviruses were able to agglutinate goose and either dog, hamster and guinea pig, or hamster red blood cells (RBC) to the same titer at the same pH; in hemagglutination-inhibition (HI) tests, titers for homologous and related sera were the same with these different types of RBC or occasionally one dilution higher with the mammalian cells. Antigens for St. Louis encephalitis and Eastern equine encephalitis viruses required use of lower antigen dilutions with human, guinea pig, and hamster RBC than with goose RBC. The results of comparative HI testing with these latter antigens and types of RBC indicate that HI titer is not directly related to the antigen dilution used with different types of RBC.     

Effect of mifepristone (RU 486) on concentrations of prostaglandin E-2 binding sites in the rat endometrium

Progesterone implants in ovariectomized rats increased endometrial concentrations of PGE-2 receptors. The increase was completely inhibited by simultaneous daily injection (7.5 mg/kg) of mifepristone (RU 486). A single injection of mifepristone on the morning of Day 1 of pseudopregnancy (day of oestrus) decreased the amount of PGE-2 receptors found in the endometrium on Day 5 by 64%. This inhibitory effect probably resulted from the antiprogesterone activity of this compound since it was not counteracted by simultaneous treatment with dexamethasone, shown to reverse totally the antiglucocorticoid action of mifepristone. The inhibition by mifepristone lasted only for 1 day; endometrial PGE-2 receptor levels on Day 6 of pseudopregnancy returned to the high values present in controls. Under these conditions, administration of the mifepristone did not affect the plasma oestradiol and progesterone concentrations during the 1st week of pseudopregnancy. The administration of mifepristone on Days 2 and 3 of pseudopregnancy kept the endometrial PGE-2 receptor levels low, even by 4 days after the end of treatment. We therefore concluded that, in the rat, progesterone priming leading to uterine receptivity can be delayed, at least by 1 day. In contrast, interruption of the progesterone action for a longer period later during the early pseudopregnant period resulted in an altered subsequent evolution of the endometrium, in terms of acquisition of the PGE-2 binding sites.     

Functional Expression of P-Glycoprotein in an Immortalised Cell Line of Rat Brain Endothelial Cells, RBE4

Abstract: The presence of P-glycoprotein in the cell plasma membrane limits the penetration of many cytotoxic substances into cells that express the gene product. There is considerable evidence also to indicate that P-glycoprotein is expressed as part of the normal blood-brain barrier in the luminal membranes of the cerebral capillary endothelial cells, where it presumably performs a protective function for the brain. This report describes the functional expression of P-glycoprotein in an immortalised cell line, RBE4, derived from rat cerebral capillary endothelial cells. The expression of P-glycoprotein is demonstrated by western immunoblotting and by immunogold and fluorescent staining with monoclonal antibodies. The cellular accumulation of [³H]colchicine and [³H]vinblastine is investigated and shown to be enhanced by the presence of azidothymidine, chlorpromazine, verapamil, cyclosporin A, and PSC 833 ([3'-keto-Bmt¹]-[Val²]-cyclosporin) at 50 or 100 µ M concentration. It is concluded that the RBE4 cell line is a valuable tool for investigating the mechanisms of P-glycoprotein activity both in the blood-brain barrier and in multidrug resistance in general.     

Pigment interactions in chlorosomes of various green bacteria

Resonance Raman experiments were performed on different green bacteria. With blue excitation, i.e. under Soret resonance or preresonance conditions, resonance Raman contributions were essentially arising from the chlorosome pigments. By comparing these spectra and those of isolated chlorosomes, it is possible to evaluate how the latter retain their native structure during the isolation procedures. The structure of bacteriochlorophyll oligomers in chlorosomes was interspecifically compared, in bacteriochlorophyllc- and bacteriochlorophylle- synthesising bacteria. It appears that interactions assumed by the 9-keto carbonyl group are identical inChlorobium limicola, Chlorobium tepidum, andChlorobium phaeobacteroides. In the latter strain, the 3-formyl carbonyl group of bacteriochlorophylle is kept free from intermolecular interactions. By contrast, resonance Raman spectra unambiguously indicate that the structure of bacteriochlorophyll oligomers is slightly different in chlorosomes fromChloroflexus auranticus, either isolated or in the whole bacteria.     

Trade-offs and synergies between ecosystem productivity and stability in temperate grasslands

Aim

It is crucial to monitor how the productivity of grasslands varies with its temporal stability for management of these ecosystems. However, identifying the direction of the productivity–stability relationship remains challenging because ecological stability has multiple components that can display neutral, positive or negative covariations. Furthermore, evidence suggests that the direction of the productivity–stability relationship depends on the biotic interactions and abiotic conditions that underlie ecosystem productivity and stability. We decipher the relationships between grassland productivity and two components of its stability in four habitat types with contrasting environments and flora.

Location

France.

Time period

2000–2020.

Major taxa

Grassland plant species.

Methods

We used c. 20,000 vegetation plots spread across French permanent grasslands and remotely sensed vegetation indices to quantify grassland productivity and temporal stability. We decomposed stability into constancy (i.e., temporal invariability) and resistance (i.e., maximum deviation from average) and deciphered the direct and indirect effects of abiotic (namely growing season length and nitrogen input) and biotic (namely plant taxonomic diversity, trait diversity and community-weighted mean traits) factors on productivity–stability relationships using structural equation models.

Results

We found a positive relationship between productivity and constancy and a negative relationship between productivity and resistance in all habitats. Abiotic factors had stronger effects on productivity and stability compared with biotic factors. A longer growing season enhanced grassland productivity and constancy. Nitrogen input had positive and negative effects on grassland productivity and resistance, respectively. Trait values affected the constancy and resistance of grassland more than taxonomic and trait diversity, with effects varying from one habitat to another. Productivity was not related to any biotic factor.

Main conclusions

Our findings reveal how vital it is to consider both the multiple components of stability and the interaction between environment and biodiversity to gain an understanding of the relationships between productivity and stability in real-world ecosystems, which is a crucial step for sustainable grassland management.     

Amino-acyl tXNA as inhibitors or amino acid donors in peptide synthesis

Xenobiotic nucleic acids (XNAs) offer tremendous potential for synthetic biology, biotechnology, and molecular medicine but their ability to mimic nucleic acids still needs to be explored. Here, to study the ability of XNA oligonucleotides to mimic tRNA, we synthesized three L-Ala-tXNAs analogs. These molecules were used in a non-ribosomal peptide synthesis involving a bacterial Fem transferase. We compared the ability of this enzyme to use amino-acyl tXNAs containing 1′,5′-anhydrohexitol (HNA), 2′-fluoro ribose (2′F-RNA) and 2′-fluoro arabinose. L-Ala-tXNA containing HNA or 2′F-RNA were substrates of the Fem enzyme. The synthesis of peptidyl-XNA and the resolution of their structures in complex with the enzyme show the impact of the XNA on protein binding. For the first time we describe functional tXNA in an in vitro assay. These results invite to test tXNA also as substitute for tRNA in translation.