The cell cycle of lymphocytes in Fanconi anemia

Summary BrdU-incorporation techniques were used to study the cell cycle in 18 cases of Fanconi's anemia (FA).By comparison with controls, a significant slowing of the cell cycle of lymphocytes in vitro was observed in all FA patients, and possibly in FA heterozygotes, although to a lesser degree. It is probable that the demonstration of the slowing is dependent on the culture conditions. No slowing was observed in other patients affected by at least one of the symptoms of FA. The slow cell cycle of FA cells is mostly due to a very long G₂-phase. A relationship between slow cell cycle and chromatid anomalies exists, the slower cells being significantly more frequently carriers of radial figures than the faster cells, in the same patient.     

Genetic Structure and Internal Rearrangements of Stable Merodiploids from BACILLUS SUBTILIS Strains Carrying the trpE26 Mutation

Transformation and transduction to tryptophan independence of strains of Bacillus subtilis carrying the "trpE26" chromosomal aberrations (a translocation and an inversion) with a "normal" 168 type strain as donor induce a tandem duplication of the thrA-ilvA region of the chromosome. The clones possessing this unstable duplication segregate besides the Trp^- some stable Trp⁺ cells which retain only part of the duplication (the trpE-ilvA region) in nontandem configuration. Such clones may also be produced directly during the crosses. The genetic map of these clones (designated as class I stable merodiploids) was constructed: they possess the tranlocation and the inversion of the trpE26 parental strain. Another type of stable Trp⁺ clones (class II) also appears, although more rarely, in similar crosses. Studies on their genetic structure revealed that they are haploid for the trpE-ilvA region and carry a nontandem duplication of the thrA-trpE region. In these clones the cysB-tre region has the orientation of the 168 type strain. The duplications in both classes are stable, that of class I being more stable than that of class II where loss of one copy of the thrA-trpE region leads to about 1% haploid cells. Detailed genetic studies on heterozygous clones from both classes have shown exchange of alleles between copies of the nontandem duplications. Models are proposed for the formation of each class of merodiploids and for recombination events taking place in them. These models imply recombination at sequences of intrachromosomal homology and (or) introduction of heterologous juncions ("novel joints") by transformation or transduction.     

Localization of Phloem Oxidases

Among oxidases, cytochrome oxidase has been localized in mitochondria of all phloem cells, catalase has been visualized in parenchyma peroxisomes and peroxidase has been localized in cell walls and in several cell organelles. In angiosperms, peroxidase is present in all phloem cell walls; it is sensitive to cyanide inhibition excepted in sieve areas and around plasmodesmata between sieve tubes and companion cells. In some species, this cyanide resistant oxidasic activity can be localized without exogenous H₂O₂. Peroxidase is localized on ribosomes, inside vacuoles, on the tonoplast and often on the plasmalemma in companion cells and differentiating sieve elements. In young sieve cells some dictyosomes can exhibit a strong peroxidasic activity. In mature parenchyma cells peroxidase can be associated with ER cisternae but not with vacuoles.     

Distribution of mRNAs of fibrinogen polypeptides and albumin in free and membrane-bound polyribosomes and induction of α-fetoprotein mRNA synthesis during liver regeneration after partial hepatectomy

To study the effect of regenerative response of the liver following partial hepatectomy on the synthesis of major plasma proteins (secretory proteins), we have determined the sequence contents and the distribution of albumin and fibrinogen polypeptide mRNAs in rat liver at intervals after partial hepatectomy and sham operation. Using a quantitative technique for the isolation of polyribosomes, we demonstrated that the distribution of RNA between free and membrane-bound polyribosomal fraction was unchanged in these experiments. There was no shift in the polyribosomal population to favor free polyribosomes after partial hepatectomy. However, there was a dramatic increase (5–6-fold) of the fibrinogen polypeptide mRNA concentration during the first 24 h after resection. In contrast, the albumin mRNA concentration decreased (2–3-fold). There were no α-fetoprotein mRNA sequences detectable in any liver RNA fraction in these experimental animals. In sham-operated rats with intact livers, similar changes of fibrinogen polypeptide and albumin mRNA concentrations as described in regenerating liver after partial hepatectomy, were observed. These results suggest that albumin and fibrinogen synthesis after partial hepatectomy is reciprocally regulated at the mRNA level and represents a nonspecific acute phase response to surgical trauma.     

The structure of cyanobacterial phycobilisomes: a model

Phycobilisomes, supramolecular complexes of water-soluble accessory pigments, serve as the major light-harvesting antennae in cyanobacteria and red algae. Regular arrays of these organelles are found on the surface of the thylakoid membranes of these organisms. In the present study, the hemi-discoidal phycobilisomes of several species of cyanobacteria were examined in thin sections of cells and by negative staining after isolation and fixation. Their fundamental structures were found to be the same. Isolated phycobilisomes possessed a triangular core assembled from three stacks of disc-shaped subunits. Each stack contained two discs which were 12 nm in diameter and 6–7 nm thick. Each of these discs was probably subdivided into halves 3–3.5 nm thick. Radiating from each of two sides of the triangular core were three rods 12 nm in diameter. Each rod consisted of stacks of 2 to 6 disc-shaped subunits 6 nm thick. These discs were subdivided into halves 3 nm thick.The average number of discs of 6 nm thickness forming the peripheral rods varied among the strains studied. For certain chromatically adapting strains, the average rod length was dependent upon the wavelength of light to which cells were exposed during growth. Analyses of phycobilisomes by spectroscopic techniques, polyacrylamide gel electrophoresis, and electron microscopy were compared. These analyses suggested that the triangular core was composed of allophycocyanin and that the peripheral rods contained phycocyanin and phycoerythrin (when present). A detailed model of the hemi-discoidal phycobilisome is proposed. This model can account for many aspects of phycobiliprotein assembly and energy transfer.Abbreviations PBS phycobilisome(s) - PBP phycobiliprotein(s) - AP allophycocyanin - PC phycocyanin - PE phycoerythrin - PEC phycoerythrocyanin - AP-B allophycocyanin B - C- cyanobacterial - R- rhodophytan - B- Bangiophycean - SDS sodium dodecyl sulfate - LPP Lyngbya-Plectonema-Phormidium group - Na-KPO₄ buffers NaH₂PO₄ titrated with a solution of KH₂PO₄ of equivalent molarity to a given pH     

L'intensité lumineuse,son influence sur la teneur en phosphore des carapaces d'Ostracodes

Actual and fossil shells of ostracodes have beenanalyzed with an electronic microprobe: all of them contain phosphorus. X—pictures teach us that the repartition of this chemical element is homogeneous in all the points of the shell. There is no relationship between phosphorus contents in the shells of ostracodes and salinity. In return, there is a relationship between phosphorus contents and temperature and, chiefly, organic phosphorus contents in the environment. However, it is interesting to observe that the analyzed shells of fresh-water ostracodes contain less phosphorus that the generality of the shells of marine ostracodes. The contents of organic phosphorus, in the biotope, depends on the growth of phytoplancton in the upper layers of water which needs a minimum light intensity.     

Composés bromés de Rytiphlea tinctoria (Rhodophyceae)

Four aromatic bromo compounds have been isolated from the ethanolic extract of Rytiphlea tinctoria after treatment with diazomethane: 2,4-dibromo-1,3,5-trimethoxy-benzene,5,6,3′,5′-tetrabromo-3,4,2′,4′,6′-pentamethoxydiphenylmethane, 5,6-dibromo-3,4-dimethoxy-benzyl alcohol and its ethyl ether. In addition to sterols, amino acids, this extract also contains quinonoid bromo-pigments which could play a rôle in photosensitisation of chlorophylls, a rôle normally taken by the phycobilins, in other Rhodophyceae.     

First case of parthenogenesis in ladybirds (Coleoptera: Coccinellidae) suggests new mechanisms for the evolution of asexual reproduction

Parthenogenesis, the development of unfertilized eggs resulting in the exclusive production of female offspring, is rare in animals relative to sexual reproduction and is mainly reported in invertebrates. It has been hypothesized that polyploidy, hybridization and endosymbiont infections are its major causal events but the mechanisms triggering asexual reproduction remain unclear. Here, we study the proximate causes at the origin of parthenogenesis in the first reported case of asexuality in the Coccinellidae (Coleoptera). The asexual populations were found in the Azores and the Mascarene archipelagos, and were identified as Nephus voeltzkowi Weise, a bisexual species widespread in sub-Saharan Africa. The specimens from both populations are diploid but present different karyotypes and heterozygosities that evoke hybrid origins, commonly associated with parthenogenesis in Coleoptera. However, the close proximity of their genomes (99.8% homology for the complete mitochondrial genome and 99.9% for the complete nuclear ribosomal cluster) together with the congruence between the mtDNA tree and the nuclear tree, and the low heterozygosity levels, suggests that the two populations are not hybrid. We propose that they belong to a single chromosomally polymorphic species undergoing Robertsonian fusions. Furthermore, specimens from both populations are infected with Wolbachia (supergroup B strain), contrary to sympatric bisexual species of the same genus. Although Wolbachia has been shown to induce parthenogenesis in haplodiploid organisms, it has been recently suggested that it could also induce parthenogenesis in hosts with other sex determination systems. Whether chromosome rearrangements and/or Wolbachia infections are post-parthenogenetic events or are at the origin of parthenogenesis still needs to be determined.     

2′-and/or 3Y-Deoxy-β-L-pentofuranosyl Nucleoside Derivatives: Stereospecific Synthesis and Antiviral Activities

Abstract

Several L-enantiomers of nucleoside analogues were stereospecifically synthesized by a multi-step reaction from L-xylose and their antiviral properties were examined in vitro. Two of them, namely β-L-2′,3,′-dideoxycytidine (β-L-ddC) and its 5-fluoro derivative (β-L-FddC) were found to have potent anti-human immunodeficiency virus (HIV) and significant anti-hepatitis B virus (HBV) activities in cell cultures.