PHYLOGENETIC ANALYSIS AND GENOME SIZE OF OSTREOCOCCUS TAURI (CHLOROPHYTA, PRASINOPHYCEAE)

Ostreococcus tauri Courties et Chrétiennot-Dinet is the smallest described autotrophic eukaryote dominating the phytoplanktonic assemblage of the marine Mediterranean Thau lagoon (France). Its taxonomic position was partly elucidated from ultrastructure and high-pressure liquid chromatography (HLPC) pigment analysis. The sequence analysis of the 18S rDNA gene of O. tauri measured here is available in EMBL Nucleotide Sequence Database (accession number: Y15814) and allowed to clarify its phylogenetic position. O. tauri belongs to the Prasinophyceae and appears very close to Mantoniella, a typical scaly Prasinophyceae, morphologically very different from the naked and coccoid Ostreococcus. An electrophoretic analysis of O. tauri shows that the nucleus contains 10.20 mbp. This small genome, fragmented into 14 chromosomes ranging in size from 300 to 1500 kbp, confirms the minimalist characteristics of Ostreococcus tauri.     

Inhibition of the in vitro 19S and 7S antibody response by immunoglobulin-binding factor (IBF) from alloantigen-activated T cells

A soluble factor secreted by alloantigen-activated mouse T cells which binds to the Fc fragment of IgG and inhibits complement activation by IgG (immunoglobulin-binding factor, IBF) suppressed the in vitro 19S and 7S antibody response by mouse spleen cells to T-dependent as well as T-independent antigens. IBF inhibited the 19S plaque response best when it was added late during PFC generation (between 48 and 72 hr). On the other hand, when it was left in cultures for up to 60 hr and then removed, antibody synthesis was not inhibited. However, its presence for only 2 hr starting after 72 hr of incubation was sufficient to inhibit PFC formation. The suppressive activity of IFB could be neutralized by adding aggregated mouse IgG prior to the critical stage around 72 hr. These data favour the view that IBF could be a suppressive T cell factor and point to the possibility that IBF may act on already triggered B cells during their final differentiation to active PFC.     

Isolation of soil Streptomyces strains capable of degrading humic acids and analysis of their peroxidase activity

Abstract Fifteen Streptomyces strains capable of decolorizing humic acids in presence of glucose were isolated from soil samples using the dilute suspension technique and spread on agar plates. Six strains, displaying a significant and stable activity, were selected for further characterization. Some features of these isolates (carbon source utilization, enzyme production, antibiotic resistance) were compared with those of the reference strain Streptomyces viridosporus ATCC 39115. Degradation properties studied in batch cultures at pH 7.0 showed that the catabolic activity on humic acids was generally stimulated by incubation with 100% oxygen and was cell surface-associated. Peroxidase activity from cell-free extracts was analysed by using the oxidation of N,N,N′,N′-tetramethyl-phenylene-diamine. PAGE analysis revealed the existence of two major types of peroxidases (molecular mass: about 39.2 and 61.6 kDa), dividing the strains into two groups. The role of cell surface-associated peroxidase activity in the breakdown of humic acids is discussed.     

ANT3 and STS are autosomal in prosimian lemurs: implications for the evolution of the pseudoautosomal region

Comparative in situ hybridization in various primate species has revealed a pseudoautosomal location for the human ANT3 gene and an X-specific location for the steroid sulfatase (STS) gene throughout the higher primate species up to the New World monkeys. However, ANT3 and STS map together on an autosome of two prosimian species of the genus Lemur and Eulemur. These results suggest an autosome-to-X/Y translocation after the simians radiated from the prosimians, resulting in a pseudoautosomal location of genes such as ANT3 and STS. In simian primates, STS then became X-specific by a pericentric inversion in the Y chromosome followed by mutational inactivation of the Y allele.     

Body size and host range in European Heteroptera

We used data on body size and host range of phytophagous Heteroptera in central Europe, an inverse measure of specialisation, to analyse the relationship of body size vs specialisation: 1) we found a clear positive relationship between body size and host range using species as independent data points. 2) However, a nested analysis of variance shows that most of the variance in body size occurred at higher taxonomic levels whereas most of the variance in host specialisation occurred between species. This suggests different phylogenetic inertia of body size and specialisation. Nevertheless, using means of different higher taxonomic levels there is still a significant positive correlation between body size and host range. 3) With more sophisticated methods of correcting for the phylogenetic relatedness between species, the positive correlation between body size and host range still holds, despite the different assumptions of each method. Thus, the relationship between body size and host range is a very robust pattern in true bugs.     

Regulation of the Saccharomyces cerevisiae Srs2 helicase during the mitotic cell cycle, meiosis and after irradiation

The expression of theSRS2 gene, which encodes a DNA helicase involved in DNA repair inSaccharomyces cerevisiae, was studied using anSRS2-lacZ fusion integrated at the chromosomalSRS2 locus. It is shown here that this gene is expressed at a low level and is tightly regulated. It is cell-cycle regulated, with induction probably being coordinated with that of the DNA-synthesis genes, which are transcribed at the G1-S boundary. It is also induced by DNA-damaging agents, but only during the G2 phase of the cell cycle; this distinguishes it from a number of other repair genes, which are inducible throughout the cycle. During meiosis, the expression ofSRS2 rises at a time nearly coincident with commitment to recombination. Sincesrs2 null mutants are radiation sensitive essentially when treated in G1, the mitotic regulation pattern described here leads us to postulate that either secondary regulatory events limit Srs2 activity to G1 cells or Srs2 functions in a repair mechanism associated with replication.     

Tonnacypris glacialis (Ostracoda, Cyprididae): taxonomic position, (palaeo-) ecology, and zoogeography

Abstract. The freshwater ostracod Tonnacypris glacialis (Sars, 1890) is reported from the European Pleistocene for the first time. The historical allocation of the species is discussed, and the species composition and characteristics of Tonnacypris Diebel & Pietrzeniuk (1975) and its phylozoogeography are considered. The significance of T. glacialis is reviewed, particularly from the viewpoint of the possible implications of parthenogenesis (and occasional-male production) for the Quaternary history of the genus, and for the use of the species in palaeoenvironmental reconstruction. It is suggested that the Pleistocene fossil occurrence of T. glacialis in modern temperature latitudes is a robust indicator of mean summer temperatures of 6°C.