Sporulation of Saccharomyces cerevisiae in the Absence of a Functional Mitochondrial Genome

The role of the mitochondrial system during sporulation of Saccharomyces cerevisiae was studied. Addition of ethidium bromide (EthBr) to cells growing in acetate medium resulted in the quantitative (>98%) conversion of the culture to the petite genotype in one generation. The cells were respiratory active (derepressed) but contained no mitochondrial deoxyribonucleic acid (mtDNA) as demonstrated by analytical ultracentrifugation in CsCl. When transferred to acetate sporulation medium, the culture sporulated. Ascus production was only slightly below that of the control culture. Synthesis of mtDNA occurred during sporulation in the control but not in the EthBr-treated culture. Mitochondrial protein synthesis was virtually eliminated in the EthBr-treated culture. Therefore, completely derepressed cells can sporulate without a functional mitochondrial genetic system. When partially repressed cells were treated with EthBr, no ascus formation was observed after transfer to sporulation medium. Control cultures underwent respiratory adaptation in sporulation medium and then sporulated. Extensive derepression of the respiratory system is thus required for sporulation, and this adaptation is dependent on a functional mitochondrial system. Our results suggest that once the cells are fully derepressed no mitochondrial genetic information has to be expressed during meiosis and ascus formation.     

Lysophosphatidylcholine disrupts the acrosome of tammar wallaby (macropus eugenii) spermatozoa

The acrosomal status of wallaby spermatozoa was evaluated by light and electron microscopy after incubation in 1–100 μM lysophosphatidylcholine (LPC) for up to 120 min. Treatment with 1 and 10 μM LPC for 120 min did not lead to acrosomal loss, or detectable alteration to the acrosome, as detected by Bryan's staining and light microscopy. Incubation with 25 μM LPC had little effect on acrosomal loss, however statistically significant changes (P < 0.05) in the acrosomal matrix (altered) were detected after 10-min incubation by light microscopy. Around 50% of acrosomes were altered after 20-min incubation in 50 μM LPC (P < 0.001), and 40% of spermatozoa had lost their acrosome after 60-min incubation (P < 0.001). Treatment with 75 and 100 μM LPC led to rapid acrosomal loss from around 50% of spermatozoa within 10 min (P < 0.001), and by 60 min acrosomal loss was 70–80%. LPC, like the diacylglycerol DiC₈ (1,2-di-octanoyl-sn-glycerol), is thus an effective agent to induce loss of the relatively stable wallaby sperm acrosome, and it also induces changes within the acrosomal matrix. Ultrastructure of the LPC-treated spermatozoa revealed that the plasma membrane and the acrosomal membranes were disrupted in a manner similar to that seen after detergent treatment (Triton X-100). There was no evidence of point fusion between the plasma membrane overlying the acrosome and the outer acrosomal membrane. The plasma membrane was the first structure to disappear from the spermatozoa. The acrosomal membranes and matrix showed increasing disruption with time and LPC concentration. Wallaby spermatozoa incubated with LPC at concentrations that induced significant acrosomal loss also underwent a rapid decline in motility that suggested that acrosomal loss may be due to cell damage, rather than a physiological AR. This study concluded that LPC-induced acrosomal loss from tammar wallaby spermatozoa is due to its action as a natural detergent and not as a phosphoinositide pathway intermediate. The study further demonstrates the unusual stability of the marsupial acrosomal membranes. © 1993 Wiley-Liss, Inc.     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.     

Parasites ofSpodoptera exigua,S. eridania [Lep.: Noctuidae] andHerpetogramma bipunctalis [Lep.: Pyralidae] collected fromAmaranthus hybridus in field corn

Three species of lepidopterous larvae were collected fromAmaranthus hybridus L. growing in field corn during 1975 and 1976 at Hastings, Florida.Spodoptera exigua (Hubner) was the predominant species in May.Spodoptera eridania (Cramer) was predominant in June andHerpetogramma bipunctalis (F.) in July and August. Nine native species of parasites, representing theBraconidae, Eulophidae, Ichneumonidae andTachinidae, emerged from these larvae.Meteorus autographae Muesebeck emerged from bothS. exigua andS. eridania. TheTachinidae, Winthemia rufopicta (Bigot),Eucelatori rubentis (Coquillett) andLespensia sp., emerged from mixtures ofS. exigua andS. eridania. Apanteles marginiventris (Cresson),Temelucha sp., andChelonus texanus Cresson emerged from bothS. exigua andH. bipunctalis larvae, andEuplectrus platyhypenae Howard andOphion sp. emerged fromS. eridania. All the species of parasites from the lepidopterous larvae that feed onAmaranthus hybridus are also reported as parasites ofS. frugiperda, a serious pest of corn. Therefore these larvae onA. hybridus may be a source of the parasites found attackingS. frugiperda.     

Identification of T-cell epitopes on E2 protein of rubella virus, as recognized by human T-cell lines and clones.

T-cell epitopes on the E2 protein of rubella virus were studied by using 15 overlapping synthetic peptides covering the E2 protein sequence. The most frequently recognized epitopes on E2 were E2-4 (residues 54 to 74), with 5 of 10 tested T-cell lines responding to it. Two CD4+ cytotoxic T-cell cloned isolated from one T-cell line responded strongly in proliferation assays with peptide E2-4 and were cytotoxic to target cells presenting the E2-4 determinant. Truncated peptides contained within the E2-4 peptide sequence were used to define the T-cell determinants. Results indicated that amino acid residues 54 to 65 were directly involved. Human cell lines with different HLA phenotypes were tested for the capacity to present the antigenic determinants. The results suggested that recognition of peptide E2-4 by T-cell clones was associated with HLA DR7.     

5-alkylvinyl-1,2,4-triazole nucleosides: Synthesis and biological evaluation

Abstract

Some 5-substituted ribavirin analogues have a high antiviral and anticancer activity, but their mechanisms of action are obviously not the same as their parent compound. The SAR studies performed on 3 (5)-substituted 1,2,4-triazole nucleosides have shown a high dependency between the structure of the 3 (5)-substituent and the level of antiviral/anticancer activity. The most active substances of the row contain coplanar with the 1,2,4-triazole ring aromatic substituent which is connected by a rigid ethynyl bond. However, the compounds with the trans-vinyl linker also had antiviral activity. We decided to study the antitumor activity of ribavirin analogues with alkyl/aryl vinyl substituents in the 5th position of the 1,2,4-triazole ring. Protected nucleoside analogues with various 5-alkylvinyl substituents were obtained by Horner-Wadsworth-Emmons reaction from the common precursor and converted to the nucleosides. Arylvinyl nucleosides were synthesised according the reported procedures. All compounds did not show significant antiproliferative activity on several tumour cell lines. Coplanar aromatic motif in the 5-substituent for the anticancer activity manifestation was confirmed.     

Clear-cutting impacts nutrient,carbon and water exchange parameters in woody plants in an east Fennoscandian pine forest

Plant and Soil - Clear-cut logging currently is a key factor transforming forest communities in many boreal regions. The dynamics of biogeochemical processes taking place in clear-cuts makes them a...