Monitoring Insect Transposable Elements in Large Double-Stranded DNA Viruses Reveals Host-to-Virus and Virus-to-Virus Transposition

The mechanisms by which transposable elements (TEs) can be horizontally transferred between animals are unknown, but viruses are possible candidate vectors. Here, we surveyed the presence of host-derived TEs in viral genomes in 35 deep sequencing data sets produced from 11 host–virus systems, encompassing nine arthropod host species (five lepidopterans, two dipterans, and two crustaceans) and six different double-stranded (ds) DNA viruses (four baculoviruses and two iridoviruses). We found evidence of viral-borne TEs in 14 data sets, with frequencies of viral genomes carrying a TE ranging from 0.01% to 26.33% for baculoviruses and from 0.45% to 7.36% for iridoviruses. The analysis of viral populations separated by a single replication cycle revealed that viral-borne TEs originating from an initial host species can be retrieved after viral replication in another host species, sometimes at higher frequencies. Furthermore, we detected a strong increase in the number of integrations in a viral population for a TE absent from the hosts’ genomes, indicating that this TE has undergone intense transposition within the viral population. Finally, we provide evidence that many TEs found integrated in viral genomes (15/41) have been horizontally transferred in insects. Altogether, our results indicate that multiple large dsDNA viruses have the capacity to shuttle TEs in insects and they underline the potential of viruses to act as vectors of horizontal transfer of TEs. Furthermore, the finding that TEs can transpose between viral genomes of a viral species sets viruses as possible new niches in which TEs can persist and evolve.     

The structural plasticity of SCA7 domains defines their differential nucleosome‐binding properties

SAGA (Spt–Ada–Gcn5 acetyltransferase), a coactivator complex involved in chromatin remodelling, harbours both histone acetylation and deubiquitination activities. ATXN7/Sgf73 and ATXN7L3, two subunits of the SAGA deubiquitination module, contain an SCA7 domain characterized by an atypical zinc‐finger. We show that the yeast Sgf73–SCA7 domain is not required to recruit Sgf73 into SAGA. Instead, it binds to nucleosomes, a property that is conserved in the human ATXN7–SCA7 domain but is lost in the ATXN7L3 domain. The solution structures of the SCA7 domain of both ATXN7 and ATXN7L3 reveal a new, common zinc‐finger motif at the heart of two distinct folds, providing a molecular basis for the observed functional differences.     

Ultrastructural evidence of the degenerative events occurring during embryogenesis of the filarial nematode Brugia pahangi after tetracycline treatment

Intracellular bacteria belonging to the genus Wolbachia have been described in filarial nematodes and these microorganisms appear to have evolved an obligatory mutualistic association with their filarial hosts. In fact, antibiotic treatment leads to the clearance of bacteria from worms resulting in a block in embryogenesis and, eventually, death of adult filariae. Currently, the antifilarial action of antibiotic treatment is interpreted as a secondary consequence of the bacteriostatic activity against Wolbachia endosymbionts. Here, we demonstrate by transmission electron microscopy the degenerative events occurring during embryogenesis of Brugia pahangi after tetracycline treatment. After 56 days of treatment the cytoplasm of hypodermal cords was totally void of Wolbachia and numerous vacuoles, residual of cytolitic activity, were observed. In the ovary, the morphology of the oocytes was well conserved 33 days after treatment, but the texture of symbiotic bacteria appeared altered. After 56 days of treatment embryogenesis was dramatically affected and the terminal portion of the ovary appeared totally empty. The authors suggest that the symbiotic bacteria play a direct role in worm metabolism and a long-term bacteriostatic effect may block bacterial activity involved in the active control of cytolysis. As a consequence, the bacteriophorous vacuole is transformed into a digestive vacuole and the whole symbiotic population is disrupted.     

Enantiomeric separation by HPLC of 1,4-dihydropyridines with vancomycin as chiral selector

The macrocyclic antibiotics represent a relatively new class of chiral selectors in CE, HPLC, and TLC. We have examined the use of the macrocyclic antibiotic vancomycin as a chiral selector in HPLC for the separation of 1,4-dihydropyridines (DHPs) calcium antagonists (CAs). Chromatographic data of six 1,4-dihydropyridine calcium channel blockers obtained on the vancomycin chiral stationary phase (Chirobiotic V) were compared with those obtained on an alpha(1)-acid glycoprotein (AGP) HPLC stationary phase. Optimization of pH and organic modifier was carried out in order to modulate the retention properties of each system. All chiral neutral DHPs were resolved on the AGP column, whereas on Chirobiotic V only basic DHPs showed a split peak. The analytical chromatographic procedure on Chirobiotic V proved suitable for semipreparative separation, since the separation factor on the analytical column was high enough to obtain pure enantiomers with high yields.     

Microsatellite-AFLP for genetic mapping of complex polyploids.

In spite of the economical relevance of polyploid crops, genetic mapping of these species has been relatively overlooked. This is because of intrinsic difficulties such as the uncertainty of the chromosome behavior at meiosis I and the need for very large segregating populations. An important, yet underestimated issue, in mapping polyploids is the choice of the molecular marker system. An ideal molecular marker system for polyploid mapping should maximize the percentage of single dose markers (SDMs) detected and the possibility of recognizing allelic markers. In the present work, the marker index for genetic mapping (MIgm) of M-AFLP is compared with that of AFLP and SAMPL. M-AFLPs have the highest MIgm values (22 vs. 18.5 of SAMPL and 9.83 of AFLP) mostly because of their high power to detect polymorphism. Owing to their prevalent codominant inheritance, it is proposed that M-AFLP can be used for the preliminary identification of hom(e)ologous groups.     

Cryopreservation of Rainbow Trout (Oncorhynchus mykiss) Blastomeres: Influence of Embryo Stage on Postthaw Survival Rate

The cryopreservation of isolated fish blastomeres is likely to provide a valid alternative to embryo cryopreservation, the results of which are still discouraging. A repeatable technique for the cryopreservation of rainbow trout blastomeres has been established and the effect of embryonic developmental stage on freezing tolerance evaluated. Embryos at Ballard 6A, 6B, and 6C stages were dechorionated and left to dissociate in a Ca2+- and Mg2+-free medium. Cryoprotection was provided by step-wise addition of 1.4 M 1,2-propanediol. Cells were loaded into the middle of 250-μl straws and slowly frozen to -80 degreesC before being plunged into LN2. A low thawing rate was adopted, followed by step-wise removal of the cryoprotectant. Morphological evaluation was by microscopy and video recording. Metabolic activity and survival rate were determined by FDA and PI staining, by recovery of the ability to reassociate after 24 h culture in Leibovitz L15 + 2% Ultroser, and by measuring DNA synthesis in 6B cells by the method of BrdU incorporation. Survival rates were 53 +/- 9.3, 88 +/- 1.7, and 95 +/- 0.5% for stage 6A, 6B, and 6C cells, respectively. While 6A cells reassociated into clumps of cells, 6B and 6C cells formed holoblastic morulas in 24 h; proliferation of 6B cells was comparable to fresh control cells. The relationship between freezing tolerance and the physiological events occurring during early embryonic development is discussed in light of these results and conclusions are drawn that envisage the transfer of frozen-thawed blastomeres into recipient embryos. Copyright 1998 Academic Press.     

Retinoic acid-induced differentiation in a human neuroblastoma cell line is associated with an increase in nitric oxide synthesis

The human neuroblastoma cell line SK-N-BE, after incubation with 10 μM retinoic acid (RA) or 20 nM phorbol 12-myristate 13-acetate (PMA), underwent biochemical and morphological signs of differentiation within 10–14 days. In parallel, SK-N-BE cells produced significantly higher amounts of nitric oxide (NO) in comparison with controls, as assessed by the measurement of nitrite and nitrate in the culture supernatant and of NO synthase (NOS) activity in the cell lysates (measured as ability to convert [³H]arginine into [³H]citrulline and as NADPH diaphorase activity). Nitrite/nitrate production was abolished by adding the NO scavenger hemoglobin in the culture medium and was inhibited by aminoguanidine (AG, a selective inhibitor of the inducible NOS isoform) but not by the less selective inhibitor N^G-nitro-L -arginine methylester (NAME). Western blotting experiments with monoclonal antibodies against the ncNOS and iNOS isoforms suggest that RA-elicited NOS activation is not attributable to an increased expression of the protein. NAME and AG were not able to revert inhibition of proliferation induced by RA, and the NO donor sodium nitroprusside did not mimic the effect of RA and PMA. These data indicate that increased NO synthesis does not mediate RA- or PMA-induced differentiation but may be an additional marker of differentiation into sympathetic-like neuronal cells. J. Cell. Physiol. 174:99–106, 1998. © 1998 Wiley-Liss, Inc.     

Sexual dimorphism and gynoecium size variation in the andromonoecious shrub Caesalpinia gilliesii

The degree of sexual dimorphism in flowers and inflorescences can be evaluated early in flower development through the study of floral organ size co-variation. In the present work, the gynoecium-androecium size relationship was studied to assess the degree of sexual expression in flowers and inflorescences of the andromonoecious shrub Caesalpinia gilliesii. The co-variation pattern of floral organ sizes was compared between small and large inflorescences, under the hypothesis that inflorescence size reflected differential resource availability. Also, staminate and perfect flowers were collected from three populations and compared on the basis of gynoecium, ovule length, filament length, pollen size and number. The obtained results indicated that staminate and perfect flowers differed only in the gynoecium and ovule length, whereas filament length, pollen size, and number varied across populations. The gynoecium size was smaller and its variability was much higher in staminate than in perfect flowers, as explained by a recent hypothesis about pollinator-mediated gynoecium size selection acting upon perfect flowers. The analysis of the gynoecium-androecium size relationship during flower development, revealed a dissociation of gynoecium growth relative to other floral structures in some buds. Lower gynoecium-androecium regression slopes and smaller gynoecia length characterized smaller inflorescences, thus reflecting the fact that sexual expression was more male-biased. This trend is in agreement with a differential resource-related response at the inflorescence level, however, post-mating resource allocation and the inclusion of other modular levels may also help us to understand the variation in sexual dimorphism in this species.