Cultured gill epithelia as models for the freshwater fish gill

We review recent progress in the development of models for the freshwater teleost gill based on reconstructed flat epithelia grown on permeable filter supports in primary culture. Methods are available for single-seeded insert (SSI) preparations consisting of pavement cells (PVCs) only from trout and tilapia, and double-seeded insert (DSI) preparations from trout, containing both PVCs (85%) and mitochondria-rich cells (MRCs, 15%), as in the intact gill. While there are some quantitative differences, both SSI and DSI epithelia manifest electrical and passive permeability characteristics typical of intact gills and representative of very tight epithelia. Both preparations withstand apical freshwater exposure, exhibiting large increases in transepithelial resistance (TER), negative transepithelial potential (TEP), and low rates of ion loss, but there is only a small active apical-to-basolateral "influx" of Cl(-) (and not of Na(+)). Responses to various hormonal treatments are described (thyroid hormone T3, prolactin, and cortisol). Cortisol has the most marked effects, stimulating Na(+),K(+)-ATPase activity and promoting active Na(+) and Cl(-) influxes in DSI preparations, and raising TER and reducing passive ion effluxes in both epithelia via reductions in paracellular permeability. Experiments using DSI epithelia lacking Na(+) uptake demonstrate that both NH(3) and NH(4)(+) diffusion occur, but are not large enough to account for normal rates of branchial ammonia excretion, suggesting that Na(+)-linked carrier-mediated processes are important for ammonia excretion in vivo. Future research goals are suggested.     

Effect of population size on the estimation of QTL: a test using resistance to barley stripe rust

The limited population sizes used in many quantitative trait locus (QTL) detection experiments can lead to underestimation of QTL number, overestimation of QTL effects, and failure to quantify QTL interactions. We used the barley/barley stripe rust pathosystem to evaluate the effect of population size on the estimation of QTL parameters. We generated a large (n=409) population of doubled haploid lines derived from the cross of two inbred lines, BCD47 and Baronesse. This population was evaluated for barley stripe rust severity in the Toluca Valley, Mexico, and in Washington State, USA, under field conditions. BCD47 was the principal donor of resistance QTL alleles, but the susceptible parent also contributed some resistance alleles. The major QTL, located on the long arm of chromosome 4H, close to the Mlo gene, accounted for up to 34% of the phenotypic variance. Subpopulations of different sizes were generated using three methods—resampling, selective genotyping, and selective phenotyping—to evaluate the effect of population size on the estimation of QTL parameters. In all cases, the number of QTL detected increased with population size. QTL with large effects were detected even in small populations, but QTL with small effects were detected only by increasing population size. Selective genotyping and/or selective phenotyping approaches could be effective strategies for reducing the costs associated with conducting QTL analysis in large populations. The method of choice will depend on the relative costs of genotyping versus phenotyping. Electronic Supplementary Material Supplementary material is available for this article at     

Endogenous PttHb1 and PttTrHb, and heterologous Vitreoscilla vhb haemoglobin gene expression in hybrid aspen roots with ectomycorrhizal interaction

Present knowledge on plant non-symbiotic class-1 (Hb1) and truncated (TrHb) haemoglobin genes is almost entirely based on herbaceous species while the corresponding tree haemoglobin genes are not well known. The function of these genes has recently been linked with endosymbioses between plants and microbes. In this work, the coding sequences of hybrid aspen (Populus tremulaxtremuloides) PttHb1 and PttTrHb were characterized, indicating that the key residues of haem and ligand binding of both genes were conserved in the deduced amino acid sequences. The expression of PttHb1 and PttTrHb was examined in parallel with that of the heterologous Vitreoscilla haemoglobin gene (vhb) during ectomycorrhiza/ectomycorrhizal (ECM) interaction. Both ECM fungi studied, Leccinum populinum and Xerocomus subtomentosus, enhanced root formation and subsequent growth of roots of all hybrid aspen lines, but only L. populinum was able to form mycorrhizas. Real-time PCR results show that the dual culture with the ECM fungus, with or without emergence of symbiotic structures, increased the expression of both PttHb1 and PttTrHb in the roots of non-transgenic hybrid aspens. PttHb1 and PttTrHb had expression peaks 5 h and 2 d after inoculation, respectively, pointing to different functions for these genes during interaction with root growth-improving fungi. In contrast, ECM fungi were not able to enhance the expression of hybrid aspen endogenous haemoglobin genes in the VHb lines, which may be a consequence of the compensating action of heterologous haemoglobin.     

Quantitative Properties of Random Amplified Polymorphic DNA (RAPD)

Random Amplified Polymorphic DNA analysis (RAPD) is a methodology that has been used as a tool for monitoring microbial communities. To be useful in this application RAPD, and any other methodology, must show properties that allows for the detection of quantitative changes in composition of the microbiota. Therefore, the objective of this study was to establish whether RAPD possesses such properties. The strategy was to use genomic DNA, extracted from a set of tertiary bacterial mixtures defined according to an experimental mixture design, and containing varying proportions of Escherichia coli, Bacillus subtilis, and Pseudomonas CF600. RAPD-PCR was performed on the mixed DNA extracts and the amplified DNA fragments were separated on sequencing gels to produce genomic fingerprints that were digitized and modeled by Partial Least Squares regression (PLS). Significant predictions were obtained using an external test set for validation, with Root Mean Square Error of Predictions (RMSEP) of 0.21, 0.19 and 0.20 for the proportion of E. coli, B. subtilis and Pseudomonas CF600 respectively. Taken together, the results showed that RAPD patterns quantitatively represented the initial mixture proportions. Therefore, the view that RAPD could be useful for whole microbial community monitoring was strengthened.     

Morphological and molecular investigations of Tubulinosema ratisbonensis gen. nov., sp. nov. (Microsporidia: Tubulinosematidae fam. nov.), a parasite infecting a laboratory colony of Drosophila melanogaster (Diptera: Drosophilidae)

A new species of microsporidia from Drosophila melanogaster was investigated by light and electron microscopy and by ribosomal RNA (rRNA) sequencing. This microsporidium and the previously described Nosema kingi and Nosema acridophagus have been transferred to the new genus Tubulinosema gen. nov. with the following characters: nuclei are in diplokaryotic arrangement during the life cycle. All stages are in direct contact with the host cell cytoplasm, slightly anisofilar polar tube with the last coils being smaller in diameter arranged in one or two rows on both sides of the diplokaryon and small tubuli on the surface of late meronts. Spores are oval or slightly pyriform. Thick endospore wall, thinner over anchoring disc. This new genus and the genus Brachiola have been placed in a new family Tubulinosematidae fam. nov. Phylogenetic analysis of small subunit rRNA sequences by different methods placed Tubulinosema spp. in one clade with the genus Brachiola forming its sister clade, which is distant from the clade containing the true Nosema spp. including Nosema bombycis.