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We previously designed a triple auxotrophic host-vector system in Aspergillus oryzae by isolating red-colored adenine auxotrophic mutants upon UV mutagenesis of a double auxotrophic host (niaD-sC-). In the present study an effort to exploit this system and construct a novel quadruple auxotrophic host was made by disrupting the argB gene involved in arginine biosynthesis. The argB gene-disruption cassette was generated by fusion PCR, which required only two steps of PCR to insert the selectable marker, adeA, into the target argB gene. The chimeric DNA fragment was transformed into the triple auxotrophic strain (niaD-sC-adeA-) and the argB disruptants were obtained with a high rate of efficiency (approximately 40%). The argB disruptants were characterized by normal colony color and reversal of arginine auxotrophy by introduction of the wild-type argB gene. Quadruple auxotrophic strains (niaD-sC-DeltaargB adeA- or niaD-sC-DeltaargB adeB-) were subsequently isolated upon UV mutagenesis of the triple auxotrophic strain (niaD-sC-DeltaargB) followed by screening of red-colored colonies for adenine auxotrophy. The results obtained showed that the adeA gene served as an efficient selection marker in developing a novel host-vector system with quadruple auxotrophy in A. oryzae, thus providing a powerful tool to breed multiple auxotrophic mutants from a deuteromycete wherein sexual crossing is impossible.

Aims/hypothesisObesity is associated with ageing and increased energy intake, while restriction of energy intake improves health and longevity in multiple organisms; the NAD+-dependent deacetylase sirtuin 1 (SIRT1) is implicated in this process. Pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP) neurons in the arcuate nucleus (ARC) of the hypothalamus are critical for energy balance regulation, and the level of SIRT1 protein decreases with age in the ARC. In the current study we tested whether conditional Sirt1 overexpression in mouse POMC or AgRP neurons prevents age-associated weight gain and diet-induced obesity.MethodsWe targeted Sirt1 cDNA sequence into the Rosa26 locus and generated conditional Sirt1 knock-in mice. These mice were crossed with mice harbouring either Pomc-Cre or Agrp-Cre and the metabolic variables, food intake, energy expenditure and sympathetic activity in adipose tissue of the resultant mice were analysed. We also used a hypothalamic cell line to investigate the molecular mechanism by which Sirt1 overexpression modulates leptin signalling.ResultsConditional Sirt1 overexpression in mouse POMC or AgRP neurons prevented age-associated weight gain; overexpression in POMC neurons stimulated energy expenditure via increased sympathetic activity in adipose tissue, whereas overexpression in AgRP neurons suppressed food intake. SIRT1 improved leptin sensitivity in hypothalamic neurons in vitro and in vivo by downregulating protein-tyrosine phosphatase 1B, T cell protein-tyrosine phosphatase and suppressor of cytokine signalling 3. However, these phenotypes were absent in mice consuming a high-fat, high-sucrose diet due to decreases in ARC SIRT1 protein and hypothalamic NAD+ levels.Conclusions/interpretationARC SIRT1 is a negative regulator of energy balance, and decline in ARC SIRT1 function contributes to disruption of energy homeostasis by ageing and diet-induced obesity.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-013-3140-5) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Basidiomycete fungi are an attractive resource for biologically active natural products for use in pharmaceutically relevant compounds. Recently, genome projects on mushroom fungi have provided a great deal of biosynthetic gene cluster information. However, functional analyses of the gene clusters for natural products were largely unexplored because of the difficulty of cDNA preparation and lack of gene manipulation tools for basidiomycete fungi. To develop a versatile host for basidiomycete genes, we examined gene expression using genomic DNA sequences in the robust ascomycete host Aspergillus oryzae, which is frequently used for the production of metabolites from filamentous fungi. Exhaustive expression of 30 terpene synthase genes from the basidiomycetes Clitopilus pseudo-pinsitus and Stereum hirsutum showed two splicing patterns, i.e., completely spliced cDNAs giving terpenes (15 cases) and mostly spliced cDNAs, indicating that A. oryzae correctly spliced most introns at the predicted positions and lengths. The mostly spliced cDNAs were expressed after PCR-based removal of introns, resulting in the successful production of terpenes (14 cases). During this study, we observed relatively frequent mispredictions in the automated program. Hence, the complementary use of A. oryzae expression and automated prediction will be a powerful tool for genome mining. IMPORTANCE The recent large influx of genome sequences from basidiomycetes, which are prolific producers of bioactive natural products, may provide opportunities to develop novel drug candidates. The development of a reliable expression system is essential for the genome mining of natural products because of the lack of a tractable host for heterologous expression of basidiomycete genes. For this purpose, we applied the ascomycete Aspergillus oryzae system for the direct expression of fungal natural product biosynthetic genes from genomic DNA. Using this system, 29 sesquiterpene synthase genes and diterpene biosynthetic genes for bioactive pleuromutilin were successfully expressed. Together with the use of computational tools for intron prediction, this Aspergillus oryzae system represents a practical method for the production of basidiomycete natural products.

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