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      Expression Profiling of Non-Aflatoxigenic Aspergillus parasiticus Mutants Obtained by 5-Azacytosine Treatment or Serial Mycelial Transfer

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          Abstract

          Aflatoxins are carcinogenic secondary metabolites produced by the fungi Aspergillus flavus and Aspergillus parasiticus. Previous studies found that repeated serial mycelial transfer or treatment of A. parasiticus with 5-azacytidine produced colonies with a fluffy phenotype and inability to produce aflatoxins. To understand how these treatments affect expression of genes involved in aflatoxin production and development, we carried out expressed sequence tag (EST)-based microarray assays to identify genes in treated clones that are differentially expressed compared to the wild-type. Expression of 183 genes was significantly dysregulated. Of these, 38 had at least two-fold or lower expression compared to the untreated control and only two had two-fold or higher expression. The most frequent change was downregulation of genes predicted to encode membrane-bound proteins. Based on this result we hypothesize that the treatments cause changes in the structure of cellular and organelle membranes that prevent normal development and aflatoxin biosynthesis.

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          Most cited references53

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          VelB/VeA/LaeA complex coordinates light signal with fungal development and secondary metabolism.

          Differentiation and secondary metabolism are correlated processes in fungi that respond to light. In Aspergillus nidulans, light inhibits sexual reproduction as well as secondary metabolism. We identified the heterotrimeric velvet complex VelB/VeA/LaeA connecting light-responding developmental regulation and control of secondary metabolism. VeA, which is primarily expressed in the dark, physically interacts with VelB, which is expressed during sexual development. VeA bridges VelB to the nuclear master regulator of secondary metabolism, LaeA. Deletion of either velB or veA results in defects in both sexual fruiting-body formation and the production of secondary metabolites.
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            Evolution of opsins and phototransduction.

            Opsins are the universal photoreceptor molecules of all visual systems in the animal kingdom. They can change their conformation from a resting state to a signalling state upon light absorption, which activates the G protein, thereby resulting in a signalling cascade that produces physiological responses. This process of capturing a photon and transforming it into a physiological response is known as phototransduction. Recent cloning techniques have revealed the rich and diverse nature of these molecules, found in organisms ranging from jellyfish to humans, functioning in visual and non-visual phototransduction systems and photoisomerases. Here we describe the diversity of these proteins and their role in phototransduction. Then we explore the molecular properties of opsins, by analysing site-directed mutants, strategically designed by phylogenetic comparison. This site-directed mutant approach led us to identify many key features in the evolution of the photoreceptor molecules. In particular, we will discuss the evolution of the counterion, the reduction of agonist binding to the receptor, and the molecular properties that characterize rod opsins apart from cone opsins. We will show how the advances in molecular biology and biophysics have given us insights into how evolution works at the molecular level.
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              GPI-anchored proteins are organized in submicron domains at the cell surface.

              Lateral heterogeneities in the classical fluid-mosaic model of cell membranes are now envisaged as domains or 'rafts' that are enriched in (glyco)sphingolipids, cholesterol, specific membrane proteins and glycosylphosphatidylinositol (GPI)-anchored proteins. These rafts dictate the sorting of associated proteins and/or provide sites for assembling cytoplasmic signalling molecules. However, there is no direct evidence that rafts exist in living cells. We have now measured the extent of energy transfer between isoforms of the folate receptor bound to a fluorescent analogue of folic acid, in terms of the dependence of fluorescence polarization on fluorophore densities in membranes. We find that the extent of energy transfer for the GPI-anchored folate-receptor isoform is density-independent, which is characteristic of organization in sub-pixel-sized domains at the surface of living cells; however, the extent of energy transfer for the transmembrane-anchored folate-receptor isoform was density-dependent, which is consistent with a random distribution. These domains are likely to be less than 70 nm in diameter and are disrupted by removal of cellular cholesterol. These results indicate that lipid-linked proteins are organized in cholesterol-dependent submicron-sized domains. Our methodology offers a new way of monitoring nanometre-scale association between molecules in living cells.
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                Author and article information

                Journal
                Toxins (Basel)
                toxins
                Toxins
                MDPI
                2072-6651
                02 August 2011
                August 2011
                : 3
                : 8
                : 932-948
                Affiliations
                [1 ] Southern Regional Research Center, ARS/USDA, 1100 Robert E. Lee Blvd., New Orleans, LA 70124, USA; Email: jrw@ 123456juno.com (J.R.W.); deepak.bhatnagar@ 123456ars.usda.gov (D.B.); jiujiang.yu@ 123456ars.usda.gov (J.Y)
                [2 ] Department of Biology, 1 Drexel Dr., Box 85B, Xavier University of Louisiana, New Orleans, LA 70125, USA; Email: skale@ 123456xula.edu
                Author notes
                [* ] Author to whom correspondence should be addressed; Email: ken.ehrlich@ 123456ars.usda.gov ; Tel.: +1-011-504-286-4369; Fax: +1-011-286-4419.
                Article
                toxins-03-00932
                10.3390/toxins3080932
                3202869
                22069749
                648ce6fa-feb8-472f-b8b9-0385e3700385
                © 2011 by the authors; licensee MDPI, Basel, Switzerland.

                This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 25 May 2011
                : 19 July 2011
                : 26 July 2011
                Categories
                Article

                Molecular medicine
                aflatoxin,microarray,5-azacytidine,aspergillus parasiticus, secondary metabolism, fluffy phenotype

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