title: Detection of marine microalgal biotoxins using bioassays based on functional expression of tunicate xenobiotic receptors in yeast.
abstract: Marine microalgae can produce biotoxins that cause widespread poisoning in marine ecosystems and may also affect human health. While established microalgal biotoxins are detectable using chemical methods, a need remains for robust, inexpensive bioassays. Ligand-binding domains (LBDs) from a tunicate nuclear receptor, VDR/PXRα, which is orthologous to both the vertebrate pregnane X receptor (PXR) and the vitamin D receptor (VDR), can be activated by microalgal biotoxins when expressed in mammalian cell lines. Building on this observation, we developed a generic recombinant yeast bioassay platform that expresses chimeric proteins containing tunicate VDR/PXRα LBDs which mediate ligand-dependent transcription of a reporter gene (lacZ) encoding an easily assayed enzyme (β-galactosidase). Recombinant yeast strains expressing VDR/PXRα LBDs from two tunicate species, Ciona intestinalis and Botryllus schlosseri, were exposed to both synthetic and natural toxins. Structurally simple synthetic chemicals (n-butyl-p-aminobenzoate, carbamazepine, p-aminobenzoic acid, and bisphenol-A) generated EC50 values in the μM range, while more structurally complex marine biotoxins (okadaic acid, pectenotoxin-11, and portimine) activated the assays in the nM range. Given the large number of tunicate species, we propose that tunicate VDR/PXR LBDs may be used as 'sensor elements' in similar yeast-based high-throughput bioassays for detection of established microalgal biotoxins and uncharacterised marine bioactive compounds.
authors.affiliation: Coastal and Freshwater Group, Cawthron Institute, Private Bag 2, Nelson 7012, New Zealand; School of Biological Science, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand. Electronic address: Ingrid.Richter@cawthron.org.nz.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Richter
authors.affiliation: Coastal and Freshwater Group, Cawthron Institute, Private Bag 2, Nelson 7012, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland 1142, New Zealand; Institute of Marine Science, University of Auckland, Auckland 1142, New Zealand. Electronic address: Andrew.Fidler@cawthron.org.nz.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Fidler
mesh_terms: D000818:Animals; D001681:Biological Assay; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017930:Genes, Reporter; D059014:High-Throughput Nucleotide Sequencing; D007783:Lactones / Q000737:chemistry; D008024:Ligands; D018942:Macrolides; D008387:Marine Toxins / Q000737:chemistry*; D058086:Microalgae / Q000737:chemistry*; D019319:Okadaic Acid / Q000737:chemistry; D000077297:Pregnane X Receptor; D011714:Pyrans / Q000737:chemistry; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014561:Urochordata / Q000737:chemistry*; D015262:Xenobiotics / Q000737:chemistry*; D000095702:Polyether Toxins
chemical_list: D004268:DNA-Binding Proteins; D007783:Lactones; D008024:Ligands; D018942:Macrolides; D008387:Marine Toxins; D019319:Okadaic Acid; D000077297:Pregnane X Receptor; D011714:Pyrans; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D015262:Xenobiotics; C052130:GAL4 protein, S cerevisiae; C556578:pectenotoxin 11; D000095702:Polyether Toxins
keywords: Bioassay; Botryllus schlosseri; Ciona intestinalis; Marine biotoxins; Pregnane X receptor; Saccharomyces cerevisiae