title: Transcriptomic signatures in Chlamydomonas reinhardtii as Cd biomarkers in metal mixtures.
abstract: In the natural environment, toxicant effects can be monitored by the signature mRNA expression patterns of genes that they generate in test organisms. The specificity and sensitivity of these transcriptome-based bioassays to a given toxicant can be confounded by temporal changes in biomarker mRNA expression, effects of other toxicants and hardness ions, and non-linear mRNA expression responses of genes. This study provides the foundation for the development of a transcriptomic-based bioassay for bioavailable Cd in the freshwater alga, Chlamydomonas reinhardtii. It characterizes: (1) the Cd regulation of nine genes with respect to their mRNA induction kinetics; (2) the effects of two additional metals common to freshwaters, Cu2+ and Pb2+, and (3) the relationships between metal bioaccumulation and the transcriptomic responses. Quantitative real time PCR was used to monitor mRNA levels of nine Cd-induced genes following an exposure to 0.01, 0.11 and 1.16 μM Cd2+. Several distinct mRNA expression patterns were observed with time. While the presence of Cu2+ and Pb2+ decreased Cd biouptake, mRNA levels increased for six genes, showing lack of Cd2+ specificity. Nonetheless, the transcriptomic effects of binary metal exposures rarely adhered to a simple additive model based on single metal exposures; rather most exhibited synergistic or antagonistic interactions. While none of these genes could be used as a specific Cd biomarker, the signature mRNA expression profile obtained from a select subset of Cd sensitive genes was a useful biomarker of sublethal effects.
authors.affiliation: Department of Chemistry, University of Montreal, P.O. Box 6128, Succ. Centre-Ville, H3C3J7 Montreal, Canada. col.hutchins@gmail.com
authors.forename: C M
authors.initials: CM
authors.lastname: Hutchins
authors.forename: D F
authors.initials: DF
authors.lastname: Simon
authors.forename: W
authors.initials: W
authors.lastname: Zerges
authors.forename: K J
authors.initials: KJ
authors.lastname: Wilkinson
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D002104:Cadmium / Q000737:chemistry / Q000633:toxicity*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D003300:Copper / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D004347:Drug Interactions; D020869:Gene Expression Profiling; D007854:Lead / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*
chemical_list: D015415:Biomarkers; D012333:RNA, Messenger; D014874:Water Pollutants, Chemical; D002104:Cadmium; D007854:Lead; D003300:Copper