title: Transcriptomic analysis of cultured whale skin cells exposed to hexavalent chromium [Cr(VI)].
abstract: Hexavalent chromium Cr(VI) is known to produce cytotoxic effects in humans and is a highly toxic environmental contaminant. Interestingly, it has been shown that free ranging sperm whales (Phyester macrocephalus) may have exceedingly high levels of Cr in their skin. Also, it has been demonstrated that skin cells from whales appear more resistant to both cytotoxicity and clastogenicity upon Cr exposure compared to human cells. However, the molecular genetic mechanisms employed in whale skin cells that might lead to Cr tolerance are unknown. In an effort to understand the underlying mechanisms of Cr(VI) tolerance and to illuminate global gene expression patterns modulated by Cr, we exposed whale skin cells in culture to varying levels of Cr(VI) (i.e., 0.0, 0.5, 1.0 and 5.0 μg/cm²) followed by short read (100 bp) next generation RNA sequencing (RNA-seq). RNA-seq reads from all exposures (≈280 million reads) were pooled to generate a de novo reference transcriptome assembly. The resulting whale reference assembly had 11K contigs and an N50 of 2954 bp. Using the reads from each dose (0.0, 0.5, 1.0 and 5.0 μg/cm²) we performed RNA-seq based gene expression analysis that identified 35 up-regulated genes and 19 down-regulated genes. The experimental results suggest that low dose exposure to Cr (1.0 μg/cm²) serves to induce up-regulation of oxidative stress response genes, DNA repair genes and cell cycle regulator genes. However, at higher doses (5.0 μg/cm²) the DNA repair genes appeared down-regulated while other genes that were induced suggest the initiation of cytotoxicity. The set of genes identified that show regulatory modulation at different Cr doses provide specific candidates for further studies aimed at determination of how whales exhibit resistance to Cr toxicity and what role(s) reactive oxygen species (ROS) may play in this process.
authors.affiliation: Molecular Biosciences Research Group, Department of Chemistry & Biochemistry, 419 Centennial Hall, Texas State University, 601 University Drive, San Marcos, TX 78666, USA.
authors.forename: Vagmita
authors.initials: V
authors.lastname: Pabuwal
authors.forename: Mikki
authors.initials: M
authors.lastname: Boswell
authors.forename: Amanda
authors.initials: A
authors.lastname: Pasquali
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Wise
authors.forename: Suresh
authors.initials: S
authors.lastname: Kumar
authors.forename: Yingjia
authors.initials: Y
authors.lastname: Shen
authors.forename: Tzintzuni
authors.initials: T
authors.lastname: Garcia
authors.forename: Carolyne
authors.initials: C
authors.lastname: Lacerte
authors.forename: John Pierce
authors.initials: JP
authors.lastname: Wise
authors.forename: John Pierce
authors.initials: JP
authors.lastname: Wise
authors.forename: Wesley
authors.initials: W
authors.lastname: Warren
authors.forename: Ronald B
authors.initials: RB
authors.lastname: Walter
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002857:Chromium / Q000008:administration & dosage / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects*; D059014:High-Throughput Nucleotide Sequencing / Q000379:methods; D008969:Molecular Sequence Data; D009152:Mutagenicity Tests; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012867:Skin / Q000166:cytology*; D050661:Sperm Whale / Q000378:metabolism*; D059467:Transcriptome / Q000235:genetics*
chemical_list: D017382:Reactive Oxygen Species; D002857:Chromium; C074702:chromium hexavalent ion