title: Sublethal levels of cadmium down-regulate the gene expression of DNA mismatch recognition protein MutS homolog 6 (MSH6) in zebrafish (Danio rerio) embryos.
abstract: MutS homolog 6 (MSH6) is the major mismatch contacting component of the MSH2-MSH6 heterodimeric complex (MutSα) that mediates DNA mismatch repair (MMR) of simple mispairs and small insertion-deletion loops in eukaryotes. This study examined the potential of cadmium (Cd) to disturb the gene expression of MSH6 in vertebrates using zebrafish (Danio rerio) embryo as a model organism. Semiquantitative RT-PCR indicated that msh2 and msh6 expressions were suppressed in embryos at 1h post fertilization (hpf), then drastically up-regulated in 2 hpf embryos and actively expressed in 3-25 hpf embryos. In the presence of a constitutive β-actin expression, exposure of 1 hpf embryos to sublethal concentrations of CdCl(2) at 0.5-3 μM for 4 or 9h caused a time and concentration-dependent down-regulation of msh6 transcription. Cd failed to inhibit msh2 transcription except at 3 μM, reflecting the higher sensitivity of msh6 than msh2 transcription to Cd. Whole mount in situ hybridization showed a wide distribution of msh6 transcripts in the front body portions of 10 hpf embryos and Cd-induced a general suppression of msh6 expression in zebrafish tissues. Cd-induced down-regulation of msh6 transcription paralleled with reduced levels of MSH6 protein synthesis and MSH6-mediated G-T mismatch binding activities identified by band shift assay using recombinant zebrafish MSH6 and an anti-human MSH6 antibody. Our results revealed the inhibition of Cd on MSH6 expression at both mRNA and protein levels and this mechanism may play a role in Cd genotoxicity.
authors.affiliation: Institute of Bioscience and Biotechnology and Center for Marine Bioenvironment and Biotechnology, National Taiwan Ocean University, Keelung 20224, Taiwan, ROC. toddhsu@mail.ntou.edu.tw
authors.forename: Todd
authors.initials: T
authors.lastname: Hsu
authors.forename: Huei-Ting
authors.initials: HT
authors.lastname: Tsai
authors.forename: Kuan-Ming
authors.initials: KM
authors.lastname: Huang
authors.forename: Mei-Chu
authors.initials: MC
authors.lastname: Luan
authors.forename: Chang-Ruei
authors.initials: CR
authors.lastname: Hsieh
mesh_terms: D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D015027:Zebrafish / Q000235:genetics* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D012333:RNA, Messenger; D014874:Water Pollutants, Chemical; D029961:Zebrafish Proteins; D002104:Cadmium