TY  - GEN
Y1  - 2011///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/12672/
ID  - heidok12672
N2  - Methyl mercury (MeHg) is known to be a teratogen and neurotoxicant. Human contact with it is unavoidable due to its widespread prevalence in the environment. There is a need for model organisms and biosensors for better monitoring its presence in the environment and investigating the underlying mechanisms of its toxicity. In this study, zebrafish was chosen as the model organism due to its ecotoxicological, developmental and genetics advantages. A global view of gene expression changes in zebrafish embryos with acute sub-lethal MeHg exposure was generated. In response to MeHg, a total of 464 MeHg-up-regulated and 379 MeHg-down-regulated genes were obtained from the microarray analysis (p-value < 0.05 and M-value > 1.3 or < -1-3, in which M-value refers to the log2 ratio of the fold change). The up-regulated genes were associated with functions of oxidative stress, cell redox homeostasis, apoptosis, inflammatory response, blood circulation, hormone stimulus and so forth; while the down-regulated ones were involved in oxidation reduction, RNA splicing, RNA elongation, fatty acid metabolism, DNA repair and so forth. Eighty-eight candidate genes were selected from the microarray for whole-mount in situ hybridisation analysis (ISH). The ISH result showed a 68% positive correlation with the microarray result. Ectopic expressions of the genes were noted in various organs including the brain, eyes, olfactory bulb, branchial arches, heart, liver, intestine or gut, pronephos, somites, lateral lines, pectoral fins, caudal fin fold, trunk and tail blood vessels, dermal epithelium, and yolk syncytial layer. The expression levels of 12 genes at 30 micro g/l and 60 micro g/l MeHg were further quantified by real-time PCR. Eleven out of twelen were significantly regulated at 60 micro g/l MeHg. arfl, c4-2, c6, cbx7l, prdx1 and zgc:101661 showed significant changes even at 30 micro g/l MeHg. The sensitive expression changes of these 6 genes suggested that they may serve as marker genes for detecting the presence of MeHg in the environment. The effects of MeHg on the nervous system and the caudal fin fold were further investigated. Although no obvious change in some of the marker genes of CNS or the neurotransmitter system examined was detected, through the toxicogenomic screen, 24 genes showing changes in the expression levels or patterns in the brain in response to MeHg exposure were identified. Besides, MeHg treatment caused a decrease in the number of neuromast hair cells in the lateral line. The expressions of 12 genes were shown to be regulated by MeHg in the lateral line. MeHg could induce a loss of the gap in the melanophore stripe, disruption of caudal fin growth zone and disruption of caudal fin fold tissue. The disruption of melanophore stripe by MeHg was restricted to a time window of exposure from 12 to 48 hpf. MeHg caused a specific loss of the GFP expression in the caudal fin growth zone of the transgenic line Tg(-2.4shha-ABC:GFP)sb15, and such an effect was induced in a significant number of embryos even in MeHg concentration as low as 6 micro g/l. Although there was a slight increase in the number of apoptotic cells in the caudal fin region, no rescue of the caudal fin tissue destruction was observed when induction of apoptosis was inhibited, excluding the possibility that apoptosis is the major cause of caudal fin fold tissue disruption. Through the toxicogenomic screen, 22 genes were shown to be ectopically expressed in the caudal fin fold of MeHg treated embryos. Among these genes, the involvement of mmp9 and mmp13a in the caudal fin fold malformation was further investigated. Pharmacological inhibition of mmp9 and mmp13a could rescue partially the caudal fin phenotype induced by MeHg, suggesting a role for these two extracellular matrix remodelling proteins in causing the caudal fin tissue disruption.
KW  - zebrafish 
KW  -  mercury 
KW  -  methyl mercury 
KW  -  nervous system 
KW  -  fin 
KW  -  mmp9 
KW  -  mmp13
TI  - Characterisation of methyl mercury toxicity and identification of methyl mercury-senstitive biomarkers in zebrafish (Danio rerio) embryos
A1  - Ho, Nga Yu
AV  - public
ER  -