RESUMO
We previously determined that the dithiocarbamate pesticide sodium metam (NaM) and its active ingredient methylisothiocyanate (MITC) were developmentally toxic causing notochord distortions in the zebrafish. In this study, developing zebrafish were exposed to isothiocyanates (ITCs), dithiocarbamates (DTCs) and several degradation products to determine the teratogenic relationship of these chemical classes at the molecular level. All dithiocarbamates tested elicited notochord distortions with notochord NOELs from <4 to 40 ppb, while none of the ITCs caused notochord distortions with the exception of MITC. Carbon disulfide (CS(2)), a common DTC degradate, also caused distortions at concentrations >200 times the DTCs. Whole mount in situ hybridization of developmental markers for collagen (collagen2a1), muscle (myoD), and body axis formation (no tail) was perturbed well after cessation of treatment with pyrolidine-DTC (PDTC), dimethyl-DTC (DMDTC), NaM, MITC, and CS(2). Therefore, distinct albeit related chemical classes share a common toxic effect on zebrafish notochord development. To test the responsiveness of the distortion to metal perturbation, five metal chelators and 2 metals were studied. The membrane permeable copper chelator neocuproine (NCu) was found to cause notochord distortions similar to DTC-related molecules. DMDTC and NCu treated animals were protected with copper, and collagen 2a1 and no tail gene expression patterns were identical to controls in these animals. PDTC, NaM, MITC, and CS(2) were not responsive to copper indicating that the chelation of metals is not the primary means by which these molecules elicit their developmental toxicity. Embryos treated with DMDTC, NaM, and NCu were rescued by adding triciaine (MS-222) which abolishes the spontaneous muscle contractions that begin at 18 hpf. In these animals, only collagen 2a1 expression showed a similar pattern to the other notochord distorting molecules. This indicates that the perturbation of no tail expression is in response to the muscle contractions distorting the notochord, while collagen 2a1 is associated with the impact of these molecules on much earlier developmental processes.
