In the self‐fertilizing hermaphroditic fish, Rivulus marmoratus, the susceptibility to tumor induction by N‐methyl‐N‐nitro‐N‐nitrosoguanidine(MNNG) was evaluated. Seven‐day‐old fish larvaewere exposed for 2 h toMNNG at concentrations ranging from 5 to 25 ppm in a static water bath. The exposed fish were observed at 2 and 4 monthsafter carcinogen treatmentto assess tumor development. Within 4‐ months after25 ppmMNNG exposure, nearly all fish developed thyroid tumors. The tumor incidenceswere dose‐ and time‐dependent, and the latent period of tumor induction was less than 2 months. Most induced neoplasms were papillary carcinomas similar histologically to those of rodents and humans, and the tumors were serially transplantable to other fish of the same species. These results demonstratethat rivulus could be useful as a model of thyroid carcinogenesis.
We isolated nickel-resistant bacterium from soil in order to identify a novel nickel resistance determinant. Using 16S rRNA gene sequencing, an isolate was identified as Enterobacter sp. Ni15. This species showed a medium-level (resistant to up to 10 mM) nickel resistance in nutrient-rich media. Enterobacter sp. Ni15 has a novel plasmid, pNi15, and an increased nickel resistance to Escherichia coli DH5alphain trans. To isolate the nickel resistance gene from pNi15, the plasmid was digested with XbaI and its fragments were cloned into pBluescriptIISK(+). The clones were transferred into E. coli DH5alpha. The nickel resistance of the clones was then assayed. From these results, a pNi15100 isolate containing a 5,328 bp XbaI fragment of pNi15 was identified and sequenced. The E. coli DH5alpha harboring the pNi15100 showed a resistance to up to 7 mM nickel. Using a subcloning analysis, we were able to identify the novel nickel resistance determinant: the nrp gene encoding the putative proteins NrpA and NrpB.
The three‐day‐old larvae of self‐fertilizing hermaphroditic fish Rivulus ocellatus marmoratus were fed a diet containing the antioxidant butylated hydroxyanisole (BHA) at levels of 0.01–0.8% for 12 days. Six months after BHA administration, hepatic tumors were found in all groups of BHA‐treated fish. The BHA‐induced tumor incidences were clearly dose‐dependent. These results show that dietary BHA is hepatocarcinogenic in Rivulus even at 0.01% dose.
The estuarine hermaphroditic teleost Rivulus marmoratus was sensitive to toxic effects of cadmium showing low 96-h LC50 values of 0.8–32.8 mg Cd/L for different life stages at 10‰ salinity, 25 °C, and pH 7.0. Toxicity was greater at higher temperatures, at higher pH, and at lower salinity. Tolerance to cadmium increased after pretreatment with a low dose of cadmium, but the effect decreased when intervals between pretreatment and challenge treatment were longer than 4 d. The gill lamellae and kidney tubules were the primary target organs for acute toxic effects of cadmium in adult fish. These results suggest that R. marmoratus, which is small, physiologically tolerant, hardy, and easy to breed, may prove to be a useful euryhaline model for estuarine metal toxicity studies.
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