Extension of the established period of diacetyl adaptation by oxygen intermediates in the nematode Caenorhabditis elegans

After pre-exposure to the odorant diacetyl, the nematode Caenorhabditis elegans showed a decline in chemotactic responses to diacetyl, a phenomenon known as diacetyl adaptation. In the present study, we found that the established period of diacetyl adaptation in nematodes increased with the breeding temperature. When wild-type (N2) nematodes were bred at 15°C, adaptation was observed from the young adult (YA) to the 3-day-old adult that is reached 3 days after the YA stage. On breeding nematodes at 20°C and 25°C, adaptation was observed between the YA and 5-day-old adult and between the YA and the 7-day-old adult, respectively. Breeding temperature has been shown to correlate with the rate of aging in nematodes, which is related to the level of oxygen consumption. Accordingly, long-lived isp-1 and clk-1 mutants that demonstrate decreased levels of oxygen consumption showed a shorter established period of adaptation than N2 nematodes, whereas short-lived gas-1 and mev-1 mutants that have a hypersensitive response to oxygen showed a longer period of adaptation than the N2. Moreover, the established period of diacetyl adaptation in N2 nematodes was shortened by the antioxidant α-lipoic acid. These results suggest that oxygen intermediates, which are produced by oxygen consumption, play a significant role in diacetyl adaptation. Although this is only one of many factors that regulate diacetyl adaptation, such as the release of neurotransmitters and changes in intracellular conditions, the acquisition of this adaptation requires an increase in the intensity of moderate oxygen signals.

Molecular signals regulating translocation and toxicity of graphene oxide in the nematode Caenorhabditis elegans

Both in vitro and in vivo studies have demonstrated the toxic effects of graphene oxide (GO). However, the molecular basis for the translocation and toxicity of GO is still largely unclear. In the present study, we employed an in vivo Caenorhabditis elegans assay system to identify molecular signals involved in the control of the translocation and toxicity of GO. We identified 7 genes whose mutations altered both the translocation and toxicity of GO. Mutations of the hsp-16.48, gas-1, sod-2, sod-3, and aak-2 genes caused greater GO translocation into the body and toxic effects on both primary and secondary targeted organs compared with wild type; however, mutations of the isp-1 and clk-1 genes resulted in significantly decreased GO translocation into the body and toxicity on both primary and secondary targeted organs compared with wild-type. Moreover, mutations of the hsp-16.48, gas-1, sod-2, sod-3, and aak-2 genes caused increased intestinal permeability and prolonged mean defecation cycle length in GO-exposed nematodes, whereas mutations of the isp-1 and clk-1 genes resulted in decreased intestinal permeability in GO-exposed nematodes. Therefore, for the underlying mechanism, we hypothesize that both intestinal permeability and defecation behavior may have crucial roles in controlling the functions of the identified molecular signals. The molecular signals may further contribute to the control of transgenerational toxic effects of GO. Our results provide an important insight into understanding the molecular basis for the in vivo translocation and toxicity of GO.