AbstractCaenorhabditis elegansis a small, free‐living hermaphroditic nematode that is widely used for the investigation of basic biological phenomena at the genetic and molecular levels. The hsp16 genes in this system encode a family of stress‐inducible 16‐kDa proteins. Stable transgenic nematode lines were derived that carry fusions of the hsp16 genes to theEscherichia coli lacZreporter gene. These transgenic strains express high levels of β‐galactosidase in the nucleus, in response to a heat shock or to a variety of chemical stressors. Agents tested to date that induce the stress response in these animals include Cd2+, Cu2+, Hg2+, Pb2+, Zn2+, AsO2−, and the herbicide paraquat. Some of these agents yield distinct tissue patterns of stress induction (e.g., Pb2+in the posterior pharynx, Cd2+throughout the pharynx, Hg2+in intestine), suggesting that classification of stress agents in complex mixtures may be a useful feature of this biomonitoring system. Using a soluble β‐galactosidase substrate, an assay was developed that allows the magnitude of the stress response to be measured. Stress reporter gene induction always occurred below the LC50 of the test substance, suggesting that this assay is a more sensitive and rapid indicator of stress than current LC50 assays usingCaenorhab
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