Rare Earth (REs) are a set of elements including scandium (Sc), yttrium (Y), and fifteen lanthanides. Because of their unique chemical properties, they are used for many High-Tech devises which support our daily life. Despite their name, REs are relatively plentiful in earth crust. Since REs are widely dispersed in soil, organism may encounter these elements during the evolutional history of life. However, effects of REs on biological systems, especially in multicellular organisms, are poorly understood. In this study, we have explored the impact of REs on the behavior, locomotion and growth of organisms by using Caenorhabditis elegans as a model system.
To see the effect of REs on the worm growth and development, wild-type eggs were soaked in RE solutions for 24 hr. In the presence of 100 mM RE, a significant part of eggs were unhatched and the large part of larval worms hatched was dead. The effects were observed for all REs except radioactive promethium which we have not tested. MAPK mutants which were hypersensitive to heavy metal (HM) ions such as Cu2+ and Cd2+ showed hypersensitivity to REs in both eggs and adult worm, suggesting that the worm used common signaling pathway for RE- and HM-stress responses. We also tested the behavior of the worm against REs using radial concentration gradient formed on an agar plate. Wild-type worms showed an avoidance behavior against all REs examined. The avoidance behavior was abolished in the chemosensory-defective
che-2 mutant worms, indicating that the worm can detect REs via the function of chemosensory neurons. By using cell-specific rescue strain of
dyf-11 mutant and cell-specific genetic cell ablation lines, we found that REs were detected by overlapped but distinct subset of sensory neurons that used for HM avoidance.