Cd/Zn exposure interactions on metallothionein response in Eisenia fetida (Annelida, Oligochaeta).

We studied metallothionein (MT) response in the manure worm Eisenia fetida after exposures to cadmium (Cd), zinc (Zn) or cadmium and zinc spiked media. MT was studied both at the protein level by Dot Immunobinding Assay, (DIA) and at the expression level by Northern blotting. Cd was highly accumulated by worms whereas Zn body concentration was regulated. In addition, Zn would limit Cd accumulation in worms exposed to low Cd concentrations (1 and 8 mg Cd kg(-1) of dry soil). Exposure to a mixture of Cd and Zn at high concentrations increased cytosolic MT levels. This increase would allow worms to regulate body Zn concentrations and also to limit Cd toxicity. Cd exposures increased gene expression of Cd-binding MT isoform (MT 2A) whereas Zn did not. However, when both metals were at high concentrations in the exposure medium, this expression was further increased. Several hypotheses are proposed to explain the results and the best approach to estimate metal exposure of this earthworm species is given. Further experiments have now to be performed to evaluate the usefulness of these MT responses for field contaminated soils toxicity assessment using this earthworm species.

Synchronization of Plodia interpunctella lepidopteran cells and effects of 20-hydroxyecdysone.

We have investigated the molecular and cellular mechanisms involved in the control of insect cell cycle by 20-hydroxyecdysone (20E) using the IAL-PID2 cell line established from imaginal wing discs of Plodia interpunctella. We first defined conditions for use of hydroxyurea, a reversible inhibitor of DNA synthesis, in order to synchronize the IAL-PID2 cells in their division cycle. A high degree of synchrony was reached when cells were exposed to two consecutive hydroxyurea treatments at 1 mm for 36 h spaced 16 h apart. Under these conditions, flow cytometry analysis demonstrated that 20E at 10(-6) m induced an inhibition of cell growth by an arrest of 90% of the cells in G2/M phase. Using cDNA probes specifically designed from E75 and HR3 nuclear receptors of Plodia interpunctella, we showed that PiE75 and PHR3 were highly induced by 20E through S and G2 phases with maximal enhancement just before the G2/M arrest of cells. These findings suggest that PiE75 and PHR3 could be involved in a 20E-induced genetic cascade leading to G2/M arrest.