Gene transcription and higher-level effects of multigenerational Zn exposure in Daphnia magna.

Zn exposure of Daphnia magna during one generation has been shown to modulate gene transcription differently in Zn exposed organisms compared to their non-exposed offspring. Here we studied the transcriptional gene regulation with a cDNA microarray in D.magna exposed to Zn for three generations (F0-F2). For the first time molecular effects of multigeneration toxicant exposure in D. magna are described. Out of 73 differentially transcribed genes in the F1Zn exposed generation (compared to the F1 control), only seven genes were also differentially transcribed in the same direction in the F0Zn exposed daphnids (up or down, compared to the F0 control). The majority of the differentially transcribed unigenes in F1Zn exposed daphnids (78%) were not differentially transcribed in the F0Zn exposed organisms. This indicates that Zn exposure affected other molecular pathways in the second exposed generation, although a reduced reproduction and a reduction in juvenile growth were observed in both Zn exposed generations, compared to the respective controls. In the third Zn exposed generation (F2), no reduction in growth or reproduction compared to the control was observed. This acclimation was reflected in a significantly lower number of differentially transcribed genes, compared to the Zn exposed F0 and F1 generations.