Gene response profiles for Daphnia pulex exposed to the environmental stressor cadmium reveals novel crustacean metallothioneins

Joseph R Shaw¹^,2^,3^,4 , John K Colbourne⁵ , Jennifer C Davey²^,3 , Stephen P Glaholt¹^,2^,4 , Thomas H Hampton²^,3 , Celia Y Chen¹^,2 , Carol L Folt¹^,2 and Joshua W Hamilton²^,3

¹Department of Biology, Dartmouth College, Hanover, New Hampshire 03755, USA

²Center for Environmental Health Sciences at Dartmouth, Dartmouth Medical School, Hanover NH 03755, USA

³Department of Pharmacology & Toxicology, Dartmouth Medical School, Hanover NH 03755, USA

⁴The School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, USA

⁵The Center for Genomics and Bioinformatics, Indiana University, Bloomington, Indiana 47405, USA

author email corresponding author email

BMC Genomics 2007, 8:477doi:10.1186/1471-2164-8-477


Published:	21 December 2007

Abstract

Background

Genomic research tools such as microarrays are proving to be important resources to study the complex regulation of genes that respond to environmental perturbations. A first generation cDNA microarray was developed for the environmental indicator species Daphnia pulex, to identify genes whose regulation is modulated following exposure to the metal stressor cadmium. Our experiments revealed interesting changes in gene transcription that suggest their biological roles and their potentially toxicological features in responding to this important environmental contaminant.

Results

Our microarray identified genes reported in the literature to be regulated in response to cadmium exposure, suggested functional attributes for genes that share no sequence similarity to proteins in the public databases, and pointed to genes that are likely members of expanded gene families in the Daphnia genome. Genes identified on the microarray also were associated with cadmium induced phenotypes and population-level outcomes that we experimentally determined. A subset of genes regulated in response to cadmium exposure was independently validated using quantitative-realtime (Q-RT)-PCR. These microarray studies led to the discovery of three genes coding for the metal detoxication protein metallothionein (MT). The gene structures and predicted translated sequences of D. pulex MTs clearly place them in this gene family. Yet, they share little homology with previously characterized MTs.

Conclusion

The genomic information obtained from this study represents an important first step in characterizing microarray patterns that may be diagnostic to specific environmental contaminants and give insights into their toxicological mechanisms, while also providing a practical tool for evolutionary, ecological, and toxicological functional gene discovery studies. Advances in Daphnia genomics will enable the further development of this species as a model organism for the environmental sciences.