Introduction and aim
Only limited genomes of flatfish have been sequenced. This limits the use of microarrays to study the effects of pollutants on endocrine function (endocrine function). The flatfish (such as Pleuronichthys verticalis/hornyhead turbot) is a preference in studying endocrine disruption risk due to chemical pollution since they reside in less expansive areas and feed at the bottom of water bodies. The study by Baker et al (2006) therefore utilized microarrays from different species (Danio reri/zebrafish-whose microarrays study disruption caused by nonylphenol and estradiol exposure) to study gene expression in hornyhead turbot. The successful analysis of gene expression in this model as, confirmed by quantitative RT-PCR, provided hope for use of microarrays of multispecies in the study of how different fish (such as Perciformes and pleuronectiformes that have limited sequenced genomes) are affected by contaminants.
Methods
Baker et al. (2008) reviewed studies conducted on exposure of zebrafish to Estradiol and 4-nonylphenol. The authors then gathered details relating to how to assay vitellogenin and estradiol in hornyhead. A sample of 7 male hornyhead turbots was collected for microanalysis purposes where their livers were to be extracted for the purpose. The sample was from the Southern California coast and had altered morphology and histology (like having immature eggs in the testis). The sampled fish also had vitellogenin and estradiol of considerably high levels while cortisol was of low levels. A control sample was also collected from an environment that was not as polluted as for the study sample. The control sample was then placed under laboratory conditions characterized by clean water. The control sample was free of vitellogen and estrogen exposure as confirmed by ELISA tests.
Baker et al (2008) then made a multispecies microarray of 65mer which was an oligonucelotid-based array. The microarray contained conserved sequences. This was to counter parity of genome data in GenBank. The available sequences were from zebrafish, stickleback and medak as well as cDNA sequences from hornyhead turbot. Sequences were selected from tetraordoniformes and perciformes. The RNA was extracted and targets were labeled fluorescently followed by hybridization in microarrays. The hornhead turbot mRNAs were then amplified and an analysis of data from the microarray was conducted. The mRNA expression level in controls was done using qRT-PCR.
Results and Discussion
The authors of this study were able to come up with a multispecies microarray using sequences of Fugu and Tetradon which were already available in GenBank and relied on conserved sequences in turbot. Differential expression of genes in the sample and the control showed significant differences in expression of endocrine disruption genes (e.g. CYP3A and RXR were up-regulated, FXR was down-regulated), with either a strong up-regulation or a strong down-regulation. qRT-PCR of expression of turbot genes confirmed that the microarray was accurate in its monitoring of gene expression in livers of the fish. The multispecies microarray that was developed was able to show patterns of gene expression in zebrafish once exposed to estradiol and 4-nonylphenol. Microarrays can effectively monitor how chemical contaminants affect aquatic organisms due to their ability to analyze changing gene expressions in a sample of tissue and deduce how the endocrine system is affected by the chemicals.
Conclusion
Baker et al (2008) were able to demonstrate several endocrine disruptors (e.g. estrogens) using the multispecies microarray. Multispecies microarrays therefore proved to be effective tools for detecting presence of endocrine disruptors in water environments. In deed, it is now possible to develop other multispecies microarrays for detecting fish that has come into contact with chemical contaminants.
Reference
Baker, M. E., Rugerri, B., Sprague, L. J., Eckhardt-Ludka, C. and Lapira, J. et al. (2008). Analysis of endocrine disruption in Southern California coastal fish using an aquatic multispecies microarray. Environmental Health Perspectives, 117(2), 223-230.