AS Dawe1, RK Bodhicharla2, NS Graham3, ST May3, T Reader2, B Loader4, A Gregory4, M Swicord5, G Bit-Babik5 and DI de Pomerai2
1South African National Bioinformatics Institute, University of Western Cape, Cape Town, South Africa
2School of Biology, University of Nottingham, Nottingham, UK
3Nottingham Arabidopsis Stock Centre, University of Nottingham, School of Biosciences, Sutton Bonington, UK
4Enabling Metrology Laboratory, National Physical Laboratory, Teddington, UK
5Motorola Research Laboratories, Fort Lauderdale, Florida, USA
Summary of research published in Bioelectromagnetics, Vol. 30, No. 8, pp. 602-612.
This work is an MTHR (UK Mobile Telecommunications Health Research)-funded study to determine the reproducibility and robustness of the effects we had earlier reported, where low-intensity continuous-wave (CW) microwave fields apparently up-regulated heat-shock gene expression in the model nematode C. elegans (de Pomerai et al., 2000, Nature 405, 417-8).
In our previous study, published 3 years ago (Dawe et al., 2006, Bioelectromagnetics 27, 88-97), we established that power leakage causing a very slight rise (0.1-0.2°C) in the temperature of exposed but not sham samples was the most likely explanation for the observed increase in hsp-16.1 reporter expression at a nominal exposure temperature of 26.0°C. The present paper follows this up with a survey of global gene-expression changes in wild-type C. elegans following exposure to similar (in fact, somewhat lower) CW microwave fields. In an effort to promote good practice (as per MIAME guidelines (Editor’s note: MIAME stands for a standards effort to identify the Minimum Information required to unambiguously specify critical details About a Microarray Experiment)) for future gene-array studies in this field, we have made our gene-array data publicly accessible through the NCBI (National Center for Biotechnology Information) GEO (Gene Expression Omnibus) database (accession number GSE10787), and have also used a statistical correction for false discovery rate.
Our overall conclusion is that no genes show reproducible and statistically convincing changes in expression level across 5 replica microwave-exposed arrays as compared to 5 sham arrays. By contrast, when comparing 2 arrays from worms subjected to mild heat shock at 30°C against the 5 original sham arrays, >1500 statistically significant changes were recorded, including very major (up to 95-fold) changes in heat-shock gene expression. The up-regulation of one of these heat-shock genes has been confirmed independently using an hsp-16.2::GFP reporter, whereas two similar reporters (cyp-34A9::GFP and daf-16::GFP) were not up-regulated, broadly confirming the gene-array results for both genes. This reinforces our previous conclusion that weak microwave irradiation does not induce a heat-shock response nor any significant changes in gene expression in the nematode C. elegans; our earlier work suggesting such a response appears to reflect a subtle thermal artefact (see Dawe et al., 2006).