title: Low-intensity microwave irradiation does not substantially alter gene expression in late larval and adult Caenorhabditis elegans.
abstract: Reports that low-intensity microwave radiation induces heat-shock reporter gene expression in the nematode, Caenorhabditis elegans, have recently been reinterpreted as a subtle thermal effect caused by slight heating. This study used a microwave exposure system (1.0 GHz, 0.5 W power input; SAR 0.9-3 mW kg(-1) for 6-well plates) that minimises temperature differentials between sham and exposed conditions (< or =0.1 degrees C). Parallel measurement and simulation studies of SAR distribution within this exposure system are presented. We compared five Affymetrix gene arrays of pooled triplicate RNA populations from sham-exposed L4/adult worms against five gene arrays of pooled RNA from microwave-exposed worms (taken from the same source population in each run). No genes showed consistent expression changes across all five comparisons, and all expression changes appeared modest after normalisation (< or =40% up- or down-regulated). The number of statistically significant differences in gene expression (846) was less than the false-positive rate expected by chance (1131). We conclude that the pattern of gene expression in L4/adult C. elegans is substantially unaffected by low-intensity microwave radiation; the minor changes observed in this study could well be false positives. As a positive control, we compared RNA samples from N2 worms subjected to a mild heat-shock treatment (30 degrees C) against controls at 26 degrees C (two gene arrays per condition). As expected, heat-shock genes are strongly up-regulated at 30 degrees C, particularly an hsp-70 family member (C12C8.1) and hsp-16.2. Under these heat-shock conditions, we confirmed that an hsp-16.2::GFP transgene was strongly up-regulated, whereas two non-heat-inducible transgenes (daf-16::GFP; cyp-34A9::GFP) showed little change in expression.
authors.affiliation: South African National Bioinformatics Institute, University of Western Cape, Cape Town, South Africa.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Dawe
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Bodhicharla
authors.forename: Neil S
authors.initials: NS
authors.lastname: Graham
authors.forename: Sean T
authors.initials: ST
authors.lastname: May
authors.forename: Tom
authors.initials: T
authors.lastname: Reader
authors.forename: Benjamin
authors.initials: B
authors.lastname: Loader
authors.forename: Andrew
authors.initials: A
authors.lastname: Gregory
authors.forename: Mays
authors.initials: M
authors.lastname: Swicord
authors.forename: Giorgi
authors.initials: G
authors.lastname: Bit-Babik
authors.forename: David I
authors.initials: DI
authors.lastname: de Pomerai
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D005786:Gene Expression Regulation / Q000528:radiation effects*; D007814:Larva / Q000235:genetics*; D008872:Microwaves; D020411:Oligonucleotide Array Sequence Analysis; D013329:Structure-Activity Relationship