Investigation of transcriptional responses of juvenile mouse bone marrow to power frequency magnetic fields

• A pilot experiment identified three transcripts potentially affected by magnetic field exposure.
• A larger replication failed to confirm the responses.
• This study illustrates the difficulty in detecting small changes in gene expression.

To seek alterations in gene transcription in bone marrow cells following in vivo exposure of juvenile mice to power frequency magnetic fields, young (21–24-day old) C57BL/6 mice were exposed to a 100 μT 50 Hz magnetic field for 2 h. Transcription was analysed by three methods, High Coverage Expression Profiling (HiCEP), Illumina microarrays and quantitative real-time polymerase chain reaction (QRT-PCR). A pilot HiCEP experiment with 6 exposed (E) and 6 non-exposed (NE) mice identified four candidate responsive transcripts (two unknown transcripts (AK152075 and F10-NED), phosphatidylinositol binding clathrin assembly protein (Picalm) and exportin 7 (Xpo7)). A larger experiment compared 19 E and 15 NE mice using two independent QRT-PCR assays and repeated microarray assays. No significant field-dependent changes were seen, although Picalm showed a trend to significance in one QRT-PCR assay (E/NE = 0.91; P = 0.06). However, the study was underpowered to detect an effect of this magnitude (52% power at P = 0.05). These data indicate the current experimental constraints in detecting small changes in transcription that may occur in response to magnetic fields. These constraints result from technical limitations in the accuracy of assays and biological variation, which together were sufficient to account statistically for the number of differentially expressed transcripts identified in the pilot experiment.