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exposed to EMF for 15-120 min have reported induction of
Fos, Jun
, and
MYC
transcription [81]. However, in a similar study of
Fos, Jun
, and
JunB
genes in
murine hematopoietic progenitor cell line, changes in gene expression were not
detectable [84].
Additional reports relating the effect of electric current on gene expression
have emerged from electroporation studies. This procedure, which entails ex-
posing living cells to a single high-voltage electric pulse, induces the formation
of transient membrane pores through which large biomolecules can pass. Orig-
inally developed for introducing exogenous DNA into cells, electroporation
has also been reported to result in differential gene expression in a number of
systems including interleukin-10 expression in monocytic cells [62]. Evidence
for transcriptional modulation has also been reported in cells exposed to super-
conducting magnets. In response to very high magnetic fields, an increase in
expression of the
rpoS
gene in
E. coli
was observed [109].
Most recently electrical induction of
hsp70
gene expression has been demon-
strated in murine astroglia and fibroblast cells. In this series of experiments
murine cells were transfected with a reporter plasmid constructed by inserting
the hsp70 promoter in front of a firefly luciferase gene. Subsequent electrical
stimulation of the transfected cells resulted in light emission from the reporter
[123]. Although very exciting, it is clear that the body of work in this area
is sometimes inconsistent and even contradictory. These discrepancies have,
in part, been attributed to lack of control of experimental variables relating to
EMF parameters such as frequency, amplitude, and duration [10].
With the objective of identifying promoters for use in genetically engineered,
electrically controllable whole-cell devices, we performed a search for current-
inducible promoters in
Bacillus subtilis
. This particular organism was targeted
both because its genome is fully sequenced and because, as spore former, it of-
fers the potential for long-term storage when interfaced with electronic devices.
In these experiments, all 4107 expressed genes in
B. subtilis
were screened
for putative current-inducible genes. Cells were grown to log phase, placed
in 35 mm
7 mm electroporation cells (1.5 ml volume), and subjected to a
current of 5 mA for a period of 10 min. An identical volume of cells was placed
in buffer without electric current exposure. Simultaneously, cells were diluted
and plated on nutrient agar plates to ascertain if the current had any lethal
effects on cells. After current exposure, the induced and untreated cells were
lysed and the RNA component isolated and quantified. Both RNA preparations
were reverse transcribed incorporating
33
P-dATP to make the labeled cDNA
that was hybridized against two identical commercial
B. subtilis
gene arrays
(Genosys Panorama, The Woodlands, TX). These arrays permit the levels of
all the expressed genes to be quantitatively assayed simultaneously.
None of the cells in the three treatment groups showed signs of lethality com-
pared with controls. Based on statistical analysis of the 4 replicate arrays, 20
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