Mutagenic Effect of UV Exposure on Metabolic Activity of Fruit Flies (Drosophila
melanogaster)
Xin Gong
Department of Biological Sciences
Saddleback College
Mission Viejo, CA 92692
Ultraviolet light has been known to impact a living organism either negatively, as
seen in plant growth, or positively, as seen in many forms of cancer. In fruit flies, UV
radiation has also been observed to have a negative effect on reproduction. This experiment
investigated the mutagenic effect of ultraviolet light on metabolic activity, using fruit flies
as the model organism. Metabolic activity was determined by how quickly the fruit flies
regained consciousness after administration of FlyNap®. Arousal times were measured
after the flies had been exposed to UV light for a certain amount of time. Results showed
that longer exposure rates actually decreased arousal time, suggesting that UV radiation
has an activating effect on fruit fly metabolism. These differences are reflected by varying
exposure times. Further genetic testing would need to be done to confirm whether these
differences are in fact a result of mutagenesis, or if it is the result of a chemical change.
Introduction
Since metabolism is facilitated in large part
by enzymes, which are coded for by DNA, inducing a
mutation in these genes can either activate or inhibit
translation of the metabolic enzymes. In a hospital
setting, variations in metabolism of IV anesthetics,
such as Propofol®, administered in metered dosesm
are commonly observed in patients during surgery,
which is why the metabolic rates of each patient must
be tested before going into surgery. Similar effects
can be observed in fruit flies when they are
administered a metered dose of FlyNap®. Individuals
with similar genetic makeup are expected to
metabolize the anesthetic at a similar rate. However,
mutations in genes that control metabolism can either
increase or decrease the rate of metabolism,
depending on whether the mutation is activating or
inhibitory.
Drosophila melanogaster serves as a useful
model organism in biology due to its short generation
time as well as its relatively simple karyogamy,
which consists of only three pairs of autosomes and
one pair of sex chromosomes, allowing for easy
genetic manipulation and testing. There have been
many compelling studies on the mutagenesis of fruit
flies in molecular genetics; however, not many
studies have been the mutagenesis of fruit flies in
metabolism
(Grigliatti,
“Temperature-sensitive
mutations in Drosophila melanogaster”). These
studies may bring to light many findings in the
metabolism of other organisms as well.
Since the major effect of UV radiation is to
create thymine dimers, which inhibit DNA
replication and transcription, it was hypothesized that
UV radiation would have an inhibitory effect on
metabolic activity. Longer exposure times to UV
would lead to longer arousal times following
anesthesia.
Materials and Methods
The following 40-mL vials with cotton
stoppers containing 15-20 flies with 10 mL of
nutrient media containing starch and active yeast
were prepared: a control, 5-, 10-, and 20- second
exposure groups. After being properly labeled, each
group of flies was fully sedated with FlyNap®, an
anesthetic mixture consisting of 50% triethylamine,
25% ethanol, and 25% fragrances (FlyNap® MSDS).
FlyNap® administered through a Fly Wand
suspended in the vial just below the plug for
approximately 45-90 seconds. To ensure that the last
fly had been anesthetized, the vial was gently tapped
to check for any movement.
The control group was not exposed to any
radiation while the three variable groups were
exposed to UV light at 254 nm for 5, 10, and 20
seconds. Following exposure, the flies were
incubated for 3 days to recover and fully express any
mutations. Flies were again knocked out with
FlyNap® using the same procedure above (t0), and
then monitored vigilantly for the next few hours.
Using a stopwatch, the time of arousal for each fly
was recorded when the first sign movement was
observed (t1,2,3,…). The time it took for each
individual fly to regain consciousness, in minutes,
was calculated by subtracting t0 from tx.
Results among the control and three
experimental groups were and analyzed by a single
factor analysis of variance (ANOVA) test followed
by a paired post-hoc test.
Results
Arousal Time (in mins)
In contrast to the initial hypothesis, arousal
time decreased with increased exposure to UV
(Figure 1). While there was no significant difference
between the average arousal times between the 5- and
10- second groups, the flies in the control group took
significantly longer to regain consciousness while
those in the 20 second group took a significantly
shorter amount of time. Results of the ANOVA test
were significant with a P value of 0.0015.
A paired post-hoc test determined that at a
95% confidence interval, there was no significant
difference between the control and 5-second groups;
however, the differences between the control and 10second groups and the control and 20-second groups
were significant (Table 1).
2: C & 10 sec
Yes
2.573
3: C & 20 sec
Yes
4.079
Discussion
In the time that it took for the fruit flies to
regain consciousness following anesthesia from
FlyNap®, there were significant differences in
arousal times between the control group and the 10and 20- second group. However, while the initial
hypothesis was that longer exposure to UV light
would lead to longer arousal times, the arousal time
actually shortened with longer exposure time. This
suggests that UV mutagenesis has an activating effect
on ability of the fruit fly to metabolize FlyNap®.
If mutagenesis occurred, the mutation may
have affected a gene coding for suppression of
metabolism, leading to an increase in metabolic
activity (Stryer, Biochemistry). However, it is not
entirely clear whether the significant increase in
metabolic activity is, in fact, due to a mutation or if it
is a result of a chemical alteration of the metabolic
enzymes within the fruit fly. Further genetic testing
must be performed to determine whether this change
is genetic or chemical.
200
Literature Cited
150
Berg, J.; Tymoczko, J.; Stryer, L. Biochemistry. W.
H. Freeman and Company 2012.
100
50
0
Control
5 sec
10 sec
20 sec
Exposure Groups
Figure 1: Bar graph displaying mean ± SEM arousal
time for control and experimental groups.
Table 1: Results of the post-hoc test (Bonferri
Correction) comparing the control group with the
three experimental groups *Results were significant
between the control and 10 second group and
between the control and 20 second group at α=0.05
and insignificant between the control and 20 second
groups*
Comparison
Significant?
(P <0.05?)
t
1: C & 5 sec
No
2.401
Grigliatti, T.; Hall L., Rosenbluth, R.; Suzuki,
D. “Temperature-sensitive mutations in Drosophila
melanogaster.” Molecular and General Genetics.
1973. 120 (2): 107-114.
Ziilstra, J.A.; Vogel, E.W. “Influence of inhibition of
the metabolic activation on the mutagenicity of some
nitrosamines, triazenes, hydrazines and seniciphylline
in Drosophila melanogaster.” Department of
Radiation Genetics and Chemical Mutagenesis,
University of Leiden, The Netherlands. 1988 Nov;
202(1):251-67.
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