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
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 10-second groups and the control and 20-second groups were significant (Table 1).
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?) / t1:C & 5 sec / No / 2.401
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 10- and 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.
Literature Cited
Berg, J.; Tymoczko, J.; Stryer, L. Biochemistry. W. H. Freeman and Company 2012.
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.
FlyNap® Material Safety Data Sheet
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s): Xin Gong
Title: Mutagenic Effect of UV Exposure on Metabolic Activity of Fruit Flies (Dorsophila melanogaster)
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
The purpose of this research was to study the effects of UV radiation on metabolic activities of living organism. The fruit flies (Dorsophila melanogaster) were used as a sample of living organism due to their fast-reproducing period and low number of chromosomes. One control and three other groups of fruit flies were used in the study. Each one of the three groups was sedated with FlyNap for a different period of time (5 second, 10 second, and 20 second). Following the exposure, the flies on each group were incubated for 3 days to recover and fully express any mutation. The time of the arousal for each fly was recorded and an ANOVA test was performed, the results demonstrated that there was a significant different between the time of arousal of control group with 10-second groups and the control with the 20-second groups; thus the arousal time shortened with longer exposure time which means that the UV mutagenesis had an excitatory effect on the ability of the gruit flies to metabolize FlyNap.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current state of knowledge.
I believe the topic of the paper was really interesting and could be useful to future scientific papers. The introduction was strong and well-detailed about how the idea of the study started and why this study’s results may be useful for future studies. The methods were mostly clear and easy to follow. However the discussion section was not as strong as the other sections of paper. The results were not explained and it isn’t clear why these results were obtained. Also the beginning of the methods and materials needs to be reworded (I understood the procedure but only after reading that paragraph a few times).
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
- The graph should be changed and the ventricle gridlines and the boarder of the graph should be removed.
- The sources weren’t correctly cited and there wasn’t enough citation on the paper related to each section of the paper.
- Other issues were point out on the paper (see the comment section of the paper on the right side)
a This paper was a final version
Recommendation
a This paper should be published with revision