To our knowledge, this study represents the first attempt to
evaluate genotoxicity associated with acute ammonia toxicity
in tilapia fish (O. niloticus) and there are no direct comparisons
in the same experiments of ammonia and hypoxia tolerance, despite
the high likelihood that fish experiencing hypoxia may
also experience high (10 mg/L) ammonia levels (and vice versa).
Ammonia was found to be the main acute toxic compounds
in leachate as determined by [18] who found that DNA damage
was induced in fish exposed to diluted raw leachate and
that coincide with the findings in this study.
In the present study, the RAPD-PCR technique was used to
determine the potential acute (6 days) ammonia genotoxicity
in O. niloticus. Different and distinctive finger pattern were obtained
from O. niloticus DNA under investigation. Primers
used in the O. niloticus DNA exposed to Ammonia yielded
RAPD patterns differ from the control fish. This indicated that
DNA from fish exposed to Ammonia created polymorphic regions
in the O. niloticus genome.
The main changes in the RAPD profiles of the present
investigation were the gain or loss of different bands (group
2 and 3) and variation in their intensity (The three groups under
investigation). These effects might be due to the structural
rearrangements in DNA caused by different types of DNA
damages. Appearance of new bands can be explained as a result
of different DNA structural changes such as breaks, transpositions
and deletions as reported by [14,4].
Estimation about the existence of mutation and structural
alterations in O. niloticus DNA exposed to ammonia on the
bases of DNA patterns could be obtained after RAPD with
a set of random primers. The variation in band intensity and
disappearance of some bands may correlate with the level of
DNA damage after exposure to ammonia, which can change
the number of binding sites for Taq polymerase. That due
to, the Taq DNA polymerase is the most commonly used enzyme
in DNA sequencing. As a result, the G track generated
during DNA sequencing by these Taq polymerases does not
terminate prematurely, and higher molecular-mass G bands
are detected. Another property of these Taq polymerases is
that the sequencing patterns produced by these enzymes are
remarkably even in band-intensity and peak-height distribution
thus resulting in a significant improvement in the accuracy
of DNA sequencing [19].
Although RAPD-PCR provides no direct information on
the functional importance of the mutated loci, further analysis
of these genetically altered loci may provide suggestive evidence
for loci that participate in the O. niloticus DNA damage.
To our knowledge, this study represents the first attempt toevaluate genotoxicity associated with acute ammonia toxicityin tilapia fish (O. niloticus) and there are no direct comparisonsin the same experiments of ammonia and hypoxia tolerance, despitethe high likelihood that fish experiencing hypoxia mayalso experience high (10 mg/L) ammonia levels (and vice versa).Ammonia was found to be the main acute toxic compoundsin leachate as determined by [18] who found that DNA damagewas induced in fish exposed to diluted raw leachate andthat coincide with the findings in this study.In the present study, the RAPD-PCR technique was used todetermine the potential acute (6 days) ammonia genotoxicityin O. niloticus. Different and distinctive finger pattern were obtainedfrom O. niloticus DNA under investigation. Primersused in the O. niloticus DNA exposed to Ammonia yieldedRAPD patterns differ from the control fish. This indicated thatDNA from fish exposed to Ammonia created polymorphic regionsin the O. niloticus genome.The main changes in the RAPD profiles of the presentinvestigation were the gain or loss of different bands (group2 and 3) and variation in their intensity (The three groups underinvestigation). These effects might be due to the structuralrearrangements in DNA caused by different types of DNAdamages. Appearance of new bands can be explained as a resultof different DNA structural changes such as breaks, transpositionsand deletions as reported by [14,4].Estimation about the existence of mutation and structuralalterations in O. niloticus DNA exposed to ammonia on thebases of DNA patterns could be obtained after RAPD witha set of random primers. The variation in band intensity anddisappearance of some bands may correlate with the level ofDNA damage after exposure to ammonia, which can changethe number of binding sites for Taq polymerase. That dueto, the Taq DNA polymerase is the most commonly used enzymein DNA sequencing. As a result, the G track generatedduring DNA sequencing by these Taq polymerases does notterminate prematurely, and higher molecular-mass G bandsare detected. Another property of these Taq polymerases isthat the sequencing patterns produced by these enzymes areremarkably even in band-intensity and peak-height distributionthus resulting in a significant improvement in the accuracyof DNA sequencing [19].Although RAPD-PCR provides no direct information onthe functional importance of the mutated loci, further analysisof these genetically altered loci may provide suggestive evidencefor loci that participate in the O. niloticus DNA damage.
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