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DNA repair processes in germ cells demonstrated in ejaculated sperms of rabbits treated with methyl methane sulfonate
Abstract:
Male rabbits were treated with a single i.v. injection of 22.5 mg/kg methyl methane sulfonate (MMS). 0--24 h later [3H]-thymidine was injected in both testicles. Incorporation of the isotope in germ cell DNA was demonstrated in ejaculated sperms. In controls labeled sperms were demonstrated first on day 40--43. These cells were in the preleptotene spermatocyte phase at the time of [3H]-thmidine injection. In rabbits treated with MMS significant radioactivity occurred in sperms collected from day 19 onwards. These cells were in late spermatocyte and early spermatid phase of maturation when [3H]-thymidine was injected. Incorporation of thymidine in these cell populations is interpreted as an expression of unscheduled DNA synthesis, a repair process initiated after chemical damage of germ cell DNA by MMS. The usefulness of the rabbit test system within the framework of conventional mutagenicity screening tests is discussed.
Insights
Methyl methane sulfonate (MMS) damages rabbit germ cell DNA, triggering unscheduled DNA synthesis. This DNA repair process was detected in ejaculated sperms, indicating MMS mutagenicity in this test system.
Area of Science:
- Toxicology
- Molecular Biology
- Reproductive Biology
Background:
- Chemical mutagens can induce DNA damage in germ cells.
- Assessing DNA repair mechanisms is crucial for understanding mutagenicity.
- The rabbit test system offers a model for evaluating genotoxicity.
Purpose of the Study:
- To investigate the DNA repair response in rabbit germ cells following methyl methane sulfonate (MMS) exposure.
- To evaluate the utility of the rabbit model for mutagenicity screening.
Main Methods:
- Male rabbits received an intravenous injection of methyl methane sulfonate (MMS).
- [3H]-thymidine was administered to assess DNA synthesis in germ cells.
- Radioactivity in ejaculated sperm was measured over time.
Main Results:
- Control rabbits showed labeled sperm from day 40-43, corresponding to preleptotene spermatocytes.
- MMS-treated rabbits exhibited radioactivity in sperm from day 19 onwards.
- This radioactivity indicated unscheduled DNA synthesis in late spermatocytes and early spermatids.
Conclusions:
- Methyl methane sulfonate (MMS) induces unscheduled DNA synthesis in rabbit germ cells, signifying DNA repair.
- The rabbit test system effectively detects DNA damage and repair following chemical exposure.
- This model is valuable for conventional mutagenicity screening tests.