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Dieldrin modifies the hydrolysis of PIP2 and decreases the fertilization rate in Bufo arenarum oocytes
T M Fonovich de Schroeder1, A M Pechén de D'Angelo
1Libiquima, Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires, Neuquén, Argentina.
Abstract:
Carbachol treatment in Bufo arenarum oocytes decreases the radioactivity in [32P]PIP2 in the following 20 min after stimulation and increases the [3H]glycerol labeling of 1,2-DAG at 1 min of stimulation. On the contrary, in Dieldrin treated oocytes carbachol stimulation produces an increase in [32P]PIP2 labeling without changes in [3H]1,2-DAG radioactivity. The sustained hydrolysis of PIP2 observed in Control oocytes is necessary to generate the intracellular second messengers which initiate the fertilization pathway. The lack of response to muscarinic stimulation in Dieldrin treated oocytes, may be associated with an early activation of PIP2-PLC by the insecticide, producing a depletion of the PIP2 pool previous to the stimulation with carbachol. These changes take place simultaneously with a decrease in the ability of Bufo arenarum oocytes to be fertilized in vitro, suggesting a correlation between impairment in the PIP2 cascade and a decrease in the fertilization rate.
Insights
Dieldrin exposure disrupts the PIP2 signaling pathway in Bufo arenarum oocytes, impairing fertilization. This insecticide depletes PIP2, preventing normal responses to carbachol stimulation and reducing fertilization rates.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Toxicology
Background:
- Phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis is crucial for initiating fertilization.
- Muscarinic receptor stimulation triggers signaling pathways involving PIP2 hydrolysis.
Purpose of the Study:
- To investigate the effects of Dieldrin on PIP2 metabolism and fertilization in Bufo arenarum oocytes.
- To determine if Dieldrin interferes with carbachol-induced signaling pathways.
Main Methods:
- Oocytes were treated with Dieldrin or served as controls.
- Radioactive labeling ([32P]PIP2 and [3H]glycerol) was used to measure PIP2 and diacylglycerol (DAG) levels.
- Oocytes were stimulated with carbachol to assess muscarinic receptor response.
- In vitro fertilization assays were performed.
Main Results:
- Carbachol decreased [32P]PIP2 and increased [3H]glycerol labeling in control oocytes.
- Dieldrin-treated oocytes showed increased [32P]PIP2 labeling and no change in [3H]DAG after carbachol stimulation.
- Sustained PIP2 hydrolysis in controls is essential for fertilization.
- Dieldrin treatment led to a decrease in Bufo arenarum oocyte fertilization rates.
Conclusions:
- Dieldrin may prematurely activate PIP2-phospholipase C (PLC), depleting the PIP2 pool before stimulation.
- Impairment of the PIP2 cascade by Dieldrin correlates with reduced fertilization capacity.
- Dieldrin disrupts essential signaling pathways for fertilization in amphibian oocytes.