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Phospholipase C in mouse oocytes: characterization of beta and gamma isoforms and their possible involvement in
G Dupont1, O M McGuinness, M H Johnson
1Babraham Institute for Molecular Signalling, Department of Zoology, University of Cambridge, U.K.
Abstract:
This study involved an investigation of the role of phospholipase C (PLC) in generating repetitive Ca2+ spikes at fertilization. Using a PCR-based strategy we have demonstrated that mouse oocytes have mRNA coding for PLC beta 1, PLC beta 3 and PLC gamma isoenzymes. Furthermore, immunodetection of PLC gamma 1 using monoclonal antibodies reveals that PLC gamma 1 protein is present in mature mouse oocytes, ruling out the possibility that mRNA was being transcribed but not expressed. We were unsuccessful at detecting the presence of PLC beta protein, but the presence of this isoform can be inferred from functional studies. The PLC inhibitor, U73122, exerted an inhibitory effect on oocytes activated by spermatozoa or acetylcholine at concentrations of 10 and 30 microM respectively, while its inactive analogue had no effect. The soluble tyrosine kinase inhibitors, genistein (100 microM), herbimycin (10 microM) and geldanamycin (0.6 microM) which could affect signalling through PLC gamma hindered but never completely inhibited Ca2+ spiking in response to fertilization. We conclude that the activation of PLC to generate InsP3 may play a critical role in fertilization.
Insights
Phospholipase C (PLC) activation generates calcium (Ca2+) spikes during fertilization. This study confirms PLC gamma 1 presence in mouse oocytes, crucial for Ca2+ signaling and fertilization.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Molecular Biology
Background:
- Fertilization triggers repetitive calcium (Ca2+) spikes, essential for oocyte activation.
- The precise molecular mechanisms, particularly the role of phospholipase C (PLC), remain under investigation.
Purpose of the Study:
- To investigate the role of phospholipase C (PLC) isoenzymes in generating repetitive Ca2+ spikes during mouse oocyte fertilization.
- To determine the expression and functional significance of PLC isoforms in this process.
Main Methods:
- Polymerase Chain Reaction (PCR) to detect mRNA for PLC beta 1, beta 3, and gamma isoenzymes.
- Immunodetection using monoclonal antibodies to identify PLC gamma 1 protein presence.
- Functional assays using PLC inhibitor U73122 and tyrosine kinase inhibitors to assess effects on Ca2+ spiking.
Main Results:
- Mouse oocytes express mRNA for PLC beta 1, beta 3, and gamma isoenzymes.
- PLC gamma 1 protein is confirmed present in mature oocytes.
- The PLC inhibitor U73122 significantly inhibited Ca2+ spiking induced by sperm or acetylcholine.
- Tyrosine kinase inhibitors partially hindered Ca2+ spiking, suggesting a role for PLC gamma signaling.
Conclusions:
- Activation of PLC to generate inositol trisphosphate (InsP3) is critical for initiating Ca2+ spikes during fertilization.
- PLC gamma 1 is likely involved in the signaling pathway leading to fertilization-induced Ca2+ oscillations.