| This study was conducted to investigate the involvement of G protein- and protein tyrosine kinase (PTK)-signal transduction in pig oocyte activation. As the first experiment, matured oocytes were microinjected with mRNA encoding a G protein coupled receptor (M1 muscarinic receptor). Stimulation of G protein coupled receptor with agonist triggered cortical granule exocytosis, pronuclear formation, and changes in protein profiles consistent with fertilization. Furthermore, these treated oocytes showed preimplantation developmental competence as measured by blastocoele formation as well as morphological changes similar to normal embryo development, i.e. reticulation of nucleoli and appearance of somatic type mitochondria. The second set of experiments was carried out to elucidate the role of PTKs in pig oocyte activation. Treatment of matured oocytes with insulin triggered pronuclear formation. Moreover, stimulation of matured oocytes with sodium orthovanadate known as an activator of PTK caused an increase in PTK activity, release of intracellular calcium, cortical granule exocytosis, pronuclear formation, and a decrease in mitogen-activated protein kinase activity. The function of PTK in pig oocyte activation is strongly supported by treatment with a specific PTK inhibitor (Tyrphostin 47). Preincubation of oocytes with this inhibitor completely blocked the ability of sodium orthovanadate to trigger activation events. The results of these experiments suggest that pig oocyte activation at fertilization might be mediated by a G protein- or PTK-coupled signal transduction pathways. |
