A protein tyrosine phosphatase inhibitor, sodium orthovanadate, causes parthenogenetic activation of pig oocytes via an increase in protein tyrosine kinase activity

This study was conducted to determine whether a protein tyrosine kinase (PT K) activity is involved in the initiation of the events that occur at ferti lization in pig oocytes. After maturation for 47 h, a 7-h treatment of oocy tes with 1 mM sodium orthovanadate, which is an inhibitor of protein tyrosi ne phosphatase, caused more than 90% pronuclear formation, cortical granule exocytosis, and a decrease in mitogen-activated protein kinase activity. I mmunoblotting with an antibody specific for phosphotyrosine showed at least three proteins whose phosphotyrosine contents were significantly increased upon treatment of oocytes with 1 mM sodium orthovanadate. Preincubation of pig oocytes with 50 mu M tyrphostin 47, a specific PTK inhibitor, complete ly blocked the ability of sodium orthovanadate to trigger activation events . In addition, when oocytes were pretreated with the calcium-chelating agen t BAPTA-AM, sodium orthovanadate-stimulated pronuclear formation was signif icantly (P < 0.01) reduced (94.0% vs. 43.1%). These results suggest that PT K may be involved in pig oocyte activation in a calcium-dependent manner an d that the stimulation of tyrosine kinase is able to signal a series of int racellular changes that lead to the activation events associated with ferti lization.