Inhibition of protein tyrosine phosphatases blocks calcium-induced activation of metaphase II-arrested oocytes of Xenopus laevis

We have studied the effect of a protein tyrosine phosphatases (PTP) inhibit or on calcium-induced activation of Xenopus laevis oocytes arrested at meta phase II. Ammonium molybdate microinjection blocked pronucleus formation fo llowing A23187 treatment while cortical granules still underwent exocytosis . Pronuclei still occurred in ammonium molybdate-injected oocytes following 6-DMAP addition. Changes that usually occurred following A23187 exposure w ere inhibited in the presence of ammonium molybdate in the oocyte: MAPK dep hosphorylation, p34(cdc2) rephosphorylation and cyclin B2 and p39(mos) prot eolysis. These results suggest that a PTP is involved in the activation of the ubiquitin-dependent degradation machinery. (C) 1999 Federation of Europ ean Biochemical Societies.