Initiation of Xenopus Oocyte Maturation by Activation of the Mitogen-activated Protein Kinase Cascade

Activation of p42 Mitogen-activated Protein Kinase (MAPK), but not c-Jun NH2-Terminal Kinase, Induces Phosphorylation and Stabilization of MAPK PhosphataseXCL100 inXenopusOocytes

“…The presence of multiple activation mechanisms may increase the robustness of the p42 MAPK/XCL100 system. Nevertheless, in the oocyte this negative feedback loop appears to be overwhelmed by a stronger positive feedback system (Gotoh et al, 1995;Matten et al, 1996;Roy et al, 1996;Howard et al, 1999; this study) that maintains p42 MAPK activity at high levels despite high levels of phosphatase activity (Sohaskey and Ferrell, 1999).In contrast, the relationship between XCL100 and its substrate JNK appears to be fundamentally different. Whereas overexpressed XCL100 does prevent JNK activation in oocytes subjected to hyperosmolar stress (our unpublished observations), JNK activation does not suffice to bring about XCL100 phosphorylation and stabilization ( Figure 3C).…”

“…The presence of multiple activation mechanisms may increase the robustness of the p42 MAPK/XCL100 system. Nevertheless, in the oocyte this negative feedback loop appears to be overwhelmed by a stronger positive feedback system (Gotoh et al, 1995;Matten et al, 1996;Roy et al, 1996;Howard et al, 1999; this study) that maintains p42 MAPK activity at high levels despite high levels of phosphatase activity (Sohaskey and Ferrell, 1999).…”

“…Activation of the p42 MAPK cascade is important at multiple points during maturation: for the initial activation of Cdc2 triggering the G2-M transition (Sagata et al, 1988;Kosako et al, 1994bKosako et al, , 1996Gotoh et al, 1995;Palmer et al, 1998); for Cdc2 reactivation and the suppression of DNA replication during the transition from meiosis 1 to meiosis 2 (Furuno et al, 1994); and for the maintenance of Article published online ahead of print. Mol.…”

Inactivation of protein kinase A is not required for c-mos translation during meiotic maturation of Xenopus oocytes

“…One of these e ects was proposed to be the inhibition of endogenous c-mos synthesis, another e ect the suppression of cdc25 activation. As microinjection of PKAc at levels that block progesteroneinduced translation of endogenous c-mos did not prevent injected c-mos from activating MAP kinase (Matten et al, 1994), and MAPK activity is required for c-mos translation in Xenopus oocytes (Gotoh et al, 1995), it was proposed that PKA may inhibit c-mos synthesis at a point downstream of MAPK, perhaps between MAPK and the polyadenylation apparatus of the translation initiation complex (Matten et al, 1996).…”

“…As microinjection of the CL100 phosphatase, which inactivates MAPK (Keyse and Emslie, 1992), inhibits progesterone-dependent synthesis and accumulation of c-mos (Gotoh et al, 1995), a likely interpretation of the above experiments is that down-regulation of PKA is required for progesterone to activate MAPK, but once Figure 4 The CL100 MAPK phosphate strongly depresses MAPK activation and c-mos translation in oocytes microinjected with the recombinant c-mos protein. Oocytes were microinjected (+) or not (7) with mRNAs encoding CL100, and after overnight incubation, microinjected with pMal-c-mos.…”