Activation of Xenopus eggs by the kinase inhibitor 6-DMAP suggests a differential regulation of cyclin B and p39(mos) proteolysis.
In Xenopus eggs, metaphase II arrest is due to the cytostatic factor that maintains a high level of MPF activity. Kinases are important in this phenomenon since p39(mos) and MAPK play a part in the cytostatic activity whereas p34(cdc2) is the catalytic subunit of MPF. Fertilization induces a rise in intracellular calcium leading to egg activation that can be mimicked by calcium-increasing agents such as calcium ionophore. We have performed on Xenopus eggs a biochemical comparison of the effects of the kinase inhibitor 6-DMAP and the calcium ionophore. Both drugs were able to induce pronucleus formation but the underlying molecular events were different. The inactivation of MAPK occurred earlier in eggs exposed to 6-DMAP. Cyclins B1 and B2 were stable and p39(mos) was proteolysed in 6-DMAP-treated eggs while the three proteins underwent degradation in A23187-treated ones. These results suggest a differential regulation of ubiquitin-dependent proteolysis of cyclin B and p39(mos).
Bodart
J F
JF
Laboratoire de Biologie du Développement, UPRES EA 1033, Villeneuve d'Ascq Cedex, F-59655, France.
Béchard
D
D
Bertout
M
M
Gannon
J
J
Rousseau
A
A
Vilain
J P
JP
Flament
S
S
D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D016203:CDC2 Protein Kinase / Q000032:analysis / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002467:Cell Nucleus / Q000201:enzymology; D019926:Cyclin B / Q000032:analysis / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D007476:Ionophores / Q000494:pharmacology; D008677:Metaphase / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000032:analysis / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D017231:Proto-Oncogene Proteins c-mos / Q000032:analysis / Q000378:metabolism*; D014982:Xenopus laevis
D019926:Cyclin B; D004791:Enzyme Inhibitors; D007476:Ionophores; D000001:Calcimycin; C001020:N(6),N(6)-dimethyladenine; D017231:Proto-Oncogene Proteins c-mos; D016203:CDC2 Protein Kinase; D019950:Mitogen-Activated Protein Kinase 1; D000225:Adenine; D002118:Calcium