Microtubule tracks can be detected in mouse oocytes with an antibody directed against a calcium transporter.

In metaphase II-arrested mouse oocytes, most microtubules are found in the meiotic spindle, a structure that remains stable for hours despite microtubule instability. Microtubule organizing centres (MTOCs) are present at the poles of the spindle and in the cytoplasm, but the latter nucleate very few microtubules. This particular organization of the microtubule network enabled us to observe the unexpected behaviour of a protein that can associate with microtubules.

The metaphase II arrest in mouse oocytes is controlled through microtubule-dependent destruction of cyclin B in the presence of CSF.

In unfertilized eggs from vertebrates, the cell cycle is arrested in metaphase of the second meiotic division (metaphase II) until fertilization or activation. Maintenance of the long-term meiotic metaphase arrest requires mechanisms preventing the destruction of the maturation promoting factor (MPF) and the migration of the chromosomes. In frog oocytes, arrest in metaphase II (M II) is achieved by cytostatic factor (CSF) that stabilizes MPF, a heterodimer formed of cdc2 kinase and cyclin.

MAP kinase becomes stably activated at metaphase and is associated with microtubule-organizing centers during meiotic maturation of mouse oocytes.

Using antisera generated against sequences conserved between the ERK1- and the ERK2-encoded species of mitogen-activated protein (MAP) kinases of the rat, species of approximate M(r) 42 and 44 kDa were identified in mouse oocytes. When oocytes underwent meiotic maturation, both species displayed a retarded electrophoretic mobility, consistent with modification by phosphorylation. The slow-migrating forms first appeared after the oocytes had entered metaphase, and their appearance was sensitive to inhibitors of protein synthesis or phosphorylation.

Okadaic acid induces spindle lengthening and disrupts the interaction of microtubules with the kinetochores in metaphase II-arrested mouse oocytes.

The cell cycle is regulated by phosphorylation events via a cascade of protein kinases and phosphatases, but many of their substrates remain unknown. To study whether proteins of the metaphase II-arrested mouse oocyte meiotic spindle are substrates for phosphorylation events, we used okadaic acid (OA), a potent phosphatase inhibitor, upon fully mature spindles. Incubation of oocytes for 3 hr with 1 microM OA led to a dramatic lengthening of the spindle and a disorganization of the metaphase plate.

Inhibition of protein kinases by 6-dimethylaminopurine accelerates the transition to interphase in activated mouse oocytes.

Mouse oocyte activation is followed by a peculiar period during which the interphase network of microtubules does not form and the chromosomes remain condensed despite the inactivation of MPF. To evaluate the role of protein phosphorylation during this period, we studied the effects of the protein kinase inhibitor 6-dimethylaminopurine (6-DMAP) on fertilization and/or parthenogenetic activation of metaphase II-arrested mouse oocytes. 6-DMAP by itself does not induce the inactivation of histone H1 kinase in metaphase II-arrested oocytes, and does not influence the dynamics of histone H1 kinase inactivation during oocyte activation.