Identification of an activator required for elevation of maturation-promoting factor (MPF) activity by gamma-S-ATP

Evaluation of Matrex cellufine GH 25

The aim of this work was to test a new matrix for group size exclusion chromatography, Matrex cellufine GH 25, and compare it with Sephadex G25 Superfine and Sephadex G25 fine. Matrex cellufine GH 25 showed a better behaviour at high flow rate (792 cm/h) without back-pressure or packing-down. Sephadex G25 superfine showed a limited flow rate (226 cm/h) with both back-pressure and packing-down and Sephades G25 fine allowed running at 792 cm/h but with packing-down fourfold superior to that of Matrex cellufine GH 25. To have the same number of theoretical plates, it was necessary to increase the height of the bed and therefore the volume of the matrix (43%). With Matrex cellufine GH 25, the sample volume was more limited (9% of column volume) than with Sephadex G25 superfine (17%) but was equivalent to Sephadex fine (9%). To have the same elution time as Sephadex G25 superfine, the flow rate had to be increased by a factor 1.7. As Matrex cellufine GH 25 allowed a high flow rate when the volume of the sample was limited to 6% of column volume, its performance is better than that of Sephadex G25.

Rescue of mouse embryos from 2-cell blocks by microinjection of maturation promoting factor

OBJECTIVE

To examine the rescue of mouse embryos from 2-cell blocks by the microinjection of maturation promoting factor (MPF) extracted from matured Xenopus eggs into one of the blastomeres of 2-cell stage mouse embryos.

DESIGN

Controlled laboratory study.

SETTING

First Department of Obstetrics and Gynecology, Toho University School of Medicine, Tokyo, Japan.

ANIMAL(S)

Eight- to 10-week-old female Crj:CD-1(ICR) mice.

INTERVENTION(S)

One of the blastomeres of the mouse 2-cell embryos was injected with MPF (MI group) or mHTF medium (MED group) at 28--32 hours after insemination.

MAIN OUTCOME MEASURE(S)

The developmental rate to blastocyst.

RESULT(S)

The developmental rate to blastocyst in the MI group (48.0%) was significantly higher than that in the MED group (0%).

CONCLUSION(S)

The 2-cell block was specifically rescued by the microinjection of MPF and not by the insertion of pipettes.

Study of the in vitro maturation of mouse oocytes induced by microinjection of maturation promoting factor (MPF)

PURPOSE

Maturation promoting factor (MPF) acts at the resumption of meiosis and nonspecifically throughout the animal species. There exists a considerable body of literature on MPF, but little work has been done to study the induction of maturation of mammalian oocytes by microinjection of extracted MPF.

METHODS

Immature (GV-stage) mouse oocytes were microinjected MPF extracted from matured Xenopus eggs in the presence of dbcAMP.

RESULTS

The rate of germinal vesicle, breakdown (GVBD) induced at 24 hr after MPF injection was significantly higher (90.5%) than that of the control (2.2%), which was injected with HTF medium containing dbcAMP (P < 0.0001). The rate of extrusion of the first polar body at 24 hr after MPF injection was significantly higher (84.1%) than that of the same control (1.1%) (P < 0.0001).

CONCLUSIONS

From these results, it is concluded that the maturation of mammalian oocytes can be induced by the microinjection of MPF extracted from other species.

The oocyte metaphase arrest

Usually, oocyte meiosis reinitiation appears as a two step process during which release from the prophase block is followed by a second arrest in metaphase I or II. In this review, we will examine the mechanisms required to maintain the metaphase arrest and stabilize MPF activity at this stage. Then, we will analyse the processes required to exit from the metaphase block. These may drive the cells forward to the metaphase-anaphase transition, as a result of fertilization, activation or protein synthesis inhibition. Instead, inhibiting protein phosphorylation drives the oocyte back to interphase. All these treatments result in derepression of DNA synthesis.

Characterization and physiological importance of a novel cell cycle regulated protein kinase in Xenopus laevis oocytes that phosphorylates cyclin B2

We have partially purified a specific cyclin B2 kinase (cyk) from prophase oocytes of Xenopus laevis after an ATP-gamma-S activation step. Phosphopeptide analysis identified Ser53 as the major in vitro phosphorylation site for cyk in cyclin B2. Using a synthetic peptide derived from cyclin B2 encompassing Ser53 (cyktide) as a substrate, cyk was shown to be activated during progesterone-induced maturation, with a peak of activity between 40 and 50% maturation. A sustained high cyk activity was observed in oscillating egg extracts. Microinjection of cyk-phosphorylated cyclin B2 into prophase oocytes accelerated progesterone-induced maturation by about 2 h, indicating that cyclin B2 is a relevant substrate for cyk and that the function of cyk is situated upstream of cdc2-cyclin B activation. Microinjection of cyk-phosphorylated cyktide or a combination of cyk and cyclin B1 into G2 fibroblasts induced significant changes in cell morphology, reminiscent of a premature prophase-like phenotype. Similarly, addition of cyk-phosphorylated cyktide in cyclin B1-dependent interphase extracts resulted in histone H1 kinase activation.

Okadaic acid mimics a nuclear component required for cyclin B-cdc2 kinase microinjection to drive starfish oocytes into M phase

G2-arrested oocytes contain cdc2 kinase as an inactive cyclin B-cdc2 complex. When a small amount of highly purified and active cdc2 kinase, prepared from starfish oocytes at first meiotic metaphase, is microinjected into Xenopus oocytes, it induces activation of the inactive endogenous complex and, as a consequence, drives the recipient oocytes into M phase. In contrast, the microinjected kinase undergoes rapid inactivation in starfish oocytes, which remain arrested at G2. Endogenous cdc2 kinase becomes activated in both nucleated and enucleated starfish oocytes injected with cytoplasm taken from maturing oocytes at the time of nuclear envelope breakdown, but only cytoplasm taken from nucleated oocytes becomes able thereafter to release second recipient oocytes from G2 arrest, and thus contains M phase-promoting factor (MPF) activity. Both nucleated and enucleated starfish oocytes produce MPF activity when type 2A phosphatase is blocked by okadaic acid. If type 2A phosphatase is only partially inhibited, neither nucleated nor enucleated oocytes produce MPF activity, although both do so if purified cdc2 kinase is subsequently injected as a primer to activate the endogenous kinase. The nucleus of starfish oocytes contains an inhibitor of type 2A phosphatase, but neither active nor inactive cdc2 kinase. Microinjection of the content of a nucleus into the cytoplasm of G2-arrested starfish oocytes activates endogenous cdc2 kinase, produces MPF activity, and drives the recipient oocytes into M phase. Together, these results show that the MPF amplification loop is controlled, both positively and negatively, by cdc2 kinase and type 2A phosphatase, respectively. Activation of the MPF amplification loop in starfish requires a nuclear component to inhibit type 2A phosphatase in cytoplasm.