SLX2 interacting with BLOS2 is differentially expressed during mouse oocyte meiotic maturation

Gametogenesis is a complex biological process of producing cells for sexual reproduction. Xlr super family members containing a conserved COR1 domain play essential roles in gametogenesis. In the present study, we identified that Slx2, a novel member of Xlr super family, is specifically expressed in the meiotic oocytes, which is demonstrated by western blotting and immunohistochemistry studies. In the first meiotic prophase, SLX2 is unevenly distributed in the nuclei of oocytes, during which phase SLX2 is partly co-localized with SYCP3 in synaptonemal complex and γH2AX in the nucleus of oocytes. Interestingly, the localization of SLX2 was found to be switched into the cytoplasm of oocytes after prometaphase I during oocyte maturation. Furthermore, yeast two-hybrid and coimmunoprecipitation studies demonstrated that SLX2 interacts with BLOS2, which is a novel centrosome-associated protein, and co-localized with γ-Tubulin, which is a protein marker of chromosome segregation in meiosis. These results indicated that SLX2 might get involved in chromosomes segregation during meiosis by interaction with BLOS2. In conclusion, SLX2 might be a novel gametogenesis-related protein that could play multiple roles in regulation of meiotic processes including synaptonemal complex assembly and chromosome segregation.     

Inhibitory effects of cAMP and protein kinase C on meiotic maturation and MAP kinase phosphorylation in porcine oocytes

The regulation of MAP kinase phosphorylation by cAMP and protein kinase C (PKC) modulators during pig oocyte maturation was studied by Western immunoblotting. We showed that both forskolin and IBMX inhibited MAP kinase phosphorylation and meiosis resumption in a dose-dependent manner, and this inhibitory effect was overcome by the protein phosphatase inhibitor, okadaic acid. Pharmacological PKC activator phorbol myristate acetate or physiological PKC activator diC8 also delayed MAP kinase phosphorylation and meiosis resumption, and their effect was abrogated by PKC inhibitors, staurosporine, and calphostin C. The results suggest that meiotic resumption is inhibited by elevation of cAMP or delayed by activation of PKC probably via down-regulation of MAP kinase activation, which is mediated by protein phosphatase, during pig oocyte maturation.     

Nuf2 is required for chromosome segregation during mouse oocyte meiotic maturation

Nuf2 plays an important role in kinetochore-microtubule attachment and thus is involved in regulation of the spindle assembly checkpoint in mitosis. In this study, we examined the localization and function of Nuf2 during mouse oocyte meiotic maturation. Myc₆-Nuf2 mRNA injection and immunofluorescent staining showed that Nuf2 localized to kinetochores from germinal vesicle breakdown to metaphase I stages, while it disappeared from the kinetochores at the anaphase I stage, but relocated to kinetochores at the MII stage. Overexpression of Nuf2 caused defective spindles, misaligned chromosomes, and activated spindle assembly checkpoint, and thus inhibited chromosome segregation and metaphase-anaphase transition in oocyte meiosis. Conversely, precocious polar body extrusion was observed in the presence of misaligned chromosomes and abnormal spindle formation in Nuf2 knock-down oocytes, causing aneuploidy. Our data suggest that Nuf2 is a critical regulator of meiotic cell cycle progression in mammalian oocytes.     

Requirements of Src family kinase during meiotic maturation in mouse oocyte

The Src family kinase (SFK) is important in normal cell cycle control. However, its role in meiotic maturation in mammalian has not been examined. We used confocal microscope immunofluorescence to examine the in vitro dynamics of the subcellular distribution of SFK during the mouse oocyte meiotic maturation and further evaluated the functions of SFK via biochemical analysis using a specific SFK pharmacological inhibitor, PP(2). Our results showed that nonphospho-SFK was absent in oocyte upon its release from follicle. Nonphospho-SFK appeared in cytoplasm 0.5 hr after the release of oocyte and translocated to germinal vesicle (GV) before germinal vesicle breakdown (GVBD). After GVBD, nonphospho-SFK colocated with condensed chromosomes. In occyte at metaphase I (MI) and telophase I, nonphospho-SFK accumulated in the cortex and the cleavage furrow respectively besides its existence in cytoplasm in both stages. In oocyte at metaphase II (MII), nonphospho-SFK concentrated at the aligned chromosomes. In contrast, phospho-SFK was absent in oocyte until 1 hr after its release from the follicle. Phospho-SFK accumulated in the GV, the cortex, and cytoplasm immediately prior to GVBD. After GVBD, phospho-SFK evenly distributed in oocyte. In oocyte at MII, phospho-SFK localized throughout the cytoplasm and under the egg member. When the SFK activity was inhibited, the oocyte failed to initiate GVBD, could not go into MII, and could not extrude the first polar body. Our results demonstrated that SFK is required for meiotic maturation in mouse oocyte.     

Characterization of polo-like kinase 1 during meiotic maturation of the mouse oocyte

We have characterized plk1 in mouse oocytes during meiotic maturation and after parthenogenetic activation until entry into the first mitotic division. Plk1 protein expression remains unchanged during maturation. However, two different isoforms can be identified by SDS-PAGE. A fast migrating form, present in the germinal vesicle, seems characteristic of interphase. A slower form appears as early as 30 min before germinal vesicle breakdown (GVBD), is maximal at GVBD, and is maintained throughout meiotic maturation. This form gradually disappears after exit from meiosis. The slow form corresponds to a phosphorylation since it disappears after alkaline phosphatase treatment. Plk1 activation, therefore, takes place before GVBD and MAPK activation since plk1 kinase activity correlates with its slow migrating phosphorylated form. However, plk1 phosphorylation is inhibited after treatment with two specific p34(cdc2) inhibitors, roscovitine and butyrolactone, suggesting plk1 involvement in the MPF autoamplification loop. During meiosis plk1 undergoes a cellular redistribution consistent with its putative targets. At the germinal vesicle stage, plk1 is found diffusely distributed in the cytoplasm and enriched in the nucleus and during prometaphase is localized to the spindle poles. At anaphase it relocates to the equatorial plate and is restricted to the postmitotic bridge at telophase. After parthenogenetic activation, plk1 becomes dephosphorylated and its activity drops progressively. Upon entry into the first mitotic M-phase at nuclear envelope breakdown plk1 is phosphorylated and there is an increase in its kinase activity. At the two-cell stage, the fast migrating form with weak kinase activity is present. In this work we show that plk1 is present in mouse oocytes during meiotic maturation and the first mitotic division. The variation of plk1 activity and subcellular localization during this period suggest its implication in the organization and progression of M-phase.     

Activation of both Mos and Cdc25 is required for G2-M transition in perch oocyte

Resumption of meiosis from diplotene arrest during the first meiotic prophase in vertebrate oocytes is universally controlled by MPF, a heterodimer of Cdk1 and cyclin B. Activation of MPF depends on the withdrawal of Cdk1 inhibition by Wee1/Myt1 kinase on the one hand and the activation of Cdk1 by Cdc25 phosphatase on the other. It is relevant to know whether both these pathways are necessary to rescue diplotene arrest or if either one of them is sufficient. In MIH (17alpha, 20beta dihydroxy-4-pregnen-3-one) incubated perch (Anabas testudineus) oocytes we have examined these possibilities. Perch oocyte extract following MIH incubation showed a significant increase in Myt1 phosphorylation from 12 to 16 hr indicating its progressive deactivation. MIH induced Mos expression markedly increased at 16 hr effecting 95% GVBD. Cycloheximide inhibited MIH induced Mos expression and its phosphorylation, which in turn reduced Myt1 phosphorylation and GVBD. Myt1 phosphorylation was blocked in Mos immunodepleted oocytes. All these suggest the involvement of Mos in Myt1 phosphorylation. Oocytes incubated in MIH for 16 hr activated Cdc25, but such activation could not rescue the inhibition of GVBD due to Myt1 in Mos immunodepleted oocytes. Blocking Cdc25 with an antisense oligo significantly inhibited GVBD even though Myt1 remained deactivated during this period. Taken together, our findings indicate that MIH requires both pathways for perch oocyte maturation: the expression and activation of Mos, which is linked to Myt1 deactivation on the one hand, and the activation of Cdc25 on the other, as blocking either pathway compromised G2-M transition in perch oocytes.     

Involvement of the metabolic hormones leptin, ghrelin, obestatin, IGF-I and of MAP kinase in control of porcine oocyte maturation

The general aim of our in vitro experiments was to study the role of the metabolic hormones leptin, ghrelin, obestatin and IGF-I and mitogen-activated protein kinase (MAPK)-dependent intracellular mechanisms in the control of nuclear maturation of porcine oocytes. For this purpose, porcine oocytes were isolated from the ovary and cultured in the presence of leptin, ghrelin, obestatin, IGF-I, MAPK blocker PD98059 and the combinations of hormones with PD98059. Proportions of matured oocytes (at metaphase II of meiosis, determined by DAPI staining) and of oocytes containing MAPK/ERK1-2 (determined by immunocytochemistry) were measured before and after culture. It was observed that the majority of oocytes isolated from the ovary before culture were immature and did not contain visible MAPK, but some oocytes were mature, and the majority of these oocytes contained MAPK. Incubation of oocytes resulted in a significant increase in the proportion of matured oocytes and in the percentage of oocytes containing MAPK in both the matured and not matured groups. Addition of IGF-I to the culture medium increased the proportion of matured oocytes, addition of leptin decreased it, and ghrelin and obestatin did not oocyte maturation. Addition of hormones did not affect the expression of MAPK in either immature or mature oocytes. PD98059, when given alone, suppressed the maturation and accumulation of MAPK in both mature and immature oocytes. When given together with hormones, PD98059 was able to reduce the stimulatory effect of IGF-I, to invert the inhibitory action of leptin to stimulatory and to induce the stimulatory action of ghrelin and obestatin on meiosis. IGF-I, ghrelin and obestatin, but not leptin, when given together with PD98059, increased the accumulation of MAPK in both immature and mature oocytes. Association of nuclear maturation and expression of MAPK in oocytes before, but not after culture, as well as the prevention of oocyte maturation by MAPK blocker suggests the involvement of MAPK-dependent intracellular mechanisms in the promotion of reinitiation, but not completion of meiosis. The effect of hormonal additions on meiosis of oocytes suggests that IGF-I is a stimulator, leptin can be an inhibitor, while ghrelin and obestatin probably do not control oocyte maturation. The ability of PD98059 to modify the effect of hormones on oocyte maturation and on MAPK expression suggests possible interference of hormones and MAPK-dependent intracellular mechanisms in oocytes. However, no influence of hormones on MAPK and lack of association between action of hormones and PD98059 on MAPK and meiosis suggest that MAPK is probably not a mediator of effect of IGF-I, leptin, ghrelin and obestatin on porcine oocyte nuclear maturation.     

MPF Amplification inXenopusOocyte Extracts Depends on a Two-Step Activation of Cdc25 Phosphatase

The activation of Cdc2 kinase induces the entry into M-phase of all eukaryotic cells. We have developed a cell-free system prepared from prophase-arrestedXenopusoocytes to analyze the mechanism initiating the all-or-none activation of Cdc2 kinase. Inhibition of phosphatase 2A, the major okadaic acid-sensitive Ser/Thr phosphatase, in these extracts, provokes Cdc2 kinase amplification and concomitant hyperphosphorylation of Cdc25 phosphatase, with a lag of about 1 h. Polo-like kinase (Plx1 kinase) is activated slightly after Cdc2. All these events are totally inhibited by the cdk inhibitor p21^Cip1, demonstrating that Plx1 kinase activation depends on Cdc2 kinase activity. Addition of a threshold level of recombinant Cdc25 induces a linear activation of Cdc2 and Plx1 kinases and a partial phosphorylation of Cdc25. We propose that the Cdc2 positive feedback loop involves two successive phosphorylation steps of Cdc25 phosphatase: the first one is catalyzed by Cdc2 kinase and/or Plx1 kinase but it does not modify Cdc25 enzymatic activity, the second one requires a new kinase counteracted by phosphatase 2A. Furthermore we demonstrate that, under our conditions, Cdc2 amplification and MAP kinase activation are two independent events.     

Mitogen-activated protein kinase activity during goat oocyte maturation and the acquisition of meiotic competence

Changes in MPF and MAPK activities during meiotic maturation of goat oocytes were investigated. Detection of MPF activity occurred concomitantly with GVBD, increased at MI, decreased during anaphase-telophase I transition, and increased thereafter in MII oocytes. The appearance of MAPK activity was delayed compared to MPF activity. MAPK activity increased after GVBD and persisted during the MI-MII transition. Whether MAPK was implicated in goat oocyte meiotic competence was also investigated by using oocytes from different follicle size categories that arrest at specific stages of the maturation process (GV, GVBD, MI, and MII). Results indicate that the ability of goat oocytes to resume meiosis is not directly related to the presence of Erk2. The ability to phosphorylate MAPK is acquired by the oocyte during follicular growth after the ability to resume meiosis. GVBD-arrested oocytes exhibited a high level of MPF activity after 27 hr of culture. However, 28% of oocytes from this group contained inactive MAPK, and 72% exhibited high MAPK activity. In addition, 29% of GVBD-arrested oocytes contained a residual interphasic network without recruitment of microtubules around the condensed chromosomes; 71% of GVBD-arrested oocytes displayed recruitment of microtubules near the condensed chromosomes and contained asters of microtubules distributed throughout the cytoplasm. These results indicate that oocytes arrested at GVBD were not exactly at the same point in the meiotic cell cycle progression, and suggest that MAPK could be implicated in the regulation of microtubule organization. The data presented here suggest that in goat oocytes, MAPK is not implicated in the early events of meiosis resumption, but rather in post-GVBD events such as spindle formation and MII arrest. © 1996 Wiley-Liss Inc.     

Histone methyltransferase SETD2 is required for meiotic maturation in mouse oocyte

SET-domain-containing 2 (SETD2), a member of the histone lysine methyltransferase family, has been reported to be involved in multiple biological processes. However, the function of SETD2 during oocyte maturation has not been addressed. In this study, we find that mouse oocytes are incapable of progressing through meiosis completely once SETD2 is specifically depleted. These oocytes present an abnormal spindle morphology and deficient chromosome movement, with disrupted kinetochore–microtubule attachments, consequently producing aneuploidy eggs. In line with this, the BubR1 signal is markedly elevated in metaphase kinetochores of oocytes with SETD2 depletion, indicative of the activation of spindle assembly checkpoint. In addition, we note that loss of SETD2 results in a drastic decrease in the trimethylation level of H3K36 in oocytes. Collectively, our data demonstrate that SETD2 is required for oocyte maturation and indicate a novel mechanism controlling the meiotic apparatus.     

Mechanisms that prevent catastrophic interactions between paternal chromosomes and the oocyte meiotic spindle

Meiosis produces haploid gametes by accurately reducing chromosome ploidy through one round of DNA replication and two subsequent rounds of chromosome segregation and cell division. The cell divisions of female meiosis are highly asymmetric and give rise to a large egg and two very small polar bodies that do not contribute to development. These asymmetric divisions are driven by meiotic spindles that are small relative to the size of the egg and have one pole juxtaposed against the cell cortex to promote polar body extrusion. An additional unique feature of female meiosis is that fertilization occurs before extrusion of the second polar body in nearly all animal species. Thus sperm-derived chromosomes are present in the egg during female meiosis. Here, we explore the idea that the asymmetry of female meiosis spatially separates the sperm from the meiotic spindle to prevent detrimental interactions between the spindle and the paternal chromosomes.     

Casein kinase G may be the target of spermine during progesterone-induced oocyte maturation

Casein kinase G (CKG) with more than 2500-fold enrichraent was purified from Bufo bufo gargarizans ovaries. The catalytic activity of the enzyme was found to be associated with its 42 kD subunit, and its 26 kD subunit was found to be the major tsrget for the enzyme autophos phorylation. Each fuU-grown oocyte contained 1.9 units of CKG corresponding to an intracellular concentration of 93 nM. After injecting an amount of 0,38 units of the enzyme into the oocyte, approximately 50% of the progesterone-induoed maturation was inhibited. The inhibitory effect was enhanced in oocytes pretreated with spermine, which was consistent with the results that the enzyme was activated in vitro in the presence of spermine, The MPF-induced oocyte maturation was delayed and even prohibited in the kinase-microinjected oocytes. A 55 kD oocyte protein was identified as an suhstrate of CKG both in vivo and in vitro, and the enhancement of the 55 kD protein phosphory[ation was associated with kinase inhibition on maturation and on protein synthesis in kinase-microinjected oocytes. As the endogenous spermine level decreased in the course of progesteroneinduced oocyte maturation. 55 kD protein was dephosphorylated, Heparin, a specific inhibitor of CKG, potentiated the progesterone-induced oocyte maturation. Altogether the experimental reSults indicated Strongly that CKG may be the physiological target of spermine.     

Activated proline‐rich tyrosine kinase 2 regulates meiotic spindle assembly in the mouse oocyte

Proline‐rich tyrosine kinase 2 (PYK2), a member of the protein tyrosine kinase family, plays an important role in various cellular processes. PYK2 can be phosphorylated on tyrosine 402 by diverse stimuli at the cell surface, and recent studies have shown that this activated form of PYK2 is enriched in oocytes and required for fertilization. However, the subcellular localization and functions of activated PYK2 in oocytes remain elusive. In this study, we demonstrate that the localization of p‐PYK2 undergoes dynamic changes during in vitro maturation of mouse oocytes. The signal of p‐PYK2 is initially dispersed in the cytoplasm, but begins to decorate organized microtubules after the germinal vesicle breakdown and localizes to spindle poles at metaphase. Our data further show that p‐PYK2 colocalizes with γ‐tubulin from the germinal vesicle stage through the end of meiosis in mouse oocytes. Nocodazole treatment and washout experiments confirm that p‐PYK2 associates with the oocyte spindle and spindle poles. Moreover, pharmacological inhibition of PYK2 activity dramatically alters the morphology of the bipolar spindle and prevents oocyte maturation. Together, these data suggest that activated PYK2 may function as a component of the microtubule organizing center to regulate spindle assembly during the meiotic process of mouse oocytes.     

原癌基因c-erbB2和c-myb经丝裂原活化蛋白激酶和成熟促进因子途径调节卵母细胞的成熟

本研究探讨了原癌基因c-erbB:和c-myb对小鼠卵母细胞成熟的影响及其在调控卵母细胞成熟中与丝裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)和成熟促进因子(mamration promoting factor,MPF)的上下游关系.c-erbB2反义寡脱氧核苷酸(antisense oligodeoxynucleotide,ASODN)和c.myb ASODN均呈剂量依赖方式抑制卵母细胞的生发泡破裂(germinalvesicle breakdown,GVBD)率和第一极体(first polar body,PBl)排放率,并显著延迟其成熟时间.小鼠卵母细胞显微注射重组人c-erbB2蛋白和c-myb蛋白后,培养6 h其GVBD率分别比对照组上升了23.1%(P<0.05)和32.2%(P<0.05),.培养12 h其PBl排放率分别比对照组上升了17.3%(P<0.05)和23.5%(P<0.05).RT-PCR结果显示,小鼠卵母细胞中存在c-erbB2mRNA和c-myb mRNA表达;c-erbB2ASODN能明显抑制卵母细胞中c-erbB2mRNA和c-myb mRNA的表达,c-myb ASODN能明显抑制卵母细胞中c-myb mRNA的表达,对c-erbB2 mRNA无明显影响;MAPK抑制剂PD98059以及MPF抑制剂roscovitine在抑制卵母细胞成熟的同时,均能阻断显微注射重组人c-erbB:蛋白和重组人c-myb蛋白对卵母细胞成熟的促进作用,但对卵母细胞中c-erbB2mRNA和c-myb mRNA表达无明显影响.Western blot结果显示,c-erbB2ASODN、c-mybASODN、PD98059、roscovitine均使卵母细胞中MAPK磷酸化水平和cyclinB 1含量下降.结果提示,原癌基因c-erbB2、c-myb在卵母细胞成熟中起重要作用,可能是调控卵母细胞成熟中关键蛋白激酶如MAPK、MPF的上游激活物.     

On the role of Cdc2 kinase during meiotic maturation of oocyte in the Chinese mitten crab,Eriocheir sinensis

Cdc2 kinase is a catalytic subunit of maturation-promoting factor (MPF), a central factor for inducing the meiotic maturation of oocyte. To understand the role of Cdc2 kinase on the oocyte maturation in crustacean, a complete cDNA sequence of Cdc2 kinase was cloned from Chinese mitten crab Eriocheir sinensis and its spatial-temporal expression profiles were analyzed during oogenesis at RNA and protein levels. The crab Cdc2 cDNA (1364 bp) encodes for a 299 amino acids protein with calculated molecular weight of 34.7 kDa. The Cdc2 mRNAs level showed no significant change in the ovary during oogenesis, whereas higher protein level was found at previtellogenesis, late vitellogenesis and germinal vesicle breakdown (GVBD) stages. Two forms (35 kDa and 34 kDa) of Cdc2 proteins were simultaneously identified in ovary at all stages. Immunocytochemistry analysis revealed that Cdc2 proteins locate exclusively in ooplasm of previtellogenic oocyte, and then relocate into germinal vesicle at vitellogenesis stage and accumulate on meiotic spindle at oocyte maturation. These findings suggest that Cdc2 kinase has essential roles in inducing GVBD and generating meiotic apparatus during the crab oocyte maturation.     

HDAC3 inhibition disrupts the assembly of meiotic apparatus during porcine oocyte maturation

Histone deacetylases (HDACs) are involved in a wide array of biological processes. However, the role of HDAC3 in porcine oocytes remains unclear. In the current study, we examine the effects of HDAC3 inhibition on porcine oocyte maturation using RGFP966, a selective HDAC3 inhibitor. We find that suppression of HDAC3 activity prevents not only the expansion of cumulus cells but also the meiotic progression of oocytes. It is interesting to note that HDAC3 displays a spindle-like distribution pattern as the porcine oocytes enter meiosis. In line with this, confocal microscopy reveals the high frequency of spindle defects and chromosomal congression failure in metaphase oocytes exposed to RGFP966. Moreover, HDAC3 inhibition results in the hyperacetylation of α-tubulin during oocyte meiosis. These findings indicate that HDAC3 activity might control the microtubule stability via the deacetylation of tubulin, which is critical for maintaining the proper spindle assembly, accurate chromosome separation, and orderly meiotic progression during porcine oocyte maturation.     

EGF-induced EGF-receptor and MAP kinase phosphorylation in goat cumulus cells during in vitro maturation

EGF has been shown to influence meiotic maturation and development competence of oocyte in various mammalian species. We previously reported, in goat, that the EGF receptor (EGF-R) was present both on cumulus cells and oocytes. Here, EGF-induced signaling was investigated during the in vitro maturation process in goat cumulus-oocyte complexes (COCs). Cumulus cells and oocytes were subjected to Western immunoblotting analysis using anti-MAP kinase, anti-phosphotyrosine, anti-phospho MAP kinase, and anti-phospho EGF-R antibodies. We demonstrated that treatment with EGF during the in vitro maturation process induced rapid tyrosine phosphorylation of EGF-R in a time and concentration dependent manner in cumulus cells. A similar pattern of activation by phosphorylation was observed for MAP kinase upon EGF stimulation. AG 1478, an inhibitor of the EGF kinase, suppressed EGF-stimulated phosphorylation of EGF-R and also affected the MAP kinase activation. Treatment with the MEK inhibitor PD 98059 abolished EGF-induced MAP kinase activation. We did not observe oocyte EGF-R phosphorylation in our experiments during the in vitro maturation process. Our data indicate, in goat cumulus cells, that activation of EGF-R by EGF triggers signaling through the MAP kinase pathway during in vitro maturation. This supports the hypothesis that the major site of action for EGF, that regulates oocyte maturation, is the cumulus cell.     

Germinal vesicle material drives meiotic cell cycle of mouse oocyte through the 3'UTR-dependent control of cyclin B1 synthesis

We compared the profile of histone H1 kinase activity, reflecting Maturation Promoting Factor (MPF) activity in oocytes bisected at the germinal vesicle (GV) stage and allowed to mature as separate oocyte halves in vitro. Whereas the oocyte halves containing the nucleus exhibited the same profile of increased kinase activity as that typical for intact oocytes, the anuclear halves revealed strong inhibition of the increase in this activity soon after germinal vesicle breakdown (GVBD). In contrast, the profile of MAP kinase activity did not differ significantly between anuclear and nucleus-containing oocyte halves throughout maturation. Of the two MPF components, CDK1 and cyclin B1, the amount of the latter was significantly reduced in anuclear halves, a reduction due to low-level synthesis and not to enhanced degradation. Expression of three reporter luciferase RNAs constructed, respectively, to contain cyclin B1-specific 3'UTR, the globin-specific 3'UTR, or no 3'UTR sequence was enhanced in nuclear halves, with significantly greater enhancement for the construct containing cyclin B1-specific 3'UTR as compared to the two other RNAs. We conclude that the profile of activity of MPF during mouse oocyte maturation is controlled by an unknown GV-associated factor(s) acting via 3'UTR-dependent control of cyclin B1 synthesis. These results require the revision of the hitherto prevailing view that the control of MPF activity during mouse oocyte maturation is independent of GV-derived material.