Effects of MEK inhibitor U0126 on meiotic progression in mouse oocytes: microtuble organization, asymmetric division and metaphase II arrest

Abstract

In this study we used U0126, a potent and specific inhibitor of MEK, to study the roles of MEK/ERK/p90 rsk signaling pathway in the meiotic cell cycle of mouse oocytes. The phosphorylation of MAP kinase and p90 rsk in the oocytes treated with 1.5 M U0126 was the same as that in oocytes cultured in drug-free medium. With 1.5 M U0126 treatment, the spindles appeared normal as they formed in oocytes, but failed to maintain its structure. Instead, the spindle lost one pole or elongated extraordinarily. After further culture, some oocytes extruded gigantic polar bodies (>30 m) that later divided into two small ones. Some oocytes underwent symmetric division and produced two equal-size daughter cells in which normal spindles formed. In oocytes with different division patterns, MAP kinase was normally phosphorylated. When the concentration of U0126 was increased to 15 M, the phosphorylation of both MAPK and p90 rsk were inhibited, while symmetric division was decreased. When incubating in medium containing 15 M U0126 for 14 h, oocytes were activated, but part of them failed to emit polar bodies. MII oocytes were also activated by 15 M U0126, at the same time the dephosphorylation of MAP kinase and p90 rsk was observed. Our results indicate that 1) MEK plays important but not indispensable roles in microtubule organization; 2) MEK keeps normal meiotic spindle morphology, targets peripheral spindle positioning and regulates asymmetric division by activating some unknown substrates other than MAP kinase /p90 rsk ; and 3) activation of MEK/ERK/p90 rsk cascade maintains MII arrest in mouse oocytes.

GM130, a cis-Golgi protein, regulates meiotic spindle assembly and asymmetric division in mouse oocyte

“…13 Deletion of MEK1/2 by intravenous and intrabursal injection of MEK inhibitor U0126 or MEK siRNA-injection treatment, causes large PB formation. 23,24 In the present study, we showed that GM130 was colocalized with p-MEK1/2 at MI and MII stages. The phenotypes in GM130 depletion oocytes were similar to what had been described in the deletion of p-MEK1/2 by U0126.…”

“…7A). Treatment of U0126, the specific MEK inhibitor, 24,25 caused disorganized spindles and GM130 dispersion into the cytoplasm in mouse oocytes.…”

“…p-MEK1/2 was no longer accumulated at spindle poles in GM130 depletion oocytes. 23,24 Furthermore, oocytes treated with U0126, resulted in GM130 detachment from the spindle poles. Collectively, these results provide us a hint that GM130 may participate in the MAPK signaling pathway to regulate the spindle migration and asymmetric division.…”

Second Meiotic Spindle Integrity Requires MEK/MAP Kinase Activity in Mouse Eggs

“…MOS activity is required for normal microtubule organization before and during the MI/MII transition [15]. Direct inhibition of MEK during MI using the specific MEK inhibitor U0126 disrupts the MI spindle and causes formation of abnormally large first polar bodies similar to the mos -/-phenotype [16]. In addition, MOS/MEK/MAPK pathway components are physically associated with meiotic spindles, including phosphorylated ERK1/2 MAPK [17,18], phosphorylated MEK [19,20] and an ERK1/2 MAPK-interacting protein, DOC1R, whose depletion during MI causes formation of abnormal MII spindles [21].…”

Comparing Pig and Amphibian Oocytes: Methodologies for Aneuploidy Detection and Complementary Lessons for MAPK Involvement in Meiotic Spindle Morphogenesis

“…First observations were made in nullizygous mice for Mos, where MEK activation is impaired and interphase-like structure of microtubules and chromosomes are found between meiotic division, as well as formation of monopolar half-spindle (Araki et al, 1996;Tong et al, 2003;Verlhac et al, 1996). Similar observations were made in other biological systems.…”