MEK1/2 Regulates Microtubule Organization, Spindle Pole Tethering and Asymmetric Division During Mouse Oocyte Meiotic Maturation

Abstract

It is well known that MAPK plays pivotal roles in oocyte maturation, but the function of MEK (MAPK kinase) remains unknown. We have studied the expression, subcellular localization and functional roles of MEK during meiotic maturation of mouse oocytes. Firstly, we found that MEK1/2 phoshorylation (p-MEK1/2, indicative of MEK activation) was low in GV (germinal vesicle) stage, increased 2h after GVBD (germinal vesicle breakdown), and reached the maximum at metaphase II. Secondly, we found that P-MEK1/2 was restricted in the GV prior to GVBD. In prometaphase I and metaphase I, P-MEK1/2 was mainly associated with the spindle, especially with the spindle poles. At anaphase I and telophase I, p-MEK1/2 became diffusely distributed in the region between the separating chromosomes, and then became associated with the midbody. The association of p-MEK1/2 with spindle poles was further confirmed by its colocalization with the centrosomal proteins, gamma-tubulin and NuMA. Thirdly, we have investigated the possible functional role of MEK1/2 activation by intravenous administration and intrabursal injection of a specific MEK inhibitor, U0126, and by microinjection of MEK siRNA into oocytes. All these manipulations cause disorganized spindle poles and spindle structure, misaligned chromosomes and larger than normal polar bodies. Our results suggest that MEK1/2 may function as a centrosomal protein and may have roles in microtubule organization, spindle pole tethering and asymmetric division during mouse oocyte maturation.

WAVE2 regulates meiotic spindle stability, peripheral positioning and polar body emission in mouse oocytes

“…Since similar phenotypes have previously been observed with MAPK pathway members such as MEK, MAPK and JNK. [38][39][40][41] Localization of γ-tubulin and MAPK was disrupted by WAVE2 RNAi, an indication that spindle formation was disrupted. Recent work showed that PAK1, the downstream effector of Rac, could form a WAVE2-PAK1-kinesin complex 18,38 and that PAK1 …”

Septin2 is modified by SUMOylation and required for chromosome congression in mouse oocytes

“…After taxol treatment, septin2 disappeared from spindle fibers and translocated to the region around chromosomes. Importantly, localization of septin2 differs from other proteins involved in spindle formation that we previously studied (e.g., MDK, 43 BARC1, 44 and PLK1, 45 ), which are present at the center of microtubule organizing centers (MTOCs) after taxol treatment, participating in microtubule nucleation or organization. Moreover, it is reported that septins regulate microtubule dynamics through MAP4.…”

Molecular insights into mechanisms regulating faithful chromosome separation in female meiosis

“…61,62 CENP-E function is essential for meiosis I in pig, 110 mouse, rat and frog, 111,112 since it is a binding partner of BubR1. The localization of MAP kinase kinase (MEK) and MAP kinase is similar to some spindle checkpoint proteins [113][114][115][116][117][118] in oocytes. Immunodepletion of MAP kinase prevents checkpoint activation, which is rescued anchoring at the kinetochore plate 80 and directly binds to Cdc20, which is the activator of APC/C.…”

“…119 Knockdown of MEK causes misalignment of chromosomes and error in chromosome separation. 118 Thus, MEK/MAP kinase may also participate in the spindle checkpoint pathway regulation in meiosis. [119][120][121][122][123] All these observations support the notion that spindle checkpoint is required for faithful segregation of chromosomes in oocyte meiosis I.…”