Inhibition of Rac1 GTPase activity affects porcine oocyte maturation and early embryo development

Si-Jing Song,Shao-Chen Sun,Ru-Xia Jia,Xiang-Shun Cui,Nam-Hyung Kim,Qiao-Chu Wang

doi:10.1038/srep34415

Si-Jing Song, Shao-Chen Sun + Show 4 more

Open Access

https://doi.org/10.1038/srep34415

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Abstract

Mammalian oocyte asymmetric division relies on the eccentric positioning of the spindle, resulting in the polar body formation. Small signaling G protein Rac1 is a member of GTPases, which regulates a diverse array of cellular events, including the control of cell growth, cytoskeletal reorganization, and the activation of protein kinases. However, effects of Rac1 on the porcine oocyte maturation and early embryo development are not fully understood. In present study we investigated the role of Rac1 in oocyte maturation and embryo cleavage. We first found that Rac1 localized at the cortex of the porcine oocytes, and disrupting the Rac1 activities by treating with NSC 23766 led to the failure of polar body emission. In addition, a majority of treated oocytes exhibited abnormal spindle morphology, indicating that Rac1 may involve into porcine oocyte spindle formation. This might be due to the regulation of Rac1 on MAPK, since p-MAPK expression decreased after NSC 23766 treatments. Moreover, we found that the position of most meiotic spindles in treated oocytes were away from the cortex, indicating the roles of Rac1 on meiotic spindle positioning. Our results also showed that inhibition of Rac1 activity caused the failure of early embryo development. Therefore, our study showed the critical roles of Rac1 GTPase on porcine oocyte maturation and early embryo cleavage.

Highlights

Mammalian oocyte asymmetric division relies on the eccentric positioning of the spindle, resulting in the polar body formation
The mature mammalian oocyte is highly polarized and undergoes asymmetrical cell division because spindle migrates to the oocyte cortex to ensure the extrusion of small polar body in meiosis I (MI), which is essential for the generation of the large egg[1]
Mammalian meiotic maturation is a process of asymmetric cytokinesis which is a unique characteristic of meiotic divisions in mammalian oocytes, producing oocytes with the small polar body size

Summary

Introduction

Mammalian oocyte asymmetric division relies on the eccentric positioning of the spindle, resulting in the polar body formation. Cdc[42], RhoA, and Rac[1] were all demonstrated to be critical for oocyte spindle positioning: RhoA plays versatile roles in many aspects of cell function such as stress fiber formation, cytokinesis, and cell polarization[16], which was recently considered to regulate cytoskeleton dynamics by affecting actin filament assembling and spindle formatting[17]. Another member of Rho family Cdc[42] was considered to be a key regulator of cytoskeleton and polarity, which is essential for meiotic maturation and oocyte asymmetry[2]. A Rac-GEF triggered a localized activation of Rac in the oocyte cortex as a result of spindle migration and in return affected polar body emission during the meiosis II (MII) arrest[22]

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