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LIM kinases (LIMK1/2) are LIM domain‐containing serine/threonine/tyrosine kinases that mediate multiple cellular processes in mitosis. In the present study, we explored the functional roles and potential signaling pathway of LIMK1/2 during mouse oocyte meiosis. Disruption of LIMK1/2 activity and expression significantly decreased oocyte polar body extrusion. Live‐cell imaging revealed that spindle migration was disturbed after both LIMK1 and LIMK2 knock down, and this might be due to aberrant distribution of actin filaments in the oocyte cytoplasm and cortex. Meanwhile, our results demonstrated that the function of LIMK1 and LIMK2 in actin assembly was related to cofilin phosphorylation levels. In addition, disruption of LIMK1/2 activity significantly increased the percentage of oocytes with abnormal spindle morphologies, which was confirmed by the abnormal p‐MAPK localization. We further, explored the upstream molecules of LIMK1/2, and we found that after depletion of ROCK, phosphorylation of LIMK1/2 and cofilin were significantly decreased. Moreover, RhoA inhibition caused the decreased expression of ROCK, p‐LIMK1/2, and cofilin. In summary, our results indicated that the small GTPase RhoA regulated LIMK1/2‐cofilin to modulate cytoskeletal dynamics during mouse oocyte meiosis. [ABSTRACT FROM AUTHOR]

LIMKs (LIMK1 and LIMK2) are serine/threonine protein kinases that involve in various cellular activities such as cell migration, morphogenesis and cytokinesis. However, its roles during mammalian early embryo development are still unclear. In the present study, we disrupted LIMK1/2 activity to explore the functions of LIMK1/2 during mouse early embryo development. We found that p-LIMK1/2 mainly located at the cortex of each blastomeres from 2-cell to 8-cell stage, and p-LIMK1/2 also expressed at morula and blastocyst stage in mouse embryos. Inhibition of LIMK1/2 activity by LIMKi 3 (BMS-5) at the zygote stage caused the failure of embryo early cleavage, and the disruption of LIMK1/2 activity at 8-cell stage caused the defects of embryo compaction and blastocyst formation. Fluorescence staining and intensity analysis results demonstrated that the inhibition of LIMK1/2 activity caused aberrant cortex actin expression and the decrease of phosphorylated cofilin in mouse embryos. Taken together, we identified LIMK1/2 as an important regulator for cofilin phosphorylation and actin assembly during mouse early embryo development. [ABSTRACT FROM AUTHOR]

FHOD1 is a member of Diaphanous-related formins (DRFs) which belongs to the Formin family. Previous studies have shown that the DFRs might affect several cellular functions such as morphogenesis, cytokinesis, cell polarity, and embryonic differentiation. However, there is no evidence showing the functions of FHOD1 during oocyte meiosis. This study is aimed at exploring the roles of FHOD1 during the mammalian oocyte maturation. Immunofluorescent staining showed that FHOD1 was restricted to the nucleus in germinal vesicle (GV) stage of the oocytes, after the GV breakdown FHOD1 was primarily located at two poles of the spindle at both metaphases I and II stages. Knockdown of FHOD1 by siRNA injection did not affect polar body extrusion but generated the large polar bodies. In addition, we observed the spindle migration failure in metaphase I oocytes, with a large number of meiotic spindles anchoring in the center of cytoplasm. The expression level of cytoplasmic actin but not cortex actin was significantly reduced, indicating that FHOD1 regulates cytoplasmic actin distribution for the spindle movement. Furthermore, we found that the disruption of ROCK (the Rho-dependent protein kinase) with inhibitor Y-27632 caused the decreased FHOD1 protein expression. Therefore, our data indicate that FHOD1 is regulated by ROCK for cytoplasm actin assembly and spindle migration during mouse oocyte meiosis. [ABSTRACT FROM AUTHOR]

Arf6 (ADP-ribosylation factor 6) is known to play important roles in membrane dynamics through the regulation of actin filament reorganization for multiple cellular processes such as cytokinesis, phagocytosis, cell migration and tumor cell invasion. However, the functions of Arf6 in mammalian oocyte meiosis have not been clarified. In present study we showed that Arf6 expressed in mouse oocytes and was mainly distributed around the spindle during meiosis. Depletion of Arf6 by morpholino microinjection caused oocytes failing to extrude first polar body. Further analysis indicated that Arf6 knock down caused the aberrant actin distribution, which further induced the failure of meiotic spindle movement. And the loss of oocyte polarity also confirmed this. The regulation of Arf6 on actin filaments in mouse oocytes might be due to its effects on the phosphorylation level of cofilin and the expression of Arp2/3 complex. Moreover, we found that the decrease of Arf6 caused the disruption of spindle formation, indicating the multiple roles of Arf6 on cytoskeleton dynamics in meiosis. In summary, our results indicated that Arf6 was involved in mouse oocyte meiosis through its functional roles in actin-mediated spindle movement and spindle organization. [ABSTRACT FROM AUTHOR]

Abstract: The inhibitor Y-27632 is a specific selective inhibitor of Rho-associated protein kinases (ROCKs), which are downstream effectors of Rho guanosine triphosphatease (GTPases) and regulate Rho-associated cellular functions, including actin cytoskeletal organization. Little is known regarding the effects of Y-27632 on mammalian oocyte maturation. In the present study, we investigated the effects of Y-27632 on porcine oocyte meiosis and possible regulatory mechanisms of ROCK during porcine oocyte maturation. We found that ROCK accumulated not only at spindles, but also at the cortex in porcine oocytes. Y-27632 treatment reduced ROCK expression, and inhibited porcine oocyte meiotic maturation, which might be because of the impairment of actin expression and actin-related spindle positioning. Y-27632 treatment also disrupted the formation of actin cap and cortical granule-free domain, which further confirmed a spindle positioning failure. Thus, Y-27632 has significant effects on the meiotic competence of mammalian oocytes by reducing ROCK expression, and the regulation is related to its effects on actin-mediated spindle positioning. [Copyright &y& Elsevier]

Background information During meiosis, a bipolar spindle forms in the central cytoplasm of an oocyte and then moves to the cortex to extrude the first polar body. This is dependent on the regulation of actin and actin-related molecules. Dynamin 2, a large guanosine triphosphatases (GTPase) known to regulate clathrin-mediated endocytosis, is involved in actin recruitment and actin-based vesicle mobility. In this study, we investigated the role of Dynamin 2 in oocyte meiosis. Results Dynamin 2 was localised at the cortex and around the spindles of oocytes. Disrupting Dynamin 2 activity by RNAi or an inhibitor resulted in polar body extrusion failure. Using time-lapse microscopy to monitor aberrant oocyte cytokinesis, the chromosomes were first separated, but then re-joined. Actin expression in oocytes was decreased; and actin cap formation was disrupted, which was confirmed by the disappearance of cortical-granule-free domains. In addition, live cell imaging showed that spindle migration had failed and that spindles were arrested centrally in oocytes. This may have been due to the Dynamin-binding protein Profilin and actin-related protein 2/3 (ARP2/3) complexes, which exhibited dispersed signals after disrupting Dynamin 2 activity. Conclusions Thus, our results indicate that Dynamin 2 regulates spindle migration and polar body extrusion during mouse oocyte meiosis through an actin-based pathway. [ABSTRACT FROM AUTHOR]

Mycotoxins, such as deoxynivalenol (DON), zearalenone (ZEN), and aflatoxin (AF), are commonly found in many food commodities and may impair the growth and reproductive efficiency of animals and humans. We investigated the effects of a mycotoxin-contaminated diet on mouse oocyte quality. Maize contaminated with DON (3.875 mg/kg), ZEN (1,897 μg/kg), and AF (806 μg/kg) was incorporated into a mouse diet at three different levels (0, 15, and 30% w/w). After 4 weeks, ovarian and germinal vesicle oocyte indices decreased in mycotoxin-fed mice. Oocytes from these mice exhibited low developmental competence with reduced germinal vesicle breakdown and polar body extrusion rates. Embryo developmental competence also showed a similar pattern, and the majority of embryos could not develop to the morula stage. Actin expression was also reduced in both the oocyte cortex and cytoplasm, which was accompanied by decreased expression of the actin nucleation factors profilin-1 and mDia1. Moreover, a large percentage of oocytes derived from mice that were fed a mycotoxin-contaminated diet exhibited aberrant spindle morphology, a loss of the cortical granule-free domain, and abnormal mitochondrial distributions, which further supported the decreased oocyte quality. Thus, our results demonstrate that mycotoxins are toxic to the mouse reproductive system by affecting oocyte quality. Environ. Mol. Mutagen. 55:354-362, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

During mitosis nucleation-promoting factors (NPFs) bind to the Arp2/3 complex and activate actin assembly. JMY and WAVE2 are two critical members of the NPFs. Previous studies have demonstrated that NPFs promote multiple processes such as cell migration and cytokinesis. However, the role of NPFs in development of mammalian embryos is still unknown. Results of the present study show that the NPFs JMY and WAVE2 are critical for cytokinesis during development of mouse embryos. Both JMY and WAVE2 are expressed in mouse embryos. After injection of JMY or WAVE2 siRNA, all embryos failed to develop to the morula or blastocyst stages. Moreover, using fluorescence intensity analysis, we found that the expression of actin decreased, and multiple nuclei were observed within a single cell indicating that NPFs-induced actin reduction caused the failure of cell division. In addition, injection of JMY and WAVE2 siRNA also caused ARP2 degradation, indicating that involvement of NPFs in development of mouse embryos is mainly through regulation of ARP2/3-induced actin assembly. Taken together, these data suggested that WAVE2 and JMY are involved in development of mouse embryos, and their regulation may be through a NPFs-Arp2/3-actin pathway. [ABSTRACT FROM PUBLISHER]

Simazine is a triazine pesticides that typically detected in ground water and soil, and can reportedly affect reproductive health in humans and animals. However, the effect of simazine on female germ cell development remains unclear. In the present study, we observed that simazine exposure decreased oocyte maturation competence and embryonic developmental capacity. Importantly, simazine exposure disrupted microtubule stability and actin polymerization, resulting in failure of spindle assembly and migration. In addition, simazine exposure impaired mitochondrial function and cytosolic Ca2+ homeostasis in both oocyte and 2-cell embryos, thus increasing the levels of reactive oxygen species (ROS). Moreover, simazine exposure induced DNA damage and early apoptosis during oocyte maturation. Collectively, our results demonstrate that simazine exposure-induced mitochondrial dysfunction and apoptosis are major causes of poor oocytes quality. • Simazine exposure causes aberrant oocyte meiotic progress and early embryonic development. • Simazine exposure disrupts cytoskeleton organization in MI oocytes. • Simazine exposure compromises mitochondrial function in oocytes. • Simazine exposure leads to increased DNA damage and apoptosis in oocytes. [ABSTRACT FROM AUTHOR]