RhoA-mediated FMNL1 regulates GM130 for actin assembly and phosphorylates MAPK for spindle formation in mouse oocyte meiosis

Formin-like 1 (FMNL1) is a member of Formin family proteins which are the actin nucleators. Although FMNL1 activities have been shown to be essential for cell adhesion, cytokinesis, cell polarization and migration in mitosis, the functional roles of mammalian FMNL1 during oocyte meiosis remain uncertain. In this study, we investigated the functions of FMNL1 in mouse oocytes using specific morpholino (MO) microinjection and live cell imaging. Immunofluorescent staining showed that in addition to its cytoplasmic distribution, FMNL1 was primarily localized at the spindle poles after germinal vesicle breakdown (GVBD). FMNL1 knockdown caused the low rate of polar body extrusion and resulted in large polar bodies. Time-lapse microscopic and immunofluorescence intensity analysis indicated that this might be due to the aberrant actin expression levels. Cortical polarity was disrupted as shown by a loss of actin cap and cortical granule free domain (CGFD) formation, which was confirmed by a failure of meiotic spindle positioning. And this might be the reason for the large polar body formation. Spindle formation was also disrupted, which might be due to the abnormal localization of p-MAPK. These results indicated that FMNL1 affected both actin dynamics and spindle formation for the oocyte polar body extrusion. Moreover, FMNL1 depletion resulted in aberrant localization and expression patterns of a cis-Golgi marker protein, GM130. Finally, we found that the small GTPase RhoA might be the upstream regulator of FMNL1. Taken together, our data indicate that FMNL1 is required for spindle organization and actin assembly through a RhoA-FMNL1-GM130 pathway during mouse oocyte meiosis.Key words: actin, FMNL1, golgi, polar body extrusion, spindle organization     

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

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. 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, γ-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.     

MEK1/2 is a critical regulator of microtubule assembly and spindle organization during rat oocyte meiotic maturation

MEK (MAPK kinase) is an upstream protein kinase of MAPK in the MOS/MEK/MAPK/p90rsk signaling pathway. We previously reported the function and regulation of MAPK during rat oocyte maturation. In this study, we further investigated the localization and possible roles of MEK1/2. First, immunofluorescent staining revealed that p-MEK1/2 was restricted to the germinal vesicle (GV). After germinal vesicle breakdown (GVBD), p-MEK1/2 condensed in the vicinity of chromosomes and then translocated to the spindle poles at metaphase I, while spindle microtubules stained faintly. When the oocyte went through anaphase I and telophase I, p-MEK1/2 disappeared from spindle poles and became associated with the midbody. By metaphase II, p-MEK1/2 was again localized to the spindle poles. Second, p-MEK1/2 was localized to the centers of cytoplasmic microtubule asters induced by taxol. Third, p-MEK1/2 co-localized with gamma-tubulin in microtubule-organizing centers (MTOCs). Forth, treatment with U0126, a non-competitive MEK1/2 inhibitor, did not affect germinal vesicle breakdown, but caused chromosome mis-alignment in all MI oocytes examined and abnormal spindle organization as well as small cytoplasmic spindle-like structure formation in MII oocytes. Finally, U0126 reduced the number of cytoplasmic asters induced by taxol. Our data suggest that MEK1/2 has regulatory functions in microtubule assembly and spindle organization during rat oocyte meiotic maturation.     

Regulation of Intracellular MEK1/2 Translocation in Mouse Oocytes: Cytoplasmic Dynein/Dynactin-Mediated Poleward Transport and Cyclin B Degradation-Dependent Release from Spindle Poles

We recently reported that MEK1/2 plays an important role in microtubule organization and spindle pole tethering in mouse oocytes, but how the intracellular transport of this protein is regulated remains unknown. In the present study, we investigated the mechanisms of poleward MEK1/2 transport during the prometaphase I/metaphase I transition and MEK1/2 release from the spindle poles during the metaphase I/anaphase I transition in mouse oocytes. Firstly, we found that p-MEK1/2 was colocalized with dynactin at the spindle poles. Inhibition of the cytoplasmic dynein/dynactin complex by antibody microinjection blocked polar accumulation of p-MEK1/2 and caused obvious spindle abnormalities. Moreover, coimmunoprecipitation of p-MEK1/2 and dynein or dynactin from mouse oocyte extracts confirmed their association at metaphase I. Secondly, disruption of microtubules by nocodazole resulted in the failure of poleward p-MEK1/2 transport. Whereas, when the nocodazole-treated oocytes were recovered in fresh culture medium, the spindle reformed and p-MEK1/2 relocalized to the spindle poles. Finally, we examined the mechanism of p-MEK1/2 release from the spindle poles. In control oocytes, polar p-MEK1/2 was gradually released during metaphase I/anaphase I transition. By contrast, in the presence of nondegradable cyclin B (△90), p-MEK1/2 still remained at the spindle poles at anaphase I. Our results indicate that poleward MEK1/2 transport is a cytoplasmic dynein/dynactin-mediated and spindle microtubule-dependent intracellular movement, and that its subsequent anaphase release from spindle poles is dependent on cyclin B degradation.     

WHAMM is required for meiotic spindle migration and asymmetric cytokinesis in mouse oocytes

WASP homolog associated with actin, membranes and microtubules (WHAMM) is a newly discovered nucleation-promoting factor that links actin and microtubule cytoskeleton and regulates transport from the endoplasmic reticulum to the Golgi apparatus. However, knowledge of WHAMM is limited to interphase somatic cells. In this study, we examined its localization and function in mouse oocytes during meiosis. Immunostaining showed that in the germinal vesicle (GV) stage, there was no WHAMM signal; after meiosis resumption, WHAMM was associated with the spindle at prometaphase I (Pro MI), metaphase I (MI), telophase I (TI) and metaphase II (MII) stages. Nocodazole and taxol treatments showed that WHAMM was localized around the MI spindle. Depletion of WHAMM by microinjection of specific short interfering (si)RNA into the oocyte cytoplasm resulted in failure of spindle migration, disruption of asymmetric cytokinesis and a decrease in the first polar body extrusion rate during meiotic maturation. Moreover, actin cap formation was also disrupted after WHAMM depletion, confirming the failure of spindle migration. Taken together, our data suggest that WHAMM is required for peripheral spindle migration and asymmetric cytokinesis during mouse oocyte maturation.     

Anillin localization suggests distinct mechanisms of division plane specification in mouse oogenic meiosis I and II

Anillin is a conserved cytokinetic ring protein implicated in actomyosin cytoskeletal organization and cytoskeletal-membrane linkage. Here we explored anillin localization in the highly asymmetric divisions of the mouse oocyte that lead to the extrusion of two polar bodies. The purposes of polar body extrusion are to reduce the chromosome complement within the egg to haploid, and to retain the majority of the egg cytoplasm for embryonic development. Anillin's proposed roles in cytokinetic ring organization suggest that it plays important roles in achieving this asymmetric division. We report that during meiotic maturation, anillin mRNA is expressed and protein levels steadily rise. In meiosis I, anillin localizes to a cortical cap overlying metaphase I spindles, and a broad ring over anaphase spindles that are perpendicular to the cortex. Anillin is excluded from the cortex of the prospective first polar body, and highly enriched in the cytokinetic ring that severs the polar body from the oocyte. In meiosis II, anillin is enriched in a cortical stripe precisely coincident with and overlying the meiotic spindle midzone. These results suggest a model in which this cortical structure contributes to spindle re-alignment in meiosis II. Thus, localization of anillin as a conserved cytokinetic ring marker illustrates that the geometry of the cytokinetic ring is distinct between the two oogenic meiotic cytokineses in mammals.     

Perturbation of survivin expression affects chromosome alignment and spindle checkpoint in mouse oocyte meiotic maturation

Survivin is a member of inhibitors of apoptosis proteins (IAPs), which have multiple regulatory functions in mitosis, but its roles in meiosis remain unknown. Here, we report its expression, localization and functions in mouse oocyte meiosis. Survivin displayed maximal expression levels in GV stages, and then gradually decreased from Pro-MI to MII stages. Immunofluorescent staining showed that survivin was restricted to the germinal vesicle, associated with centromeres from pro-metaphase I to metaphase I stages, distributed at the midzone and midbody of anaphase and telophase spindles, and located to centromeres at metaphase II stages. Depletion of survivin by antibody injection and morpholino injection resulted in severe chromosome misalignment, precocious polar body extrusion, and larger-than-normal polar bodies. Overexpression of survivin resulted in severe chromosome misalignment and prometaphase I or metaphase I arrest in a large proportion of oocytes. Our data suggest that survivin is required for chromosome alignment and that it may regulate spindle checkpoint activity during mouse oocyte meiosis.     

TGN38 is required for the metaphase I/anaphase I transition and asymmetric cell division during mouse oocyte meiotic maturation

The cellular functions of the trans-Golgi network protein TGN38 remain unknown. In this research, we studied the expression, localization and functions of TGN38 in the meiotic maturation of mouse oocytes. TGN38 was expressed at every stage of oocyte meiotic maturation and colocalized with γ-tubulin at metaphase I and metaphase II. The spindle microtubule disturbing agents nocodazole and taxol did not affect the colocalization of TGN38 and γ-tubulin. Depletion of TGN38 with specific siRNAs resulted in increased metaphase I arrest, accompanied with spindle assembly checkpoint activation and decreased first polar extrusion (PB1). In the oocytes that had extruded the PB1 after the depletion of TGN38, symmetric division occurred, leading to the production of 2 similarly sized cells. Moreover, the peripheral migration of metaphase I spindle and actin cap formation were impaired in TGN38-depleted oocytes. Our data suggest that TGN38 may regulate the metaphase I/anaphase I transition and asymmetric cell division in mouse oocytes.     

Small GTPase RhoA is required for ooplasmic segregation and spindle rotation, but not for spindle organization and chromosome separation during mouse oocyte maturation, fertilization, and early cleavage

RhoA, a small GTPase, plays versatile roles in many aspects of cell function such as stress fiber formation, cytokinesis, and cell polarization. In this study, we investigated the subcellular localization of RhoA and its possible roles during oocyte maturation and fertilization. RhoA was localized in the cytoplasm of eggs from the germinal vesicle (GV) stage to 2-cell stage, especially concentrating in the midbody of telophase spindle when oocyte extruded PB1 and PB2. The RhoA kinases (ROCKs) specific inhibitor Y-27632 blocked GV breakdown (GVBD) and first polar body extrusion, but did not affect apparatus formation and anaphase/telophase I entry. Anti-RhoA antibody microinjection into the oocytes showed similar results. RhoA inhibitor caused abnormal organization of microfilaments, failure of spindle rotation, PB2 extrusion as well as cleavage furrow formation, while sister chromatid separation was not affected. Microinjection of RhoA antibody also blocked PB2 emission. Our findings indicate that RhoA, by regulating microfilament organization, regulates several important events including GVBD, polar body emission, spindle rotation, and cleavage.     

Nek9 regulates spindle organization and cell cycle progression during mouse oocyte meiosis and its location in early embryo mitosis

Nek9 (also known as Nercc1), a member of the NIMA (never in mitosis A) family of protein kinases, regulates spindle formation, chromosome alignment and segregation in mitosis. Here, we showed that Nek9 protein was expressed from germinal vesicle (GV) to metaphase II (MII) stages in mouse oocytes with no detectable changes. Confocal microscopy identified that Nek9 was localized to the spindle poles at the metaphase stages and associated with the midbody at anaphase or telophase stage in both meiotic oocytes and the first mitotic embyros. Depletion of Nek9 by specific morpholino injection resulted in severely defective spindles and misaligned chromosomes with significant pro-MI/MI arrest and failure of first polar body (PB1) extrusion. Knockdown of Nek9 also impaired the spindle-pole localization of γ-tubulin and resulted in retention of the spindle assembly checkpoint protein Bub3 at the kinetochores even after 10 h of culture. Live-cell imaging analysis also confirmed that knockdown of Nek9 resulted in oocyte arrest at the pro-MI/MI stage with abnormal spindles, misaligned chromosomes and failed polar body emission. Taken together, our results suggest that Nek9 may act as a MTOC-associated protein regulating microtubule nucleation, spindle organization and, thus, cell cycle progression during mouse oocyte meiotic maturation, fertilization and early embryo cleavage.     

Hec1 inhibition alters spindle morphology and chromosome alignment in porcine oocytes

Aneuploidy is caused by incorrect chromosome segregation and can result in cancer or birth defects. The spindle assembly checkpoint (SAC) guarantees proper cell cycle progression. Highly Expressed in Cancer protein 1 (Hec1, also called Ndc80) is the core component of the Ndc80 complex and is involved in regulating both kinetochore-microtubule interactions and the SAC during mitosis in multiple cell types. However, its involvement in pig oocyte meiotic maturation remains uncertain. Thus, we investigated Hec1 expression, localization, and possible functions during porcine oocyte meiosis. Immunofluorescent staining showed that Hec1 was expressed in porcine oocytes and was associated with centromeres at both the metaphase I and metaphase II stages. Disrupting Hec1 function with its inhibitor INH1 resulted in polar body extrusion defects in porcine oocytes. Moreover, inhibiting Hec1 activity also resulted in severe chromosome misalignments and aberrant spindle morphology. Our results showed a unique localization pattern for Hec1 in porcine oocytes and suggested that Hec1 was required for chromosome alignment and spindle organization. Thus, Hec1 might regulate spindle checkpoint activity during mammalian oocyte meiosis.     

Cover Image,Volume 234, Number 10, October 2019

Cytoskeleton which includes microtubule and actin filaments plays important roles during mammalian oocyte maturation. In the present study, we showed that protein kinase C mu (PKC mu) was one potential key molecule which affected cytoskeleton dynamics in mouse oocytes. Our results showed that PKC mu expressed and localized at the poles of the spindle during oocyte maturation, and PKC mu expression reduced in the oocytes from 6-month-old mice or 24 hr in vitro culture. We knocked down the expression of PKC mu in oocytes using morpholino injection to explore the relationship between PKC mu and subcellular structure defects. The loss of PKC mu reduced oocyte maturation competence, showing with decreased polar body extrusion rate and increased rate of symmetric division. Further analysis indicated that PKC mu decrease caused the spindle organization defects, and this could be confirmed by the decreased tubulin acetylation level. Moreover, we found that PKC mu affected the phosphorylation level of cofilin for actin assembly, which further affected cytoplasmic actin distribution and spindle positioning. In summary, our data indicated that PKC mu is one key factor for oocyte maturation through its roles on the spindle organization and actin filament distribution.     

PKCβ1 regulates meiotic cell cycle in mouse oocyte

PKCβI, a member of the classical protein kinase C family, plays key roles in regulating cell cycle transition. Here, we report the expression, localization and functions of PKCβI in mouse oocyte meiotic maturation. PKCβI and p-PKCβI (phosphor-PKCβI) were expressed from germinal vesicle (GV) stage to metaphase II (MII) stage. Confocal microscopy revealed that PKCβI was localized in the GV and evenly distributed in the cytoplasm after GV breakdown (GVBD), and it was concentrated at the midbody at telophase in meiotic oocytes. While, p-PKCβI was concentrated at the spindle poles at the metaphase stages and associated with midbody at telophase. Depletion of PKCβI by specific siRNA injection resulted in defective spindles, accompanied with spindle assembly checkpoint activation, metaphase I arrest and failure of first polar body (PB1) extrusion. Live cell imaging analysis also revealed that knockdown of PKCβI resulted in abnormal spindles, misaligned chromosomes, and meiotic arrest of oocytes arrest at the Pro-MI/MI stage. PKCβI depletion did not affect the G2/M transition, but its overexpression delayed the G2/M transition through regulating Cyclin B1 level and Cdc2 activity. Our findings reveal that PKCβI is a critical regulator of meiotic cell cycle progression in oocytes.

Abbreviations: PKC, protein kinase C; COC, cumulus-oocyte complexes; GV, germinal vesicle; GVBD, germinal vesicle breakdown; Pro-MI, first pro-metaphase; MI, first metaphase; Tel I, telophase I; MII, second metaphase; PB1, first polar body; SAC, spindle assembly checkpoint     

Involvement of Polo-like kinase 1 in MEK1/2-regulated spindle formation during mouse oocyte meiosis

Our recent studies have shown that MEK1/2 is a critical regulator of microtubule organization and spindle formation during oocyte meiosis. In the present study, we found that Plk1 colocalized with p-MEK1/2 at various meoiotic stages after GVBD when microtubule began to organize. Also, Plk1 was able to coimmunoprecipitate with p-MEK1/2 in metaphase I stage mouse oocyte extracts, further confirming their physical interaction. Taxol-treated oocytes exhibited a number of cytoplasmic asters, in which both Plk1 and p-MEK1/2 were present, indicating that they might be complexed to participate in the acentrosomal spindle formation at the MTOCs during oocyte meiosis. Depolymerization of microtubules by nocodazole resulted in the complete disassembly of spindles, but Plk1 remained associated with p-MEK1/2, accumulating in the vicinity of chromosomes. More importantly, when p-MEK1/2 activity was blocked by U0126, Plk1 lost its normal localization at the spindle poles, which might be one of the most vital factors causing the abnormal spindles in MEK1/2-inhibited oocytes. Taken together, these data indicate that Plk1 and MEK1/2 regulate the spindle formation in the same pathway and that Plk1 is involved in MEK1/2-regulated spindle assembly during mouse oocyte meiotic maturation.     

Asymmetric positioning and organization of the meiotic spindle of mouse oocytes requires CDC42 function

The mature mammalian oocyte is highly polarized because asymmetrical spindle migration to the oocyte cortex ensures extrusion of small polar bodies in the two meiotic divisions, essential for generation of the large egg. Actin filaments, myosin motors, and formin-2, but not microtubules, are required for spindle migration. Here, we show that Cdc42, a key regulator of cytoskeleton and cell polarity in other systems , is essential for meiotic maturation and oocyte asymmetry. Disrupting CDC42 function by ectopic expression of its GTPase-defective mutants causes both halves of the first meiotic spindle to extend symmetrically toward opposing cortical regions and prevents an asymmetrical division. The elongated spindle has numerous astral-like microtubules, and aPKCzeta, normally associated with the spindle poles, is distributed along its length. Dynactin is displaced from kinetochores, consistently homologous chromosomes do not segregate, and polar body extrusion is prevented. Perturbing the function of aPKCzeta also causes elongation of the meiotic spindle but still permits spindle migration and polar body extrusion. Thus, at least two pathways appear to be downstream of CDC42: one affecting the actin cytoskeleton and required for migration of the meiotic spindle, and a second affecting the spindle microtubules in which aPKCzeta plays a role.     

Characterization of aurora-a in porcine oocytes and early embryos implies its functional roles in the regulation of meiotic maturation, fertilization and cleavage

Aurora-A is a serine/threonine protein kinase that plays important regulatory roles during mitotic cell cycle progression. In this study, Aurora-A expression, subcellular localization, and possible functions during porcine oocyte meiotic maturation, fertilization and early embryonic cleavage were studied by using Western blot, confocal microscopy and drug treatments. The quantity of Aurora-A protein remained stable during porcine oocyte meiotic maturation. Confocal microscopy revealed that Aurora-A distributed abundantly in the nucleus at the germinal vesicle stage. After germinal vesicle breakdown, Aurora-A concentrated around the condensed chromosomes and the metaphase I spindle, and finally, Aurora-A was associated with spindle poles during the formation of the metaphase II spindle. Aurora-A concentrated in the pronuclei in fertilized eggs. Aurora-A was not found in the spindle region when colchicine or staurosporine was used to inhibit microtubule organization, while it accumulated as several dots in the cytoplasm after taxol treatment. In conclusion, Aurora-A may be a multifunctional kinase that plays pivotal regulatory roles in microtubule assembly during porcine oocyte meiotic maturation, fertilization and early embryonic mitosis.     

Nek9 regulates spindle organization and cell cycle progression during mouse oocyte meiosis and its location in early embryo mitosis

Nek9 (also known as Nercc1), a member of the NIMA (never in mitosis A) family of protein kinases, regulates spindle formation, chromosome alignment and segregation in mitosis. Here, we showed that Nek9 protein was expressed from germinal vesicle (GV) to metaphase II (MII) stages in mouse oocytes with no detectable changes. Confocal microscopy identified that Nek9 was localized to the spindle poles at the metaphase stages and associated with the midbody at anaphase or telophase stage in both meiotic oocytes and the first mitotic embyros. Depletion of Nek9 by specific morpholino injection resulted in severely defective spindles and misaligned chromosomes with significant pro-MI/MI arrest and failure of first polar body (PB1) extrusion. Knockdown of Nek9 also impaired the spindle-pole localization of γ-tubulin and resulted in retention of the spindle assembly checkpoint protein Bub3 at the kinetochores even after 10 h of culture. Live-cell imaging analysis also confirmed that knockdown of Nek9 resulted in oocyte arrest at the pro-MI/MI stage with abnormal spindles, misaligned chromosomes and failed polar body emission. Taken together, our results suggest that Nek9 may act as a MTOC-associated protein regulating microtubule nucleation, spindle organization and, thus, cell cycle progression during mouse oocyte meiotic maturation, fertilization and early embryo cleavage.     

The involvement of Fyn kinase in resumption of the first meiotic division in mouse oocytes

The process of resumption of the first meiotic division (RMI) in mammalian oocytes includes germinal vesicle breakdown (GVBD), spindle formation during first metaphase (MI), segregation of homologous chromosomes, extrusion of the first polar body (PBI) and an arrest at metaphase of the second meiotic division (MII). Previous studies suggest a role for Fyn, a non-receptor Src family tyrosine kinase, in the exit from MII arrest. In the current study we characterized the involvement of Fyn in RMI. Western blot analysis demonstrated a significant, proteasome independent, degradation of Fyn during GVBD. Immunostaining of fixed oocytes and confocal imaging of live oocytes microinjected with Fyn complementary RNA (cRNA) demonstrated Fyn localization to the oocyte cortex and to the spindle poles. Fyn was recruited during telophase to the cortical area surrounding the midzone of the spindle and was then translocated to the contractile ring during extrusion of PBI. GVBD, exit from MI and PBI extrusion were inhibited in oocytes exposed to the chemical inhibitor SU6656 or microinjected with dominant negative Fyn cRNA. None of the microinjected oocytes showed misaligned or lagging chromosomes during chromosomes segregation and the spindle migration and anchoring were not affected. However, the extruded PBI was of large size. Altogether, a role for Fyn in regulating several key pathways during the first meiotic division in mammalian oocytes is suggested, particularly at the GV and metaphase checkpoints and in signaling the ingression of the cleavage furrow.     

The spindle protein CHICA mediates localization of the chromokinesin Kid to the mitotic spindle

Microtubule-based motor proteins provide essential forces for bipolar organization of spindle microtubules and chromosome movement, prerequisites of chromosome segregation during the cell cycle. Here, we describe the functional characterization of a novel spindle protein, termed "CHICA," that was originally identified in a proteomic survey of the human spindle apparatus [1]. We show that CHICA localizes to the mitotic spindle and is both upregulated and phosphorylated during mitosis. CHICA-depleted cells form shorter spindles and fail to organize a proper metaphase plate, highly reminiscent of the phenotype observed upon depletion of the chromokinesin Kid, a key mediator of polar ejection forces [2-6]. We further show that CHICA coimmunoprecipitates with Kid and is required for the spindle localization of Kid without affecting its chromosome association. Moreover, upon depletion of either CHICA or Kid (or both proteins simultaneously), chromosomes collapse onto the poles of monastrol-induced monopolar spindles. We conclude that CHICA represents a novel interaction partner of the chromokinesin Kid that is required for the generation of polar ejection forces and chromosome congression.     

Survivin regulates Plk1 localization to kinetochore in mouse oocyte meiosis

Survivin is a member of inhibitors of apoptosis proteins (IAPs), and also belongs to be a member of the chromosomal passenger complex (CPC) which has multiple functions including inhibition of apoptosis and regulation of cell division and SAC activity. Plk1 (polo-like kinase 1) associates with the spindle poles and also distributes to the kinetochores and is shown to involve in spindle organization, APC/C activation and cytokinesis in many models. Our recent work has shown that Survivin is a critical regulator of chromosome segregation and spindle assembly checkpoint (SAC) in meiosis. In the present study, we found that Plk1 co-localized with Survivin at metaphase I (MI) and telophase I (TI) stage after GVBD. Plk1 dispersed into the oocyte cytoplasm or accumulated near the chromosomes after the depletion of Survivin by morpholino (MO) injection. Our results showed that the localization of Plk1 to kinetochores required the involvement of Survivin.