Polar bodies-more a lack of understanding than a lack of respect

Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island, USA.
Molecular Reproduction and Development (Impact Factor: 2.68). 01/2011; 78(1):3-8. DOI: 10.1002/mrd.21266
Source: PubMed

ABSTRACT Polar bodies are as diverse as the organisms that produce them. Although in many animals these cells often die following meiotic maturation of the oocyte, in other organisms they are an essential and diverse part of embryonic development. Here we highlight some of this diversity and summarize the evolutionary basis for their utility.

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    ABSTRACT: Polar body cytokinesis is the physical separation of a small polar body from a larger oocyte or ovum. This maternal meiotic division shares many similarities with mitotic and spermatogenic cytokinesis, but there are several distinctions, which will be discussed in this review. We synthesize results from many different model species, including those popular for their genetics and several that are more obscure in modern cell biology. The site of polar body division is determined before anaphase, by the eccentric, cortically associated meiotic spindle. Depending on the species, either the actin or microtubule cytoskeleton is required for spindle anchoring. Chromatin is necessary and sufficient to elicit differentiation of the associated cortex, via Ran-based signaling. The midzone of the anaphase spindle serves as a hub for regulatory complexes that elicit Rho activation, and ultimately actomyosin contractile ring assembly and contraction. Polar body cytokinesis uniquely requires another Rho family GTPase, Cdc42, for dynamic reorganization of the polar cortex. This is perhaps due to the considerable asymmetry of this division, wherein the polar body and the oocyte/ovum have distinct fates and very different sizes. Thus, maternal meiotic cytokinesis appears to occur via simultaneous polar relaxation and equatorial contraction, since the polar body is extruded from the spherical oocyte through the nascent contractile ring. As such, polar body cytokinesis is an interesting and important variation on the theme of cell division. © 2012 Wiley Periodicals, Inc.
    Cytoskeleton 11/2012; 69(11). DOI:10.1002/cm.21064 · 3.01 Impact Factor
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    ABSTRACT: Recent work shows that cytokinesis and other cellular morphogenesis events are tuned by an interplay among biochemical signals, cell shape, and cellular mechanics. In cytokinesis, this includes cross-talk between the cortical cytoskeleton and the mitotic spindle in coordination with cell cycle control, resulting in characteristic changes in cellular morphology and mechanics through metaphase and cytokinesis. The changes in cellular mechanics affect not just overall cell shape, but also mitotic spindle morphology and function. This review will address how these principles apply to oocytes undergoing the asymmetric cell divisions of meiosis I and II. The biochemical signals that regulate cell cycle timing during meiotic maturation and egg activation are crucial for temporal control of meiosis. Spatial control of the meiotic divisions is also important, ensuring that the chromosomes are segregated evenly and that meiotic division is clearly asymmetric, yielding two daughter cells - oocyte and polar body - with enormous volume differences. In contrast to mitotic cells, the oocyte does not undergo overt changes in cell shape with its progression through meiosis, but instead maintains a relatively round morphology with the exception of very localized changes at the time of polar body emission. Placement of the metaphase-I and -II spindles at the oocyte periphery is clearly important for normal polar body emission, although this is likely not the only control element. Here, consideration is given to how cellular mechanics could contribute to successful mammalian female meiosis, ultimately affecting egg quality and competence to form a healthy embryo.
    Molecular Reproduction and Development 10/2011; 78(10-11):769-77. DOI:10.1002/mrd.21358 · 2.68 Impact Factor
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    ABSTRACT: Background: The importance of oocyte/embryo ploidy to achieve implantation and a subsequent pregnancy. Aim: To correlate first and second polar bodies and day-3 blastomere ploidy, embryo morphology and biochemical (sHLA-G) characteristics with blastocyst development and in vitro pregnancy outcome. Materials and Methods: All oocytes/zygotes and embryos were individually cultured to the blastocyst stage. PB-I, PB-II and blastomeres underwent complete karyotyping and sHLA-G expression was measured on day 2. Results: 57 mature (MII) donor oocytes were obtained, 33/57 (57.9%) were aneuploid, 21/57 (36.8%) were euploid, and 3/57 (5%) were 'inconclusive'. No correlation was found between comparative genomic hybridization (CGH) status of PB-I, PB-II and the graduated embryo score. Furthermore, no correlation was established between PB-I CGH results and blastocyst morphology grade. There was a significant correlation between PB-I CGH and blastomere CGH results. Euploid and aneuploid PB-I developed into 58 and 67% blastocysts, respectively. ĸ statistics (>0.7) revealed a positive correlation between the ploidy of PB-I, PB-II and the blastomeres. Conclusion: Following ICSI and sequential genetic karyotyping of the oocyte/zygote and subsequent blastomeres, the majority of oocytes fertilized and subsequent zygotes developed into blastocysts, despite their ploidy status. We therefore conclude that blastocyst development is not associated with ploidy.
    Gynecologic and Obstetric Investigation 08/2012; 74(4). DOI:10.1159/000339632 · 1.25 Impact Factor


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