Talk:Cell Division - Meiosis

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How eggs arrest at metaphase II: MPF stabilisation plus APC/C inhibition equals Cytostatic Factor http://www.celldiv.com/content/2/1/4


Mammalian egg activation: from Ca2+ spiking to cell cycle progression. http://www.ncbi.nlm.nih.gov/pubmed/16322541

Mammalian eggs arrest at metaphase of the second meiotic division (MetII). Sperm break this arrest by inducing a series of Ca(2+) spikes that last for several hours. During this time cell cycle resumption is induced, sister chromatids undergo anaphase and the second polar body is extruded. This is followed by decondensation of the chromatin and the formation of pronuclei. Ca(2+) spiking is both the necessary and solely sufficient sperm signal to induce full egg activation. How MetII arrest is established, how the Ca(2+) spiking is induced and how the signal is transduced into cell cycle resumption are the topics of this review. Although the roles of most components of the signal transduction pathway remain to be fully investigated, here I present a model in which a sperm-specific phospholipase C (PLCzeta) generates Ca(2+) spikes to activate calmodulin-dependent protein kinase II and so switch on the Anaphase-Promoting Complex/Cyclosome (APC/C). APC/C activation leads to securin and cyclin B1 degradation and in so doing allows sister chromatids to be segregated and to decondense.



Trisomy X - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2883963/?tool=pubmed


Sperm chromatin-induced ectopic polar body extrusion in mouse eggs after ICSI and delayed egg activation

PLoS One. 2009 Sep 29;4(9):e7171.

Deng M, Li R.

Stowers Institute for Medical Research, Kansas City, Missouri, United States of America. Mdeng3@BICS.BWH.Harvard.edu Abstract Meiotic chromosomes in an oocyte are not only a maternal genome carrier but also provide a positional signal to induce cortical polarization and define asymmetric meiotic division of the oocyte, resulting in polar body extrusion and haploidization of the maternal genome. The meiotic chromosomes play dual function in determination of meiosis: 1) organizing a bipolar spindle formation and 2) inducing cortical polarization and assembly of a distinct cortical cytoskeleton structure in the overlying cortex for polar body extrusion. At fertilization, a sperm brings exogenous paternal chromatin into the egg, which induces ectopic cortical polarization at the sperm entry site and leads to a cone formation, known as fertilization cone. Here we show that the sperm chromatin-induced fertilization cone formation is an abortive polar body extrusion due to lack of spindle induction by the sperm chromatin during fertilization. If experimentally manipulating the fertilization process to allow sperm chromatin to induce both cortical polarization and spindle formation, the fertilization cone can be converted into polar body extrusion. This suggests that sperm chromatin is also able to induce polar body extrusion, like its maternal counterpart. The usually observed cone formation instead of ectopic polar body extrusion induced by sperm chromatin during fertilization is due to special sperm chromatin compaction which restrains it from rapid spindle induction and therefore provides a protective mechanism to prevent a possible paternal genome loss during ectopic polar body extrusion.

PMID: 19787051 http://www.ncbi.nlm.nih.gov/pubmed/19787051

Mouse Emi2 is required to enter meiosis II by reestablishing cyclin B1 during interkinesis

J Cell Biol. 2006 Sep 11;174(6):791-801.

Madgwick S, Hansen DV, Levasseur M, Jackson PK, Jones KT.

Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle NE2 4HH, England, UK. suzanne.madgwick@ncl.ac.uk Abstract During interkinesis, a metaphase II (MetII) spindle is built immediately after the completion of meiosis I. Oocytes then remain MetII arrested until fertilization. In mouse, we find that early mitotic inhibitor 2 (Emi2), which is an anaphase-promoting complex inhibitor, is involved in both the establishment and the maintenance of MetII arrest. In MetII oocytes, Emi2 needs to be degraded for oocytes to exit meiosis, and such degradation, as visualized by fluorescent protein tagging, occurred tens of minutes ahead of cyclin B1. Emi2 antisense morpholino knockdown during oocyte maturation did not affect polar body (PB) extrusion. However, in interkinesis the central spindle microtubules from meiosis I persisted for a short time, and a MetII spindle failed to assemble. The chromatin in the oocyte quickly decondensed and a nucleus formed. All of these effects were caused by the essential role of Emi2 in stabilizing cyclin B1 after the first PB extrusion because in Emi2 knockdown oocytes a MetII spindle was recovered by Emi2 rescue or by expression of nondegradable cyclin B1 after meiosis I.

PMID: 16966421 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2064334/?tool=pubmed


Spindle dynamics during meiosis in Drosophila oocytes

J Cell Biol. 1997 Jun 16;137(6):1321-36. Endow SA, Komma DJ.

Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA. endow@galactose.mc.duke.edu Abstract Mature oocytes of Drosophila are arrested in metaphase of meiosis I. Upon activation by ovulation or fertilization, oocytes undergo a series of rapid changes that have not been directly visualized previously. We report here the use of the Nonclaret disjunctional (Ncd) microtubule motor protein fused to the green fluorescent protein (GFP) to monitor changes in the meiotic spindle of live oocytes after activation in vitro. Meiotic spindles of metaphase-arrested oocytes are relatively stable, however, meiotic spindles of in vitro-activated oocytes are highly dynamic: the spindles elongate, rotate around their long axis, and undergo an acute pivoting movement to reorient perpendicular to the oocyte surface. Many oocytes spontaneously complete the meiotic divisions, permitting visualization of progression from meiosis I to II. The movements of the spindle after oocyte activation provide new information about the dynamic changes in the spindle that occur upon re-entry into meiosis and completion of the meiotic divisions. Spindles in live oocytes mutant for a loss-of-function ncd allele fused to gfp were also imaged. The genesis of spindle defects in the live mutant oocytes provides new insights into the mechanism of Ncd function in the spindle during the meiotic divisions.

PMID: 9182665

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2132525/?tool=pubmed