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Rat eggs cannot wait: Spontaneous exit from meiotic metaphase‐II arrest
Author(s) -
Chebotareva Tatiana,
Taylor Jane,
Mullins John J.,
Wilmut Ian
Publication year - 2011
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.21385
Subject(s) - metaphase , biology , meiosis , microbiology and biotechnology , oocyte activation , chromatin , polar body , embryo , andrology , oocyte , genetics , chromosome , dna , gene , medicine
Mammalian eggs await fertilisation while arrested at the second metaphase stage of meiotic division. A network of signalling pathways enables the establishment and maintenance of this metaphase‐II arrest. In the absence of fertilisation, mammalian eggs can spontaneously exit metaphase II when parthenogenetically stimulated, or sometimes without any obvious stimulation. Ovulated rat eggs abortively release from metaphase‐II arrest once removed from egg donors. Spontaneously activated rat eggs extrude the second polar body and proceed to the so‐called metaphase III‐‘like’ stage, with clumps of condensed chromatin scattered in the egg cytoplasm. It is still unclear what makes rat eggs susceptible to spontaneous activation; however, a vague picture of the signalling pathways involved in the process of spontaneous activation is beginning to emerge. Such cell cycle instability is one of the major reasons why it is more difficult to establish nuclear transfer in the rat. This review examines the known predisposing factors and biochemical mechanisms involved in spontaneous activation. The strategies used to prevent spontaneous metaphase‐II release in rat eggs will also be discussed. Mol. Reprod. Dev. 78:795–807, 2011. © 2011 Wiley Periodicals, Inc.