Meiosis-activating sterol protects oocytes from precocious chromosome segregation.
BACKGROUND
Follicular fluid meiosis-activating sterol (FF-MAS) overcomes hypoxanthine (HX)-mediated meiotic arrest in mammalian oocytes.


METHODS
In order to determine whether chromosome segregation was normal in oocytes matured in FF-MAS, the development, chromosomal constitution and chromosome alignment was analysed in spontaneously matured as well as HX-arrested mouse oocytes cultured in the absence or presence of FF-MAS.


RESULTS
FF-MAS-induced meiotic maturation was significantly less effective compared with spontaneous maturation in supporting cytokinesis ( approximately 40 and approximately 90% polar body formation respectively). The majority of oocytes stimulated by FF-MAS to overcome the HX block developed to metaphase II (MII), but 23.4% of meiosis II oocytes were diploid. Chromosomes were well aligned on the spindle, and hyperploidy was low in spontaneously matured oocytes and HX-arrested oocytes cultured with or without FF-MAS. Unexpectedly, almost 40% of spontaneously matured MII oocytes contained chromatids/monads. Precocious loss of chromatid cohesion was significantly reduced in spontaneously matured as well as HX-arrested oocytes cultured in the presence of FF-MAS but not lanosterol.


CONCLUSIONS
FF-MAS induces full nuclear maturation to MII, and chromosomes segregate with high fidelity. However, in delayed FF-MAS-stimulated meiotic maturation, anaphase I may occur in the absence of cytokinesis. FF-MAS appears to protect mammalian oocytes from precocious chromatid segregation.
Cukurcam
S
S
Research Laboratories of Schering AG, Berlin, Germany. Suna.Cukurcan@Uni-Bielefeld.de
Hegele-Hartung
C
C
Eichenlaub-Ritter
U
U
D000818:Animals; D002467:Cell Nucleus / Q000502:physiology; D002478:Cells, Cultured; D016922:Cellular Senescence; D002782:Cholestenes / Q000494:pharmacology*; D002842:Chromatids / Q000187:drug effects / Q000502:physiology; D020090:Chromosome Segregation / Q000187:drug effects*; D002875:Chromosomes / Q000187:drug effects / Q000502:physiology; D003470:Culture Media / Q000494:pharmacology; D019610:Cytoprotection; D004171:Diploidy; D005260:Female; D019271:Hypoxanthine / Q000494:pharmacology; D008540:Meiosis / Q000187:drug effects; D051379:Mice; D008808:Mice, Inbred CBA; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology*; D011003:Ploidies; D008941:Spindle Apparatus / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
D002782:Cholestenes; D003470:Culture Media; D019271:Hypoxanthine; C100324:4,4-dimethylcholesta-8,14,24-trienol