Submitted May 3, 2007
Returned for revision May 28, 2007
Accepted December 16, 2007
Reproductive Technology
Timing of Nuclear Maturation and Post-Ovulatory Aging in Oocytes of In Vitro-Grown Mouse Follicles with or Without Oil Overlay
Ingrid Segers *,
Tom Adriaenssens ,
Wim Coucke ,
Rita Cortvrindt ,
and
Johan Smitz
* To whom correspondence should be addressed. E-mail: isegers{at}vub.ac.be.
Abstract
Meiotic maturation of the oocyte is a timed sequence of events induced by the ovulatory LH-surge. In vitro maturation of oocytes is known to alter the meiotic time course. This study documented the timing of meiosis in oocytes grown in vitro for 12-days from the preantral follicle stage onwards and the influence of an oil-overlay. In the oil-free culture, the stability of the metaphase II spindle was further explored to determine the postovulatory aging events. In vitro grown oocytes were collected at 2h intervals after the maturation stimulus spanning the period of meiosis (0h-18h) and at 3h intervals during early post- ovulatory aging (18h-27h). Stage of maturation was assessed both morphologically and by detailed spindle analysis and chromosome alignment. Results revealed that oil-overlay did not impair the competence of cultured oocytes to proceed to meiosis II, but delayed meiosis I progression. Oil-overlay during culture causes a different hormonal exposure of the follicles by a differential segregation into the oiloverlay. The use of a progesterone receptor antagonist however, did not induce a delay in meiotic progression. Aging effects in oil-free cultured follicles were detected 5h after the establishment of the metaphase II spindle comparable to their in vivo grown counterparts. The predominant effect of aging was an interphase-like appearance of the cytoskeleton. So an optimal time window for fertilization after in vitro follicular growth was determined to be 16h to 21h after maturation induction.
Key words:
Aging •
Follicle •
Meiosis •
in vitro culture •
spindle
