Contribution of cumulus cells and serum to the maturation of oocyte cytoplasm as revealed by intracytoplasmic sperm injection (ICSI)
The fertilisability and developmental capacity of mouse oocytes matured in vitro were examined by in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI). While more than 50% of cumulus-enclosed oocytes were fertilised by IVF after maturation in serum-supplemented medium, none were fertilised when the oocytes matured without serum. By ICSI, the majority (78-94%) of the oocytes were fertilised regardless of the presence or absence of serum in oocyte maturation media. Although the majority (88-92%) of cumulus-free germinal vesicle oocytes underwent nuclear maturation in both serum-free and serum-containing media, those matured in the presence of serum were more readily fertilised by ICSI (43%) than those matured without it (3-5%). The cumulus-free oocytes co-cultured with cumulus cells but without serum were fertilised at 36%, suggesting some secreted factor promotes the oocyte's cytoplasmic maturation. The oocytes fertilised by ICSI developed into normal-term fetuses regardless of the presence or absence of serum or cumulus cells in oocyte maturation medium. These results lead us to conclude that (a) the cytoplasm of the oocytes can mature in serum-free medium and (b) the presence of both the serum and the cumulus cells in the medium surrounding maturing oocytes is beneficial for the development of the fertilisation- and development-competence of oocyte cytoplasm.(Received November 20 00)
(Accepted January 2 01)
Key Words: Cumulus cells; Fertilisation; Intracytoplasmic sperm injection; Maturation; Oocyte; Serum.
c1 All correspondence to: Dr Yukiko Yamazaki, The Institute for Biogenesis Research, Department of Anatomy and Reproductive Biology, University of Hawaii School of Medicine, 1960 East-West Road, Honolulu, HI 96822, USA. Tel: +1 (808) 956 5475. Fax: +1 (808) 956 7316. e-mail: firstname.lastname@example.org
p1 Present address: Department of Vertebrate Developmental Neurogenetics, The Rockefeller University, New York, New York, USA