Hum. Reprod. Advance Access published online on December 9, 2008
Human Reproduction, doi:10.1093/humrep/den407
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Assessment of the developmental competence of human somatic cell nuclear transfer embryos by oocyte morphology classification
1 State Key Laboratory of Reproductive Biology, Institute of Zoology, Datun Road, Chaoyang District, Beijing 100101, People's Republic of China 2 Graduate School, Chinese Academy of Sciences, Beijing, People's Republic of China 3 Reproductive Medical Center, First Affiliated Hospital of SUN YAT-SEN University, Zhongshan Er Road 58, Guangzhou, Guangdong 510080, People's Republic of China
4 Correspondence address. Tel:/Fax: +86-10-64807299; E-mail: qzhou{at}ioz.ac.cn (Q.Z.), Tel:/Fax: +86-20-87786029; E-mail: zhoucanquan{at}hotmail.com (C.Z.)
BACKGROUND: The oocyte plays a key role in reprogramming the epigenetic status of donor cell nuclei, and the absence of reprogramming elements in the cytoplasm or aberrant accumulation of proteins can trigger the abnormal development of nuclear transfer (NT) embryos. Previous studies have demonstrated the relationship between oocyte morphology and both embryo development and pregnancy outcome. In the present study, we compared the morphology of oocytes with subsequent development of human somatic cell NT (SCNT) embryos.
METHODS: Piezo-assisted SCNT technology was used to produce reconstructed embryos, with almost 92% of oocytes reconstructed successfully. Depending on their morphologies, we separated metaphase II oocytes into four grades according to criteria which assess oocyte morphology, first polar body and perivitelline space, and especially, cytoplasm granula distribution.
RESULTS: Embryos from oocytes of Grades A and B could develop to the blastocyst stage with similar development efficiency for every developmental stage. However, embryos from Grade C oocytes arrested at or before the 8-cell stage then degraded, and the donor cell genome could not be activated and reprogrammed in such oocytes. For Grade D oocytes, cleavage was not observed in the reconstructed embryos, suggesting that the oocytes themselves have no developmental potential.
CONCLUSIONS: Our study revealed that different levels of developmental competence of SCNT embryos resulting from different oocyte reprogramming potentials associated with different morphologies. The results suggest that effective methods for improving oocyte quality should be studied, and that human SCNT efficiency would be increased following simple assessment of established oocyte morphology criterion.
Key words: human somatic cell nuclear transfer (SCNT)/oocyte morphology/oocyte donation/blastocyst development
These authors contributed equally to this work. Submitted on June 24, 2008; resubmitted on October 7, 2008; accepted on October 9, 2008.