Assessment of the developmental competence of human somatic cell nuclear transfer embryos by oocyte morphology classification.
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.
Yu
Yang
Y
State Key Laboratory of Reproductive Biology, Institute of Zoology, Datun Road, Chaoyang District, Beijing 100101, People's Republic of China.
Mai
Qingyun
Q
Chen
Xinjie
X
Wang
Liu
L
Gao
Ling
L
Zhou
Canquan
C
Zhou
Qi
Q
D000818:Animals; D001755:Blastocyst / Q000166:cytology; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D044127:Epigenesis, Genetic; D005260:Female; D006801:Humans; D007621:Karyotyping; D008677:Metaphase; D051379:Mice; D053652:Nuclear Transfer Techniques; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D011247:Pregnancy; D011256:Pregnancy Outcome; D027724:Reproductive Techniques, Assisted