Injection of somatic cell cytoplasm into oocytes before intracytoplasmic sperm injection impairs full-term development and increases placental weight in mice.
This study investigated the effects on fertilized embryo development of somatic cytoplasm after its injection into intact mouse oocytes. Mature oocytes collected from female B6D2F1 mice were injected with cumulus cell cytoplasm of different volumes and from different mouse strains (B6D2F1, ICR, and C57BL/6), or with embryonic cytoplasm. After culture for 1 h, B6D2F1 sperm were injected into those oocytes by intracytoplasmic sperm injection (ICSI). The oocytes were examined for pre- and postimplantation developmental competence. Increases in the volume of the somatic cytoplasm from onefold to fourfold resulted in an impairment of blastocyst development and full-term development (28% and 7%, respectively, vs. 96% and 63%, respectively, in the control group; P < 0.01). An increase in the volume of somatic cytoplasm reduced the expression of POU5F1 (more commonly known as OCT4) in expanded blastocysts. The frequency of embryos that developed to the blastocyst stage did not differ when B6D2F1 or ICR somatic cytoplasm was injected, but injection of C57BL/6 somatic cytoplasm induced a two-cell block in embryo development. Injection of the cytoplasm from fertilized embryos did not reduce the frequency of embryos attaining full-term development. Interestingly, somatic cytoplasm significantly increased the placental weight of ICSI embryos, even the injection of onefold cytoplasm (0.20 +/- 0.02 [n = 32] vs. 0.12 +/- 0.02 in the control group [n = 87]; P < 0.01). These findings indicate that the injection of somatic cytoplasm into oocytes before ICSI causes a decrease in preimplantation development, clearly impairs full-term development, and causes placental overgrowth in fertilized embryos. To our knowledge, placental overgrowth phenotypes are only caused by interspecies hybridization and cloning, and in genetically modified mice. Here, we report for the first time that somatic cytoplasm causes abnormal placentas in fertilized embryos. This study suggests that somatic cell cytoplasmic material is one cause of the low rate of full-term development in cloned mammals.
Van Thuan
Nguyen
N
RIKEN Kobe Institute, Center for Developmental Biology, Laboratory for Genomic Reprogramming, Kobe City, Hyogo 650-0047, Japan. nvthuan@cdb.riken.jp
Wakayama
Sayaka
S
Kishigami
Satoshi
S
Ohta
Hiroshi
H
Hikichi
Takafusa
T
Mizutani
Eiji
E
Bui
Hong-Thuy
HT
Wakayama
Teruhiko
T
D000818:Animals; D001755:Blastocyst / Q000378:metabolism; D001757:Blastomeres / Q000502:physiology; D003593:Cytoplasm / Q000502:physiology / Q000637:transplantation*; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D047109:Fetal Development / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D008845:Microinjections; D050814:Octamer Transcription Factor-3 / Q000378:metabolism; D009865:Oocytes / Q000254:growth & development*; D010929:Placentation; D011247:Pregnancy; D020554:Sperm Injections, Intracytoplasmic
D050814:Octamer Transcription Factor-3; C494174:Pou5f1 protein, mouse