57 INVESTIGATION OF CYNOMOLGUS MONKEY (MACACA FASCICULARIS) FETUS FIBROBLAST CELL NUCLEAR TRANSFER

Abstract

Use of nuclear transfer (NT) in the cynomolgus monkey to establish tailor-made ES cells with the final goal of cloned embryo production was investigated. Activation stimulus conditions previously confirmed in parthenote production were used. Injection method NT was conducted using cynomolgus monkey fetus fibroblast cells in order to investigated the time it takes, from injection to activation, to reprogram the donor nuclei. Oocytes were collected under laparoscopic observation from mature cynomolgus monkeys 40 h after hCG (400 IU/kg) administration 9 days after follicle stimulation by i.m. injection of FSH (25 IU/kg). Donor cells, 40-day-old fetus fibroblast cells, were cultivated and synchronized at G0/G1 phase. After mature (MII) oocytes were enucleated using a Piezo-drive unit, donor cells were injected. At 2 h (Experiment 1, E1) and 4 h (Experiment 2, E2) after donor cell injection, activation was carried out by 2-min treatment with ionomycin and cultivation by 6-dimethylaminopurine for 4 h. As a control, parthenote production was carried out under the same activation conditions as NT. After activation, in vitro culture was carried out for about 9 days under conditions of 38°C, 5% CO₂, and 5% O₂. Whole-mount specimens of NT embryos were made immediately post-injection, 2 and 4 h post-injection, and 2 h after activation. Pronuclear formation (PN) and cleavage rates of NT embryos were 82.1% and 95.7% for E1, and 53.8% and 92.8% for E2, respectively. Control PN and cleavage rates were each 100%. Subsequent embryo development arrested at the 6-cell stage (8.7%) in E1 and 5-cell stage (7.1%) in E2 but proceeded to blastocyst stage (27.3%) in the control. For whole mount specimens, donor nuclei caused premature chromosome condensation in enucleated oocyte cytoplasm, and decondensation due to activation was seen, so injected donor nuclei reconstruction had occurred. No difference was seen between E2 and E1 embryo development and whole mount specimens, but E1 PN rate was clearly higher than that of E2. So 2 h of reprogramming time is more appropriate than 4 h. In this study, most NT embryos arrested at the 4-cell stage. These results suggest that development did not proceed beyond MET (maternal-embryonic transition) which is believed to occur between the 4- and 8-cell stage in cynomolgus monkey. Further study will be necessary to find the condition that completely reprograms injected donor nuclei for cloned embryo production.

Table 1.
Development of cynomolgus monkey fibroblast nuclear transfer embryos

This work was supported by grants from the ministry of Education, Science, Sports, and Culture (13358014, 14380382).