Comparison of early development in utero of cloned fetuses derived from bovine fetal fibroblasts at the G1 and G0/G1 phases

PRIMARY FIBROBLAST CELL CYCLE SYNCHRONIZATION AND EFFECTS ON HANDMADE CLONED (HMC) BOVINE EMBRYOS

Abstract Spatial and temporal synchrony and compatibility between the receptor oocyte and the donor cell nucleus are necessary for the process of embryo cloning to allow nuclear reprogramming and early embryonic development. The objective of the present study was to evaluate three cell cycle synchronization methods on a primary bovine fibroblast culture for 24, 48, or 72 h. These fibroblasts were used as nuclear donors to evaluate their in vitro developmental potential and the quality of the embryos produced through handmade cloning (HMC). No differences were found between the methods used for fibroblast synchronization in G0/G1 (p > 0.05). Production of clones from fibroblasts in four groups- no treatment at 0 h and using serum restriction SR, high culture confluence HCC, and SR+HCC at 24 h- resulted in high cleavage rates that were not different. Embryo production rates were 37.9%, 29.5%, and 30.9% in the 0h, SR24h, and SR+HHC24h groups, respectively, and 19.3% in the HCC group, which was significantly different from the other three (p < 0.05). There were no differences in the quality parameter among the clones produced with fibroblasts subjected to the different synchronization. Finally, when overall clone production was compared versus parthenotes and IVF embryos, the only difference was between clones and parthenogenetic embryos with zona pellucida (30.2% vs 38.6%). The number of blastomeres from the blastocytes produced through IVF was significantly greater than those from embryos activated parthenogenetically and from clones (117, 80, 75.9, and 67.1, respectively). The evaluation of three synchronization methods at different time points did not demonstrate an increase in the percentage of fibroblasts in the G0/G1 phases of the cell cycle; however, good quality and high cloning rates were obtained, suggesting that it is not always necessary to subject the cells to any synchronization treatments, as they would yield equally good cloning results.

Generation of exogenous germ cells in the ovaries of sterile NANOS3-null beef cattle

Blastocyst complementation (BC) systems have enabled in vivo generation of organs from allogeneic pluripotent cells, compensating for an empty germ cell niche in gene knockout (KO) animals. Here, we succeeded in producing chimeric beef cattle (Wagyu) by transferring allogenic germ cells into ovaries using somatic cell nuclear transfer and BC technology. The KO of NANOS3 (NANOS3^−/−) in Wagyu bovine ovaries produced a complete loss of germ cells. Holstein blastomeres (NANOS3^+/+) were injected into NANOS3^−/− Wagyu embryos. Subsequently, exogenous germ cells (NANOS3^+/+) were identified in the NANOS3^−/− ovary. These results clearly indicate that allogeneic germ cells can be generated in recipient germ cell-free gonads using cloning and BC technologies.

Factors affecting the development of somatic cell nuclear transfer embryos in Cattle

Nuclear transfer is a complex multistep procedure that includes oocyte maturation, cell cycle synchronization of donor cells, enucleation, cell fusion, oocyte activation and embryo culture. Therefore, many factors are believed to contribute to the success of embryo development following nuclear transfer. Numerous attempts to improve cloning efficiency have been conducted since the birth of the first sheep by somatic cell nuclear transfer. However, the efficiency of somatic cell cloning has remained low, and applications have been limited. In this review, we discuss some of the factors that affect the developmental ability of somatic cell nuclear transfer embryos in cattle.

Effect of synchronization of donor cells in early G1-phase using shake-off method on developmental potential of somatic cell nuclear transfer embryos in cattle

In this study, we compared the developmental ability of somatic cell nuclear transfer (SCNT) embryos reconstructed with three bovine somatic cells that had been synchronized in G0-phase (G0-SCNT group) or early G1-phase (eG1-SCNT group). Furthermore, we investigated the production efficiency of cloned offspring for NT embryos derived from these donor cells. The G0-phase and eG1-phase cells were synchronized, respectively, using serum starvation and antimitotic reagent treatment combined with shaking of the plate containing the cells (shake-off method). The fusion rate in the G0-SCNT groups (64.2 ± 1.8%) was significantly higher than that of eG1-SCNT groups (39.2 ± 1.9%) (P < 0.05), but the developmental rates to the blastocyst stage of SCNT embryos per fused oocytes were similar for all groups. The overall production efficiency of the clone offspring in eG1-SCNT groups (12.7%) per recipient cow was higher than that in G0-SCNT groups (3%) (P < 0.05). The mean birth weight of cloned calves and the average calving score in the G0-SCNT groups (48.1 ± 3.4 kg and 3.3 ± 0.3, respectively) was significantly higher (P < 0.05) than those of eG1-SCNT groups (37.2 ± 2.1 kg and 2.3 ± 0.2, respectively). Results of this study indicate that synchronization of donor cells in eG1-phase using the shake-off method improved the overall production efficiency of the clone offspring per transferred embryo.