Cloned piglets born after nuclear transplantation of embryonic blastomeres into porcine oocytes matured in vivo

Nuclear transplantation in the pig is more difficult than in other domestic animals and only one embryonic nuclear transplantation (NT) pig has been born to date. In this study, reconstituted porcine embryos were produced by electrofusion of blastomeres from in vivo four-cell embryos to enucleated in vivo or in vitro matured (IVM) oocytes. Nuclear transfer using cumulus cells as nuclear donors was also conducted. When blastomeres were used as donors, the electrofusion rate was significantly higher in oocytes matured in vivo (91.5%) than in those matured in vitro (66.1%) (p < 0.01). After fusion, the NT embryos reconstituted from in vivo matured oocytes developed to blastocysts at a rate of 10.3% after culture in rabbit oviducts for up to 5 days, while only 5.9% of the NT embryos reconstructed from in vitro matured oocytes developed to blastocyst stage. Electrofusion rate of cumulus cell nuclei with enucleated IVM oocytes was lower (47.6%) and only 1.5% (2/136) of the reconstituted eggs developed in vitro to morula stage, and 1.9% developed to blastocysts when cultured in the ligated rabbit oviducts. Transfer of 94 embryos reconstructed by blastomere NT with in vivo matured oocytes to five synchronous recipients resulted in the birth of two cloned piglets. No piglet was born following transfer to two recipients of embryos (n = 39) derived from NT with in vitro matured oocytes. The results demonstrate that in vivo matured oocytes are better recipients than those matured in vitro for pig cloning.     

Birth of mice after nuclear transfer by electrofusion using tail tip cells

Mice have been successfully cloned from cumulus cells, fibroblast cells, embryonic stem cells, and immature Sertoli cells only after direct injection of their nuclei into enucleated oocytes. This technical feature of mouse nuclear transfer differentiates it from that used in domestic species, where electrofusion is routinely used for nuclear transfer. To examine whether nuclear transfer by electrofusion can be applied to somatic cell cloning in the mouse, we electrofused tail tip fibroblast cells with enucleated oocytes, and then assessed the subsequent in vitro and in vivo development of the reconstructed embryos. The rate of successful nuclear transfer (fusion and nuclear formation) was 68.8% (753/1094) and the rate of development into morulae/blastocysts was 40.8% (260/637). After embryo transfer, seven (six males and one female; 2.5% per transfer) normal fetuses were obtained at 17.5-21.5 dpc. These rates of development in vitro and in vivo are not significantly different from those after cloning by injection (44.7% to morulae/blastocysts and 4.8% to term). These results indicate that nuclear transfer by electrofusion is practical for mouse somatic cell cloning and provide an alternative method when injection of donor nuclei into recipient oocytes is technically difficult.     

Effects of sucrose treatment on the development of mouse nuclear transfer embryos with morula blastomeres as donors

In this study, nuclear transfer (NT) embryos were produced by using C57Bl/6 mouse morula blastomeres and Kunming mouse metaphase II (MII) oocytes as donors and recipients, respectively, to investigate the effects of sucrose treatment of MII oocytes with different concentrations on the manipulation time of NT, electrofusion and the in vitro and in vivo development of reconstructed embryos. The results demonstrated that: (i) when the oocytes were enucleated with 1, 2 and 3% sucrose treatment, respectively, the enucleating rates were not affected by the different sucrose concentrations, but the manipulation time had significant difference and the mean nuclear transfer manipulation times of every oocyte were 180+/-10 s, 130+/-10 s and 120+/-10 s, respectively; (ii) different sucrose concentrations had no significant effects on the fusion rate and the in vitro developmental potential of the NT embryos (p>0.05). Furthermore, 59 embryos were transplanted into the oviducts of two recipients. In the end, three dead full-term developed fetuses were obtained on 21 days post coitus (dpc). These results suggested that the mouse MII oocytes enucleated via sucrose treatment might be an alternative source for mouse cloning and could support the embryonic NT embryos developed to term in vivo.     

未经休眠处理的体细胞用于异种核移植（简报）

It is the point at issue in intraspecies nuclear transfer whether quiescence is necessary for development of nuclear transfer reconstructed embryos. In the interspecies nuclear transfer, some reports have proved that quiescent cell is able to support preimplantation development of the interspecies reconstructed embryos. Are non-quiescent cells able to support preimplantation development of the interspecies reconstructed embryos? We used non-quiescent somatic cells from C57BL/6 mice and giant pandas as donors to transfer into enucleated rabbit oocytes. After electrofusion (the electrofusion rates were 62.2% and 71.6%, respectively) and electrical activation, 5.1% of those mouse-rabbit reconstructed embryos developed to blastocyst in vitro, and 4.2% of panda-rabbit reconstructed embryos developed to blastocyst after transferring into ligated rabbit oviduct. These results indicate that non-quiescent cell from C57BL/6 mouse and giant panda could be dedifferentiated in enucleated rabbit oocytes and support early embryo development.     

Mouse cloning and somatic cell reprogramming using electrofused blastomeres

Mouse cloning from fertilized eggs can assist development of approaches for the production of "genetically tailored" human embryonic stem (ES) cell lines that are not constrained by the limitations of oocyte availability. However, to date only zygotes have been successfully used as recipients of nuclei from terminally differentiated somatic cell donors leading to ES cell lines. In fertility clinics, embryos of advanced embryonic stages are usually stored for future use, but their ability to support the derivation of ES cell lines via somatic nuclear transfer has not yet been proved. Here, we report that two-cell stage electrofused mouse embryos, arrested in mitosis, can support developmental reprogramming of nuclei from donor cells ranging from blastomeres to somatic cells. Live, full-term cloned pups from embryonic donors, as well as pluripotent ES cell lines from embryonic or somatic donors, were successfully generated from these reconstructed embryos. Advanced stage pre-implantation embryos were unable to develop normally to term after electrofusion and transfer of a somatic cell nucleus, indicating that discarded pre-implantation human embryos could be an important resource for research that minimizes the ethical concerns for human therapeutic cloning. Our approach provides an attractive and practical alternative to therapeutic cloning using donated oocytes for the generation of patient-specific human ES cell lines.     

未经休眠处理的体细胞用于异种核移植

自“多莉”诞生以来,在全世界掀起了一场体细胞克隆的浪潮,许多体细胞克隆动物,如小鼠、山羊、牛、猪等纷纷问世。围绕体细胞克隆的供体细胞周期问题,学术界存在两种不同的观点,一是Wilmut等认为体细胞必须经过休眠处理,使细胞停滞在G0/G1期,或者采用以G0/G1期为主的活体细胞作为供体,这是克隆成功的关键,这一方面的报道已有很多。第二是Cibelli等认为不必对细胞作     

体细胞来源及培养代数对核移植重构胚发育的影响

为探讨体细胞来源及培养代数对核移植重构胚发育的影响,实验采用电融合法将小鼠2—细胞胚胎卵裂球、胚胎干细胞(ES)、胎儿成纤维细胞、耳成纤维细胞、尾尖成纤维细胞、睾丸支持细胞和精原细胞以及不同培养代次的胎儿成纤维细胞进行了核移植。结果显示：2—细胞胚胎卵裂球供核重构胚发育最好,囊胚率为7．4％;ES细胞重构胚虽然发育率低,但仍有囊胚出现,比例为0．7％;胎儿成纤维细胞重构胚最高发育阶段为桑椹胚,比例为0．2％;精原细胞重构胚只能发育到8-细胞阶段,比例为0．3％;其他几类细胞重构胚则仅能发育至4-细胞阶段。不同培养代数的胎儿成纤维细胞重构胚除第3代外都可发育到8-细胞阶段,且发育率差异不显著,但第一代细胞重构胚2-细胞发育率(40．7％)显著低于2、3和4代细胞重构胚。结果表明：不同分化程度的细胞核移植后,重新编程的难易程度是不一样的,分化程度越高则重新编程越难;未调整细胞周期的ES细胞由于多数处于S期,所以重构胚发育率很低;体外培养传代有利于体细胞核移植后重新编程。     

Production of rabbit chimeric embryos by aggregation of zona-free nuclear transfer blastomeres

The objective of this study was to compare in vitro developmental capacity of zona-free aggregated rabbit chimeric embryos and the allocation of EGFP (enhanced green fluorescence protein) gene expression to the inner cell mass (ICM). We produced chimeric embryos by synchronous aggregation of zona-free blastomeres from embryonic cell nuclear transfer (EMB-NT) or somatic cell nuclear transfer (SC-NT) and blastomeres from normal zona-free embryos (N) at the 16-cell stage. In the control group, transgenic (TR) and normal zona-free embryos were used to produce chimeric embryos (TR<>N). EMB-NT embryos were produced by fusion of enucleated oocytes with embryonic cells, which were derived from 32-cell stage transgenic embryos bearing the EGFP gene. The SC-NT embryos were produced by fusing enucleated oocytes with cumulus cells, which were derived from homozygotes transgenic for the EGFP gene female oocytes at 16h post-coitum. Nuclei of transgenic blastomeres emitted a green signal under fluorescence microscopy. Zona-free EMB-NT or zona-free SC-NT rabbit embryos, both with EGFP fluorescence, as well as TR and zona-free rabbit embryos with no fluorescence (EMB-NT<>N, SC-NT<>N, TR<>N) were aggregated on day 2.5 and evaluated on day 5. The proportion of EMB-NT<>N embryos that developed to the blastocyst stage was significantly higher compared with SC-NT derived cells (p < 0.05), but significantly lower than in TR<>N chimeric blastocysts (p < 0.001). Similarly, a higher proportion (p < 0.001) of EGFP-positive cells allocated to ICM of chimeric blastocysts was revealed in TR<>N chimeras (55%), compared with EMB-NT<>N (35%) and SC-NT<>N (21%). Our results indicate that synchronous chimeric embryos reconstructed from TR embryos were better able to develop and colonize the ICM area than EMB-NT and SC-NT embryos. In this study we have demonstrated for the first time that rabbit NT-derived embryos are able to develop into chimeric blastocysts and participate in the ICM area.     

Developmental ability of enucleated bovine oocytes matured in vitro after fusion with single blastomeres of eight-cell embryos matured and fertilized in vitro

Single blastomeres from eight-cell stage bovine embryos matured and fertilized in vitro were electrically fused with enucleated oocytes matured in vitro. In experiment 1, The percentage of these reconstituted embryos developed to the two- to eight-cell stage 48 hr after electrofusion was increased when both the eight-cell embryos and the enucleated oocytes were derived from oocytes cultured with granulosa cells (14% vs. 38%). In experiment 2, the relationship between activation of oocytes and developmental ability of reconstituted embryos was examined. Although both ethanol and electrical stimulation efficiently induced parthenogenetic activation of oocytes matured in vitro for 26–28 hr (ethanol, 89%; electrical stimulation, 73%), the ratio of the second polarbody extrusion differed (80% vs. 22%). Ethanol-treated enucleated oocytes, however, were not significantly different from the early cleavage of the reconstituted embryos 48 hr after electrofusion (nontreated, 38%; treated, 43%). In experiment 3, reconstituted embryos at the two- to eight-cell stage 48 hr after the electrofusion were cocultured with granulosa cells for 6–7 days. Of 69 embryos, one developed to a morula and three developed to blastocysts. © 1993 Wiley-Liss, Inc.     

Full-term development of rat after transfer of nuclei from two-cell stage embryos

Cloning technology would allow targeted genetic alterations in the rat, a species which is yet unaccessible for such studies due to the lack of germline-competent embryonic stem cells. The present study was performed to examine the developmental ability of reconstructed rat embryos after transfer of nuclei from early preimplantation stages. We observed that single blastomeres from two-cell embryos and zygotes reconstructed by pronuclei exchange can develop in vitro until morula/blastocyst stage. When karyoplasts from blastomeres were used for the reconstruction of embryos, highest in vitro cleavage rates were obtained with nuclei in an early phase of the cell cycle transferred into enucleated preactivated oocytes or zygotes. However, further in vitro development of reconstructed embryos produced from blastomere nuclei was arrested at early cleavage stages under all conditions tested in this study. In contrast, immediate transfer to foster mothers of reconstructed embryos with nuclei from two-cell embryos at an early stage of the cell cycle in preactivated enucleated oocytes resulted in live newborn rats, with a general efficiency of 0.4%-2.2%. The genetic origin of the cloned offspring was verified by using donor nuclei from embryos of Black Hooded Wistar rats and transgenic rats carrying an ubiquitously expressed green fluorescent protein transgene. Thus, we report for the first time the production of live cloned rats using nuclei from two-cell embryos.     

Nuclear transfer in the bovine embryo: a comparison of 5-day, 6-day, frozen-thawed, and nuclear transfer donor embryos

Micromanipulation and electrofusion were utilized for nuclear transfer in bovine embryos. Embryonic blastomeres from 5-day (estrus = day 0), 6-day, frozen-thawed 5-day, and first-generation nuclear transfer embryos (embryos were themselves a product of nuclear transfer with the original donor being a 5-day embryo) were transferred into bisected bovine oocytes by electrofusion. The percentage of donor cells fusing with the recipient oocytes was compared between different types of donor embryos. The percentage of embryos developing normally into morula or blastocysts following 6 days culture in the sheep oviduct was also recorded and compared between different donor embryo types. No significant differences were found between donor blastomeres for the percent successfully fused to oocytes: 5-day, 294 of 513 (57.3%); 6-day, 252 of 405 (62.2%); frozen-thawed 5-day, 111 of 144 (77.1%); nuclear transfer, 142 of 223 (63.7%); or the percent developing normally following nuclear transfer: 5-day, 92 of 444 (20.7%); 6-day, 84 of 357 (23.5%); frozen-thawed 5-day, 32 of 127 (25.2%); nuclear transfer, 31 of 199 (15.6%). These data suggest that a variety of donor embryos can successfully be utilized for bovine embryo cloning. Also, development of blastomeres from frozen-thawed 5-day donors and from donors that are themselves the product of nuclear transfer suggest that the production of multiple identical offspring is possible by frozen storage of seed stock and serial recloning.     

Viable embryos and normal calves after nuclear transfer into Hoechst stained enucleated demi-oocytes of cows.

Bovine oocytes were bisected, stained with Hoechst 33342 and observed under a fluorescent microscope to identify nucleated and enucleated demi-oocytes. Other oocytes were bisected but not stained, or bisected and only half of each oocyte stained, and viewed under a fluorescent microscope. The oocytes were then used for nuclear transfer by fusing them with embryonic blastomeres from a 5-6 day bovine embryo. The fusion rate and proportion developing into compact morulae or blastocysts was compared among different types of demi-oocytes. Expt 1 examined the effect of staining and indicated no effect on either fusion rate or embryonic development whether or not the oocytes were stained. In Expt 2, stained and unstained nucleated and enucleated oocytes were compared. As in the first experiment, there were no differences between stained and unstained demi-oocytes. There was no difference between fusion rates of nucleated and enucleated oocytes. However, there was a significant difference in embryonic development between nucleated (10.4%) and enucleated (22.6%) demi-oocytes (P less than 0.05). In a final experiment, stained and unstained enucleated oocytes were used for nuclear transfer and the resulting embryos transferred into recipient cows. There was no difference in pregnancy rates or in the number of normal calves born whether stained or unstained recipient oocytes were used. Results from these experiments indicate that Hoechst staining and fluorescent microscopy can be used to identify enucleated demi-oocytes, and that these can be used for nuclear transfer, and result in viable embryos and normal calves.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heterogeneous nuclear-transferred-embryos reconstructed with camel (Camelus bactrianus) skin fibroblasts and enucleated ovine oocytes and their development H-M

This study reconstructed heterogeneous embryos using camel skin fibroblast cells as donor karyoplasts and ovine oocytes as recipient cytoplasts for investigating the developmental potential of the reconstructed embryos. Serum-starved adult camel skin fibroblast cells were used as donor somatic cells. Ovine oocytes matured in vitro were employed as recipient cytoplasts. The fusion of fibroblast cells into recipient cytoplasm was induced by electrofusion. The fused oocytes were activated by 5mM/ml inomycin with 2mM/ml 6-dimethylaminopurine (6-DMAP). The activated reconstructed embryos were co-cultured with ovine cumulus cells in synthetic oviduct fluid supplemented with amino acid (SOFaa) and 10% fetal calf serum (FCS) for 168h. A total of 300 enucleated ovine oocytes were available for xenonuclear embryo reconstruction. The results showed that 71% of the nuclear transfer couplets were successfully fused, 55% of the fused oocytes cleaved within 48h after activation, 82% of the cleaved oocytes developed to 2-16-cell embryo stages and 18% of the cleaved nuclear transfer zygotes developed to the morula stage. This study demonstrated that the xenonuclear transfer camel embryos can undergo the first embryonic division and subsequent development to morula stage in vitro.     

The effects of chemical enucleation combined with whole cell intracytoplasmic injection on panda-rabbit interspecies nuclear transfer

Conventional methods of somatic cell nuclear transfer either by electrofusion or direct nucleus injection have very low efficiency in animal cloning, especially interspecies cloning. To increase the efficiency of interspecies somatic cell nuclear transfer, in the present study we introduced a method of whole cell intracytoplasmic injection (WCICI) combined with chemical enucleation into panda-rabbit nuclear transfer and assessed the effects of this method on the enucleation rate of rabbit oocytes and the in vitro development and spindle structures of giant panda-rabbit reconstructed embryos. Our results demonstrated that chemical enucleation can be used in rabbit oocytes and the optimal enucleation result can be obtained. When we compared the rates of cleavage and blastocyst formation of subzonal injection (SUZI) and WCICI using chemically enucleated rabbit oocytes as cytoplasm recipients, the rates in the WCICI group were higher than those in the SUZI group, but there was no statistically siginificant difference (p > 0.05) between the two methods. The microtubule structures of rabbit oocytes enucleated by chemicals and giant panda-rabbit embryos reconstructed by WCICI combined with chemical enucleation were normal. Therefore the present study suggests that WCICI combined with chemical enucleation can provide an efficient and less labor-intensive protocol of interspecies somatic cell nuclear transfer for producing giant panda cloned embryos.     

Development of reconstituted mouse embryos produced from the cytoplast of bisected oocytes or pronuclear-stage embryos and single blastomeres of 2-cell stage embryos

The present study investigated the in vitro developmental potential of reconstituted mouse embryos produced from the cytoplast of pronuclear-stage embryos or oocytes and single blastomeres of 2-cell stage embryos by electrofusion. The cytoplast of pronuclear-stage embryos and oocytes were obtained by manual bisection with a fine glass needle under a dissecting microscope. The fusion rates of the reconstituted embryos produced from the cytoplast of oocytes and single blastomeres of 2-cell stage embryos (O-SB2: 38.1 and 41.5%) were significantly lower than those produced from the cytoplast of pronuclear-stage embryos and single blastomeres of 2-cell stage embryos (P-SB2: 91.2 and 97.6%; P<0.001). Reconstituted embryos were encapsulated in alginate gel and were cultured for 96 hours. Similarly, the cleavage and development rates to the blastocyst stage of O-SB2 (56.3, 61.2 and 2.0, 3.1%, respectively) were significantly lower than those of the P-SB2 (91.0, 91.2 and 18.6, 20.7%; respectively, P<0.05). The cleavage and development rates to the blastocyst stage (61.2 and 2.0%) of reconstituted embryos produced from single blastomeres of late 2-cell stage embryos and oocyte cytoplast improved after activation by ethanol treatment (76.1 and 21.7%). However, the use of single blastomeres of early 2-cell stage embryos as nuclear donors did not enhance the cleavage and development rates of the reconstituted embryos to the blastocyst stage.     

Mouse cloned from embryonic stem (ES) cells synchronized in metaphase with nocodazole

Full-term development occurred when nuclei from mouse embryonic stem (ES) cells, synchronized in metaphase with nocodazole, were fused with enucleated oocytes or nuclei of reconstituted eggs and again fused with the enucleated blastomeres of fertilized two-cell embryos using inactivated Sendai virus. Two surviving male mice were derived from undifferentiated ES cell nuclei, one from single nuclear transfer and another from serial nuclear transfer. Both were noticeably small and died within 24 hr of birth for unknown reasons. These findings demonstrate that nuclear transfer of ES cells using the fusion method produces young, as does the piezoelectric-actuated nuclear transfer. J. Exp. Zool. 289:139-145, 2001.     

Cloned mice derived from somatic cell nuclei

In 1997, a cloned sheep "Dolly" was produced by nuclear transfer of somatic cell. The first birth of cloned mice derived from some somatic cells were succeeded in 1998. At present, it is shown that somatic cells, cumulus cells, fibroblasts and Sertoli cells can be used to the study of cloned animal as nuclear donor. In this study investigation was designed to compare with efficiency on the production of cloned embryos by using the microinjection and the electrofusion methods for nuclear transfer. Oocyte enucleation was performed with a micromanipulator. The oocyte was held by holding pipette, and was enucleated using a beveled pipette. Microinjection method: Cell's nucleus injection was carried out by piezo-micromanipulator. Cytochalasin B treated cumulus cell was aspirated into a injection pipette, and was broken its plasma membrane using the injection pipette. Then, the cumulus cell was injected into the enucleated ooplasm directly. Electrofusion method: The cell was aspirated into a beveled pipette, and then an aspirated cell was inserted into perivitelline space. Then, the pair of enucleated oocyte and cell was fused using electrical cell fusion apparatus. The reconstituted embryos were activated after nuclear transfer using St2+. Reconstituted embryos had been produced by the microinjection showed the embryonic development to over 8-cell stages. But, the rate of fragmentation of reconstituted embryos by the microinjection showed a little high rate in comparison with the electrofusion. When some reconstituted embryos by the microinjection were transplanted to pseudopregnant females' oviduct, 9 fetuses were observed at 14 days post coitum.     

Development of reconstituted embryos derived from somatic cell nuclei in the rabbit

Production of cloned laboratory animals is helpful in the establishment of medical models. In this study, we examined to produce reconstituted embryos derived from somatic cell nuclei, and to establish embryonic stem (ES) cell lines from the embryo in rabbits. Metaphase II (M-II) oocytes from superovulated rabbit were used as nuclear recipients. Nuclear donor cells were fibroblasts collected from a Dutch Beleted rabbit. The M-II chromosome and the 1st polar body were aspirated, and a fibroblast was inserted into the perivitelline space of the enucleated oocyte. The pairs were electrofused for cell membrane fusion using a cell fusion apparatus and reconstituted embryos were produced. The embryos were activated and cultured in modified HTF medium and DMEM. The embryos developed to the blastocyst stage were removed their zona pellucida, and they were cultured on the feeder cell layer. As a result of having observed development of reconstituted embryos, 21.2% of the embryos were developed to the blastocyst stage. In the embryos cultured on the feeder cells, the adhesion on feeder cells was observed. We obtained inner cell mass (ICM) colony derived from reconstituted embryos At present, we are investigating to establish the ES cell lines derived from the embryos reconstituted by nuclear transfer.