Oocyte genome cloning used in biparental bovine embryo reconstruction.

Oocyte genome cloning is a method by which haploid maternal embryos are obtained in such a way that parthenogenetic haploid blastomeres from these embryos can be considered as a clone of the original gamete. Our objective was to generate oocyte genome replicates and use them to reconstruct biparental embryos by fusion with haploid male hemizygotes. Furthermore, we generated biparental homogeneous transgene-expressing embryos using parthenogenetic haploid blastomeres that expressed a transgene (EGFP). In the first experiment, parthenogenetic haploid embryos were generated by incubation of oocytes in ionomycin and 6-dimethylaminopurine (DMAP) with a 3 h interval to permit their second polar body extrusion. The cleavage rate was 87.3%. To generate transgene-expressing blastomeres, activated oocytes were injected with pCX-EGFP-liposome complexes 3 h post ionomycin exposure, resulting in a cleavage rate of 84.4%. In the second experiment, haploid parthenogenetic blastomeres that were positive or negative for EGFP expression were used to reconstruct biparental embryos. Cleavage and blastocyst rates for the reconstructed embryos were 78.4% and 61.1% and 10.8% and 8.4%, using EGFP-positive or -negative blastomeres, respectively (P < 0.05). All of the reconstructed embryos showed EGFP expression, with 96.6% of them showing homogenic expression. Oct-4 expression in the reconstructed blastocysts displayed a similar pattern as IVF-blastocyst controls. In conclusion, our results proved that it is possible to use oocyte genome replicates to reconstruct biparental bovine embryos and that this technique is efficient to generate homogeneous transgene-expressing embryos.

Equine cloning: in vitro and in vivo development of aggregated embryos.

The production of cloned equine embryos remains highly inefficient. Embryo aggregation has not yet been tested in the equine, and it might represent an interesting strategy to improve embryo development. This study evaluated the effect of cloned embryo aggregation on in vitro and in vivo equine embryo development. Zona-free reconstructed embryos were individually cultured in microwells (nonaggregated group) or as 2- or 3-embryo aggregates (aggregated groups). For in vitro development, they were cultured until blastocyst stage and then either fixed for Oct-4 immunocytochemical staining or maintained in in vitro culture where blastocyst expansion was measured daily until Day 17 or the day on which they collapsed. For in vivo assays, Day 7-8 blastocysts were transferred to synchronized mares and resultant vesicles, and cloned embryos were measured by ultrasonography. Embryo aggregation improved blastocyst rates on a per well basis, and aggregation did not imply additional oocytes to obtain blastocysts. Embryo aggregation improved embryo quality, nevertheless it did not affect Day 8 and Day 16 blastocyst Oct-4 expression patterns. Equine cloned blastocysts expanded and increased their cell numbers when they were maintained in in vitro culture, describing a particular pattern of embryo growth that was unexpectedly independent of embryo aggregation, as all embryos reached similar size after Day 7. Early pregnancy rates were higher using blastocysts derived from aggregated embryos, and advanced pregnancies as live healthy foals also resulted from aggregated embryos. These results indicate that the strategy of aggregating embryos can improve their development, supporting the establishment of equine cloned pregnancies.

Sperm genome cloning used in biparental bovine embryo reconstruction.

The generation of androgenetic haploid embryos enables several haploid blastomeres to be obtained as identical copies of a single spermatozoon genome. In the present study, we compared the developmental ability of bovine androgenetic haploid embryos constructed by different methods, namely IVF and intracytoplasmic sperm injection (ICSI) before and after oocyte enucleation. Once obtained, the blastomeres of these androgenetic haploid embryos were used as male genome donors to reconstruct biparental embryos by fusion with matured oocytes. To verify the cytoplasmic contribution of androgenetic haploid blastomeres, we used spermatozoa incubated previously with exogenous DNA that coded for a green fluorescent protein gene (pCX-EGFP) and the enhanced green fluorescent protein (EGFP)-positive androgenetic haploid blastomeres generated were fused with mature oocytes. Of the reconstructed embryos reaching the cleavage and blastocyst stages, 85.1% and 9.0%, respectively, expressed EGFP (P>0.05). EGFP expression was observed in 100% of reconstructed embryos, with 91.2% exhibiting homogenic expression. To confirm sperm genome incorporation, androgenetic haploid blastomeres generated by ICSI prior to enucleation and using Y chromosome sexed spermatozoa were used for biparental embryo reconstruction. Incorporation of the Y chromosome was confirmed by polymerase chain reaction and fluorescence in situ hybridisation analysis. In conclusion, the results of the present study prove that it is possible to use sperm genome replicates to reconstruct biparental bovine embryos and that it is a highly efficient technique to generate homogeneous transgene-expressing embryos.

In Vitro and In Vivo Development of Horse Cloned Embryos Generated with iPSCs, Mesenchymal Stromal Cells and Fetal or Adult Fibroblasts as Nuclear Donors.

The demand for equine cloning as a tool to preserve high genetic value is growing worldwide; however, nuclear transfer efficiency is still very low. To address this issue, we first evaluated the effects of time from cell fusion to activation (<1h, n = 1261; 1-2h, n = 1773; 2-3h, n = 1647) on in vitro and in vivo development of equine embryos generated by cloning. Then, we evaluated the effects of using different nuclear donor cell types in two successive experiments: I) induced pluripotent stem cells (iPSCs) vs. adult fibroblasts (AF) fused to ooplasts injected with the pluripotency-inducing genes OCT4, SOX2, MYC and KLF4, vs. AF alone as controls; II) umbilical cord-derived mesenchymal stromal cells (UC-MSCs) vs. fetal fibroblasts derived from an unborn cloned foetus (FF) vs. AF from the original individual. In the first experiment, both blastocyst production and pregnancy rates were higher in the 2-3h group (11.5% and 9.5%, respectively), respect to <1h (5.2% and 2%, respectively) and 1-2h (5.6% and 4.7%, respectively) groups (P<0.05). However, percentages of born foals/pregnancies were similar when intervals of 2-3h (35.2%) or 1-2h (35.7%) were used. In contrast to AF, the iPSCs did not generate any blastocyst-stage embryos. Moreover, injection of oocytes with the pluripotency-inducing genes did not improve blastocyst production nor pregnancy rates respect to AF controls. Finally, higher blastocyst production was obtained using UC-MSC (15.6%) than using FF (8.9%) or AF (9.3%), (P<0.05). Despite pregnancy rates were similar for these 3 groups (17.6%, 18.2% and 22%, respectively), viable foals (two) were obtained only by using FF. In summary, optimum blastocyst production rates can be obtained using a 2-3h interval between cell fusion and activation as well as using UC-MSCs as nuclear donors. Moreover, FF line can improve the efficiency of an inefficient AF line. Overall, 24 healthy foals were obtained from a total of 29 born foals.