Efficient transgene expression in IVF and parthenogenetic bovine embryos by intracytoplasmic injection of DNA-liposome complexes

SOX2 plays a crucial role in cell proliferation and lineage segregation during porcine pre-implantation embryo development

OBJECTIVES

Gene regulation in early embryos has been widely studied for a long time because lineage segregation gives rise to the formation of a pluripotent cell population, known as the inner cell mass (ICM), during pre-implantation embryo development. The extraordinarily longer pre-implantation embryo development in pigs leads to the distinct features of the pluripotency network compared with mice and humans. For these reasons, a comparative study using pre-implantation pig embryos would provide new insights into the mammalian pluripotency network and help to understand differences in the roles and networks of genes in pre-implantation embryos between species.

MATERIALS AND METHODS

To analyse the functions of SOX2 in lineage segregation and cell proliferation, loss- and gain-of-function studies were conducted in pig embryos using an overexpression vector and the CRISPR/Cas9 system. Then, we analysed the morphological features and examined the effect on the expression of downstream genes through immunocytochemistry and quantitative real-time PCR.

RESULTS

Our results showed that among the core pluripotent factors, only SOX2 was specifically expressed in the ICM. In SOX2-disrupted blastocysts, the expression of the ICM-related genes, but not OCT4, was suppressed, and the total cell number was also decreased. Likewise, according to real-time PCR analysis, pluripotency-related genes, excluding OCT4, and proliferation-related genes were decreased in SOX2-targeted blastocysts. In SOX2-overexpressing embryos, the total blastocyst cell number was greatly increased but the ICM/TE ratio decreased.

CONCLUSIONS

Taken together, our results demonstrated that SOX2 is essential for ICM formation and cell proliferation in porcine early-stage embryogenesis.

Disulphide-less crotamine is effective for formation of DNA-peptide complex but is unable to improve bovine embryo transfection

This study aimed to investigate the ability of disulphide-less crotamine (dLCr) to complex DNA and to evaluate whether the DNA-dLCr complex is capable of improving transfection in bovine embryos. Three experiments were performed to: (i) evaluate the formation and stability of the DNA-dLCr complex; (ii) assess the dLCr embryotoxicity by exposure of bovine embryos to dLCr; and (iii) assess the efficiency of bovine embryo transfection after microinjection of the DNA-dLCr complex or green fluorescent protein (GFP) plasmid alone (control). DNA complexation by dLCr after 30 min of incubation at 1:100 and 1:50 proportions presented higher efficiency (P < 0.05) than the two controls: native crotamine (NCr) 1:10 and lipofectamine. There was no difference between DNA-dLCr 1:25 and the controls. The DNA-dLCr complexation was evaluated at different proportions and times. In all, at least half of maximum complexation was achieved within the initial 30 min. No embryotoxicity of dLCr was verified after exposure of in vitro fertilized embryos to different concentrations of the peptide. The effectiveness of dLCr to improve exogenous gene expression was evaluated by microinjection of the DNA-dLCr complex into in vitro fertilized zygotes, followed by verification of both embryo development and GFP expression. From embryos microinjected with DNA only, 4.6% and 2.8% expressed the GFP transgene at day 5 and day 7, respectively. The DNA-dLCr complex did not increase the number of GFP-positive embryos. In conclusion, dLCr forms a complex with DNA and its application in in vitro culture is possible. However, the dLCr peptide sequence should be redesigned to improve GFP expression.

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.

Efficient delivery of DNA into bovine preimplantation embryos by multiwall carbon nanotubes

The pellucid zone (PZ) is a protective embryonic cells barrier against chemical, physical or biological substances. This put, usual transfection methods are not efficient for mammal oocytes and embryos as they are exclusively for somatic cells. Carbon nanotubes have emerged as a new method for gene delivery, and they can be an alternative for embryos transfection, however its ability to cross the PZ and mediated gene transfer is unknown. Our data confirm that multiwall carbon nanotubes (MWNTs) can cross the PZ and delivery of pDNA into in vitro-fertilized bovine embryos. The degeneration rate and the expression of genes associated to cell viability were not affected in embryos exposed to MWNTs. Those embryos, however, had lower cell number and higher apoptotic cell index, but this did not impair the embryonic development. This study shows the potential utility of the MWNT for the development of new method for delivery of DNA into bovine embryos.

Crotamine, a cell-penetrating peptide, is able to translocate parthenogenetic and in vitro fertilized bovine embryos but does not improve exogenous DNA expression

PURPOSE

Crotamine is capable of penetrating cells and embryos and transfecting cells with exogenous DNA. However, no studies are available regarding its uptake by parthenogenetic (PA) embryos or its use for transfection in in vitro fertilized (IVF) embryos. This study aimed to determine the translocation kinetics of crotamine into PA and IVF bovine embryos and assess its effect over in vitro development of PA embryos. Moreover, crotamine-DNA complexes were used to test the transfection ability of crotamine in bovine IVF zygotes.

METHODS

PA and IVF embryos were exposed to labeled crotamine for four interval times. Embryo toxicity was assayed over PA embryos after 24 h of exposure to crotamine. Additionally, IVF embryos were exposed to or injected with a complex formed by crotamine and pCX-EGFP plasmid.

RESULTS

Confocal images revealed that crotamine was uptaken by PA and IVF embryos as soon as 1 h after exposure. Crotamine exposure did not affect two to eight cells and blastocyst rates or blastocyst cell number (p > 0.05) of PA embryos. Regarding transfection, exposure or injection into the perivitelline space with crotamine-DNA complex did not result in transgene-expressing embryos. Nevertheless, intracytoplasmic injection of plasmid alone showed higher expression rates than did injection with crotamine-DNA complex at days 4 and 7 (p < 0.05).

CONCLUSIONS

Crotamine is able to translocate through zona pellucida (ZP) of PA and IVF embryos within 1 h of exposure without impairing in vitro development. However, the use of crotamine does not improve exogenous DNA expression in cattle embryos, probably due to the tight complexation of DNA with crotamine.

Optimized production of transgenic buffalo embryos and offspring by cytoplasmic zygote injection

Background

Cytoplasmic injection of exogenous DNA into zygotes is a promising technique to generate transgenic livestock. However, it is still relatively inefficient and has not yet been demonstrated to work in buffalo. We sought to improve two key technical parameters of the procedure, namely i) how much linear DNA to inject and ii) when to inject it. For this, we introduced a constitutively expressed enhanced green fluorescent protein (EGFP) plasmid into buffalo zygotes.

Results

First, we found that the proportion of EGFP-expressing blastocysts derived from zygotes injected with 20 or 50 ng/μL DNA was significantly higher than from those injected with 5 μg/mL. However, 50 ng/μL exogenous DNA compromised blastocyst development compared to non-injected IVF controls. Therefore the highest net yield of EGFP-positive blastocysts was achieved at 20 ng/μL DNA. Second, zygotes injected early (7–8 h post-insemination [hpi]) developed better than those injected at mid (12–13 hpi) or late (18–19 hpi) time points. Blastocysts derived from early injections were also more frequently EGFP-positive. As a consequence, the net yield of EGFP-expressing blastocysts was more than doubled using early vs late injections (16.4 % vs 7.7 %). With respect to blastocyst quality, we found no significant difference in cell numbers of EGFP-positive blastocysts vs non-injected blastocysts. Following embryo transfer of six EGFP-positive blastocysts into four recipient animals, two viable buffalo calves were born. Biopsied ear tissues from both buffalo calves were analyzed for transgene presence and expression by Southern blot, PCR and confocal laser scanning microscopy, respectively. This confirmed that both calves were transgenic.

Conclusions

Our cytoplasmic injection protocol improved generation of transgenic embryos and resulted in the first transgenic buffalo calves produced by this method.

DNA fragmentation, transgene expression and embryo development after intracytoplasmic injection of DNA-liposome complexes in IVF bovine zygotes

Summary This study was designed to evaluate the quality and viability of bovine embryos produced by in vitro fertilization (IVF), after intracytoplasmic injection of pCX-EGFP-liposome complexes or pBCKIP2.8-liposome complexes (plasmids that codify the human insulin gene). Cleavage, blastocysts and expanded blastocysts rates of these both groups were not different from that of controls (IVF or IVF embryos injected with liposomes alone; IVF-L). The percentage of EGFP-positive (EGFP+) blastocysts was 41.8%. In Experiment 2, the blastocysts obtained after injection of pCX-EGFP-liposome complexes that did or did not express the transgene, were analyzed by TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labelling) assay at days 6, 7 and 8 of culture in vitro(Bd6, Bd7 and Bd8), in order to evaluate DNA fragmentation. The EGFP+ blastocysts showed different proportions of TUNEL-positive cells (T+) at Bd6, Bd7 and Bd8 (91, 73.7 and 99.5%, respectively) while blastocysts without EGFP expression (EGFP-) showed statistically lower numbers of fragmented nuclei (0, 44.6 and 85%, respectively; P < 0.05). There was no evidence of DNA fragmentation in either Bd6 or Bd7 IVF and IVF-L control blastocysts, but T+ nuclei were detected at Bd8 in both groups (66.4 and 85.8% respectively). Finally, IVF blastocysts (n = 21) injected with insulin-liposome complexes, cultured for 6, 7 and 8 days, were transferred to recipient cows. Pregnancy rates of 18.2% (2/11) and 40% (2/5) resulted from the transfer of Bd6 and Bd7 cells, respectively. Two pregnancies developed to term but they were not transgenic for the insulin gene. In conclusion, EGFP expression affects DNA integrity but not embryo development. Moreover, additional transfers are required in order to overcome the drawbacks generated by in vitro culture length and transgene expression.

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.